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Mineral apposition rates of human cancellous bone at the interface of porous coated implants
Abstract
Human cancellous bone ingrowth studies were conducted on 19 consenting bilateral total knee arthroplasty (TKA) patients. Titanium porous coated cylinders were implanted into the medial femoral condyle of the contralateral knee during the first of two TKAs. Retrieval was performed at the time of the second TKA (6-131 weeks later), and fluorochrome analysis was conducted. Mean mineral apposition rates (MAR) at the interface measured 1.0 micron/day, whereas 4 mm away, the peripheral bone had a mean MAR of 0.8 micron/day. This represented a 25% acceleration in the interface bone remodeling rate when compared with the periphery (P < .05). This study showed the bone advanced appositionally at the interface at a rate of approximately 1 micron/day. Analysis showed that when bone was over 50 microns from the porous coating, bone ingrowth did not occur. These results emphasize the need for surgical precision and careful postoperative management to achieve bone ingrowth.
... However, it is Brånemark's research with titanium and bone integration that is mostly recognized as contributing to the current understanding of "osseointegration" [6]. From this work, titanium has become commonplace in dental implants, total joint replacements, fracture fixation plates, intramedullary nails and external fixators [7] [8]. ...
... This condition does not provide the skeletal attachment required for secondary implant stability (which results from bone remodeling that occurs over time [72]) and does not have the structural integrity to withstand the dynamic mechanical forces from during ambulation [73]. While initial implant fixation is required to prevent micromotion and fibrous encapsulation [7] [69] [74]- [80], the long-term success of orthopaedic implants requires firm skeletal attachment, which may require up to 9 months in human cancellous bone [74]. Therefore, the primary step in initial implant fixation is to minimize gaps greater than 50 μm since this has been noted to be unstable and prevents integration [7]. ...
... While initial implant fixation is required to prevent micromotion and fibrous encapsulation [7] [69] [74]- [80], the long-term success of orthopaedic implants requires firm skeletal attachment, which may require up to 9 months in human cancellous bone [74]. Therefore, the primary step in initial implant fixation is to minimize gaps greater than 50 μm since this has been noted to be unstable and prevents integration [7]. ...
Over the past 200 years, there has been significant advancements in the fields of bioengineering
and orthopaedics. Investigators, clinicians and manufactures are learning that the success of
implant systems is not limited to a single factor, but a combination of variables that must work in
unison to provide stability and high survivorship. Innovations continue to advance these fields
and include: biomimetic alterations, three-dimensional, patient-specific reconstructions and novel
coatings to mitigate aseptic loosening or other pathologies. However, implant systems continue to
fail in clinical practice since they do not adhere to key fundamental principles. Therefore, this
article is intended to highlight 5 hallmarks of biomaterials that should be considered during design,
surgery, and post-operative rehabilitation.
... Current descriptions of OI include the need of the periprosthetic bone to resist shear and tensile forces 4 and to be within 50 µm distance from the implant surface to host bone to prevent fibrous tissue attachment. 5 Since the initial scientific discovery by Brånemark and his colleagues, fixation of metallic and nonmetallic implants to bone has increased exponentially in the fields of dentistry and orthopedics. OI has been used as a means to fix dental implants, bone-anchored hearing aids, spinal fusion implants, and endo-exo prostheses. ...
... 44 Aside from the biomechanical advantage of cortical bone, Charnley also noted that cancellous bone does not have a periosteum along the surface of the trabeculae, 50 thus contributing to one of the known metabolic differences between cortical and cancellous bone remodeling. 5,51,52 Moreover, cancellous bone heals in an appositional manner, with very little callus formation (,1%), which significantly differs from the healing patterns/cascades of fractured cortical bone; this would affect bone remodeling if accidental trauma occurred to the site where an osseointegrated implant was placed. ...
... 58 Gaps in excess of 50-150 µm between the implant surface texture and host bone may lead to fibrous tissue without skeletal attachment. 5,59,60 To improve the likelihood for dental implant survivorship, novel techniques have been developed that use computed tomography scans from the patient's mouth, and computeraided design. 61 Advanced implant planning in a virtual environment may improve the accuracy of dental implant fabrication and provide patient-specific replicas for surgery. ...
Direct skeletal fixation, termed osseointegration, has expanded in the last century and includes use in total joint replacements, the edentulous mandible and maxilla, and percutaneous osseointegrated prosthetics. Although it is well known that titanium and bone have the ability to form a durable bone–implant interface, new applications have emerged in the field of orthopedics, which requires a more thorough assessment of the literature. This review aims to introduce the basic biological principles for attaining osseointegration and discusses the major factors for assuring successful cementless fixation.
... Several studies used dynamic histomorphometry to identify the effects of implant treatments on peri-implant bone remodeling in animal models, 9,[13][14][15] the effect of cortical screw placement on osteonal remodeling in the dog, 16 and bone remodeling in close proximity to knee replacement implants in humans. 17 It is unclear from these studies, however, if the RAP is transient or persistent when an intramedullary implant is placed at the site of skeletal injury. ...
... While there have been indirect measures of an implant's influence on bone remodeling 26,27 and more direct studies, 9,[13][14][15][16][17] to our knowledge this is the first study to measure the effect of an intramedullary implant on peri-implant bone remodeling in a time-dependent manner. Compared to baseline controls, both sham-ovx and ovx rats had increased rates of trabecular, endocortical, and periosteal bone formation 4 or 8 weeks after implant surgery. ...
... The period of elevated bone resorption may have occurred before our earliest observation time of 4 weeks, or our method of Bone formation markers tended to be elevated longer at the trabecular and endocortical surfaces compared to the periosteal surface, indicating that the implant's effect was most pronounced in close proximity to the site of implant placement, consistent with a previous prediction 6 and direct observations. 17,28 The differences between trabecular and endocortical versus periosteal surfaces could also be due to the prevalence of modeling at the periosteal surface and remodeling at the other two surfaces. ...
To examine bone remodeling following implant placement, 88 female Sprague-Dawley rats underwent either sham ovariectomy (sham-ovx) or ovariectomy (ovx) at 4.5 months. At 11 months, 17 baseline control animals were euthanized, while 71 rats received bilateral intramedullary femoral implants. Implanted rats were randomized to 4-, 8-, or 12-week follow-up times. Microcomputed tomography was used to assess cortical area and trabecular architecture in all rats. Dynamic and static histomorphometry were performed in a subset to examine the trabecular and endocortical bone in the distal femoral metaphysis adjacent to the implant and the periosteal surface at the midshaft superior to the implant (n = 59). Implantation did not affect bone volume in either sham-ovx or ovx rats compared to baseline controls. Implant placement significantly increased mineralizing surface, mineral apposition rate, and bone formation rate in both sham-ovx and ovx rats at the trabecular and endocortical surfaces at four and sometimes 8 weeks, with a return to baseline values by 12 weeks. At the periosteal surface, implant placement increased bone formation at 4 weeks with a return to baseline levels by 8 weeks. Thus, implant placement increases bone remodeling transiently without affecting bone volume in sham-ovx and ovx rats. © 2012 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res.
... The unique features of the design at the time were an asymmetrical tibial tray that matched the resected surface of the human tibia, a metal-backed patella, and a femoral component with a deep-groove titanium alloy (Ti 6 Al 4 V) articulating surface to allow optimal ROM (Fig. 1). Before its introduction, institutional review board (IRB)-approved biocompatibility studies were performed using plugs with the cancellous structured titanium porous coating in a patient population receiving staged bilateral TKAs [4,18,19,21]. During the first operation of a staged bilateral TKA, one of two types of porous-coated plugs were implanted into the patient's opposite medial femoral condyle; the plugs were implanted in such a way as to avoid compromising preparation for femoral component placement at the second operation. ...
... The plugs remained implanted until resection at the second staged operation 3, 6, 9, and 12 months later. The resected bone with implanted plugs was subsequently analyzed, demonstrating the potential for human skeletal attachment indicated by bone ingrowth into the cancellous structured titanium of the Natural-Knee 1 design [4,18,19], and reported in the current investigation. The ingrown bone displayed active mineral apposition rates; more bone ingrowth occurred in the cancellous structured titanium than in hydroxyapatite-coated plugs [4,18,19]. ...
... The resected bone with implanted plugs was subsequently analyzed, demonstrating the potential for human skeletal attachment indicated by bone ingrowth into the cancellous structured titanium of the Natural-Knee 1 design [4,18,19], and reported in the current investigation. The ingrown bone displayed active mineral apposition rates; more bone ingrowth occurred in the cancellous structured titanium than in hydroxyapatite-coated plugs [4,18,19]. These studies also provided support for the use of autograft bone chips [21]; more bone in the porous coating was observed in plugs treated with autologous bone chips. ...
Cementless fixation remains controversial in TKA due to the challenge of achieving consistent skeletal attachment. Factors predicting durable fixation are not clearly understood, but we presumed bone ingrowth could be enhanced by the quantity of host bone and application of autograft bone chips.
We asked: (1) Did the amount of bone ingrowth exceed the amount of periprosthetic and host bone with the addition of autograft bone chips? (2) Did the amount of bone ingrowth increase with implantation time? And (3) did osteolysis along the porous-coated interface and screw tracts progress with implantation time?
We measured the amount of bone in the porous-coated, periprosthetic, and host bone regions in 19 postmortem retrieved cementless primary total knee implants. The amount of bone in apposition to the implant surface, and alternatively lysed bone, was analyzed radiographically to assess the progression of osteolysis.
While bone ingrowth tended to be less than periprosthetic and host bone in all three components, it was only significantly less in the patellar component. Bone ingrowth increased in all three components over time, but progression of osteolysis did not.
Even after long-term followup, the amount of bone ingrowth did not surpass host bone levels, suggesting the amount of a patient's host bone is a limiting factor in the amount of bone ingrowth achievable for this cementless design. It remains unknown whether compromised osteopenic bone could achieve the amount of bone attachment necessary to provide durable fixation over time.
... There is a common agreement made by researchers that dynamic culture could enhance cell proliferation and Guo et al. [9]. found that dynamic culture could provide a higher cell seeding efficiency than static culture [10]. ...
... However, even with a lower cell seeding efficiency, lots of researchers found that cell growth much faster in dynamic culture than in static culture system [9]. The reason is that dynamic culture provides much more nutrients than static culture. ...
In tissue engineering field, it is important to develop a suitable numerical model to evaluate scaffold geometry design. The experimental evaluation of the effect of each specific scaffold parameter on tissue regeneration requires large cost and long time expend. Dynamic cell culture is commonly used for generating tissues which could replace damaged tissues. A perfusion bioreactor model is developed which is able to simulate dynamic cell culture, to evaluate scaffold quality. The wall-film model is used to simulate cell attachment with the assumption that cells could be seen as liquid drops. In the process of cell attachment, the cells could impinge to a solid surface and form a liquid film which were considered as cell attached on the scaffold surface. Two types of cell-scaffold interactions were involved in numerical models including trap model and Stanton-Rutland (Cell impinge model—CIM) model. For trap model, all cells impinged the scaffold are seen as attached. For Stanton-Rutland model, four regimes of cell-scaffold interaction are involved in the cell attachment, including stick, rebound, spread, and splash, and only stick and spread are seen as attached. By comparison with two different numerical methods, the results showed that CIM model result is more related to the experimental results than trap model, which indicated that four regimes of cell-scaffold interaction occurred in cell attachment process. By evaluating two different geometry scaffold’s cells seeding by these two models, the results further indicated that this model are able to use for assessing the scaffold design.
... 35 As predicted, both bone formation markers, PINP and Bone-ALP, significantly increased at PoS2-M1 (Figure 2). The significant increase in bone formation markers may be attributed to accelerated bone remodeling during this initial period, which has been reported as an "accelerated bone remodeling phase" in other human studies 36,37 and in our ovine preclinical data. [38][39][40] In these studies, 48% of bone ingrowth occurred within 3 months after the initial loading of the endoprosthesis. ...
Patients implanted with osseointegrated (OI) prosthetic systems have reported vastly improved upper and lower extremity prosthetic function compared with their previous experience with socket‐suspension systems. However, OI systems have been associated with superficial and deep‐bone infections and implant loosening due, in part, to a failure of the osseointegration process. Although monitoring the osseointegration using circulating biomarkers has clinical relevance for understanding the progression of osseointegration with these devices, it has yet to be established. Ten patients were enrolled in this study. Blood samples were collected at pre‐selected times, starting before implantation surgery, and continuing to 12 months after the second surgery. Bone formation markers, bone resorption markers, and circulating amino acids were measured from blood samples. A linear mixed model was generated for each marker, incorporating patient ID and age with the normalized marker value as the response variable. Post hoc comparisons were made between 1 week before Stage 1 Surgery and all subsequent time points for each marker, followed by multiple testing corrections. Serial radiographic imaging of the residual limb containing the implant was obtained during follow‐up, and the cortical index (CI) was calculated for the bone at the porous region of the device. Two markers of bone formation, specifically bone‐specific alkaline phosphatase (Bone‐ALP) and amino‐terminal propeptide of type I procollagen (PINP), exhibited significant increases when compared with the baseline levels of unloaded residual bone prior to the initial surgery, and they subsequently returned to their baseline levels by the 12‐month mark. Patients who experienced clinically robust osseointegration experienced increased cortical bone thickness at the porous coated region of the device. A medium correlation was observed between Bone‐ALP and the porous CI values up to PoS2‐M1 (p = .056), while no correlation was observed for PINP. An increase in bone formation markers and the lack of change observed in bone resorption markers likely reflect increased cortical bone formation induced by the end‐loading design of the Utah OI device used in this study. A more extensive study is required to validate the correlation observed between Bone‐ALP and porous CI values.
... The understanding of osseointegration had evolved with the help of new radiological investigations to assess the surface between bone and implant [4] . Currently in osseointegration the bone around implant should counteract compressive, bending and tensile loads [5] and present within 50 micrometer from implant to avoid fibrous tissue formation [6] . Osseointegration is useful for clinical follow-up in many implants e.g. ...
Abstract: Background: Various situations in orthopedic surgery needed a second surgery. Though the need of a second surgery cannot always predicted. Despite a well-done procedure, 3.6% cases may still need a second surgery. In modern-day-trauma, with increasing speed-of-travel, we have to face the challenges of 21st-century and rate of Complex-Comminuted-Devitalized-Fractures (CCD) have tremendously increased.
Aim and Objectives: To help identify common orthopedic situations which need a second surgery.
Material and Methods: This retrospective study was carried from 1989-2010, on 25,550-procedures operated at our-centre of total 3060 patients. The study included patients from 5-80 years of age, and excluded surgeries done for congenital and neoplastic disorders.
Results: Out of 25,550 procedures, 3,060 procedures were second surgeries. Indications for the second surgeries were studied and analyzed.
Conclusion: We conclude that this is a revolutionary concept and would help each orthopaedic surgeon across world to classify every fracture with this classification, where they feel need for second surgery. It would improve our rationale of treatment and significantly improve prognosis and final outcomes.
... To achieve stabilizing OI, the bone attachment region of percutaneous OI endoprostheses requires intimate bone-endoprosthesis contact. It has been shown that host bone more than 50 μm away from the endoprosthesis cannot bridge the interface before the formation of fibrous connective tissue [7], making it the most important region to match the bone endoprosthesis interface. For systems that use press-fit fixation, a conical taper allows for a tight fit in the medullary canal. ...
Percutaneous osseointegrated (OI) devices have an endoprosthesis attached to the residual bone of an amputated limb, then pass permanently through the skin to be connected to the distal prosthetic componentry outside of the body. Whether the bone-anchoring region of current OI endoprostheses are cylindrical, and/or conical, they require intimate bone-endoprosthesis contact to promote stabilizing bone attachment. However, removing too much cortical bone to achieve more contact leads to thinner and, subsequently, weaker cortical walls. Endoprostheses need to be designed to balance these factors, namely maximizing the contact, while minimizing the volume of bone removed. In this study, 27 human tibias were used to develop and validate a virtual implantation method. Then, 40 additional tibias were virtually implanted with mock cylindrical and conical bone-anchoring regions at seven residual limb lengths to measure resultant bone-endoprosthesis contact and bone removal. The ratio of bone-endoprosthesis contact to bone volume removed showed the conical geometry had more contact area per volume bone removed for all amputation levels (p≤0.001). In both mock devices, cortical penetration of the endoprosthesis at 20% residual length occurred in 74% of cases evaluated, indicating that alternative endoprosthesis geometries may be needed for clinical success in that region of bone.
... Even the rate of cell growth and migration are determined by it (J.A. Sanz-Herrera et al., 2009). Some researchers suggest that 100-400-µm pore sizes are optimal for bone tissue regeneration (Hulbert et al., 1970;Schliephake et al., 1991;Bloebaum et al., 1994). Accordingly, two types of scaffolds, including TO structure and cubic structure, were designed, and the structure parameters are listed in Table 2. ...
Cell attachment to a scaffold is a significant step toward successful tissue engineering. Cell seeding is the first stage of cell attachment, and its efficiency and distribution can affect the final biological performance of the scaffold. One of the contributing factors to maximize cell seeding efficiency and consequently cell attachment is the design of the scaffold. In this study, we investigated the optimum scaffold structure using two designs – truncated octahedron (TO) structure and cubic structure – for cell attachment. A simulation approach, by ANSYS Fluent coupling the volume of fluid (VOF) model, discrete phase model (DPM), and cell impingement model (CIM), was developed for cell seeding process in scaffold, and the results were validated with in vitro cell culture assays. Our observations suggest that both designs showed a gradual lateral variation of attached cells, and live cell movements are extremely slow by diffusion only while dead cells cannot move without external force. The simulation approaches supply a more accurate model to simulate cell adhesion for three-dimensional structures. As the initial stages of cell attachment in vivo are hard to observe, this novel method provides an opportunity to predict cell distribution, thereby helping to optimize scaffold structures. As tissue formation is highly related to cell distribution, this model may help researchers predict the effect of applied scaffold and reduce the number of animal testing.
... The implants need to be fused completely with the surrounding tissues and provide the platform for cellular adhesion, proliferation, and maturation. Osseointegration is considered to be established, provided that the peri-implant bone is capable to resist surrounding shear forces and to maintain the maximum gap of 50 μm between implant and tissue to prevent forming fibrous capsule (Bloebaum et al. 1994). Bone formation around machined implants occurs through new bone deposition on existing bone tissue (distance osteogenesis) and direct osteoblastic activity on microroughened implants via contact osteogenesis (Yamaki et al. 2012;Amor et al. 2011;Davies 2003). ...
Titanium implants are considered the gold standard of treatment for dental and orthopedic applications. Biocompatibility, low elasticity, and corrosion resistance are some of the key properties of these metallic implants. Nonetheless, a long-term clinical failure of implants may occur due to inadequate osseointegration. Poor osseointegration induces mobility, inflammation, increased bone resorption, and osteolysis; hence, it may result in painful revision surgeries. Topographical modifications, improvement in hydrophilicity, and the development of controlled-release drug-loading systems have shown to improve cellular adhesion, proliferation, and differentiation. Surface modifications, along with drug coating, undoubtedly demonstrate better osseointegration, especially in challenged degenerative conditions, such as osteoporosis, osteoarthritis, and osteogenesis imperfecta. Anabolic bone-acting drugs, such as parathyroid hormone peptides, simvastatin, prostaglandin-EP4-receptor antagonist, vitamin D, strontium ranelate, and anti-catabolic bone-acting drugs, such as calcitonin, bisphosphonates, and selective estrogen receptor modulators, expedite the process of osseointegration. In addition, various proteins, peptides, and growth factors may accessorize the idea of localized therapy. Loading these substances on modified titanium surfaces is achieved commonly by mechanisms such as direct coating, adsorption, and incorporating in biodegradable polymers. The primary approach toward the optimum drug loading is a critical trade-off between factors preventing release of a drug immediately and those allowing slow and sustained release. Recent advances broaden the understanding of the efficacy of adsorption, hydrogel coating, and electrospinning layer-by-layer coating facilitated by differential charge on metallic surface. This review discusses the existing approaches and challenges for the development of stable and sustained drug delivery systems on titanium implants, which would promote faster and superior osseointegration.
... increase in the MAR compared to host bone (0.85 ± 0.07 μm/day) confirming a regional acceleratory phenomenon (RAP) adjacent to the porous coatings (Table 5). (Bloebaum, Bachus, Momberger, & Hofmann, 1994) No statistical difference was observed between the Ti and CoCr coatings MAR that ABI values ranging from 61 to 100% were to be considered clinically successful and that had successfully obtained skeletal attachment (Bloebaum et al., 1997;Bloebaum et al., 1998 ...
The use of cobalt‐chromium (CoCr)‐bearing surfaces in total joint replacement (TJR) remains the predominate bearing surface. The conundrum with using this biomaterial has been selecting an ideal porous coating to assure reproducible skeletal attachment. There has been evidence that smooth CoCr beads may be inferior for skeletal attachment compared to identically shaped titanium (Ti) beads. Recent in vitro studies have demonstrated that an increased surface area and roughness favors osteoblast adhesion to metallic biomaterials. Therefore, we hypothesized that an irregular shape CoCr bead with an increased surface texture would help correct the negative bone responses that have been reported with smooth beaded CoCr coatings and thus allowing for bone ingrowth equivalently as an irregular commercially pure Ti porous coating with similar porosity. This investigation employed a weight‐bearing translational sheep cancellous bone model to accurately simulate a cancellous bone response as it would be clinically in a human TJR. The data analyses obtained from this investigation revealed similar bone responses between the porous coatings. By 12 weeks the irregular shape CoCr coating was able to achieve similar bone ingrowth with skeletal interlock when compared to a clinically proven Ti porous coating.
... 19 Primary stability allows the patient to bear weight until permanent secondary stability is achieved as a result of bone ingrowth into the porous surface. 20 This study focused on micromotion at the bone-cup interface 19,[21][22][23] and interfacial gaps 24,25 which may delay, inhibit, or prevent bone ingrowth. How representative the generated subsets are of the full cohort was assessed by comparing the distribution in output metrics in the subsets to the distribution in the full cohort. ...
Total hip replacements must be robust to patient variability for long‐term success in the population. The challenge during the design process is evaluating an implant in a diverse population but the computational cost of simulating a population of subject‐specific finite element (FE) models is not practical. We examined five strategies to generate representative subsets of subjects from a cohort of 103 implanted hip joint FE models to approximate the variability in output metrics. Comparing to the median and distribution of the 95th percentile composite peak micromotion (CPM) and polar gap in the full cohort (CPM median: 136 μm, interquartile range (IQR): 74 – 230 μm) (Polar Gap median: 467 μm, IQR: 434 – 548 μm), the Anatomic Sampling strategy (12 subjects) achieved the best balance of computational cost and approximation of the output metrics (CPM median: 169 μm, IQR: 78 – 236 μm) (Polar Gap median: 469 μm, IQR: 448 – 537 μm). Convex Hull Sampling (41 subjects) more closely captured the output metrics (CPM median: 99 μm, IQR: 70 – 191 μm) (Polar Gap median: 456 μm, IQR: 418‐533 μm) but required over three times the number of subjects. Volume reduction of the convex hull captured the extremes of variability with subsets of 5 to 20 subjects, while the Largest Minimum‐Distance strategy captured the variability toward the middle of the cohort. These strategies can estimate the level of variability in FE model output metrics with a low computational cost when evaluating implants during the design process.
... 6 Instability stimulates the formation of fibrous tissue at the implant-bone interface, thus impeding osseointegration, predisposing the construct to aseptic loosening and implant failure. Bloebaum et al 7 reported that a bone-implant gap of more than 50 μm in a human knee arthroplasty is sufficient to prevent bone ingrowth into a porous coating. In another study, a bone-implant gap exceeding 500 μm had a negative impact on osseointegration. ...
Objective: To determine whether the surgeon can influence the accuracy of milling during the TATE elbow arthroplasty by applying force to the milling arm during the milling procedure.
Study design: In vitro study on Sawbone specimens.
Sample population: Thirty identical solid foam models of the canine right humerus, elbow joint, and antebrachium (size large).
Methods: TATE elbow arthroplasty was performed on 30 elbows equally divided into 3 types of forces applied to the milling arm: (1) no force, (2) a maximally con- verging force, and (3) a maximally diverging force using the center of rotation post as a reference point. The resulting component-bone interface and post fit were quantified with digital photography.
Results: The component-bone interface gap differed between techniques for most angles. The application of convergent or divergent milling forces frequently increased the component-bone interface gap. Post fit was also influenced by the milling technique, application of a convergent or divergent milling force affecting the fit of multiple posts. Interface gaps tended to be greater on the lateral aspect, an area that is not visible to the surgeon intraoperatively.
Conclusion: In this bone model study, application of convergent or divergent forces during milling frequently resulted in greater component-bone interface gaps and poorer post fit than when a neutral position was maintained.
Clinical significance: Surgeons may affect implant fit within the constraints of the current arthroplasty system if they do not maintain a neutral position during mill- ing. Greater component-bone interface gaps and poorer post fit may affect compo- nent osseointegration and lead to aseptic implant loosening.
... Histological data indicated that MAR levels were 1.7 times higher than nonpathological human bone at the time of surgical intervention (1.7 ± 0.7 µm/day; range: 1.3-2.6 µm/day) compared to the known 1.0 µm/day of nonpathological human bone. 39 The amount of single and double labels calculated during fluorochrome labeling was 2.0 ± 2.0 and 1.3 ± 0.6, respectively; these values were substantially lower than ectopic bone observed in our previous study of soldiers who experienced traumatic combat-related injuries. 26 Scanning electron microscopic and light microscopic images showed that HO had a trabecular structure with bone chips and varying degrees of mineralization (Figs. ...
Heterotopic ossification (HO) is frequently reported following total joint replacement (TJR) surgery. Symptomatic HO may limit the range of motion, cause pain, and require surgical excision. Deciding an appropriate time for ectopic bone excision is based on clinical judgment, and a more well-defined link between clinical predictors and histological analysis is needed to minimize recurrence. A case series was performed with military healthcare system patients undergoing TJR, who required removal of periarticular ectopic bone. Patients were prescribed oxytetracycline to assess the mineral apposition rate (MAR; ie, bone growth rate) of HO, and excised specimens were analyzed using scanning electron microscopy and light microscopy. Two males and one female were enrolled in this study, with height of 69.0 ± 7.8 inches, weight of 237.7 ± 28.3 pounds, and age of 61 ± 7 years at the time of HO removal. Ectopic bone occurred in two cases following total knee arthroplasty and one total hip arthroplasty. Data indicated that MAR levels were 1.7 times higher than that reported previously for nonpathological human bone (1.7 ± 0.7 μm/day; range: 1.3–2.6 μm/day), and microscopic imaging confirmed that the osseous tissues were still actively remodeling at the time of surgical intervention. Further characterization is needed to optimize HO excision timing and to better understand this pathological bone disorder.
... Fluorescent light microscopy was used to quantify the number of double and single tetracycline labels in the cortical bone and calcified fibrocartilage for the total cross-sectional area of each thin section. Both double and single labels were quantified to assess remodeling activity of the tissues and to account for any possible differences in the mineral apposition rates between the tissues (Bloebaum et al., 1994). ...
It is well known that the incidence of hip fractures increases exponentially with age and that hip fractures can be a major cause of morbidity and morality among elderly humans; this has prompted substantial research on hip fractures. The majority of research on hip fractures has focused on morphological changes of the proximal femur with age. Recently calcified fibrocartilage in the proximal femur has been shown to increase in fractional area with age and can ultimately make up to 60% of the fractional area of the cortex. However, the capacity of the tissue to remodel and heal is currently unknown. The purpose of the present study was to determine the remodeling capacity of calcified fibrocartilage on the proximal femur compared to the underlying cortical bone. The remodeling capacity of calcified fibrocartilage and cortical bone was assessed in adult female sheep by means of tetracycline labeling. The number of double and single labels within each tissue type was quantified and analyzed with a paired t-test. The data showed very few labels in the calcified fibrocartilage compared to the cortical bone. This indicated that calcified fibrocartilage lacked a capacity to remodel in a manner similar to bone. The results of this investigation demonstrate that while the underlying cortical bone was actively remodeling, the calcified fibrocartilage appeared to have no remodeling capacity similar to that of cortical bone.
... It would be helpful if quantitative analysis could be done on mineralized cemented bone specimens using scanning electron microscopy (SEM) imaging without embedding the specimens. Before SEM imaging, it is common practice to embed mineralized bone with implant in situ in polymethylmethacrylate (PMMA) (1)(2)(3)(4)(5). ...
Although effective, the embedment of bone tissue and orthopaedic devices using polymethylmethacrylate (PMMA) has challenges and limitations. To embed using PMMA, specimens must first be fixed in 70% ethanol, dehydrated in ascending grades of ethanol, and then infiltrated and polymerized in polymethylmethacrylate using standard techniques. This process can take more than 22 d for large bone specimens. Additionally, PMMA embedment has been shown to dissolve bone cement, thus enabling the analysis of the bone-cement interfaces. To conserve processing time while preserving the bone-cement interface, a method was developed for processing mineralized bone tissue in preparation for scanning electron microscopy (SEM) imaging that does not require PMMA embedment. This technique does not require the traditional dehydration and PMMA polymerization process. Instead, fresh mineralized cemented bone specimens were serially sectioned and the marrow removed after formalin fixation. The sections were air-dried then desiccated. The sections were then prepared for SEM imaging and examination. This process takes a fraction of the tissue processing time while not compromising the bone-cement integrity. The SEM image quality was shown to be comparative to images obtained with PMMA-embedded bone specimens.
... This frequency was selected as it was the sampling rate of the digital images, ensuring that one frame from the pressure mat corresponded to one frame from the video recordings, allowing each limb strike to be analyzed correctly. The rationale for the frequent time periods chosen in this investigation was based on the endosteal bone response to endoprosthesis (Bloebaum et al., 1994;Hofmann et al., 1997;Willie et al., 2004). The fracture healing model time periods previously used (Duda et al., 1998) did not allow for the longer term 12-month follow up used in this study. ...
Percutaneous osseointegrated prostheses are being investigated as an alternative strategy to attach prosthetic limbs to patients. Although the use of these implants has shown to be promising in clinical trials, the ability to maintain a skin seal around an osseointegrated implant interface is a major challenge to prevent superficial and deep periprosthetic infections. The specific aim of this study was to establish a translational load-bearing ovine model to assess postoperative limb compensation and gait symmetry following a percutaneous osseointegrated implant. We tested the following hypotheses: (1) the animals would return to pre-amputation limb loads within 12-months; (2) the animals would return to a symmetrical gait pattern (stride length and time in stance) within 12-months. The results demonstrated that one month following surgery, the sheep loaded their amputated limb to a mean value of nearly 80% of their pre-amputation loading condition; by 12-months, this mean had dropped to approximately 74%. There was no statistical differences between the symmetry of the amputated forelimb and the contralateral forelimb at any time point for the animals stride length or the time spent in the stance phase of their gait cycle. Thus, the data showed that while the animals maintained symmetric gait patterns, they did not return to full weight-bearing after 12-months. The results of this study showed that a large animal load-bearing model had a symmetric gait and was weight bearing for up to 12 months. While the current investigation utilizes an ovine model, the data show that osseointegrated implant technology with postoperative follow-up can help our human patients return to symmetric gait and maintain an active lifestyle, leading to an improvement in their quality of life following amputation.
... Histologic investigations by Puzas et al. have previously reported that HO bone formation was three times faster than age-matched bone with a bone growth rate of 0.98 6 0.16 mm/d compared to 0 to 0.30 6 0.19 mm/d, respectively [52]. However, the mineral apposition rate (MAR) of human cancellous bone has been well known to be approximately 1.0 mm per d [53] and demonstrates measurement errors with Puzas' technique. Future investigations that accu-rately determine the MAR of HO may provide valuable insight into a more appropriate time for ectopic bone resection to prevent recurrence and corroborate bone mineralization levels determined in this study using BSE. ...
Heterotopic ossification (HO) has been reported as a pathologic process characterized by ectopic bone growth in muscle and/or periarticular regions. Previous reports have speculated that HO manifests as cancellous bone, cortical bone, or woven bone. Confusion regarding HO bone morphology has resulted from radiographic assessments and light microscopy, which lack the resolution required for accurately determining advanced bone architecture. Therefore, a more thorough histologic assessment using scanning electron microscopy (SEM) and backscatter electron (BSE) imaging was needed to improve HO characterization.
HO samples were collected from five adult trauma patients after surgical resection and examined with radiography, BSE, and histologic stains.
BSE data demonstrated that HO was composed of a heterogeneous mixture of cortical and cancellous bone with distinct regions of fibrocartilage. Bone mineralization levels varied on a patient-specific basis, with the highest percentage of hypermineralization occurring in the oldest patient. BSE and histologic stains also indicated HO remodeling continued even after 3 y from injury to resection, as evident by osteoclastic resorption and osteoid deposition.
BSE provided a more accurate understanding of HO bone mineralization and structure which may lead to improved surgical planning and treatment strategies for prevention of HO recurrence after resection.
... However, a complete circumference of bone was noted for the ESI group even when the implant was not in close apposition to the endosteal wall, as indicated by the 750-lm gap in Figure 9. SEM images demonstrated similar skeletal fixation between the ESI and UCI groups when the implant and bone were in close apposition. However, in the cases where the bone-implant contact exceeded the 50 lm, as recommended by Bloebaum et al., 24 only the ESI had stimulated bone ongrowth around the periphery of the intramedullary implant ( Figure 10). Results also indicated a greater periosteal response around the periphery of the cortical bones in the ESI group. ...
Transcutaneous osseointegrated implants (TOI) have been shown to improve functionality for patients with limb loss by allowing direct skeletal attachment between an exoprosthesis and host bone. However, a lengthy rehabilitation period has limited the expansion of TOI and may be accelerated with electrical stimulation. The purpose of this study was to determine the ability of direct current (DC) cathode stimulation to enhance osseointegration of intramedullary implants in skeletally matured rabbits. Bilateral implants were inserted in the hind limbs of 25 adult female rabbits. The left hind limb of each animal was continually stimulated with a potential difference of 0.55 volts based on finite element analysis predictions. After sacrifice, the limbs were divided into two groups: Group I for histology and Group II for biomechanical testing. The bone-implant construct was evaluated in the Group I animals using appositional bone index (ABI), mineral apposition rates (MAR), histological staining, and scanning electron microscopy (SEM). Group II implants were sectioned and subjected to mechanical push-out tests. Data indicated no statistical differences for ABI, MAR, and porosity between the electrically stimulated implants (ESI) and the unstimulated control implants (UCI) at three weeks and six weeks. Higher mechanical push-out forces were observed in the UCI group at six weeks (p = 0.034). Data indicated that DC cathode stimulation may improve suboptimal implant "fit and fill" as an increase in trabecular bone was noted around the cathode in the ESI group. However, longer time duration animal studies and variations in electrical modalities may be required before electrically induced osseointegration becomes clinically feasible.
Hydroxyapatite (HA) coatings have been widely used for improving the bone-implant interface (BII) bonding of the artificial joint prostheses. However, the incidence of prosthetic revisions due to aseptic loosening remains high. Porous materials, including three-dimensional (3D) printing, can reduce the elastic modulus and improve osseointegration at the BII. In our previous study, we identified a porous material with a sintered bionic trabecular structure with in vitro and in vivo bio-safety as well as in vivo mechanical safety. This study aimed to compare the difference in osseointegration ability of the different porous materials and HA-coated titanium alloy in the BII. We fabricated sintered bionic trabecular porous titanium acetabular cups, 3D-printed porous titanium acetabular cups, and HA-coated titanium alloy acetabular cups for producing a hip prosthesis suitable for beagle dogs. Subsequently, the imaging and histomorphological analysis of the three materials under mechanical loading in animals was performed (at months 1, 3, and 6). The results suggested that both sintered bionic porous titanium alloy and 3D-printed titanium alloy exhibited superior performances in promoting osseointegration at the BII than the HA-coated titanium alloy. In particular, the sintered bionic porous titanium alloy exhibited a favorable bone ingrowth performance at an early stage (month 1). A comparison of the two porous titanium alloys suggested that the sintered bionic porous titanium alloys exhibit superior bone in growth properties and osseointegration ability. Overall, our findings provide an experimental basis for the clinical application of sintered bionic trabecular porous titanium alloys.
For achieving early intervention treatment to help patients delay or avoid joint replacement surgery, a personalized scaffold should be designed coupling the effects of mechanical, fluid mechanical, chemical, and biological factors on tissue regeneration, which results in time- and cost-consuming trial-and-error analyses to investigate the in vivo test and related experimental tests. To optimize the fluid mechanical and material properties to predict osteogenesis and cartilage regeneration for the in vivo and clinical trial, a simulation approach is developed for scaffold design, which is composed of a volume of a fluid model for simulating the bone marrow filling process of the bone marrow and air, as well as a discrete phase model and a cell impingement model for tracking cell movement during bone marrow fillings. The bone marrow is treated as a non-Newtonian fluid, rather than a Newtonian fluid, because of its viscoelastic property. The simulation results indicated that the biofunctional bionic scaffold with a dense layer to prevent the bone marrow flow to the cartilage layer and synovia to flow into the trabecular bone area guarantee good osteogenesis and cartilage regeneration, which leads to high-accuracy in vivo tests in sheep . This approach not only predicts the final bioperformance of the scaffold but also could optimize the scaffold structure and materials by their biochemical, biological, and biomechanical properties.
Introduction
The goal was to determine if the addition of a metaphyseal stem extension limits micromotion of a cementless tibial component during cyclic loading in primary total knee arthroplasty (TKA). The hypothesis tested was that the use of a 50mm stem extension on a cementless tibial component would limit motion compared to an identical cementless component without a stem extension.
Materials and Methods
The study employed 3 variations of a tibial component from the same TKA system. Group 1 consisted of a cementless tibial component without a stem extension. Group 2 used the same cementless component as Group 1, but with the addition of a short 50-mm stem and Group 3 consisted of a cemented tibial component without a stem extension to serve as a “control” (gold standard). The tibial specimens were implanted into a synthetic bone model and tested using a physiological medial-lateral 60/40 load distribution for 5,000 cycles.
Results
The results demonstrated a significant decrease in motion at the anterior region of the cementless stem extension (Group 2) components compared to the cementless with no stem extension (Group 1). The cementless with stem extension (Group 2) demonstrated similar results at all cycles to the cemented (Group 3) components at the anterior region
Conclusion
The addition of a short metaphyseal stem (50mm) to a keel plus 4-peg tibial component design provides a significant reduction in micromotion during cyclic loading of a cementless tibial baseplate in a synthetic foam bone model, similar to a cemented implant.
The primary stability achieved during total hip arthroplasty determines the long-term success of cementless acetabular cups. Pre-clinical finite element testing of cups typically use a model of a single patient and assume the results can be extrapolated to the general population. This study explored the variability in predicted primary stability of a Pinnacle ® cementless acetabular cup in 103 patient-specific finite element models of the hemipelvis and examined the association between patient-related factors and the observed variability. Cups were inserted by displacement-control into the FE models and then a loading configuration simulating a complete level gait cycle was applied. The cohort showed a range of polar gap of 284 to 1112 µm and 95th percentile composite peak micromotion (CPM) of 18 to 624 µm. Regression analysis was not conclusive on the relationship between patient-related factors and primary stability. No relationship was found between polar gap and micromotion. However, when the patient-related factors were categorised into quartile groups, trends suggested higher polar gaps occurred in subjects with small and shallow acetabular geometries and cup motion during gait was affected most by low elastic modulus and high bodyweight. The variation in primary stability in the cohort for an acetabular cup with a proven clinical track record may provide benchmark data when evaluating new cup designs. This article is protected by copyright. All rights reserved
Despite four decades of research on material and porous coatings intended for cementless fixation in total joint replacement (TJR), aseptic mechanical loosening unrelated to particulate disease remains a concern. One main question asked is how translational are the animal models used to screen material and porous coatings intended for TJR fixation? Another question is how specific are the translational models at targeting the cementless TJR components that have the highest loosening rates? The hypothesis tested was that the bone response would be different between the two bone types—cortical and cancellous—used in translational animal modeling. The osteoblastic jumping distance (OJD), percent ingrowth, and appositional bone response were measured to assess the response between cancellous and cortical bone at two different anatomical locations, within the same limb. With 500 µm inset, titanium porous coated implants and negative control dinosaur (coprolite) implants were investigated. The data demonstrated that cortical bone had 7 times OJD than cancellous bone. The bone ingrowth data demonstrated 16 times higher bone ingrowth than the cancellous bone. Light microscopy showed predominately fibrous tissue attachment (98%) in cancellous bone. Screening of materials intended for TJR require a translational model predictive of the clinical condition. The results demonstrated that the transcortical model rendered false-positive data. © 2017 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 2017.
Recent reports with up to 10-year clinical follow-up have demonstrated that cementless total knee arthroplasty can yield excellent results in young, active patients when sound implant design principles and surgical techniques are followed. Intimate apposition of the prosthesis to host bone is achieved with instrumentation that allows precise bone resection, and by the routine application of morselized autogenous bone chips to the cut surfaces. Revision of cementless total knee components without porous-coated pegs, keels, or stems has proven to be bone-sparing, which is an important consideration in the younger patient who may outlive their prosthesis. The authors believe that cementless fixation is a superior alternative to cemented fixation for primary total knee arthroplasty in younger patients with higher functional demands and good bone stock.
Background:
Heterotopic ossification (HO) is a debilitating condition that occurs following traumatic injury and may restrict range of motion and delay rehabilitation. The timing and efficacy of surgical resection have varied widely, and there is a gap in knowledge between clinical predictors of HO recurrence and histological analysis.
Methods:
Thirty-three service members seen at Walter Reed National Military Medical Center for symptomatic HO were enrolled in an institutional review board-approved study. Participants took oxytetracycline on four scheduled days prior to HO resection to determine the mineral apposition rate (bone growth rate).
Results:
Detailed histological analyses included scanning electron microscopy with backscattered electron imaging and light microscopy. Data indicated that the mineral apposition rate of trauma-induced HO was approximately 1.7 μm/day at the time of operative intervention, which was 1.7 times higher than the rate in non-pathological human bone. The mineral apposition rate and postoperative alkaline phosphatase values were demonstrated to be positively and significantly related (ρ = 0.509, p = 0.026, n = 19). When the analysis was limited to patients with no more than a two-year period from injury to excision (thereby removing outliers who had a longer time period than their counterparts) and traumatic brain injury and nonsteroidal anti-inflammatory drugs (known correlates with HO development) were controlled for in the statistical analysis, the mineral apposition rate and recurrence severity were significantly related (ρ = -0.572, p = 0.041, n = 11).
Conclusions:
Data demonstrated a link between benchtop research and bedside care, with the mineral apposition rate elevated in patients with HO and correlated with recurrence severity; however, a larger sample size and more clinical factors are needed to refine this model.
Level of evidence:
Prognostic Level II. See Instructions for Authors for a complete description of levels of evidence.
Cementless fixation has been a principal method for fixation of orthopedic implants for decades. Accordingly, different rough and porous surfaces have been developed and applied in clinical use. A variety of these coatings are continuously investigated in order to improve bone-implant integration and enhance osteogenesis at the implant surface. One of the most important elements used in joint arthroplasty is titanium.
One of the major advances in the use of metals for long-term implants was the serendipitous use of titanium (Ti). The nonreactive properties of this metal [1] made it an ideal material for the aerospace industry. Many of these same properties made it equally ideal for use in the body. Unlike stainless steel, Ti forms a surface oxide that prevents leaching of ions [2]. The oxide is biocompatible in that there is little, if any, immune response [3]. Early literature noted the lack of an immune response and defined Ti as biologically inert [4]. While we now know that Ti is not inert, there is no question that it is exceptionally well-tolerated by the body. Consequently, Ti has become the material of choice for dental implants [5] (See Chaps. 24 and 25) and cardiovascular stents [6] (See Chap. 26), and its alloys are commonly used in orthopaedics where greater strength is needed [7] (See Chap. 21).
Porous silicon nitride preforms designed for bone substitutes were prepared by two different forming methods: by introduction of semolina as pore forming agent and by template method with polyurethane sponge. Silicon nitride-based green bodies were sintered in air at two different temperatures, while the Si + 20 % Si3N4 samples were sintered by reaction bonding process in nitrogen. Template method yields samples with interconnected macroporous structure comparable to the bone structure while introduction of semolina results only in isolated macropores formation. All sintered samples were characterized in terms of phase composition and microstructure. Moreover, some of the mechanical properties (hardness, elastic modulus, bending strength) were measured and compared to the bone properties in order to select the most suitable method for the preparation of trabecular bone substitute. Despite of relatively low strength, the template method with subsequent sintering in air appeared to be the most promising way for the preparation of trabecular bone-like silicon nitride-based porous ceramic structures, whereas the hardness and elastic modulus of as prepared samples were in perfect accordance with bone characteristics.
Periprosthetic joint infection (PJI) following total knee arthroplasty is a globally increasing procedural complication. These infections are difficult to treat and typically require revision surgery. Antibiotic-loaded bone cement is frequently utilized to deliver antibiotics to the site of infection; however, bone cement is a nondegrading foreign body and known to leach its antibiotic load, after an initial burst release, at subtherapeutic concentrations for months. This work characterized a resorbable, antibiotic-eluting bone void filler designed to restore bone volume and prevent PJI. Three device formulations were fabricated, consisting of different combinations of synthetic inorganic bone graft material, degradable polymer matrices, salt porogens, and antibiotic tobramycin. These formulations were examined to determine the antibiotic's elution kinetics and bactericidal potential, the device's degradation in vitro, as well as osteoconductivity and device resorption in vivo using a pilot rabbit bone implant model. Kirby-Bauer antibiotic susceptibility tests assessed bactericidal activity. Liquid chromatography with tandem mass spectrometry measured antibiotic elution kinetics, and scanning electron microscopy was used to qualitatively assess degradation. Results indicated sustained antibiotic release from all three formulations above the Staphylococcus aureus minimum inhibitory concentration for a period of 5 to 8 weeks. Extensive degradation was observed with the Group 3 formulation after 90 days in phosphate-buffered saline, with a lesser degree of degradation observed in the other two formulations. Results from the pilot rabbit study showed the Group 3 device to be biocompatible, with minimal inflammatory response and no fibrous encapsulation in bone. The device was also highly osteoconductive-exhibiting an accelerated mineral apposition rate. © 2015 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 2015.
© 2015 Wiley Periodicals, Inc.
Porous silicon nitride ceramics having properties similar to the human trabecular bone have been sintered and characterized in order to develop a material applicable as bone substitute. At first, human trabecular bone was characterized especially in terms of pore structure which is, besides the non-toxicity, the most critical for acceptation of the substitute. The pore network of highly porous trabecular bone is formed by interconnected large pores of approximately 300-1000 mu m. Similar pore structure of silicon nitride-based ceramics was attained by the replica method with polyurethane sponge as pore forming agent. Porous ceramics were prepared in two ways, namely as air-sintered silicon nitride and sintered reaction-bonded silicon nitride. The materials were characterized using the same methods as for the human bone samples. Both types of ceramic materials fulfilled the microstructural requirements for bioapplications. Moreover, their non-cytotoxicity was proved by measuring the yellow tetrazolium MTT proliferation assay using human fibroblast cell line.
Bone metastasis will impact most men with advanced prostate cancer. The vicious cycle of bone degradation and formation driven by metastatic prostate cells in bone yields factors that drive cancer growth. Mechanistic insights into this vicious cycle have suggested new therapeutic opportunities, but complex temporal and cellular interactions in the bone microenvironment make drug development challenging. We have integrated biologic and computational approaches to generate a hybrid cellular automata model of normal bone matrix homeostasis and the prostate cancer-bone microenvironment. The model accurately reproduces the basic multicellular unit bone coupling process, such that introduction of a single prostate cancer cell yields a vicious cycle similar in cellular composition and pathophysiology to models of prostate-to-bone metastasis. Notably, the model revealed distinct phases of osteolytic and osteogenic activity, a critical role for mesenchymal stromal cells in osteogenesis, and temporal changes in cellular composition. To evaluate the robustness of the model, we assessed the effect of established bisphosphonate and anti-RANKL therapies on bone metastases. At approximately 100% efficacy, bisphosphonates inhibited cancer progression while, in contrast with clinical observations in humans, anti-RANKL therapy fully eradicated metastases. Reducing anti-RANKL yielded clinically similar results, suggesting that better targeting or dosing could improve patient survival. Our work establishes a computational model that can be tailored for rapid assessment of experimental therapies and delivery of precision medicine to patients with prostate cancer with bone metastases. Cancer Res; 74(9); 2391-401. ©2014 AACR.
Hydroxyapatite coatings were fabricated on Ti substrates by laser cladding (LC) using mixed powders of CaCO3 and dicalcium phosphate dihydrate (DCPD, CaHPO4·2H2O). The effect of the mass ratio of CaCO3 to DCPD on phase and microstructure formation of the coatings was investigated. The reactions between CaCO3 and DCPD can produce high crystallized hydroxyapatite (HA, Ca5(PO4)3(OH)) in the coatings as well as tetracalcium phosphate (TTCP, Ca4P2O9), α-tricalcium phosphate (α-TCP, α-Ca3(PO4)2), β-tricalcium phosphate (β-TCP, β-Ca3(PO4)2) and Ca2P2O7. The Ca/P molar ratio (CMR) of the mixed powders (CMRP) has a great influence on the contents of the phases in the coating. HA can be produced in the coating only when the CMRP is higher than 1.54, and its content increases slowly as the CMRP increases. The coating contains only about 25wt% HA when CMRP reaches 2.00, and there exists large amount of TTCP in the coating. So a post heat treatment with furnace cooling is recommended to increase the amount of HA in the coating. All the coatings have porous structures because the reactions between the powders produce lots of gases during LC. The pore size in the coating fabricated by the powders with CMR equal to 2.00 is about 100–300 μm. CMRP also has a great influence on the bond strength, porosity and cracks of the coatings. Along with the increase of the CMRP, the bond strength and porosity decrease, whereas the number of cracks increases.
Maintaining bone geometric and structural integrity is a necessity for normal mobility. After fracture, bone disease or other conditions resulting in skeletal loss or compromise, porous materials offer the possibility for near faultless replacement of the normal bone material. Ceramics, and to a lesser extent, metals, are the predominant porous materials currently used in bone engineering. This latter term is used as a blanket term for orthodontics, orthopedics and related fields in which the replacement of bone is either required or selectively chosen. Because bone is a porous material, there is a physiological rationale for the use of porous materials in its replacement. Moreover, porous bone implant material is advantageous for the early incorporation of the implant into or apposed to the bony tissue surrounding it. There is, however, a difference in the size and extent of the bone and implant porosities for optimal bone incorporation of the material. This review intends to clarify both the nature of and reason for this difference. Accordingly, a review of the principal types of porous materials (organics, ceramics, metals, metallorganics and organoapatites and composites) used in bone engineering will be provided. This will springboard a consideration of the important engineering considerations of material property matching, machining and forming, corrosion and biocompatibility, fatigue and lifecycle, coating, and interfacial properties. The importance of matching the porous material to the particular bone engineering application will then be discussed. In providing this review, the authors hope to bring an appreciation of the complexity of the field to the fore, while also demonstrating how much has already been accomplished due to the efforts of many research groups. The ultimate porous bone implant, perhaps, is yet to be designed; however, there is reason to believe that such a material is not long in coming. We hope to demonstrate some possible pathways to this material.
Of 300 consecutive knees (238 patients) that had undergone arthroplasty with the cementless Natural Knee prosthesis from 1985 to 1989, 176 knees (141 patients) were available for followup at an average of 12 ± 1 years after the operation. Knee function was improved significantly. Modified Hospital for Special Surgery knee scores improved from 59.1 ± 13.2 points preoperatively to 97.8 ± 4.7 points at last followup. At last followup, knee range of motion averaged 0° ± 2° to 120° ± 10°. Implant survival was 93.4% (including infection and simple polyethylene exchanges) and 95.1% (excluding infection and simple polyethylene exchanges) at 10 years when applying the Kaplan-Meier survival analysis, using loose components, revision, or both as failure criteria. Besides the three revisions for infection, only two femoral and one tibial component required revision. The patellar component survivorship at 10 years was 95.1%. All patellar revisions were attributed to edge wear. Subsequent operative and design changes, including patellar component medialization and countersinking, have decreased the incidence of patellar revision. The long-term results of this cementless knee system compare favorably with those of cemented systems. The Natural Knee design has provided excellent and predictable long-term clinical results in the current series of active patients.
Antibiotic resistant bacterial infections are a growing problem in patient care. These infections are difficult to treat and severely affect the patient's quality of life. The goal of this translational experiment was to investigate the antimicrobial potential of cationic steroidal antimicrobial-13 (CSA-13) for the prevention of perioperative device-related infections in vivo. It was hypothesized that when incorporated into a polymeric device coating, the release of CSA-13 could prevent perioperative device-related infection without inhibiting skeletal attachment. To test this hypothesis, 12 skeletally mature sheep received a porous coated titanium implant in the right femoral condyle. Group 1 received the titanium implant and an inoculum of 5 × 10(8) CFU of methicillin-resistant Staphylococcus aureus (MRSA). Group 2 received a CSA-13 coated implant and the MRSA inoculum. Group 3 received only the CSA-13 coated implant and Group 4 received only the implant-without the CSA-13 coating or MRSA inoculum. In conclusion, the CSA-13 combination coating demonstrated bactericidal potential without adversely affecting skeletal attachment. The CSA-13 containing groups exhibited no evidence of bacterial infection at the conclusion of the 12 week study and established skeletal attachment consistent with Group 4. In contrast, all of the Group 1 animals became infected and required euthanasia within 6-10 days. The significance of this finding is that this combination coating could be applied to implanted devices to prevent perioperative device-related infections. This method may facilitate significantly reduced incidences of device-related infections as well as a new method to treat and prevent resistant strain bacterial infections. © 2013 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 2013.
Bioceramic processing using rapid prototyping technique (RPT) results in a fragile device that requires thermal treatment to improve the mechanical properties. This investigation evaluates the effect of thermal treatment on the mechanical, porosity, and bioactivity properties as well as the cytotoxicity of a porous silica-calcium phosphate nanocomposite (SCPC) implant prepared by RPT. Porous SCPC implant was subject to 3-h treatment at 800°C, 850°C, or 900°C. The compressive strength (s) and modulus of elasticity (E) were doubled when the sintering temperature is raised from 850 to 900°C measuring (s = 15.326 ± 2.95 MPa and E = 1095 ± 164 MPa) after the later treatment. The significant increase in mechanical properties takes place with minimal changes in the surface area and the percentage of pores in the range 1-356 μm. The SCPC implant prepared at 900°C was loaded with rh-BMP-2 and grafted into a segmental defect in the rabbit ulna. Histology analyses showed highly vascularized bone formation inside the defect. Histopathological analyses of the liver, spleen, kidney, heart, and the lung of rabbits grafted with and without SCPC demonstrated healthy tissues with no signs of toxicity or morphology alterations. Results of the study suggest that it is possible to engineering the mechanical properties of the SCPC implant without compromising its bioactivity. The enhanced bone formation inside the porous SCPC facilitated cell-mediated graft resorption and prohibited any accumulation of the material in the body organs. © 2013 Wiley Periodicals, Inc. J Biomed Mater Res Part A, 2013.
The classical method of separation of variables along with the novel features of Biot theory of dynamic poroelasticity and the translational addition theorem for cylindrical wave functions are employed to present an exact solution for interaction of a plane acoustic wave with a composite cylindrical sound absorber suspended in air. The analytical results are illustrated with numerical examples in which a compound cylindrical absorber made of selected configurations of two common sound absorbent materials (plastic foam and light glass wool), is insonified by plane sound waves at selected angles of incidence. The backscattered form function amplitude as well as the absorption cross section spectra are calculated and discussed for representative values of the parameters characterizing the system. The effects of incident wave frequency, angle of incidence, core eccentricity and coating thickness are examined. Limiting cases are considered and fair agreements with available solutions are obtained.
Osseointegration is a new technique for prosthetic suspension in individuals with limb loss. The objective of this study was to determine perceptions and acceptance of osseointegration as a means of prosthetic suspension among individuals with lower limb amputations. A survey instrument was developed and administered to individuals 18 years or older with a lower limb amputation at or above the transtibial level. Of the 73 participants who completed the survey, 33% stated that they would consider undergoing the osseointegration procedure for prosthetic attachment. Anticipated improvements in prosthetic function, improved activity level, the security of the suspension system, improved walking ability, and ease of prosthetic attachment were cited as the top advantages to the procedure. Forty-two percent of the participants responded that they would not consider having the procedure. In this group, infection, potential activity limitations due to implant failure, long rehabilitation course, and risk of a broken bone in the residual limb were cited as the top concerns. Characteristics that significantly correlated with a participant considering osseointegration included living in a rural community, pain interfering with daily activity, and problems with the prosthesis falling off. Based on these findings, it seems that improvements in infection prevention, efficient rehabilitation strategies, and the prevention of implant failure will be important for increased acceptance of osseointegration procedures among individuals with lower limb amputations.
This study reports the retrospective radiographic outcome of a series of 63 consecutive total knee arthroplasties using an uncemented hydroxyapatite-coated Duracon cruciate-retaining tibial baseplate (Stryker Howmedica Osteonics Corp, Mahwah, NJ). Sixty-three knees were assessed at a mean follow-up of 65 months. The knees were primarily diagnosed with osteoarthritis with a mean age of 61 years. Radiographic analysis showed 6 knees with tibial baseplate radiolucencies, with all of these resolving or improving over the course of the study. All tibial baseplates were implanted with the concomitant use of autologous bone slurry. There were no reoperations for aseptic loosening, fracture, or patellofemoral problems. This intermediate study demonstrates excellent radiographic outcomes for uncemented hydroxyapatite-coated Duracon cruciate-retaining tibial baseplates and evaluates other factors felt to be important in the success of a cementless implant.
The clinical use of plasma-sprayed hydroxyapatite (HA) coatings on metal implants has aroused as many controversies as interests over the last decade. Although faster and stronger fixation and more bone growth have been revealed, the performance of HA-coated implants has been doubted. This article will initially address the fundamentals of the material selection, design, and processing of the HA coating and show how the coating microstructure and properties can be a good predictor of the expected behavior in the body. Further discussion will clarify the major concerns with the clinical use of HA coatings and introduce a comprehensive review concerning the outcomes experienced with respect to clinical practice over the past 5 years. A reflection on the results indicates that HA coatings can promote earlier and stronger fixation but exhibit a durability that can be related to the coating quality. Specific relationships between coating quality and clinical performance are being established as characterization methods disclose more information about the coating. © 2001 John Wiley & Sons, Inc. J Biomed Mater Res (Appl Biomater) 58: 570–592, 2001
Based on the histological findings of 23 patients who had received implants of the bovine hydroxyapatite ceramic Endobon® for a period of up to 16 months, the biocompatibility, nature and extent of osseointegration as well as the resorption and degradation behaviour of the ceramic were investigated. The investigation material consisted mainly of small fragments that had been retrieved during revision operations that were indicated for other reasons. The results confirm the good tolerability and suitability that have been systematically investigated in experimental studies and described for hydroxyapatite ceramic as bone substitute in a vital cancellous bone bed that is not exposed to excessive strain (due to its brittle character). The importance of fulfilling certain requirements in order to achieve a successful result, such as stable implantation in a well vascularized, infection-free bone bed also with a minimization of the contact with local connective tissue has been further substantiated. Good success has been achieved by simultaneous loading with autogenous bone marrow as is practised by many ceramic users. In some cases a widening of intergrain boundaries as well as partial dissociation of superficial hydroxyapatite crystallites were observed in the implant surface.
Recent reports with up to 10-year clinical follow-up have demonstrated that cementless total knee arthroplasty can yield excellent
results in young, active patients when sound implant design principles and surgical techniques are followed. Intimate apposition
of the prosthesis to host bone is achieved with instrumentation that allows precise bone resection, and by the routine application
of morselized autogenous bone chips to the cut surfaces. Revision of cementless total knee components without porous-coated
pegs, keels, or stems has proven to be bone-sparing, which is an important consideration in the younger patient who may outlive
their prosthesis. The authors believe that cementless fixation is a superior alternative to cemented fixation for primary
total knee arthroplasty in younger patients with higher functional demands and good bone stock.
We developed a titanium fiber mesh block (TFMB) to use as an alternative to autogenous bone, grafts for vertebral interbody
fusion. In in vitro tests, we measured the surface pore size and conducted weight loading tests of TFMB with porosities of
50% and 60%. For invivo testing, we grafted TFMB in 11 mongrel dogs for intervertebral fusion and evaluated bone ingrowth
into the grafts and the bonding of TFMB with bone. The mean surface pore size was 375±289 μm for 50% porosity TFMB and 445±440
μm for 60% porosity TFMB. In the in vitro weight loading test, 60% porosity TFMB showed 50%–60% of the elastic modulus of
50% porosity TFMB, and both materials showed a similar yielding load. After the grafting of 60% porosity TFMB, bone in-growth
occurred to a depth of 2.3 mm at 3 months and to a depth of 3.6 mm at 6 months; while the values were 0.7 mm and 1.5 mm, respectively,
in 50% porosity TFMB. In a push-out test conducted 6 months after grafting, 50% and 60% porosity TFMB showed similar bone
bonding strengths. These results suggest that 60% porosity TFMB implant will be suitable to using for spinal interbody fusion.
The projected number of American amputees is expected to rise to 3.6 million by 2050. Many of these individuals depend on artificial limbs to perform routine activities, but prosthetic suspensions using traditional socket technology can prove to be cumbersome and uncomfortable for a person with limb loss. Moreover, for those with high proximal amputations, limited residual limb length may prevent exoprosthesis attachment all together. Osseointegration technology is a novel operative procedure that allows integration between host tissue and an orthopaedic implant and has been shown to improve clinical outcomes by allowing direct transfer of loads to a bone-implant interface. However, the associated surgical procedures require long rehabilitation programs that may be reduced through expedited skeletal attachment via electrical stimulation. To determine optimal electrode size and placement, we have developed a system for computational modeling of the electric fields that arise during electrical stimulation of residual limbs. Three patients with retrospective CT scans were selected and three dimensional reconstructions were created using customized software (Seg3D and SCIRun). These software packages supported the development of patient specific models and allowed for interactive manipulation of electrode position and size; all variables that could affect the electric fields around a percutaneous osseointegrated implant. Preliminary results of the electric fields at the implant interface support the need for patient specific modeling in order to achieve the homogenous electric field distribution required to induce osteoblast migration and enhance skeletal fixation.
This study describes the response of human cancellous bone when autologous bone chips are added at operation to the interface between host bone and porous-coated implants. During the first operation of a staged bilateral total knee arthroplasty, seven patients consented to have paired porous-coated devices implanted into their opposite medial femoral condyle. One device of each pair had autologous bone chips applied to the porous-coating, and the other was not grafted and was a control. The devices were removed en bloc at the second total knee arthroplasty 6 to 49 weeks later. Backscattered electron imaging showed significantly more bone (p < or = 0.05) in the porous-coating of the implant treated with autologous bone chips which significantly increased (p < or = 0.05) the amount of bone available at the interface. The grafted devices had a mineral apposition rate of 1.04 +/- 0.20 microns/day for the interface and 0.81 +/- 0.09 microns/day for the peripheral bone. This compared with corresponding figures of 1.03 +/- 0.38 microns/day and 0.79 +/- 0.19 microns/day at the ungrafted devices. The mineral apposition rate at the interface of the porous-coated implants was significantly increased (p < or = 0.05) relative to the host bone in the periphery. Our results support the view that autologous bone chips are effective in attaching cementless porous-coated total knee replacements to the human skeleton by bone ingrowth.
Postmortem evaluation was conducted on two cementless knee prostheses considered clinically successful. The two retrieved uncemented porous-coated tibial components of different designs, and materials were evaluated by microradiography, backscattered electron (BSE) imaging, and light microscopy. The right prosthesis, in place for 25 months, was a Porous-Coated Anatomic (PCA) implant with double-layered, sintered, cobalt-chromium alloy beads. The left prosthesis was a Natural-Knee (N-K) implant with a porous coating of cancellous-structured pure titanium implanted for 19 months. A quantitative microradiographic index, the appositional bone index (ABI), was developed to indicate the probability of bone ingrowth occurring into the porous coating. The ABI is a ratio of bone in apposition with porous coating divided by the total amount of porous coating available. The PCA had an average ABI of 9%, and the N-K, 67%. BSE images of the PCA demonstrated no bone within the porous coating. BSE images of the N-K implant showed bone ingrowth into 22% of the pore volume when porous coating was in apposition to host bone. Histology of the PCA revealed fibrous connective tissue throughout the porous coating and between the porous coating-bone interface. Histology of the N-K implant revealed bone ingrowth and osteoblastic activity along the bone within the porous coating.
Sintered hydroxyl-apatite implants form very tight bonds with living bone but are susceptible to fatigue failure. Plasma-sprayed apatite coatings on titanium substrates overcome the fatigue problem. The static tensile substrate bond strength of the apatite coating is in excess of 85 megapascals (MPa) (12,000 psi). In a plug implant study designed to discount mechanical retention, a bone bonding shear strength of 64 MPa (9280 psi) was achieved, comparable to the strength of cortical bone. Histologic sections confirm the close bonding between apatite coating and living bone. In a canine total hip arthroplasty study, the apatite-coated implants proved far superior to the uncoated controls. Uncoated prostheses were surrounded by fibrous tissue and were easily extracted from the femur at any postoperative time. The apatite-coated implants were rigidly fixed within three weeks with demonstrable bone formation up to the implant surface. Bony defects up to 2 mm in depth were filled with bone within six weeks. The hypothetical mechanism of bone bonding is chemical. Hydroxyl-apatite coatings permit an implant fixation far superior to current methods using either cemented or cementless techniques. The plan is to study a human total hip prosthesis with hydroxyl-apatite coating for chemical fixation to bone.
A simple modified polymethyl methacrylate method is described for large mineralized bone specimens with implants and bioactive materials which produces consistently good histological preservation of the interface between bone and implant. Human femoral heads, whole rabbit condyles and canine tibias and femurs containing implants consisting of hydroxyapatite, smooth polyethylene, porous polyethylene and carbon were dehydrated in ascending grades of ethanol and cleared with xylene on an automated tissue processor which alternated vacuum and pressure for 22 hr. Infiltration was done with washed polymethyl methacrylate at 4 C under vacuum for 13 days. Polymerization was carried out in wide-mouth glass jars at 38 C for 36 hr so that the total processing time was less than 20 days. The only important modification was in the polymethyl methacrylate, which had less plasticizer than usual in order to give a harder block. This enabled production of 4 micron sections with good preservation of mineralized and cellular areas for the study of metabolic bone diseases, morphometry, fluorochrome labelling and interface analysis with the implant in situ.
Porous surfaced femoral components of hip prostheses stabilized by tissue ingrowth are often situated a certain distance away from the endosteal cortex in the diaphysis. The purpose of this study was to examine the significance of this space between an implant and the cortex on bone growth into the porous surface of the implant. Intramedullary rods of different diameters with porous surface regions made of powder metal were inserted into the femurs of adult beagles. The rods had outside diameters of 2.5, 3.2, 4.5, and 5.5 millimeters; this variation produced endosteal bone-implant surface spaces ranging from 0 to 4 millimeters. The animals were sacrificed at 4, 8, 12, and 16 weeks. Histological sections revealed that by 12 weeks the implants became generally surrounded by a thin shell of spongy bone which was joined to the endosteal cortex by bony trabeculae. This feature was most prominent for implants which were approximately 2 millimeters or less from the endosteum. Denser, more haversian-like bone developed up to and within those areas of implants which were in contact with the cortex. The development of this intramedullary type of bone could significantly contribute to the fixation strength of clinical porous surfaced prostheses whose stems do not completely fill the medulla.
This study reports on the results of the implant and tissue analysis of clinically retrieved hydroxyapatite (HA)-coated implants. Five of the patients with fixed HA-coated stems had been clinically diagnosed with osteolysis. The semiquantitative histologic grading in these patients showed HA, polyethylene, and metal particles were all present (Grade 3+) in the osteolytic regions of the periprosthetic tissue. Additionally, inflammatory cells (Grade 3+) were present in these regions. Back-scattered electron (BSE) and correlated elemental analysis showed HA particulate was present in the polyethylene inserts. The HA could be distinguished from bone chips in the polyethylene based on morphology and anatomic number gray level differences. This study was limited in that no clinical results of particular HA-coated implant series were reported. Careful follow-up care in patients with coated devices is recommended.
Glass jars are routinely used as molds for embedding hard tissue specimens such as bone and metal prostheses in polymethylmethacrylate. Our laboratory has successfully adopted the routine use of polypropylene disposable containers as the standard polymethylmethacrylate embedding mold. Polypropylene is less expensive and safer to use than glass, and the polymerization of the embedding medium is controlled, predictable, and fast. (The J Histotechnol 13:131, 1990).
Quantitative histomorphometric analyses of iliac crest trabecular bone were performed after tetracycline double-labeling in 20 hyper- and 10 hypethyroid patients, in 20 epileptics receiving long-term anticonvulsant therapy, in 17 renal transplant patients receiving long-term immunosuppressive treatment and in various sex- and age-matched normal control groups. The bone formation rate was determined at the active cellular level, the basic multicellular unit (BMU) level and the tissue level. The average maturation period of osteold (OMP) was calculated from the bone formation rate at BMU level and the mean width of osteoid seams.In the hyperthyroid patients the bone formation rate was increased at all three levels, indicating an accelerated rate of formation of new remodelling units and a decrease in the duration of the formative phase of the remodelling cycle. In the hypothyrold patients and in renal transplant patients the findings were opposite to those in the hyperthyroid patients. In the epileptic patients an increase in bone formation rate at the tissue level alone suggested an increase in the rate of formation of new remodelling units and a normal duration of the formative. period. OMP, which was about 21–27 days in normal individuals, was decreased in hyperthyroidism, normal in anticonvulsant osteomalacia and increased in hypothyroldism and in renal transplant patients. OMP was inversely related to the average cellular activity of the osteoblasts in the different groups.
The results of bilateral postmortem analysis of titanium and plasma-sprayed hydroxyapatite (HA) porous-coated femoral components of the same Anatomic Porous Replacement design retrieved from a 35-year-old female donor are reported. Analysis was conducted using backscattered electron imaging, histology, and radiographic techniques. The appositional bone index, percent bone ingrowth, and mineral content were measured for both implants. The results showed a 177% higher appositional bone index (P=.014) for the HA porous-coated Anatomic Porous Replacement component compared to the titanium Anatomic Porous Replacement component. Backscattered electron analysis showed 50% more bone in the HA porous-coated implant (P=.028). The mineral content analysis demonstrated that the bone ingrown into the HA porous-coated device was 23% less mineralized (P=.016). The data from this case study suggested that plasma-sprayed HA porous-coated implants may assist in increasing the amount of bone ingrowth and skeletal attachment in total hip arthroplasties.
Advances in ground section histology of hard tissues and implants have been made with the use of plastic slides in combination with a cyanoacrylate glue. This paper describes the techniques used to prepare ground sections containing implant and bone for microradiography, light microscopy, and scanning electron microsopic analysis. The use of plastic slides can reduce specimen loss and provide flat, thin sections for backscattered electron microscopic and histological analysis. (The J Histotechnol 12:307, 1989)
This study reports on the results of the implant and tissue analysis of clinically retrieved hydroxyapatite (HA)-coated implants. Five of the patients with fixed HA-coated stems had been clinically diagnosed with osteolysis. The semiquantitative histologic grading in these patients snowed HA, polyethylene, and metal particles were all present (Grade 3+) in the osteolytic regions of the periprosthetic tissue. Additionally, inflammatory cells (Grade 3+) were present in these regions. Back-scattered electron (BSE) and correlated elemental analysis showed HA participate was present in the polyethylene inserts. The HA could be distinguished from bone chips in the polyethylene based on morphology and anatomic number gray level differences. This study was limited in that no clinical results of particular HA-coated implant series were reported. Careful follow-up care in patients with coated devices is recommended.
(C) Lippincott-Raven Publishers.
A histomorphometric evaluation of the iliac crest trabecular bone remodeling was performed after tetracycline double-labeling in 41 normal Danes (12 males and 29 females) aged 19 to 56 years. The fraction of formative (osteoid covered) and resorptive surfaces was unrelated to age but higher in males than in females (P less than 0.02 and P less than 0.05, respectively). The appositional rate (0.65 +/- 0.12 micrometer/day) was unrelated to age and sex, whereas the fractional labeled surfaces were higher (P less than 0.01) in the males (0.18 +/- 0.08 micrometer2/micrometer2) than in the females (0.12 +/- 0.05 micrometer2/micrometer2), and among the females inversely related to age (R = -0.38, P less than 0.05). The bone formation rate at BMU level (0.50 +/- 0.20 micrometer3/micrometer2/day) was unrelated to sex, but among the females inversely related to age R = -0.49, P less than 0.01). The bone formation rate at tissue level was higher (P less than 0.02) in the males (0.13 +/- 0.07 micrometer3/micrometer2/day) than in the females (0.07 +/- 0.03 micrometer3/micrometer2/day) and among the females inversely correlated to age (R = -0.43, P less than 0.05). the age- and sex-dependent variations in the dynamic parameters underline the importance of a more elaborated normal material.
Experiments have been devised to study the rate of ingrowth of bone into porous metal with pore sizes up to 100 μ and to study the significance of a gap between the porous metal surface and bone.
When the porous coat was in direct apposition with bone, the implant was firmly locked in place after a three week period and the plateau value of implanttissue shear strength was reached at four weeks. A gap of 1.5 mm between the bone and the implant was bridged by new bone wihtin four weeks.
Ten asymmetric porous-coated tibial knee components were consecutively retrieved from nine patients with implantation times ranging from 1 week to 48 months. Morselized autograft bone chips were applied to the resected surface of the tibia prior to component implantation. Microradiographic analysis showed bone in contact with 64 +/- 10% of the porous-coated interface. Backscattered electron imaging of the bone-implant interface revealed bone within 8-22% of the porous coating. Although bone in the form of autograft bone chips was observed in the porous coating of the 1 and 3 week specimens, it was not connected to the host bone. By 3 and 6 months, the bone chips were integrated and connected to the host bone providing osseous continuity from the porous coating to the skeleton. This study shows that reproducible bone ingrowth into porous-coated tibial components is achievable using autograft bone chips to promote bone fixation.
A hydroxyapatite-coated hip hemi-prosthesis was retrieved from a 98-year-old osteoporotic woman 12 weeks after implantation. Histologic analysis revealed bone and fibrous tissue almost evenly distributed around the surface of the implant circumference. Quantitative histologic analysis showed that 48% of the hydroxyapatite surface was covered by bone. Fibrous tissue covered 30% of the prosthetic surface, and 20% of the surface had no tissue coverage. Scanning electron microscopy showed direct contact without any clear boundary between the newly formed bone and the hydroxyapatite ceramic.
To evaluate cancellous allogenic bone graft incorporation into porous-coated implants, the fixation of titanium alloy-(Ti) and hydroxyapatite-(HA) coated implants with and without bone graft was compared. An unloaded model with unilateral carragheenin-induced osteopenia of the knee was used in 12 mature dogs. Ti- and HA-coated cylinders were implanted in the distal femoral condyles and centralized in 2-mm overreamed drill holes. Allogenic, fresh-frozen (-80[degrees]) cancellous bone graft was packed around the implants in six dogs. In a matched group of six other dogs, the implants were left in overreamed canals without bone graft. After six weeks the interface shear strength of grafted Ti-coated implants had significantly increased compared to the nongrafted Ti implants.
However, HA coating used without bone graft was capable of enhancing the bone-implant interface shear strength to nearly the same degree. The fixation of grafted Ti- and HA-coated implants was equal. No significant difference in implant fixation was found between osteopenic and control bone. Histomorphometric evaluation of mineralizing surfaces in direct contact with the implant confirmed the results from the push-out test. Boneimplant fixation when using allogeneic fresh-frozen cancellous bone graft in osteopenic and control bone was enhanced by hydroxyapatite coating but the HA coating alone appeared to offer almost the same improvement in anchorage in 2-mm defects. Loss of bone stock around loose prosthetic implants often requires bone grafting. However, because of anatomic constraints in joint prosthetic surgery, a complete filling of defects with bone graft is difficult, and areas of gaps between bone and implant will remain. Provided mechanical stability of the prosthesis, the results reported here suggest that these areas will probably be filled early with new mineralizing bone if the prosthesis is coated with a thin layer of hydroxyapatite.
(C) Lippincott-Raven Publishers.
A versatile mineralized bone stain (MIBS) for demonstrating osteoid seams and tetracycline fluorescence simultaneously in thin or thick undecalcified sections has been developed. Bone specimens are fixed in 70% ethanol, but 10% buffered formalin is permissible. Depending upon one's preference, these specimens can be left unstained or be prestained before plastic embedding. Osteoid seams are stained green to jade green, or light to dark purple. Mineralized bone matrix is unstained or green. Osteoblast and osteoclast nuclei are light to dark purple, cytoplasm varies from slightly gray to pink. The identification of osteoid seams by this method agrees closely with identification by in vivo tetracycline uptake using the same section from the same biopsy. The method demonstrates halo volumes, an abnormal, lacunar, low density bone around viable osteocytes in purple. This phenomenon is commonly seen in vitamin D-resistant rickets, fluorosis, renal osteodystrophy, hyperparathyroidism, and is sometimes seen in fluoride treated osteoporotic patients. In osteomalacic bone, most osteoid seams are irregularly stained as indicated by the presence of unmineralized osteoid between mineralized lamellae. The method has been used effectively in staining new bone formation in hydroxyapatite implants and bone grafts. Old, unstained, plastic embedded undecalcified sections are stained as well as fresh sections after removal of the coverslip. This stain also promises to be valuable in the study of different metabolic bone diseases from the point of view of remodeling, histomorphometry, and pathology.
The bone healing process normally unites fractures, arthrodeses, osteotomies, and bone grafting operations. The process normally proceeds in successive stages named the fracture, granulation, and modeling/remodeling stages. A separate regional acceleratory phenomenon speeds up each of the other stages. The osteoclast and osteoblast cells that make intercellular substances of each stage do not exist in sufficient numbers to heal the bone at the moment of fracture or operation. They are made by local multicellular mediator mechanisms that contain precursor and supporting cells, capillaries, lymph, and innervation, plus local autocrine and paracrine regulation. Under the influences of local and systemic agents, these mediator mechanisms determine whether new local osteoclasts and osteoblasts will appear, in addition to when, where, how many, what kind, and for how long. Errors in those functions can then lead to several kinds of retarded or otherwise abnormal bone healing that will be discussed in Part II of this work.
The host response to porous-coated prostheses appears favorable; there is little evidence of any adverse tissue response or significant osteoclastic activity except in grossly loose specimens. While the nature of retrieval specimens makes any statistical correlation problematic, some generalizations can be made. Femoral hip prostheses are most likely to present bone ingrowth along the lateral quadrant of their porous coating. The frequency of bone ingrowth of femoral components was nearly twice that of acetabular devices. Pore size, geometry, and porous-coating composition did not appear to influence the appearance of bone and fibrous tissue ingrowth. Direct bonding of bone to the uncoated portion of the prosthesis was rarely seen and occurred only in closest proximity to the porous-coated regions. Indications of pain and looseness are evidence that fibrous tissue ingrowth alone is not always sufficient to ensure stability. Additionally, some bone-ingrown prostheses were retrieved because of pain, which leads to the conclusion that local bone ingrowth cannot ensure a general freedom from pain, especially with partially coated prostheses. Bone and fibrous tissue response to the porous coatings generally consists of interdigitation, while the response to uncoated regions is fibrous tissue encapsulation. Burnishing the distal tips of many of the partially coated femoral prostheses is an indication of relative motion in that region, which may be a potential source of pain.
A retrieved uncemented, porous-coated human patellar component was evaluated histologically and microradiographically. The metal portion of the component and porous coating were made of cobalt--chromium-based alloy. Because of adhesive capsulitis and inadequate knee flexion, the patient had revision surgery 11 months after the original total knee arthroplasty. Clinically, the device was not grossly loose. Contact microradiography of the porous material showed no calcified tissue ingrowth. Undecalcified histologic sections demonstrated only fibrous tissue ingrowth, with obvious bone-resorptive activity as well as numerous multinucleated giant cells adjacent to the porous metal.
The mineral apposition rate of trabecular bone was determined in several skeletal sites of young adult beagles. Tetracycline derivatives were administered intravenously or orally on 2 separate occasions preceding the day of sacrifice in order to label actively mineralizing bone surfaces. The rate of mineral apposition was calculated by dividing the distance between the 2 tetracycline markers by the time interval between their administration. The lumbar vertebra, proximal humerus, and pelvis, each of which contains red marrow, were found to have a significantly higher (P less than 0.001) rate of mineral apposition in trabecular bone than the skeletal sites containing yellow marrow--the proximal ulna and distal humerus. The mean apposition rate in the former 3 sites was 1.3 +/- 0.3 micrometers/day, while that in the latter 2 was 0.9 +/- 0.2 micrometers/day (uncorrected for plane of sectioning). It is tempting to speculate that this finding may be a consequence of differences in vascularity between red and yellow marrow.
Powder metal-made orthopedic implants with a porous coating provide an effective means for implant fixation by tissue ingrowth. Additionally, the use of metal alloy powders for forming porous surfaces offers the advantage of uniform coatings on complex part shapes. With proper processing, implants with strong, porous surface layers and good substrate mechanical properties can be formed. The in vivo tests have demonstrated the need for initial implant stability to achieve bony ingrowth. Animal studies indicate an optimum pore size range of 50-400 mu, and human hip prostheses with pores in this range appear to function well. A porous surface integrated with a compatible implant design avoids undesirable bone remodeling with these types of implants.
Sixteen porous polysulfone-coated canine femoral stems were inserted into 14 dogs. Coatings were approximately 40% porous, with an average pore size of 125 or 250 microns. Bone was formed within at least about 30% of the surface pores of the implants. The tissue ingrowths filling the pores included marrow and fibrous tissue. Correlated roentgenographic and histologic observations revealed a trabecular "lamina dura" at the coating-bone interface and relatively dense trabeculae distal to the stem tip. These observations support the concept of coating femoral prostheses with porous material for cement-free stabilization.
To evaluate a porous fiber titanium composite as a fixation method, total hip arthroplasty was performed in 13 large male mongrel dogs. In seven both acetabular and femoral composites were fixed with a porous titanium fiber composite, and in the other six the acetabulum was fixed with acrylic cement. The animals were killed one, three, and six months following implantation. At autopsy all components were fixed by bony ingrowth. There was progressive remodeling of the ingrown bone and of the bone trabeculae surrounding the prosthesis in the three- and six-month animals, with gradual thickening and development of haversian structures. Cortical osteoporosis, which did not appear to be progressive, was detected in both the one- and six-month specimens.
Implantation of a newly designed acetabular component with a porous coating has resulted in superior fixation when compared with acrylic cementation in the short term. Experiments in dogs demonstrate rapid ingrowth within the porous layers, resulting in rigid fixation of the acetabular components despite defects in the prepared bony bed. Acute infection prevents bony ingrowth and causes loosening. The absence of any foreign-body response to the titanium fiber mesh components suggests that this is a biocompatible metal. The fixation has been excellent; progressive or delayed loosening is not encountered once successful ingrowth is achieved. Progressive radiolucent zones generally do not appear in the short term but when visible soon after surgery, may consolidate and disappear. Ingrowth fixation of acetabular components appears to offer an attractive alternative to the use of acrylic cement and may even be feasible in patients with periarticular bony abnormalities.
Thirty‐six regions of trabecular bone from two 18‐month‐old beagles and transilial biopsies of 25 female beagles aged 28–52 months were studied following in vivo double tetracycline labeling. Turnover rate varied from about 20% per year to 200% per year among the 36 regions. It was highest in the vertebral bodies and the proximal humerus, and lowest in the proximal ulna and foot‐bones. The mineral apposition rate varied from 0.35 to 1.02 μm/day, with a mean of about 0.7 μm/day, tending to be lower in areas of lower turnover. The specific surface varied from 10.9 to 23.8 mm/mm ² with a mean of 17.5 mm/mm ² , tending to be higher in areas of high turnover. Specific surface varied only about twofold around the skeleton, while turnover varied by one order of magnitude. The average annual turnover rate for all trabecular bone in the young adult beagle is estimated at 140% per year. The accuracy of this estimate would be improved by knowing the exact mass of trabecular bone at each site.
The annual turnover rate in the ilium of 25 female beagles was 134 ± 94% per year. The iliac trabecular bone turnover rate is two to three times faster in young adult female beagles than in young adult female humans. Using a human to beagle ratio of 1:2.5, the average annual turnover rate for all trabecular bone in the young adult human could be estimated at 40–55% per year. The beagle may be an appropriate model for certain experiments involving the adult bone remodeling system, because it may show a quicker response than humans to various experimental conditions and drugs, due to its faster turnover rate.
For a study on the effects of pore size variation on the rate of bone growth into porous-surfaced metallic implants and on the strength of fixation resulting from this ingrowth, 4 distinct pore size ranges were prepared on cobalt-base alloy implants with cobalt-base alloy powder particles of different dimensions. The porous implants were placed into canine femurs for periods of 4, 8, and 12 weeks. Mechanical tests were performed to measure the shear strength of fixation of the implants to cortical bone. For implants with powder-made porous surfaces, a pore size range of approximately 50 to 400 microns provided the optimum or maximum fixation strength (17 MPa) in the shortest time period (8 weeks).
The canine is frequently used as a model for human hip arthroplasty research. In order to better understand the appropriateness of the canine as a model for human total hip replacement studies, the external morphology of canine and human femurs were examined and compared. Several differences were found between canine and human femora, including angular measurements, anterior bow, and femoral head position relative to the femoral diaphysis. In addition, the human femur was noted to undergo age-related changes in several of the measured parameters. The canine femur did not exhibit any age-related changes in the measured parameters. This study suggests that there are limitations to the use of the canine model in human hip arthroplasty research, and that discretion must be exercised when attempting to extrapolate results from a canine study to the human clinical condition.
The clinical and histological results of hydroxyapatite (HA) coating separation from a press-fit total hip arthroplasty 3.3 years after surgery are documented. Semiquantitative histological analysis showed grade 3+ mononuclear histiocytes and giant cells present in the retrieved capsule and periprosthetic tissues. Grade 3+ (titanium alloy, HA, and polyethylene) particles could be seen throughout the tissues. Backscattered electron and correlated elemental analysis confirmed that the HA coating had migrated to the articulating surface of the polyethylene insert causing third-body wear. The authors suggest that the orthopedic surgeon be cautioned in the routine use of HA-coated implants if osteolysis associated with HA separation and migration is to be avoided.
The human cancellous bone response was compared in weight-bearing porous hydroxyapatite (HA) and titanium-coated implants placed in the distal medial femoral condyles of consenting staged bilateral knee patients. The Institutional Review Board approved study quantified the amount of bone ingrowth, the mineral apposition rate, and the bone mineral content. Results showed that the osteoconductive HA coating increased the amount of bone ingrowth by 8% (P = .018). The HA coating did not effect the mineral apposition rate of the bone but had an 8% lower bone mineral content at the implant interface (P = .042). The influence of HA coatings on human cancellous bone appears highly focal along the coating surface. Gaps of 50-500 microns filled with fibrous connective tissue were observed along the porous-coated surfaces of both implant types suggesting that HA coatings still require precision placement adjacent to human cancellous bone.
Bony ingrowth fixation of newly de-145-153
- A K Hedley
- M Kabo
- W Kim
- I Coster
- H C Amstutz
A. K. Hedley, M. Kabo, W. Kim, I. Coster, and H. C. Amstutz, " Bony ingrowth fixation of newly de-145-153 (1981). 544 11. 12. 13. 14. 15. 16. 17. 18. 19. 20. 21. 22. 23. 24. 25. 26. 27. 28. signed acetabular components in a canine model, " Clin. Ortkop., 176, 12-23 (1983).
Bone ingrowth into porous polymers
- M Spector
M. Spector, " Bone ingrowth into porous polymers, " in: Biocompatibility of Orthopaedic Implants, D. F. Williams (ed.), CRC Press, Boca Raton, 1982,55-88.
Hydroxyapatite coating converts fi-brous anchorage to bony fixation during continuous implant loading
- K Serballe
- E S Hansen
- H B Rasmussen
- C Bunger
K. Serballe, E.S. Hansen, H.B. Rasmussen, and C. Bunger, " Hydroxyapatite coating converts fi-brous anchorage to bony fixation during continuous implant loading, " Trans. Ortkopaed. Res. SOC., 17, 292 (1 992).
Tissue growth into retrieved noncemented human hip and knee components
- K Thomas
- S Cook
- K Thomas
- R J Haddad
K. Thomas, S. Cook, K. Thomas, and R. J. Haddad, " Tissue growth into retrieved noncemented human hip and knee components, " in: Biomedical Engineer-ing V, Recent Developments, s. Saha (ed.), Pergamon Press, New York, 1986, 198-203. 583-586 (1981). 147-170 (1987).
The histology of porous coated knee prostheses
- Mayor M.
M. Mayor and J. Collier, " The histology of porous coated knee prostheses, " Ortkop. Trans., 10,441 -442 (1986).
A versatile new mineralized bone stain for simultaneous assessment of tetracycline and osteoid seams Stain Tecknol The biology of fracture healing. An overview for clinicians. Part I The regional acceleratory phenome-non: A review
- A R Villanueva
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A. R. Villanueva and K. D. Lundin, " A versatile new mineralized bone stain for simultaneous assessment of tetracycline and osteoid seams, " Stain Tecknol., 64, H.M. Frost, " The biology of fracture healing. An overview for clinicians. Part I, " Clin. Ortkop., 248, H. M. Frost, " The regional acceleratory phenome-non: A review, " Henry Ford Hosp. Med. I., 31, 3-9 (1983).
- Bloebaum
Hydroxyapatite coating converts fibrous anchorage to bony fixation during continuous implant loading
- Søballe K.
Bilateral total knee arthroplasty: Indications of simultaneous versus staged procedures
- Weiss A. A.
Plastic slides in the preparation of implant and tissue for interface analysis
- Bloebaum R. D.