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Adaptive bone remodeling and biomechanical design considerations
Abstract
Clinical problems with noncemented total hip arthroplasty (THA) stems, directly or indirectly related to load transfer, include mid-thigh pain due to relative (micro) motions or excessive endosteal interface stresses, subsidence and loosening due to inadequate primary stability and fit, and proximal femoral bone atrophy due to stress shielding. In this article, the load-transfer mechanisms associated with noncemented THA stems and their resulting stress patterns are discussed in relation to design features, bonding characteristics, and materials choice. Nonlinear finite-element models and computer simulation programs for strain-adaptive bone remodeling have been used for this study. Canal-filling, fully bonded metal stems have been found likely to cause proximal bone atrophy, possibly leading to long-term failure of the implant/bone composite. The use of flexible (isoelastic) materials and/or press-fit fixation reduces stress shielding, but also reduces the potential for interface stability. The stem material, the stem shape, and the coating geometry interact in relation to the load-transfer mechanism, and it is suggested that optimal combinations of these characteristics can be determined through the computer simulation methods presented.
... Clinical results with HA-coated prostheses have shown reliable osseo-integration with negligible mid-thigh pain (19)(20)(21). The long-term success of most prostheses is closely related to the distribution of stress transfer, which largely depends on prosthetic design and bonding characteristics (22,23). Predominance of stress transfer more distally in the femur caused by a tight diaphyseal fit, leads to an unfavourable stemto-bone stiffness ratio, which is thought to be a reason for a higher incidence of thigh pain (22)(23)(24)(25)(26). ...
... The long-term success of most prostheses is closely related to the distribution of stress transfer, which largely depends on prosthetic design and bonding characteristics (22,23). Predominance of stress transfer more distally in the femur caused by a tight diaphyseal fit, leads to an unfavourable stemto-bone stiffness ratio, which is thought to be a reason for a higher incidence of thigh pain (22)(23)(24)(25)(26). This leads to augmented proximal stress shielding-induced bone resorption, which may start a failure scenario (27). ...
... Instead we found that the region in which the most prominent cancellous and cortical densifications were observed gradually shifted from proximally in Gruen zones 2 and 6 to more distally in these same zones. Formation of new bone in the area near the lower edge of HA coatings was predicted by Huiskes et al (22) using finite element analysis. The explanation was that particularly in this area endosteal stress concentrations are caused by the abrupt transition from a bonded to a loose interface. ...
We prospectively studied 152 hips in 126 patients with a proximally porous and hydroxyapatite coated double tapered straight femoral prosthesis. The follow-up period was 4.2 to 9.6 years. All but two prostheses showed osseo-integration. The mean Harris hip score (HHS) increased from 40 to 92 points and 97% of the patients had no or only mild pain. Limping and the use of walking aids decreased substantially after the operation. The morphology of positive bone remodelling with either endosteal bone formation or periosteal bone formation was correlated with the stem fit in the medullary canal (p=0.0001). Negative bone remodelling features could not be demonstrated. There was no correlation between the clinical parameters and the radiological phenomena.
... The stiffness of a femoral stem determines its interaction with the surrounding bone, which exhibits very different mechanical properties. Bone is a living tissue whose structure is continuously remodelled by the concurrent action of two classes of cells: the osteoblasts, which build up the bone structure, and the osteoclasts, which break it down [107]. Therefore, bone remodelling is a lifelong process where mature bone tissue is removed from the skeleton (bone resorption) or newly formed (ossification) in response to the local loading conditions. ...
... This means that bone may be locally resorbed, where it is not loaded, and recreated or strengthened where more load has to be carried. The implantation of a hip prosthesis is drastically changing the normal physiological load transfer leading to bone response [107,108]. ...
... The relationship between implant flexibility and the extent of bone loss is clinically well established. It has been confirmed that changes in bone morphology are a result of adaptive bone remodelling following stress shielding [107,109]. ...
Recently increasing revision rates of certain types of metal-on-metal (MoM) hip prostheses , introduced on the medical device market during the last decade, have created uncertainty concerning the safety and effectiveness of artificial hip joints . Eventhough medical progress is generally expected to be a continuous process leading to improved medical treatment, problems occured with some hip-resurfacing systems that failed to deliver the expected improvement. Moreover, this created severe health problems for many patients worldwide . This report reviews the historical development and the state-of-the-art of total hip arthroplasty from a biomedical engineering point of view and illustrates the motivation for the efforts to improve the quality of hip prostheses. The report also aims at explaining the peculiar problems related to evaluating the safety and effectiveness of hip prostheses, which are supposed to last for at least 20 to 25 years. Furthermore, it addresses some medical and biological aspects of total hip arthroplasty (THA).
... In cases of cortical hypertrophy and stress shielding, bone remodeling is commonly observed in uncemented hip replacement, resulting in changes of bone density and micro-architecture [7]. The patterns of remodeling depend on biological and mechanical factors [8], such as preoperative bone mass, age, and weight of the patient [9]. Among the mechanical factors, an altered load distribution is caused by specific features of the implant (size, implant design, alloy) and type of stem fixation in the femur [9][10][11][12][13]. ...
... The aim is to achieve an alteration of the physiological strain patterns [14], considering an implant-delivering load through bone while adjacent areas are no longer stressed. This is of clinical importance because such load patterns can lead to proximal bone loss [8,14,15], which in turn is a potential risk factor for aseptic loosening of the femoral implant [16][17][18]. Nevertheless, most of the reports have proved that these designs do not completely prevent proximal bone atrophy [19][20][21][22][23][24][25][26]. ...
PurposeThe purpose of this study was to evaluate the osseointegration and radiological outcomes in patients after total hip arthroplasty, hypothesizing different load patterns with one cementless stem design and different CCD angles (CLS Spotorno femoral stem 125° vs 135°).Methods
All cases of degenerative hip osteoarthritis fulfilling strict inclusion criteria were treated with cementless hip arthroplasty between 2008 and 2017. Ninety-two out of one hundred six cases were clinically and radiologically examined three and 12 months after implantation. Two groups with each 46 patients were rendered prospectively and compared in clinical (Harris Hip Score) and radiological outcome.ResultsAt final follow-up, no significant difference regarding Harris Hip Score was detected between the two groups (mean 99.2 ± 3.7 vs. 99.3 ± 2.5; p = 0.73). Cortical hypertrophy was found in none of the patients. Stress shielding was seen in a total of 52 hips (n = 27 vs. n = 25; 57% of the 92 hips). No significant difference regarding stress shielding was detected when comparing both groups (p = 0.67). Significant bone density loss was detected in Gruen zone one and two in the 125° group. The 135° group showed significant radiolucency in Gruen zone seven. No overall radiological loosening or subsidence of the femoral component was observed.Conclusion
According to our results, the use of a femoral component with a 125° CCD angle versus a 135° CCD did not result in a different osseointegration and load transfer with a clinically relevant significance.
... The inferior surface of the distal tibia was fixed in all directions (Fig. 4). A conservatively low value for damage stress (2.8 MPa) of the cancellous bone was adopted, and a resorption threshold of 0.1 MPa was used to assess possible bone resorption [18]. Seven FEA models were set up to determine the differences between screw angles with one or two screws ( Table 2). ...
... Stresses at the 6 points on the midcourt line of the medial and lateral plateaus are shown in Fig. 7. All stresses measured were within the normal range (0.1-2.8 MPa) [18]. The stresses of the medial plateau in model 7 (0.14-0.21 ...
Background
The cement-screw technique is a convenient method to repair tibial plateau defects in primary and revision total knee arthroplasty (TKA). However, the optimal angle of screw insertions is unknown. This study aimed to perform a finite element analysis (FEA) to determine the optimal screw angle for the repair of tibial plateau defects in TKA.
Methods
Seven FEA models were set and two common different defects (defect 1: area < 12%, depth < 12 mm; defect 2: area > 12%, depth > 12 mm) were simulated. One screw was used in defect 1, and one or two screws were used in defect 2. Screws were parallel to the proximal cortical bone (oblique screw) or perpendicular to the upper surface (vertical screw) of the tibia. Contact stresses on cancellous bone in different areas were determined. Maximum principal stress on the cancellous bone around each screw was also compared.
Results
The FEA models showed that stresses on the surface of cancellous bone in tibial defect (0.13–0.39 MPa) and stress focus spot (0.45 MPa) around the screw were lower when one vertical screw was used in defect 1. The stresses on the surface of cancellous bone in tibial defect (0.09–0.44 MPa), stresses in the medial tibial plateau (0.14–0.21 MPa), and stress focus spot around the screws were lowest (0.42 MPa and 1.37 MPa) when two vertical screws were used in defect 2, followed by of one vertical and one oblique (0.16–0.48 MPa; 0.15–0.21 MPa; 1.63 MPa and 1.11 MPa). No other statistically significant differences were found.
Conclusions
Either for one or two screws, those perpendicular to the upper surface achieve better stability than those parallel to the proximal cortical bone of the tibia. If two vertical screws cannot be performed, one vertical and one oblique is also acceptable.
... Theoretical and experimental studies have shown that cementless femoral stems result in more normal stress and strain transfer in the proximal medial femur than cemented stems (Huiskes 1989, Zhou et al 1990. However, this optimal load transfer is very dependent on the stem with accurate fit. ...
... The strains and stresses in the bone of the femur change considerably after total hip replacement. These altered stresses and strains will gradually induce femoral remodelling (Brown 1985, Hill 1988and Huiskes 1989, which can lead to stem loosening and clinical failure. ...
The clinical results of uncemented total hip replacement are strongly influenced by the geometry of the stem and its fit within the femoral canal. Particularly where the femoral canals are severely distorted such as in CDH or JRA, the femoral canal can not be accurately fitted by conventional hip stems. The condition of the femur on revision is highly variable, making it difficult to achieve consistently satisfactory constructs in each case. Therefore, there is a strong case for suggesting that custom-designed stems should play an important role in hip reconstruction. For this purpose, a Hip Design Workstation was developed, with the ability to design and manufacture custom femoral intramedullary stems for both primary and revision cases by using the technique of Computer-Aided-Design (CAD) and Computer-Aided-Manufacture (CAM). This system can three dimensionally reconstruct the femoral canal by digitizing A-P and M-L views of the femoral contour from plain radiographic images. In addition, the femoral canal can be reconstructed from CT scans. During reconstructing the femoral canal from plain X-ray films, special software was developed which can correct rotations of radiographs up to 30 degrees in the lateral view and 60 degrees in the frontal view. After the canal was reconstructed, the software then designed the stem for the individual canal with optimal design algorithms, allowing for multiple design options to be specified by the user. In order to evaluate the custom stems, several comparative studies with standard stems were carried out. The hypotheses for these studies were that custom femoral stems would produce a closer fit in critical regions, would be more stable on stem-bone interface motion, and would produce closer-to-normal stress distributions. In addition, the advantages of the custom stems would be reflected on the clinical results and radiographic appearances. The stem-canal fit study was conducted by analysing the gaps between stems and canals in four quadrants. Strains on the surface of a femoral bone before and after stem insertion was measured by using a photoelastic coating technique. Stem-bone interface motion under cyclic loading were quantified in four axes by using Linearly Variable Differential Transducers (LVDT). The data from six channels were simultaneously recorded by a linked computer. Radiographic studies including measurement of stem migration and bone density changes were conducted by using a newly developed technique and DEXA scan. In addition, a biological study of tissue osseointegration with titanium stems of different stiffness was carried out on rat femurs. The results from the studies showed that the custom stems were superior to the standard stems in terms of canal fit, strain distribution and interface motions. For the radiographic follow up, the results showed that 79% of custom stems were stable from zero to six months and 96% from six to twelve months, which was comparable with cemented stems. Bone mineral density changes were found to be less than 10% from zero to six months and from six to twelve months. In the biological study, the results showed that less stiffness of the implant could enhance the osseointegration onto the stems. This provides useful information for hip stem design. This study demonstrated that custom stems provide a better solution for uncemented total hip replacement. The CAD-CAM technique offers great accuracy and flexibility in designing and manufacturing individual stems. The method does however require additional time and expense compared with using an off-the-shelf stem. Nevertheless it is fully justified for many cases at this time, while a further reduction in cost will extend the indications to the more standard cases.
... Using such models, changes in the bone mass, as well as the cell population, can be evaluated during the bone remodelling process; however, their computational cost is much higher and their performance quite sensitive to diverse aspects, in particular integration step size (Komarova et al. 2003). The hip joint has been the main focus of the experimental and numerical studies carried out on bone remodelling, mainly due to the significant stress shielding which arises around hip implants Doblaré and Garcia 2002;Huiskes et al. 1989;Kwon et al. 2013). On the other hand, limited research has been conducted on bone remodelling of the knee joint (Martínez-Reina et al. 2016;Levadnyi et al. 2017;Jacobs et al. 1995;Weinans et al. 1992;Quilez et al. 2017;Jia et al. 2017), some examples being the studies of Quilez et al. (2017) and Jia et al. (2017), who examined the influence of various knee prosthesis stem types in total knee arthroplasty (TKA) implants on bone mineral density (BMD) of the tibia postoperatively. ...
... In the subroutine, the maximum and minimum densities were set to 2e−06 and 2e−07 kg/mm 3 , respectively (Soffiatti et al. 2017c;Hall 2014). For the model without the implant, the remodelling process was started with a density value of 1e−06 kg/mm 3 in order to achieve a density distribution which qualitatively represents the bone morphology, as done in previous studies Doblaré and Garcia 2002;Huiskes et al. 1989;Jacobs et al. 1995;Weinans et al. 1992). Bone density was then extracted from this model (using MATLAB ® routines) and assigned to the model with the implant in which the geometry of the bones is slightly different due to the implant fixation holes. ...
Bone remodelling is a crucial feature of maintaining healthy bones. The loading conditions on the bones are one of the key aspects which affect the bone remodelling cycle. Many implants, such as hip and knee implants, affect the natural loading conditions and hence influence bone remodelling. Theoretical and numerical methods, such as adaptive bone remodelling, can be used to investigate how an implant affects bone mineral density (BMD). This research aimed to study the influence of an extra-articular implant on bone remodelling of the knee joint using adaptive bone remodelling. Initially, a finite element (FE) model of the knee joint was created. A user-defined material subroutine was developed to generate a heterogeneous BMD distribution in the FE model. The heterogeneous density was then assigned to the knee model with the implant in order to investigate how the implant would affect BMD of the knee joint, five years postoperatively. It was observed that in the medial compartments of the femur and tibia, bone mineral density increased by approximately 3.4% and 4.1%, respectively, and the density for the fixation holes of both bones increased by around 2.2%. From these results, it is concluded that implanting of this load-sharing device does not result in significantly adverse BMD changes in the femur and tibia.
... It influences the interaction with the surrounding bone tissue which exhibits very different and varying mechanical properties, due to bone remodeling. Therefore, the implantation of a hip prosthesis is drastically changing the normal physiological load transfer leading to bone response [66]. ...
... This mechanical mismatch may cause stress shielding where the prosthesis do not transfer load to the surrounding bone. Insufficiently loaded bone responds with bone resorption which will compromise the long-term clinical performance of the prosthesis [66]. ...
... A homeostatic equilibrium between bone formation and bone loss is achieved during natural biomechanical loading, whereas unnatural stresses or strains induce morphological changes and alteration in bone remodeling [6,10,11]. After THA, a similar process occurs when abnormal stress or strain is applied to the bone surrounding the prosthetic implants [5,10,11]. ...
... A homeostatic equilibrium between bone formation and bone loss is achieved during natural biomechanical loading, whereas unnatural stresses or strains induce morphological changes and alteration in bone remodeling [6,10,11]. After THA, a similar process occurs when abnormal stress or strain is applied to the bone surrounding the prosthetic implants [5,10,11]. An associated bone weakness and possible bone fracture or implant loosening and subsequent implant failure may result [5,6,8,9]. ...
Background
Coxofemoral osteoarthritis is a chronic, disabling condition affecting people and dogs, with THA providing an excellent return to function in severely affected joints. The principal role of THA is to restore an adequate range of motion to the hip joint while transferring load from the acetabulum in order to improve the survival of the implant and enhance the limb function in the short and long terms. The objectives of the study reported here were, therefore, to radiographically evaluate periprosthetic acetabular bone GV and to assess prosthetic head acetabular coverage after 4 months of uncemented and cemented THA in dogs. Means periprosthetic acetabular GV for each and combined 3 regions of interest (zones 1, 2 and 3) were calculated immediately and 4 months after THA. Prosthetic head Norberg (PHN) angle was also measured to assess the degree of prosthetic head acetabular coverage after 4 months of surgery. ResultsZones 2 and 3 showed a significant increase in the mean bone GV after 4 months of uncemented THA. No differences in zones 1–3 after 4 months of cemented THA. Combined zones showed a significant increase in overall mean bone GV 4 months after uncemented THA; whereas, no changes were identified after 4 months of cemented THA. The PHN angles did not change after 4 months of uncemented and cemented THA and did not differ significantly between the 2 designs of hip arthroplasty. Conclusions
Regional periprosthetic acetabular bone GV varies with the design of THA. None of the designs showed periprosthetic acetabular bone lucency. No differences identified in the degree of prosthetic head acetabular coverage in both designs, indicating proper implant stability after 4 months of surgery. Further longer–term investigation on larger population is however still warranted.
... Stress transfer in the femur after THA depends on the stem size, design, material and whether the stem is cemented or cementless. Femoral remodelling occurs in response to variations in stress transfer [12,21]. Bone atrophy due to stress shielding, particularly in the proximal femur, remains an unresolved problem [5]. ...
Purpose
Thermoelastic stress analysis (TSA) was used to evaluate stress changes over the entire surface of a specimen. This study aimed to assess the relationship between femoral stress distribution, analysed using TSA and changes in bone mineral density (BMD) after total hip arthroplasty (THA).
Methods
Stress changes in the simulated bone before and after taper‐wedge stem insertion were measured using the TSA. Stress changes were compared with BMD changes around the stem 1 year after surgery in a THA patient (58 hips) with the same taper‐wedge stem. Subsequently, we compared the correlation between stress changes and BMD changes.
Results
TSA revealed significant stress changes before and after stem insertion, with prominent alterations in the proximal medial region. The BMD changes at 1 year post‐THA exhibited a 15%–25% decrease in the proximal zones, while Zones 2–6 showed a −6% to 3% change. Notably, a strong positive correlation (0.886) was found between the stress change rate and BMD change rate.
Conclusions
This study demonstrated a high correlation between femoral stress distribution assessed using TSA and subsequent BMD changes after THA. The TSA method offers the potential to predict stress distribution and BMD alterations postsurgery, aiding in implant development and clinical assessment. Combining TSA with finite element analysis could provide even more detailed insights into stress distribution.
Level of Evidence
Case series (with or without comparison).
... The distal tibia's inferior surface was fixed in all directions to simulate the anatomical conditions (Fig. 1C). Referring to previous literature, the study implemented conservative values for the damage stress of cancellous bone (2.8 MPa) and assessed possible bone resorption using a resorption threshold of 0.1 MPa [17]. ...
In total knee arthroplasty (TKA), the mechanical mismatch between cobalt-chromium (CoCr) alloy tibial implant and bone has been implicated in stress shielding and subsequent implant failure and bone resorption. This study investigates the biomechanical advantages of poly-ether-ether-ketone (PEEK) tibial implant, which exhibit properties analogous to those of the surrounding bone. A finite element analysis (FEA) was employed to assess and compare the biomechanical performances of PEEK and CoCr tibial implants in patients with and without osteoporosis. Four FEA models were constructed with PEEK and CoCr alloy implants in normal and osteoporotic tibias. Based on previous literature and our clinical experience, stresses measurements were taken at 16 points on the tibial plateau and 8 points on the two surfaces which were 10 mm and 20 mm apart from the tibial plateau, with specific regions quantified for stress shielding. The results showed significant differences in stress distribution between PEEK and CoCr implants. The PEEK implants exhibited higher equivalent stresses on the tibial plateau in all models (normal bone: 0.22 ± 0.07 MPa vs. 0.13 ± 0.06 MPa, p < 0.01; osteoporotic bone: 0.39 ± 0.06 MPa vs. 0.17 ± 0.07 MPa, p < 0.01). In non-osteoporotic models, the mean equivalent stresses on proximal tibial surfaces were similarly elevated for PEEK implants (0.29 ± 0.13 MPa vs. 0.21 ± 0.08 MPa, p = 0.02). The CoCr implants demonstrated more stress shielding across all measured regions (tibial plateau: 23.47% vs. 2.73%; surface 1: 15.93% vs. 1.37%; surface 2: 10.71% vs. 6.56%). These disparities were even more pronounced in osteoporotic models in the CoCr group (tibial plateau: 32.50% vs. 8.36%). The maximum equivalent stresses on the tibial plateau further supported this trend (normal bone: 1.02 MPa vs. 0.52 MPa; osteoporotic bone: 1.43 MPa vs. 0.67 MPa). These data confirm the hypothesis that a PEEK tibial implant can reduce peri-prosthetic stress shielding, suggesting that PEEK implants have the capability to distribute loads more uniformly and maintain a closer approximation to physiological conditions.
... To simulate the loading and fixing conditions, a total load of 1100 N (2.2 times of the body weight) was applied, each of the medial and lateral plateau was 550 N respectively, and the distal tibia was fixed in all directions, as shown in Fig. 3 [17]. A resorption threshold of 0.1 MPa was used to evaluate possible resorption of cancellous bone, while a conservatively low stress value of 2.8 MPa was adopted for damage of cancellous bone [18]. Fig. 1. ...
Cement can be reinforced with cancellous screws for repairing tibial defect in total knee arthroplasty (TKA). However, it is still unknown which size (diameter, length) of screws is better, and the purpose of this study was to perform a finite element analysis (FEA) to determine it. Twelve FEA models were set to represent the cement-screw technique with different diameters (3.5 mm, 5 mm and 6.5 mm) and lengths (20 mm, 25 mm, 30 mm and 35 mm). Contact stresses on the surface of cancellous bone in different areas were calculated. Compared to screws with diameter of 3.5 mm, stresses on the surface of bone defect reduced 5.75% of 5 mm and 10.68% of 6.5 mm for the screw length of 20 mm, 4.23% of 5 mm and 9.16% of 6.5 mm for 25 mm, 6.65% of 5 mm and 12.30% of 6.5 mm for 30 mm, and 5.05% of 5 mm and 12.16% of 6.5 mm for 35 mm. Compared to screws with diameter of 5 mm, stresses on the surface of defect reduced 5.24%, 5.15%, 6.05%, and 7.49% of 6.5 mm for the screw length of 20, 25, 30, and 35 mm. However, it did not show any significant difference in other comparisons. For the treatment of tibial defect in TKA with cement-screw technique, longer screw may not achieve better stability, but the thicker screw can reduce more stresses on the surface of tibial defect and achieve better stability. However, the depth of bone defect must be considered when making a choice.
... Stress transfer depends on stem design, size, material, and fixation method (cemented or cementless). Femoral remodeling occurs in response to changes in stress transfer [15], [20]. Among the problems caused by femoral remodeling, bone atrophy of the proximal femur is particularly problematic. ...
Purpose: The aim of this study was to evaluate the stress distribution in a synthetic femur that was implanted with a fully hydroxyapatite-coated stem using thermoelastic stress and finite element analyses, and to clarify the differences in the stress distributions between these two methods. Methods: Thermoelastic stress analysis is a stress-analysis technique that employs the thermoelastic effect. Sinusoidal vertical loads were applied to the head of the stem placed on the synthetic femur, and surface stress distribution images were acquired using an infrared stress measurement system. The finite element model for the synthetic femur and stem were set up similarly to the thermoelastic stress analysis experiment, and vertical load was applied to the head of the stem. Surface stress distribution and stress values obtained via these two methods were compared. Results: Thermoelastic stress analysis showed that compressive and tensile stresses were distributed from the proximal femur to the diaphysis, not only on the medial and lateral surfaces, but also on the anterior and posterior surfaces. However, finite element analysis showed that compressive stress was not distributed on the anterior and posterior surfaces of the femoral intertrochanter. The stress values of thermoelastic stress analysis tended to be higher in the proximal femur than that obtained via the finite element analysis. Conclusions: The surface stress distribution obtained by these two methods were different specifically in the proximal femur. Our results imply that thermoelastic stress analysis has a better potential than finite element analysis to show the surface stress distribution that reflects the stem design.
... External loading conditions influence bone remodelling. [70][71][72][73] Galileo Galilei, a famous Italian physicist, first recognized a link between mechanical forces (bodyweight) and bone shape in the 17th century. 74 Following that, there was a lot of scientific interest in describing the relationship between bone structure and function. ...
Post-operative bone growth and long-term bone adaptation around the orthopaedic implants are simulated using the mechanoregulation based tissue-differentiation and adaptive bone remodelling algorithms, respectively. The primary objective of these algorithms was to assess biomechanical feasibility and reliability of orthopaedic implants. This article aims to offer a comprehensive review of the developments in mathematical models of tissue-differentiation and bone adaptation and their applications in studies involving design optimization of orthopaedic implants over three decades. Despite the different mechanoregulatory models developed, existing literature confirm that none of the models can be highly regarded or completely disregarded over each other. Not much development in mathematical formulations has been observed from the current state of knowledge due to the lack of in vivo studies involving clinically relevant animal models, which further retarded the development of such models to use in translational research at a fast pace. Future investigations involving artificial intelligence (AI), soft-computing techniques and combined tissue-differentiation and bone-adaptation studies involving animal subjects for model verification are needed to formulate more sophisticated mathematical models to enhance the accuracy of pre-clinical testing of orthopaedic implants.
... The inferior surface of the distal tibia was xed in all directions (Fig. 3). A conservatively low value for damage stress (2.8 MPa) of cancellous bone was adopted, and a resorption threshold of 0.1 MPa was used to assess possible bone resorption [17]. Seven FEA models were set up to determine the differences between different screw angles with one or two screws (Table 2). ...
Background: The cement-screw technique is always used to repair tibial plateau defects in primary or revision total knee arthroplasty (TKA). However, it is unknown which screw angle is better. This study aimed to perform a finite element analysis (FEA) to determine the optimal screw angle for the repairment of tibial plateau defects in TKA.
Methods: Seven FEA models were set and two common different defects (defect 1: area<12%, depth <12 mm; defect 2: area>12%, depth >12 mm) were simulated. One screw was used in defect 1, one or two screws were used in defect 2. Screws were parallel to the proximal cortical bone (oblique screw) or perpendicular to the upper surface (vertical screw) of tibia. Contact stresses on cancellous bone in different areas were determined. Besides, maximum principal stress of cancellous bone around each screw were also compared.
Results: The FEA models showed that stresses on the surface of cancellous bone in tibial defect (0.13-0.39 MPa) and stress focus spot (0.45 MPa) around the screw were lower when one vertical screw was used in defect 1. Meanwhile, stresses on the surface of cancellous bone in tibial defect (0.09-0.44 MPa), stresses in medial tibial plateau (0.14-0.21 MPa) and stress focus spot (0.42 MPa and 1.37 MPa) around the screws were lowest when two vertical screws were used in defect 2, followed by two screws consisting of one vertical and one oblique (0.16-0.48 MPa; 0.15-0.21 MPa; 1.63 MPa and 1.11 MPa). No other statistically significant difference was found.
Conclusions: Either for one screw or two screws, screw perpendicular to the upper surface can achieve better stability than paralleling to the proximal cortical bone of tibia. If two vertical screws cannot be performed, one vertical screw and one oblique screw are also acceptable.
... There are, however, disadvantages to using distally fixed stems in primary cases including cost of the implant and the potential for thigh pain that can result from canal-filling stems [39,47]. There is also stress shielding that can be seen for a long term in patients receiving long distally fixed stems, which occurs less commonly with tapered proximal fit designs [39,48,49]. The fractures in this study were created with a force large enough to represent a displaced fracture averaging over 75 mm in length, and cabling was still able to provide the same time zero strength, which may aid surgeons in making the decision to use distally fixed vs proximally tapered stems when treating intraoperative insertional fractures. ...
Background
The purpose of this study was to compare the biomechanical strength of femurs before an iatrogenic periprosthetic fracture vs after an initial fracture with supporting cerclage fixation during cementless total hip arthroplasty.
Material and methods
Nineteen composite femurs and 5 matched pairs of cadaveric femurs were implanted with a single-wedge or dual-wedge tapered femoral stem and tested for ultimate load to failure producing a periprosthetic fracture. Following initial fracture, each femur was cerclaged with Vitallium cables and retested for ultimate load to failure. The mean force eliciting iatrogenic fracture before cabling and that after cabling were compared with a two-sided paired Student’s t-test.
Results
All composite femurs developed periprosthetic fractures with an average length extension from the calcar of 75.17 mm. For the 19 composite femurs, the mean ultimate load to failure before cabling and that after cabling were not significantly different (2422.95 N vs 2505.14 N, P = .678). For the 10 cadaveric femurs, the mean ultimate load to failure for the initial fracture vs that after cabling was statistically comparable (5828.62 N vs 7002.63 N, P = .126). Subanalysis of the 5 cadaveric femurs with a double-wedge stem revealed a significantly higher mean load to failure following cabling (5007.38 N vs 7811.17 N, P = .011).
Conclusion
Biomechanical strength was similar for femurs that sustained an initial iatrogenic periprosthetic fracture and the same femurs cabled with cerclage wires after being fractured. These data may assist in operative decision-making for treating iatrogenic fractures during total hip arthroplasty.
... This theory assumes that the adaptation process of bone follows a trilinear curve, based on different levels of mechanical signal. The bone's adaptive activities were divided into three stages with respect to the magnitude of mechano-regulated signal, representing resorption at low mechanical stimuli, formation at high mechanical stimuli and a "quiescent zone", where the formation and resorption processes were in balance, with a moderate level of stimuli (Carter, 1984), (Cowin and Hegedus, 1976), (Huiskes et al., 1989). Furthermore, experimental evidence showed that resorption cavities occur preferentially in regions with micro-damage, suggesting that the remodelling process should also be driven by damage removal (Martin, 2007), (Mori and Burr, 1993). ...
An abnormal remodelling process of bones can lead to various bone disorders, such as osteoporosis, making them prone to fracture. Simulations of load-induced remodelling of trabecular bone were used to investigate its response to mechanical signal. However, the role of mechanostat in trabecular-bone remodelling has not yet been investigated in simulations underpinned by a longitudinal in-vivo study in humans.
In this work, a finite-element model based on a 6-month longitudinal in-vivo HR-pQCT study was developed and validated to investigate the effect of mechanical stimuli on bone remodelling. The simulated changes in microstructural parameters and density of trabecular bone were compared with respective experimental results. A maximum principal strain (MPS) and a maximum principal strain gradient (∇MPS) were used as mechanical signals to drive a five-stage mechanostat remodelling model, including additional over-strain and damage stages. It was found that the density distribution varied with the studied mechanical signals, along with decreasing with time levels of bone volume fraction BV/TV, trabecular thickness Tb.Th and bone surface area Tb.BS as well as increased trabecular separation Tb.Sp. Among these parameters, BV/TV and Tb.Th together with the bone-remodelling parameters from the MPS model demonstrated a significant correlation with the experimental data. The developed model provides a good foundation for further development and investigation of the relationships between mechanical loading and human-bone microarchitecture.
... This theory describes the adaptation process of bone with a trilinear curve based on different levels of mechanical signal. The bone adaptive activities were divided into three stages with respect to the magnitude of mechanical stimuli, representing resorption (low mechanical stimuli) and formation (high mechanical stimuli) along with a 'quiescent zone', where formation and resorption processes were in balance (hence moderate stimuli) [14][15] [16]. It was also proposed that strain could also contribute towards mechanical stimuli, therefore, affecting the remodelling process [17]. ...
Finite-element models are used to estimate numerically the distribution of bone mineral density (BMD) as a result of bone remodelling process from the loads applied. However, the effect of initial BMD distribution on trabecular-bone remodelling is still unknown. In this paper, the effect of initial density distributions as an input in the finite-element model on a structural-functional relationship of trabecular bone was investigated. A multi-material model representing a realistic density distribution was used based on the grey-scale value (GV) distribution and compared with a traditional single-material model. Different trabecular morphologies with density distributions were observed for these two material models. Similar character of the occurrence of density (in terms of element and volume fraction) of trabecular bone from a femur head were found, with the same highest number of elements in the density range from 1.25 to 1.35 g/cm3. These results indicate that previous simplified models using single-material properties for trabecular bone may not lead to considerable errors.
... The DIC technique has been introduced into the field of biomechanics for accurate determination of surface strain in inhomogeneous, anisotropic, non-linear materials such as bone. The strain distribution patterns induced by different materials have been studied previously in the laboratory setting using strain gauge analysis [28,[42][43][44][45], photoelastic coating techniques [46,47] and finite element analysis [48][49][50]. Traditionally, strain gauges have been considered the 'gold standard' in the experimental testing for evaluation of the biomechanical behavior of bone in vitro since their introduction in the late 1950s [51]. Although they are known to be reliable and despite their widespread use, strain gauges require surface preparation and provide strain results only at the restricted area of application. ...
Background:
The progressive evolution in hip replacement research is directed to follow the principles of bone and soft tissue sparing surgery. Regarding hip implants, a renewed interest has been raised towards short uncemented femoral implants. A heterogeneous group of short stems have been designed with the aim to approximate initial, post-implantation bone strain to the preoperative levels in order to minimize the effects of stress shielding. This study aims to investigate the biomechanical properties of two distinctly designed femoral implants, the TRI-LOCK Bone Preservation Stem, a shortened conventional stem and the Minima S Femoral Stem, an even shorter and anatomically shaped stem, based on experiments and numerical simulations. Furthermore, finite element models of implant-bone constructs should be evaluated for their validity against mechanical tests wherever it is possible. In this work, the validation was performed via a direct comparison of the FE calculated strain fields with their experimental equivalents obtained using the digital image correlation technique.
Results:
Design differences between Trilock BPS and Minima S femoral stems conditioned different strain pattern distributions. A distally shifting load distribution pattern as a result of implant insertion and also an obvious decrease of strain in the medial proximal aspect of the femur was noted for both stems. Strain changes induced after the implantation of the Trilock BPS stem at the lateral surface were greater compared to the non-implanted femur response, as opposed to those exhibited by the Minima S stem. Linear correlation analyses revealed a reasonable agreement between the numerical and experimental data in the majority of cases.
Conclusion:
The study findings support the use of DIC technique as a preclinical evaluation tool of the biomechanical behavior induced by different implants and also identify its potential for experimental FE model validation. Furthermore, a proximal stress-shielding effect was noted after the implantation of both short-stem designs. Design-specific variations in short stems were sufficient to produce dissimilar biomechanical behaviors, although their clinical implication must be investigated through comparative clinical studies.
... The DIC technique has been introduced into the eld of biomechanics for accurate determination of surface strain in inhomogeneous, anisotropic, non-linear materials such as bone. The strain distribution patterns induced by different materials have been studied previously in the laboratory setting using strain gauges analysis (28,(42)(43)(44)(45), photoelastic coating techniques (46,47) and nite element analysis (48)(49)(50). Traditionally, strain gauges have been considered the 'gold standard' in the experimental testing for evaluation of the biomechanical behavior of bone in vitro since their introduction in the late 1950s (51). ...
Background: The progressive evolution in hip replacement research is directed to follow the principles of bone and soft tissue sparing surgery. Regarding hip implants, a renewed interest has been raised towards short uncemented femoral implants. A heterogeneous group of short stems have been designed with the aim to approximate initial, post-implantation bone strain to the preoperative levels in order to minimize the effects of stress shielding. This study aims to investigate the biomechanical properties of two distinctly designed femoral implants, the TRI-LOCK Bone Preservation Stem, a shortened conventional stem and the Minima S Femoral Stem, an even shorter and anatomically shaped stem, based on experiments and numerical simulations. Furthermore, finite element models of implant–bone constructs should be evaluated for their validity against mechanical tests wherever it is possible. In this work, the validation was performed via a direct comparison of the FE calculated strain fields with their experimental equivalents obtained using the digital image correlation technique.
Results: Design differences between Trilock BPS and Minima S femoral stems conditioned different strain pattern distributions. A distally shifting load distribution pattern as a result of implant insertion and also an obvious decrease of strain in the medial proximal aspect of the femur was noted for both stems. Strain changes induced after the implantation of the Trilock BPS stem at the lateral surface were greater compared to the non-implanted femur response, as opposed to those exhibited by the Minima S stem. Linear correlation analyses revealed a reasonable agreement between the numerical and experimental data in the majority of cases.
Conclusion: The study findings support the use of DIC technique as a preclinical evaluation tool of the biomechanical behavior induced by different implants and also identify its potential for experimental FE model validation. Furthermore, a proximal stress shielding effect was noted after the implantation of both short stem designs. Design specific variations in short stems were sufficient to produce dissimilar biomechanical behaviors, although their clinical implication must be investigated through comparative clinical studies.
... Bone remodeling after a hip arthroplasty occurs with all models of cementless femoral stems because of the change in the pattern of load transmission produced after the surgery. The magnitude of these adaptive changes is multifactorial, with factors attributable to the patient, to the surgical technique, and to the implant [1][2][3][4]. ...
Background
Periprosthetic bone remodeling, which is a phenomenon observed in all femoral stems, has a multifactorial origin as it depends on factors related to the patient, the surgical technique, and the design of the implant. To determine the pattern of remodeling produced by 2 models of anatomic cementless implants, we quantified the changes in bone mineral density (BMD) in the 7 areas of Gruen observed at different moments after surgery during the first postoperative year.
Methods
A prospective, comparative, controlled, 1-year follow-up densitometric study was carried out in 2 groups of patients suffering from primary unilateral hip osteoarthritis. In the first group, with 68 patients, an ABG-II stem was implanted. In the second, with 66 patients, the ANATO stem was used. The contralateral, healthy hip was taken as a control.
Results
Both groups showed a decrease in BMD at 3 months in all the areas, which recovered at the end of the study, except in zone 7: there was a 17.7% decrease in the ABG-II group and a 5.9% decrease in the ANATO group. In zones 2 and 6, where more loads are transmitted, conservation of BMD is observed in response to Wolff's law. The differences in the pattern of remodeling between groups were maintained despite the age, gender, and BMI of the patients or the size of the implants.
Conclusion
The ANATO stem achieved a more efficient transmission of loads at the metaphyseal level, which promotes bone preservation at the proximal femur, than the ABG-II stem.
... The DIC technique has been recently introduced into the field of biomechanics for accurate determination of surface strain in inhomogeneous, anisotropic, non-linear materials such as bone. The strain distribution patterns induced by different materials have been studied previously in the laboratory setting using strain gauges analysis (28,(42)(43)(44)(45), photoelastic coating techniques (46,47) and finite element analysis (48)(49)(50). Traditionally, strain gauges have been considered the 'gold standard' in the experimental testing for evaluation of the biomechanical behavior of bone in vitro since their introduction in the late 1950s (51). Although they are known to be reliable and despite their widespread use, strain gauges require surface preparation and provide strain results only at the restricted area of application. ...
Background
The progressive evolution in hip replacement research is directed to follow the principles of bone and soft tissue sparing surgery. Regarding hip implants, a renewed interest has been raised towards short uncemented femoral implants. A heterogeneous group of short stems have been designed with the aim to approximate initial, post-implantation bone strain to the preoperative levels in order to reduce the risk of stress shielding. This study aims to investigate the biomechanical properties of two distinctly designed femoral implants based on experiments and numerical simulations. Nevertheless, finite element models of implant–bone constructs should be evaluated for their validity against mechanical tests wherever it is possible. In this work, the validation was performed via a direct comparison of the FE calculated strain fields with their experimental equivalents obtained using the digital image correlation technique.
Results
Design differences between Trilock BPS and Minima S femoral stems conditioned different strain pattern distributions. A distally shifting load distribution pattern as a result of implant insertion and also an obvious decrease of strain in the medial proximal aspect of the femur was noted for both stems. Strain changes induced after the implantation of the Trilock BPS stem at the lateral surface were greater compared to the non-implanted femur response, as opposed to those exhibited by the Minima S stem. Linear correlation analyses of the FE model-predicted strains against corresponding experimentally-measured strains revealed a strong correlation indicating that the developed FE models can be used for the calculation of stresses and strains at the implanted femurs.
Conclusion
The study findings support the use of DIC technique as a preclinical evaluation tool of the biomechanical behavior induced by different implants and also identify its potential for experimental FE model validation. Furthermore, this study demonstrates that stress shielding effect cannot be avoided as proximal unloading of the femur was noted after the implantation of both short stem designs. Design specific variations in short stems were sufficient to produce dissimilar biomechanical behaviors, although their clinical implication must be investigated through comparative clinical studies.
... As a matter of fact, bone remodeling relies on mechanical and biological elements [5]. The mechanical part is associated with stress distribution enforced by the femoral stem, as well as implant features, i.e., size, shape, alloy, and also the kind of bone fixation [2,[6][7][8][9][10][11]. ...
An efficient reliability algorithm is developed to transfer the system reliability problem to a single-component reliability problem, considering the uncertainty of loading cases and the material properties. The main difficulty is that femoral bone densities change after hip arthroplasty and, thus, the mechanical properties of the distinctive bone tissues and, therefore, the corresponding elasticity modulus and yield stress values change. Therefore, taking these changes into account during the hip prosthesis design process is strongly needed. As the bone possesses anisotropic behaviors, as the material properties in both radial and tangential directions in long bone (femur, tibia) are almost similar, the bone anisotropy is represented in this study by transversal isotropy. Two optimized formulations for yield stress against the elasticity modulus relationship are first developed and then integrated into an efficient reliability algorithm. Thus, a coupling between reliability and optimization, so-called reliability-based design optimization (RBDO), is introduced in order to control the reliability level. The proposed RBDO algorithm using optimum safety factors (OSF) takes into account the material uncertainties and leads to new stem dimensions. An in-depth numerical analysis on a cementless hip prosthesis is implemented to demonstrate the appropriateness of the proposed algorithm with the consideration of many different loading cases. The results show that the studied model can be effectively used when compared to previous works, which concerns the changes in both geometry and material properties.
... They distinguished between the 'pressure tension' hypothesis assuming that bone resorption will occur owing to compression [2,3] , the 'alveolar bending' hypothesis assuming that strain gradients in the bone are responsible for bone remodelling [4,5] , and the 'stretched fibres' hypothesis assuming that the tooth will stretch the fibres in the periodontal ligament (PDL) on one side and unload the fibres on the other side, thus leading to bone resorption in the direction of the orthodontic force and bone apposition on the other side [6] . Only the last of the mentioned hypotheses agrees with Wolff's law that is widely used in orthopaedics to explain bone remodelling as a result of changes in mechanical loading [7] . * Corresponding author. ...
Many hypotheses have been formulated to explain orthodontic tooth movement. However, none of them can satisfactorily explain how small static orthodontic forces can induce bone remodelling. Our hypothesis assumes that small orthodontic forces do not lead to bone remodelling response directly, but rather indirectly by offsetting the tooth, leading to changes in bone loading during chewing that far exceed the changes caused by the orthodontic force alone. We developed a finite element model of a tooth with the periodontal ligament and the surrounding bone, and calculated the changes in strain energy density caused by the chewing force alone, the orthodontic force alone, and the combined action of the chewing and orthodontic forces. The results (average strain energy density 0.0005–0.01 kPa) demonstrate that the orthodontic loading alone does not produce strain energy density values in a range that is expected to induce remodelling (0.016–1.6 kPa). However, when the chewing and orthodontic forces are applied together, the highest values for the average strain energy density (0.02–0.99 kPa) as well as large changes in the bone tissue strain energy density (31.19–166.65%) are obtained. We conclude that the proposed hypothesis can indeed explain the observed bone remodelling that agrees with Wolff's law.
... For bone, several remodelling theories based on Wolff's law have been formulated to predict changes in bone density related to changes in mechanical loading [25]. It has been demonstrated that such models can successfully predict changes in bone density after total hip [26] and knee arthroplasty [27]. In the case of spinal fusion, however, the situation is more complicated since changes in overall loading for neighbouring segments are expected due to the reduced flexibility of the fused segment, but also changes in local load transfer due to degeneration of adjacent discs. ...
Spinal fusion is a standard surgical treatment for patients suffering from low back pain attributed to disc degeneration. However, results are somewhat variable and unpredictable. With fusion the kinematic behaviour of the spine is altered. Fusion and/or stabilizing implants carrying considerable load and prevent rotation of the fused segments. Associated with these changes, a risk for accelerated disc degeneration at the adjacent levels to fusion has been demonstrated. However, there is yet no method to predict the effect of fusion surgery on the adjacent tissue levels, i.e. bone and disc. The aim of this study was to develop a coupled and patient-specific mechanoregulated model to predict disc generation and changes in bone density after spinal fusion and to validate the results relative to patient follow-up data. To do so, a multiscale disc mechanoregulation adaptation framework was developed and coupled with a previously developed bone remodelling algorithm. This made it possible to determine extra cellular matrix changes in the intervertebral disc and bone density changes simultaneously based on changes in loading due to fusion surgery. It was shown that for 10 cases the predicted change in bone density and degeneration grade conforms reasonable well to clinical follow-up data. This approach helps us to understand the effect of surgical intervention on the adjacent tissue remodelling. Thereby, providing the first insight for a spine surgeon as to which patient could potentially be treated successfully by spinal fusion and in which patient has a high risk for adjacent tissue changes.
... New designs of uncemented hip stems focus on enhancing osseointegration, improved interface sealing, optimized load transfer, diminishing the rate of loosening, and on improving clinical outcomes. For these purposes, optimizations can be realized in the geometry of the stem, the choice of material, surface texture, and the type and extent of the osseointegrative coating [1][2][3][4][5][6]. These considerations resulted in the development of the uncemented Symax stem design (Stryker Orthopaedics, Amsterdam, the Netherlands) as an optimization of the well-documented, second-generation uncemented Omnifit hip stem [3,7,8]. ...
Background:
The uncemented Symax hip stem is developed through optimization of the uncemented Omnifit hip stem. The Symax stem design combines an anatomical anteverted proximal geometry with a straight distal section. The proximal part is coated with a biomimetic hydroxyapatite (HA) coating for improved osseointegration to enhance load transfer and to minimize proximal bone loss. The distal part is treated with an anodization surface treatment in order to prevent distal bone apposition, which is expected to prevent distal loading and reduce proximal stress shielding. Aim of this study is to report mid-term clinical performance and evaluate whether the radiographic features are in line with the design principles of the Symax hip.
Methods:
The biomimetic hydroxyapatite-coated uncemented Symax hip stem was evaluated in 80 patients during a 5-year prospective clinical international study. Harris Hip Score (HHS), Oxford Hip Score (OHS), and Western Ontario and McMaster Universities Arthritis Index (WOMAC) were performed preoperatively and postoperatively at 6 months and 1, 2, 3 and 5 years. Anteroposterior radiographs of the pelvis and axial radiographs of the operated hips were evaluated immediately postoperative and at follow-up 6 months and 1, 2, 3, and 5 years. Wilcoxon signed-rank test was used to analyse whether clinical outcome scores changed statistically significant over time. The overall percentage of agreement between two radiology assessment teams was used to evaluate observer agreement of radiology results. The Cohen's Kappa was evaluated as a measure of reliability to quantify the agreement between raters, corrected for chance agreement.
Results:
Clinical outcome scores were excellent at 5 years with mean HHS of 98.1, mean OHS of 16.2 and mean WOMAC of 6.9. Only 2.7% of the patients had pain at rest or on weight-bearing, and mid-thigh pain was reported by 1.4% of the patients after 5 years. The percentage of agreement between radiology assessment teams was 94 to 100%, except for distal line formation (48%). Radiographic evaluation showed stable stems and signs of excellent progressive proximal fixation and favourable bone remodeling.
Conclusions:
The excellent mid-term clinical and radiographic performances are in line with the design principles and coating properties of this new implant and earlier published results.
Trial registration:
http://ClinicalTrials.gov , NCT03469687 . Registered 19 March 2018 - Retrospectively registered.
... Wolff's law recognizes the response of bone to mechanical stimulation and states that as a consequence of continuous loading, bone changes its internal architecture according to mathematical rules and, as a secondary effect and governed by the same mathematical rules, also changes it shape 10 . This alteration of the normal biomechanics results in a phenomenon called adaptive bone remodeling, which is nothing but physiological remodeling occurring in a new biomechanical environment 36 . The above-mentioned theories of bone remodeling have been used successfully in conjunction with the FEM to predict density and bone adaptation. ...
Introduction:
The aim of commencing treatment in younger age is to rectify the developing dento-alveolar, skeletal and muscular imbalances. With growing dependence on arch development and expansion, the pendulum is oscillating more towards the non-extraction treatment lately, in resolving constriction and crowding issues. Since, a limited number of attempts have been made for mandibular expansion, this study aimes to evaluate the effect of different modes and sites of loading on the expansion of preadolescent mandible using biomechanics.
Study design:
To address the research purpose, a total of 9 Finite Element models were simulated. Biomechanical response of the mandibular bone and dentition was analyzed under different loading conditions including site and mode, using the simulated FE models.
Results:
The values of displacement envisaged by the FE models, predict hybrid mode to offer substantial expansion of the mandibular bone as compared to tooth borne and bone borne. In addition, biomechanical effect of site II on mandibular expansion in terms of displacement on X-axis, was significant.
Conclusion:
In conclusion, the results of our study suggest hybrid mode at site II to be better option for true bony expansion in preadolescent mandible.
... Several studies have been done in order to evaluate the bone tissue behavior around cementless femoral prosthesis. Huiskes et al. (1989) present a pioneer study where is evaluated a two-dimensional femoral cementless prosthesis model, composed by different materials. Authors evaluate the load dissipation along the interface and investigate the relation between the stress distribution and prosthesis design related to the problems that can happen. ...
Total Hip Arthroplasty (THA) is a surgery that replaces the damaged natural joint by an artificial one composed by biomaterial. This procedure is a bone-adaptation example, which occurs mainly because the change of loading condition applied on femur after THA, loaded by shear forces in interface. The higher material stiffness, the less is the load dissipation in femoral proximal epiphyses. Resorption and apposition cells make the biological adaptation process, replacing damage bone tissue for a new and healthy one. This process is called bone remodeling. Development of mathematical models combined with Finite Element Method (FEM) enable the evaluation of bone tissue behavior. The present study aims the evaluation of bone-remodeling process around total hip prosthesis made by different biomaterials (cobalt-chrome and titanium alloys and a virtual material with Young’s modulus similar to cortical bone). FEM is applied coupled with the Stanford isotropic bone-remodeling model in the software Abaqus. The total hip prosthesis is considered totally bonded with host tissue. The results show that flexible materials allow a high dissipation of loads along the interface region, which promotes the bone maintenance. However, it can generate high-levels of stress, mainly in proximal femoral portion, which can cause a bone fracture.
... El concepto de un vástago en cuña busca la fijación en el área metafisaria y una disminución de la posibilidad de stress shielding con pérdida de reserva ósea. La cobertura completa con hidroxiapatita (HA) con propiedades osteoinductoras y con formación de nuevo hueso trabecular 4,5 compensa el posible imperfecto relleno del canal femoral, logrando una fijación estable aun en presencia de micromovimiento inicial y con buenos resultados clínicos y radiográficos [6][7][8][9] . ...
Introduction
Total hip arthroplasty (THA) using uncemented stems is a popular practice in the last decades.
The implant survivorship is critical and a less than 10% revision at 10 years is been proposed for commercialisation and use.
Objective
To analyse the clinicoradiological results of an uncemented hydroxiapatite covered wedge stem with a 5 years minimum follow up.
Material and methods
Prospective study, patients aged from 21 to 75 years were included. All patients received an Element stem (Exactech) and uncemented cup with crosslink poly and 32 mm metal head, and posterior approach with piriformis retention was used.
Scheduled clinical and radiographic evaluation at 3 weeks, 3–6 month, year and subsequent years using Harris Hip Score and Merle d’Aubigné Postel. Intraoperative and during follow up complications were recorded.
Results
One hundred and fourteen total hip replacements in 104 patients: 54 females and 50 males (52%/48%). Follow-up of 5.7 years (range, 5–6.2 years). Average age 56.8 years (range, 42–75 years).
Clinical evaluation the Merle d’Aubigné score improved 6.8 points and from the initial Harris Hip Score 47.3–93.1 points at last follow up.
Radiographic evaluation shows osteointegration in all stems. And in 6 cases (5.3%) at 3 months subsidence was detected, average 1.4 mm (range 0–2.6 mm) with no clinical manifestation, 3 cases of subsidence were associated to intraoperative fractures (1 greater trochanter and 2 in the calcar area, all resolved with wire cerclaje).
Subjective evaluation: 86 cases (82.6%) excellent, 9 patients (8.6%) good, 6 cases (5.9%) satisfactory and 3 cases (2.9%) poor. All poor results linked to the intraoperative complications.
No patient lost during follow up period.
No femoral pain dislocation or aseptic or loosening detected. All implants were in situ at last follow up.
Conclusions
The radiological results confirm the benefits of this type of stem with good osteointegration.
The clinical and subjective results are promising.
With good surgical technical and without complications the risk of aseptic loosening should be absent or minimal.
... Another I. Levadnyi et al. Clinical Biomechanics 50 (2017) 122-129 similar effect noted from numerical results is the largest variation in the bone density distribution that takes place until the end of the first year after THA and becomes practically constant during the rest of the analysis, as found by other authors (Gibbons et al., 2001;Huiskes et al., 1989;Panisello et al., 2009;Sköldenberg et al., 2006;Sychter and Engh, 1996). It should be noted, however, that there are also other studies that have found variation in the density until the end of the second year after the THA (Herrera et al., 2008;Scanell and Prendergast, 2009;Kwon et al., 2013;Herrera et al., 2014;Jake and Scott, 1996;Nysted et al., 2011). ...
Background
The change in mechanical properties of femoral cortical bone tissue surrounding the stem of the hip endoprosthesis is one of the causes of implant instability. We present an analysis used to determine the best conditions for long-term functioning of the bone–implant system, which will lead to improvement of treatment results.
Methods
In the present paper, a finite element method coupled with a bone remodelling model are is used to evaluate how different three-dimensional prosthesis models influence distribution of the density of bone tissue. The remodelling process begins after the density field is obtained from a computed tomography scan. Then, an isotropic Stanford model is employed to solve the bone remodelling process and verify bone tissue adaptation in relation to different prosthesis models.
Findings
The study results show that the long-stem models tend not to transmit loads to proximal regions of bone, which causes the stress-shielding effect. Short stems or application in the calcar region provide a favourable environment for transfer of loads to the proximal region, which allows for maintenance of bone density and, in some cases, for a positive variation, which causes absence of the aseptic loosening of an implant. In the case of hip resurfacing, bone mineral density changes slightly and is closest to an intact femur.
Interpretation
Installation of an implant modifies density distribution and stress field in the bone. Thus, bone tissue is stimulated in a different way than before total hip replacement, which evidences Wolff’'s law, according to which bone tissue adapts itself to the loads imposed on it. The results suggest that potential stress shielding in the proximal femur and cortical hypertrophy in the distal femur may, in part, be reduced through the use of shorter stems, instead of long ones, provided stem fixation is adequate.
... El concepto de un vástago en cuña busca la fijación en el área metafisaria y una disminución de la posibilidad de stress shielding con pérdida de reserva ósea. La cobertura completa con hidroxiapatita (HA) con propiedades osteoinductoras y con formación de nuevo hueso trabecular 4,5 compensa el posible imperfecto relleno del canal femoral, logrando una fijación estable aun en presencia de micromovimiento inicial y con buenos resultados clínicos y radiográficos [6][7][8][9] . ...
Introduction:
Total Hip Arthroplsty (THA) using uncemented stems is a popular practice in the last decades. The implant survivorship is crtitical and a less than 10% revision at 10 years is been propesed for commercialization and use.
Objective:
To analyse the clinicoradiological results of an uncemented hydroxiapatite covered wedge stem with a 5 years minimum follow up.
Material and methods:
Prospective study, patients aged from 21-75years were included. All patients received an Element stem (Exactech) and uncemented cup with crosslink poly and 32 mm metal head, and posterior approach with piriformis retention was used. Scheduled clinical and radiographic evaluation at 3 weeks, 3-6 month, year and subsequent years using Harris Hip Score and Merle d'Aubigné Postel. Intraoperative and during follow up complications were recorded.
Results:
One hundred and fourteen total hip replacements in 104 patients: 54 females and 50 males (52%/48%). Follow-up of 5.7 years (range, 5-6.2years). Average age 56.8years (range, 42-75years). Clinical evaluation the Merle d'Aubigné score improved 6.8 points and from the initianl Harris Hip Score 47.3 to 93.1 points at last follow up. Radiographic evaluation shows osteointegration in all stems. And in 6 cases (5.3% at 3 months subsidence was detected, average 1.4 mm (range 0-2.6 mm) with no clinical manifestation, 3 cases of subsidence were associated to intraoperative fractures (1 greater trochanter and 2 in the calcar area, all resolved with wire cerclaje). Subjective evaluation: 86 cases (82.6%) excellent, 9 patients (8.6%) good, 6 cases (5.9%) satisfactory and 3 cases (2.9%) poor. All poor results linked to the intraoperative complications. No patient lost during follow up period. No femoral pain dislocation or aseptic or loosening detected. All implants were in situ at last follow up.
Conclusions:
The radiological results confirm the benefits of this type of stem with good osteointegration. The clinical and subjective results are promising. With good surgical technical and without complications the risk of aseptic loosening should be absent or minimal.
... Stress can be spread to the distal femur via intramedullary prosthesis despite its support by the proximal femur, which leads to stressshielding, affecting the osseous integrity and resistance [30]. Longer stems are believed to give higher stresses at the femur and then be capable of reducing stress shielding problems, whereas shorter stems decrease the loadtransfer to the cortical bone and encourages stress shielding and bone resorption, which results in failure of the prosthesis sometimes [31]. Chen WP et al. revealed that less stress shielding occurs in those femurs with fully cemented fixation [32]. ...
Abstract Background There is no universal hip implant suitably fills all femoral types, whether prostheses of porous short-stem suitable for Hip Arthroplasty is to be measured scientifically. Methods Ten specimens of femurs scanned by CT were input onto Mimics to rebuild 3D models; their *stl format dataset were imported into Geomagic-Studio for simulative osteotomy; the generated *.igs dataset were interacted by UG to fit solid models; the prosthesis were obtained by the same way from patients, and bored by punching bears designed by Pro-E virtually; cements between femora and prosthesis were extracted by deleting prosthesis; in HyperMesh, all compartments were assembled onto four artificial joint style as: (a) cemented long-stem prosthesis; (b) porous long-stem prosthesis; (c) cemented short-stem prosthesis; (d) porous short-stem prosthesis. Then, these numerical models of Finite Element Analysis were exported to AnSys for numerical solution. Results Observed whatever from femur or prosthesis or combinational femora-prostheses, “Kruskal-Wallis” value p > 0.05 demonstrates that displacement of (d) ≈ (a) ≈ (b) ≈ (c) shows nothing different significantly by comparison with 600 N load. If stresses are tested upon prosthesis, (d) ≈ (a) ≈ (b) ≈ (c) is also displayed; if upon femora, (d) ≈ (a) ≈ (b)
... In the case of bone adaptation, Frost's mechanostat theory (1987) has become widely accepted. It been applied to simulate the time dependent effects of mechanical loading on bone (Beaupre et al. 1990, Fischer et al. 1996, and to the design and material selection for orthopaedic implants (Huiskes et al. 1989, 1987. In this theory, bone adapts to a signal, which is a function of mechanical stress or strain (Fig. 1). ...
... Regardless of bonding condition, von Mises stress was increased at the distal site of the cementless stems, and decreased proximally. Changes in stress distribution depend on stem stiffness, and stress shielding is known to influence current cementless stems [16,30,31]. Furthermore, the extent of stress shielding is affected by the bonding conditions of the implant-bone interface [32]. ...
Background:
Femoral bone remodeling in response to stress shielding induces periprosthetic bone loss. Computerized finite element analysis (FEA) is employed to demonstrate differences in initial stress distribution. However, FEA is often performed without considering the precise sites at which the stem was fixed. We determined whether FEA reflects mid-term radiological examination exactly as predicted following long-term stress shielding.
Methods:
Femur-stem fixation sites were evaluated radiologically according to the location of spot welds in two anatomical cementless stem designs. Based on mid-term radiological results, four femur-stem bonding site conditions were defined as: (Condition A) no bonding; (Condition B) bonding within the 10 mm area proximal to the distal border of the porous area; (Condition C) bonding of the entire porous area; and (Condition D) bonding of the entire femoral stem, prior to conducting FEA analysis. Furthermore, we radiographically evaluated mid- and long-term stress shielding, and measured bone mineral density of the femur 10 years after total hip arthroplasty.
Results:
Spot welds appeared frequently around the border between the porous and smooth areas. FEA showed that, based on mid-term radiological evaluation, von Mises stress was reduced in condition B in the area proximal to the femur-stem bonding sites for both stem designs compared with condition A (no bonding). Conversely, von Mises stress at all areas of the femur-stem bonding sites in conditions C and D was higher than that in condition A. With respect to stress shielding progression, there was no significant difference between the two types of stem designs. However, stress shielding progressed and was significantly higher in the presence of spot welds (p = 0.001). In both stem designs, bone mineral density in zone VII was significantly lower than that in the contralateral hips.
Conclusions:
These results indicate that FEA based on mid-term radiological evaluation may be helpful to predict the influence of long-term stress shielding more precisely.
... 39 This alteration of the normal biomechanics results in a phenomenon termed adaptive bone remodeling. 40 In addition, the muscles attached to the surface of compact bones can significantly influence the intensity of a load, 41 which might contribute to changes in the biomechanical properties of bone. A similar biomechanical response was observed in the present study, with changes in osteotomy design and site mode of load application. ...
Purpose:
Surgically assisted mandibular arch expansion has proved to be an effective treatment modality in alleviating constriction and crowding issues. However, only mandibular symphyseal distraction osteogenesis has been in favor for the purpose of mandibular arch expansion. In addition, no relevant study has compared the biomechanical response of different osteotomy designs on mandibular expansion. The present study evaluated the effect of different osteotomy approaches and modes of loading on the expansion of the adult mandible using biomechanics.
Materials and methods:
To address the research purpose, 9 finite element (FE) models, including 2 novel osteotomy designs, were simulated. Stress, strain, and displacement of crown, root, and bone were calculated and compared under different osteotomy approaches and loading conditions.
Results:
The biomechanical response envisaged by the FE models in terms of displacement on the X axis was consistent from the anterior to posterior teeth with parasymphyseal step osteotomy and a hybrid mode of force application. In addition, the amount of displacement predicted by parasymphyseal step osteotomy with the hybrid mode was greater compared with that of the other models.
Conclusions:
The results of our study suggest parasymphyseal step osteotomy with the hybrid mode is a viable treatment option for true bony expansion in the adult mandible.
Description
One of the causes or results (or both) of medical implant failure is the release of particulate material debris from the device because of wear, physical deterioration, or chemical attack by the harsh physiological environment. STP 1144 examines tissue response to particles of implant material in order to identify factors, such as materials selection, surgical protocol, implant design, or postoperative prophylactic drug treatment, that might limit debris generation or moderate the tissue response.
19 peer-reviewed papers written by principal researchers in the field are divided into two sections: clinical experience with the generation of material debris from implants; and in vitro and in vivo models for the clinical situation and methods for generating and characterizing wear debris particles that may be used in laboratory models. For medical implant designers/orthopaedics, orthopaedic surgeons, medial libraries, and biomaterials researchers.
This study reviews the progression of our research, from modeling growth theories for cartilage tissue engineering, to the formulation of constrained reactive mixture theories to model inelastic responses in any solid material, such as theories for damage mechanics, viscoelasticity, plasticity, and elasto-plastic damage. In this framework, multiple solid generations α can co-exist at any given time in the mixture. The oldest generation is denoted by α=s and is called the master generation, whose reference configuration Xs is observable. The solid generations α are all constrained to share the same velocity vs, but may have distinct reference configurations Xα. An important element of this formulation is that the time-invariant mapping Fαs=∂Xα/∂Xs between these reference configurations is a function of state, whose mathematical formulation is postulated by constitutive assumption. Thus, reference configurations Xα are not observable (α≠s). This formulation employs only observable state variables, such as the deformation gradient Fs of the master generation and the referential mass concentrations ρrα of each generation, in contrast to classical formulations of inelastic responses which rely on internal state variable theory, requiring evolution equations for those hidden variables. In constrained reactive mixtures, the evolution of the mass concentrations is governed by the axiom of mass balance, using constitutive models for the mass supply densities ρˆrα. Classical and constrained reactive mixture approaches share considerable mathematical analogies, as they both introduce a multiplicative decomposition of the deformation gradient, also requiring evolution equations to track some of the state variables. However, they also differ at a fundamental level, since one adopts only observable state variables while the other introduces hidden state variables. In summary, this review presents an alternative foundational approach to the modeling of inelastic responses in solids, grounded in the classical framework of mixture theory.
Background
There are no reported results for longer than 20 years of a pure proximal-loading anatomic cementless femoral stem without diaphyseal stem fixation. The purpose of this study was to evaluate the long-term (minimum 20 years) clinical results, bone remodeling, revision rate, and survivorship of these implants in patients younger than 60 years.
Methods
We included 523 patients (657 hips), including 319 men and 204 women. The mean body mass index was 26.7 (range, 23 to 29 kg/m²). The mean age of patients at index surgery was 55 years (range, 20 to 59 years). The Harris Hip Score, the Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC), and the University of California, Los Angeles (UCLA) activity score were recorded preoperatively and at each follow-up. Mean follow-up was 23.5 years (range, 20 to 27 years).
Results
The Harris Hip Score at the final follow-up was a mean 93 points (range, 70 to 100 points). The WOMAC and UCLA activity scores at the final follow-up were 16 and 7.6 points, respectively. Five femoral components (0.8%) and 13 acetabular components (2.0%) were revised. All cases in the current series had grade 2 stress shielding; no hips had grade 3 or 4 stress shielding. Kaplan-Meier survivorship of the implants at 23.5 years was 98.0% (95% confidence interval [CI] 92-100%) for the acetabular component and 99.2% (95% CI 93-100%) for the femoral component.
Conclusion
A pure proximal-loading metaphyseal-fitting anatomic cementless stem with alumina-on-alumina ceramic bearing couples functioned well, with no osteolysis or mild stress-shielding at an average 23.5-year follow-up.
Introduction:
The human knee is one of the most complex human joints, by the number of components, by the stresses to which it is subjected, by the complicated spatial geometry of the components and by the existence of multiple contacts between different components.
Material and method:
A series of modern devices and equipment that were used for the three-dimensional reconstruction of the components of the analyzed systems.
Results:
Also, the elements of a knee prosthesis were modeled in a parameterized virtual environment and six orthopedic systems were compared. These systems have been studied using the finite element method using loads specific to normal human gait.
Discussion:
The results obtained consisting of maps of displacements, deformations and stresses were stored, analyzed and compared.
Conclusions:
Finally, important conclusions were highlighted.
Bone tissue exhibits piezoelectric properties and thus is capable of transforming mechanical stress into electrical potential. Piezoelectricity has been shown to play a vital role in bone adaptation and remodelling processes. Therefore, to better understand the interplay between mechanical and electrical stimulation during these processes, strain-adaptive bone remodelling models without and with considering the piezoelectric effect were simulated using the Python-based open-source software framework. To discretise numerical attributes, the finite element method (FEM) was used for the spatial variables and an explicit Euler scheme for the temporal derivatives. The predicted bone apparent density distributions were qualitatively and quantitatively evaluated against the radiographic scan of a human proximal femur and the bone apparent density calculated using a bone mineral density (BMD) calibration phantom, respectively. Additionally, the effect of the initial bone density on the resulting predicted density distribution was investigated globally and locally. The simulation results showed that the electrically stimulated bone surface enhanced bone deposition and these are in good agreement with previous findings from the literature. Moreover, mechanical stimuli due to daily physical activities could be supported by therapeutic electrical stimulation to reduce bone loss in case of physical impairment or osteoporosis. The bone remodelling algorithm implemented using an open-source software framework facilitates easy accessibility and reproducibility of finite element analysis made.
Background:
A short stem hip arthroplasty can be revised in many cases using a conventional stem. Furthermore, in some cases the implantation of a short stem is intended, but intraoperatively reasons may lead to the decision to implant a conventional stem after previous preparation of a short stem.
Objective:
In both cases it is questionable if the anchorage of a conventional stem is negatively affected by the previous preparation of a short stem. In clinical practice mid- or long-term follow up for these special cases hardly exist.
Methods:
The strain patterns for the conventional Bicontact stem in primary implantation and after preparation of the proximal femur for a METHA short stem were tested biomechanically in three pairs of cadaveric femora.
Results:
The strain patterns for the conventional Bicontact after preparation of the METHA short stem were similar to conditions after testing the conventional stem in primary conditions.
Conclusions:
These data lead to the consequence that in clinical practise the implantation of a conventional stem after preparation of a short stem and even after revision of a short stem is possible without increased risk of loosening or long-term stress-shielding.
This paper investigates the need to use stems in conjunction with cementless metaphyseal sleeves in total knee replacement (TKR) to treat cavity type-3 defects. Finite element models of TKR with type-3 defects of two sizes were modelled with and without stems. The use of sleeves result in stress concentrations at the bone/sleeve interface. The use of stems shows a reduction in these stresses but also an increased risk of bone resorption in the proximal tibia. Based on this investigation the authors recommend that stems are not required in TKR with cementless metaphyseal sleeves.
The purpose of this paper is to examine whether the rationale for CAD-CAM Custom Hips is realised in clinical practice. Previous studies demonstrated that custom uncemented stems, with a close fit proximally and a sliding fit distally, produced stresses closer to normal than for other stem types, which should result in the preservation of proximal bone. Custom stems showed less micromotion, especially in torsional loading, and hence should demonstrate interface osseointegration. The hips are designed and manufactured using specially written software. The standard design includes proximal macro-grooves with HA coating, an anterior flare, a lateral flare, a collar, and a smooth distal stem for a sliding fit. Elective features are added such as proximal stem twist and neck retroversion in CDH, increased stem length to bypass defects, curvatures in AP and ML views, and distal cutting flutes when extra torsional stability is required. From 1989 to 1994, 411 cases were carried out, approximately one-third in each of the categories of OA, JCA/CDH, and revision. Studies were made of the available radiographs at yearly intervals, while DEXA scans were taken of the RNOHT patients pre-operatively, at 6 months and then yearly. There were four failures requiring revision, three of the early primary design without HA coating, and one a revision design. The radiographs in primary hips showed complete proximal bone-implant apposition in 81% of all cases. The DEXA scans showed that the mean bone mass after two years for all seven Gruen zones was greater than 90%. It was concluded that the CAD-CAM HA-coated Custom Hips showed bone and interface stability up to this time. The hip has played a useful role in providing the ideal stem for each particular case, which may result in an improvement of long-term results, compared with the use of off-the-shelf implants.
In total knee arthroplasty, the optimal length and material of tibial stem remain controversial. This study aimed to evaluate influences of lengths and materials of cementless stems on tibial remodeling behaviors. Three groups of lengths were investigated (i.e., 110, 60, and 30 mm), and four materials (i.e., titanium, flexible ‘iso-elastic’ material, and two functionally graded materials [FGMs]) were selected for each group. FGM is a kind of material whose composition gradually varies in space. In this study, the compositions of two FGMs were Ti and hydroxyapatite (FGM I), and Ti and bioglass (FGM II), respectively. Tibial models were incorporated with finite element analysis to simulate bone remodeling. Distributions of bone mineral density, von Mises stress, and interface shear stress were obtained. For the length, the long stem produced more serious stress shielding and stress concentration than the short stem, but it could provide better mechanical stability. For the material, FGM I could reduce stress shielding and stress concentration and reduce the risk of loosening. Compared with the length, the material had a pronounced effect on remodeling. This study provided theoretical basis for optimal design of stem to improve service life of tibial components and to reduce pain of patients.
The bioengineering design process can be divided in many specific phases. The present work lean over three of these phases: the Modulation, the Simulation and the Analysis. All this process is recurrent by nature, always looking for the numerical approach which better reproduces the studied phenomenon. At the present time, there are many numerical methods available and capable to successfully handle the referred bioengineering design process phases. This work presents, develop and extends a new advance discretization meshless technique. From the simple solid mechanical problems to the complex nonlinear bone tissue remodelling analysis in biomechanics, this work shows that the proposed numerical method is flexible and accurate.
The main aim of, and the most significant benefit to be derived from, total hip arthroplasty (THA) is the relief of pain. In this regard THA continues to be an extremely successful procedure with ever-broadening indications, frequent improvements in materials of implant fabrication and design and methods of fixation, and constant improvement in surgical technique. The success or failure of the surgical procedure correlates directly with the presence or absence of pain. Pain is probably the only true measure of the quality of the surgical result, and the symptom stands alone as an index of “end point” or failure in any survivorship analysis. Only pain correlates positively with the patient’s expectations, and furthermore it is only pain that can define disappointment or predict the decision if there is a need for a revision procedure.
Thigh pain after THA has attracted considerable debate but only since the mid-1980s. The introduction of and the increasing popularity of cementless implant fixation has provoked much of the discussion as to its cause. This chapter reviews the observed incidence of thigh pain and debates the many morphologic reasons implicated in the causation of the symptom. This chapter also discusses many of the causes, the effects, the diagnosis, and the management of thigh pain, and relates the discussion to a clinical experience of more than 1000 THA procedures.
Various mechanical causes of thigh pain are reviewed, and it remains clear that many of these remain an enigma. Specifically, a review of the concept of homoelasticity and the (as yet theoretical) potential benefit to be derived from the use, in implant fabrication, of novel materials and designs to modify section modulus and to optimize stress transfer are reviewed.
The correlation between radiographic and scintigraphic findings and the clinical presentation is reviewed. It is concluded that any positive correlation between these imaging techniques and the incidence of thigh pain is questionable and is more likely, in the majority of cases, to be coincidental. Furthermore, it has not been possible to positively correlate changes in bone morphology, implant fit and fill, and mode of implant stabilisation (bony vs fibrous) with the incidence of thigh pain. The only positive correlation identified between persisting thigh pain and a specific cause has been found to be associated with revision arthroplasty and with the use of femoral stem implants of greater than 17 mm diameter. A lower-than-usual incidence of thigh pain has been associated with fully sintered femoral stems of the Mittelmeier Autophor design and with femoral implants proximally coated with hydroxyapatite.
The authors conclude that, at this time, thigh pain is an inevitable complication of total hip arthroplasty. The morphologic reasons for the symptom remain unclear. Fortunately, the symptom is not always a clinical problem and in a great many cases the symptom is observed to improve with time. Unfortunately, persistent thigh pain can be a significant clinical problem and a cause for failure of the expectation of both the patient and the surgeon. A program of management is recommended and the “Higgs” surgical stress by-pass procedure for relief of intractable thigh pain of mechanical origin is described.
Charley Davidson’ s pal Sanza Time had a similar accident, but, instead of fracturing his tibia, he sustained a closed fracture of the femur. This fracture was treated by closed intramedullary rodding, and Sanza, against the advice of his surgeon, was back on his bike as soon as the repair shop pronounced it ready. Also against the advice of his doctor, he went back to his job in a steel mill, where he was on his feet all day, and even played a little Softball on weekends. His doctor was hardly surprised, then, that, about 11 weeks after his operation, Sanza had a sudden pain in the thigh. A roentgenogram showed a broken rod associated with an ununited femur. How could such a thing happen?
The possibilities for artificial reconstruction of diseased human joints have improved tremendously since the early 1960s, and the numbers of joint replacements in orthopedic surgery have grown almost exponentially. For the hip and the knee in particular, a multitude of different artificial joint designs are available, usually made of special metal alloys in combination with several kinds of plastics (Walker, 1977). Roughly speaking, artificial joint components can be categorized into intramedullary fixated ones, where a stem is fixed into the medullary canal of a long bone, and surface replacements, which are more or less fixed against the (spongeous) bone at the joint site (Figure 18.1).
A thermomechanical continuum theory involving a chemical reaction and mass transfer between two constituents is developed here as a model for bone remodeling. Bone remodeling is a collective term for the continual processes of growth, reinforcement and resorbtion which occur in living bone. The resulting theory describes an elastic material which adapts its structure to applied loading.
Compression tests of human and bovine trabecular bone specimens with and without marrow in situ were conducted at strain rates of from 0.001 to 10.0 per second. A porous platen above the specimens allowed the escape of marrow during testing. The presence of marrow increased the strength, modulus, and energy absorption of specimens only at the highest strain rate of 10.0 per second. This enhancement of material properties at the highest strain rate was due primarily to the restricted viscous flow of marrow through the platen rather than the flow through the pores of the trabecular bone. In specimens without marrow, the strength was proportional to the square of the apparent density and the modulus was proportional to the cube of the apparent density. Both strength and modulus were approximately proportional to the strain rate raised to the 0.06 power. These power relationships, which were shown to hold for all bone in the skeleton, allow meaningful predictions of bone tissue strength and stiffness based on in vivo density measurements.
This paper describes a biomechanical investigation of the human hip during level walking, while climbing and descending stairs, and when rising from a sitting position. Triads of flashing, light-emitting diodes attached to the pelvis, thigh, shank, and foot are photographed by a biplanar technique to generate kinematic data. Kinetic data is collected using a piezoelectric force platform. The inverse dynamics problem associated with the three lower extremity segments is solved for the time variations of the intersegmental force and moment resultants at the hip, knee, and ankle. An optimization technique is used to distribute these resultants to the load-carrying structures in the neighborhood of the hip, and to the two-joint muscles that flex and extend the knee and ankle. Typical results for a group of normal volunteers are presented and discussed.
Thirty-four cases of RM isoelastic total hip arthroplasty were followed for an average period of 42 months after surgery. Eleven (32%) were revised because of purely mechanical loosening of the femoral stem. Of the remaining cases, 16 (69%) had poor Mayo hip scores and only 2 (9%) had good results. Radiologic evidence of loosening of the uncemented femoral stem, as exemplified by radiopaque lines within radiolucent zones, the so-called "pedestal sign" of increased density at the stem tip, and proximal bony overgrowth around the collar were present in all 11 cases that were revised. Marked stem shift and localized cortical hypertrophy were noted in nine revised cases. Radiopaque lines were observed in 11 nonrevised cases, all with poor Mayo hip scores.
Two Lord prostheses, bilaterally implanted in cadavers, were sectioned. the contact areas between bone and prosthesis were studied and measured using a specially developed reproducible method. Primary fixation of the femoral components appeared to be based principally on wedging of the prosthetic stem in the femoral shaft with a rather small contact surface. In both acetabuli the screw threads of the rings were only marginally in contact with the acetabular bone. © 1988 Informa UK Ltd All rights reserved: reproduction in whole or part not permitted.
The subject of this article is the development and application of computer-simulation methods to predict stress-related adaptive bone remodeling, in accordance with 'Wolff's Law'. These models are based on the Finite Element Method (FEM) in combination with numerical formulations of adaptive bone-remodeling theories. In the adaptive remodeling models presented, the Strain Energy Density (SED) is used as a feed-back control variable to determine shape or bone density adaptations to alternative functional requirements, whereby homeostatic SED distribution is assumed as the remodeling objective. These models are applied to investigate the relation between 'stress shielding' and bone resorption in the femoral cortex around intramedullary prostheses, such as used in Total Hip Arthroplasty (THA). It is shown that the amount of bone resorption depends mainly on the rigidity and the bonding characteristics of the implant. Homeostatic SED can be obtained when the resorption process occurs at the periosteal surface, rather than inside the cortex, provided that the stem is adequately flexible.
The method of considering a single loading condition in the study of stress/morphology relationships in trabecular bone is expanded to include the multiple loading conditions experienced by bone in vivo. The bone daily loading histories are characterized in terms of stress magnitudes or cyclic strain energy density and the number of loading cycles. Relationships between local bone apparent density and loading history are developed which assume that bone mass is adjusted in response to strength or energy considerations. Three different bone maintenance criteria are described which are formulated based upon: (1) continuum model effective stress, (2) continuum model fatigue damage accumulation density, and (3) bone tissue strain energy density. These approaches can be applied to predict variations in apparent density within bone and among bones. We show that all three criteria have similar mathematical forms and may be related to the density (or concentration) of bone strain energy which is transferred (dissipated) in the mineralized tissue. The loading history and energy transfer concepts developed here can be applied to many different situations of growth, functional adaptation, injury, and aging of connective tissues.
The purposes of this study were to compare ingrowth of bone into three types of porous coating and to determine the effect of the type of porous coating and the degree of coverage of the stem on the remodeling of bone on the femoral side in cementless hip arthroplasty. A left total hip arthroplasty was performed in forty dogs. Thirty of the dogs had a titanium-alloy femoral prosthesis that had had one of three types of commercially pure titanium porous material applied along the length of the anterior and posterior surfaces of the stem: ten with sintered fiber-metal, ten with sintered beads, and ten with plasma flame-spray coating. The remaining ten dogs had a femoral component that was circumferentially coated with commercially pure titanium that was plasma flame-sprayed along the length of the stem. In each group, five animals were killed at one month and five were killed at six months. Ingrowth of bone into all three types of porous coating was observed, indicating secure fixation of all components. By six months, there was more ingrowth of bone and new medullary bone adjacent to the proximal and distal aspects of the stems compared with the middle level of the stems in all groups. No significant difference in ingrowth of bone was observed in the beaded surface (25.2 per cent) and the fiber-metal surface (16.6 per cent) at one month, but at six months there was significantly less ingrowth into the beaded surface (23.3 per cent) than into the fiber-metal surface (37.3 per cent). In all groups, a proximal-to-distal gradient of loss of cortical bone was observed by six months. The group of dogs that had the stem with the circumferential coating experienced more severe loss of bone than did the three groups that had a stem with a partial coating. The magnitude of loss of bone was dependent on the extent rather than the type of porous coating.
Total hip replacement using porous-coated cobalt-chrome femoral implants designed for biological fixation has been evaluated in 307 patients after two years and in 89 patients after five years. Histological study of 11 retrieved specimens showed bone ingrowth in nine and fibrous tissue fixation in two. Fixation by bone ingrowth occurred in 93% of the cases in which a press fit of the stem at the isthmus was achieved, but in only 69% of those without a press fit. The clinical results at two years were excellent. The incidence of pain and limp was much lower when there was either a press fit of the stem or radiographic evidence of bone ingrowth. Factors such as age, sex, and the disease process did not influence the clinical results. Most cases showed only slight resorptive remodelling of the upper femur, but in a few cases with a larger, more rigid stem, more extensive bone loss occurred. The results after five years showed no deterioration with time. Fixation by the ingrowth of bone or of fibrous tissue both appeared to be stable, but bone ingrowth gave better clinical results.
The phenomenon of bone remodeling is a complex biological process which is dependent on genetic, hormonal, metabolic, and age-related factors as well as functional requirements. The possibility of successfully developing a mathematical model to describe and predict the adaptive response of bone to load will be significantly increased after identification of the nature of the transducer(s) which senses functional requirements and provides signals for the cellular processes responsible for bone synthesis and bone removal. In spite of the present limitations in knowledge about the functional dependence of bone remodeling, a phenomenological model has been developed that assumes that the output signal from the (as yet unspecified) transducer is a remodeling potential that can be modulated by genetic, hormonal, and metabolic factors. An attempt has been made to cast the mathematical model in such a form that the constants and variables appearing in the equations are not mere abstractions, but can be related to biological parameters. In order to use the adaptive hypothesis with specific structural model examples, a numerical procedure has been developed to determine the strain distribution, predict the remodeling (assuming that the remodeling rate is related to the strain history), and update the model by changing the geometry and material properties in response to the remodeling. This numerical procedure is repeatedly iterated to determine the structural architecture at subsequent times. The numerical approach allows use of the remodeling concepts with models of irregular geometry, inhomogeneous material distribution, and anisotropic material properties.
A cementless total hip system of modular design is presented. The design of the stem provides for a firm seating on the cortical bone over a large area. Therefore primarily stable fixation is accomplished. The stem in seven different sizes is made of hot forged Ti-6Al-4V Protasul-64 WF alloy of high corrosion fatigue strength. The Biolox ceramic ball with three different neck lengths is connected to the high strength stem by means of a special selflocking conical spigot with a structured surface. The ceramic ball is combined with a polyethylene screw socket in four different sizes, designed by Endler and anchored in the acetabulum without acrylic cement. This hip prosthesis system has proved itself in clinical application since 1979.
The myth of "press-Fit" in the proximal femur
- Noble
- Alexander
- M L Granberry
Stress-shielding stress-bypassing and bone resorption around "press-fit" and bone ingrowth THA
- H Huiskes R Weinans
- D R Sumner
Prothèse non cimentée de première intention. Experience a moyem terme avec la prothèse de Lord
- P F Dutoit M Roquin B De Leyvraz
Huiskes R Chao EYS: A survey of finite element methods in orthopaedic biomechanics