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The Impaction Variables Studied: Both In- creases in Drop Mass and Velocity Were Used to Increase the Impaction Energy.
Source publication
Seating a cementless acetabular cup via impaction is a balancing act; good cup fixation must be obtained to ensure adequate bone in‐growth and cup apposition, while acetabular fracture must be avoided. Good impaction technique is essential to the success of hip arthroplasty. Yet little guidance exists in the literature to inform surgeons on ‘how ha...
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Citations
... The impaction process has recently gained attention, such as different combinations of mass and velocity for impaction 27 or different energy levels. 28 Increasing the impaction frequency from 1 Hz to 6 Hz was shown to reduce the impaction force. 29 The application of vibrations has been demonstrated to be an advantageous approach in other fields: in the construction industry, vibratory pile driving is shown to be beneficial compared to impact driving in terms of reducing the required force for pile installation as well as the frictional force. ...
... In this study, polyurethane (PU) foam blocks with varying densities were used as bone surrogates, given their widespread use as bone substitutes in other studies. 27,28,31,32 Methods Bone surrogates and acetabular component PU foam blocks (SYNBONE, Switzerland) with densities of 15 and 30 pounds per cubic foot (PCF) with computer numerical control (CNC)-milled hemispherical cavities (diameter of 51 mm centred 2 mm below the top surface of the foam block; Figure 1) were used as bone surrogates. The cavity had two cut-outs creating a simplified acetabular anatomy model with similar component deformation as measured in cadaver experiments. ...
... The cavity had two cut-outs creating a simplified acetabular anatomy model with similar component deformation as measured in cadaver experiments. 28,32 Press-fit acetabular components (cups) (Pinnacle, Sector hole, Gription Coating; DePuy Synthes, UK) with a nominal size of 52 mm were inserted into the cavities. ...
Aims
Periprosthetic fracture and implant loosening are two of the major reasons for revision surgery of cementless implants. Optimal implant fixation with minimal bone damage is challenging in this procedure. This pilot study investigates whether vibratory implant insertion is gentler compared to consecutive single blows for acetabular component implantation in a surrogate polyurethane (PU) model.
Methods
Acetabular components (cups) were implanted into 1 mm nominal under-sized cavities in PU foams (15 and 30 per cubic foot (PCF)) using a vibratory implant insertion device and an automated impaction device for single blows. The impaction force, remaining polar gap, and lever-out moment were measured and compared between the impaction methods.
Results
Impaction force was reduced by 89% and 53% for vibratory insertion in 15 and 30 PCF foams, respectively. Both methods positioned the component with polar gaps under 2 mm in 15 PCF foam. However, in 30 PCF foam, the vibratory insertion resulted in a clinically undesirable polar gap of over 2 mm. A higher lever-out moment was achieved with the consecutive single blow insertion by 42% in 15 PCF and 2.7 times higher in 30 PCF foam.
Conclusion
Vibratory implant insertion may lower periprosthetic fracture risk by reducing impaction forces, particularly in low-quality bone. Achieving implant seating using vibratory insertion requires adjustment of the nominal press-fit, especially in denser bone. Further preclinical testing on real bone tissue is necessary to assess whether its viscoelasticity in combination with an adjusted press-fit can compensate for the reduced primary stability after vibratory insertion observed in this study.
... Third, the acetabulum was assumed hemispherical and defect-free. However, the natural acetabulum may have defects, including the acetabular notch, lateral defects, and an acetabular fossa, the influence of which also requires examination [37][38][39][40]. Fourth, despite the simulation of shell installation position, in vivo loads are dynamic, thus individual differences such as spino-pelvic dynamics, supine versus standing as well as limb positions were not reflected in this study. ...
Uncemented acetabular shell primary stability is essential for optimal clinical outcomes. Push-out testing, rotation testing, and lever-out testing are major evaluation methods of primary stability between the shell and bone. However, these test methods do not consider shell loads during daily activity and shell installation angle. This study proposes a novel evaluation method of acetabular shell primary stability considering load during level walking and acetabular installation angles such as inclination and anteversion. To achieve this, a novel primary stability test apparatus was designed with a shell position of 40° acetabular inclination and 20° anteversion. The vertical load, corresponding to walking load, was set to 3 kN according to ISO 14242–1, which is the wear test standard for artificial hip joints. The vertical load was applied by an air cylinder controlled by a pressure-type electro-pneumatic proportional valve, with the vertical load value monitored by a load cell. Torque was measured when angular displacement was applied in the direction of extension during the application of vertical load. For comparison, we also measured torque using the traditional lever-out test. The novel primary stability test yielded significantly higher primary stabilities; 5.4 times greater than the lever-out test results. The novel primary stability test failure mode was more similar to the clinical failure than the traditional lever-out test. It is suggested that this novel primary stability test method, applying physiological walking loads and extension motions to the acetabular shell, better reflects in vivo primary stability than the traditional lever-out test.
... This should be aimed at comparing the 3D printed reamers against used conventional reaming kits, testing for superiority. Testing the push-out forces when implanting acetabular cups into the reamed cavities produced, would allow us to see how the different reamer systems and techniques affected the press-fit stability of acetabular implants although it is evident that small differences in reamed cavity size and hence press fit affect push out, periacetabular strain and cup deformation [28,29]. Further analysis of the whirlwind reaming technique should take place to identify the optimal rotation angles, cutting forces and speed, to further improve accuracy and precision. ...
Introduction
Successful press-fit implantation relies on an accurately reamed bone cavity. Inaccurate reaming can lead to a suboptimal press-fit risking fracture and cup deformation or excessive micromotion and loosening. Several factors may impact reaming accuracy including the reamer design, the surgeon’s technique and the bone quality. The aim of this study is to investigate the accuracy of reaming techniques and the accuracy of a novel reamer design.
Methods
Eighty composite bone models, half high density and half low density, were reamed with either a conventional or an additively manufactured reamer with a novel design employing either a straight or ‘whirlwind’ reaming technique. Reamed cavities were scanned using a 3D laser scanner and the median difference between achieved and expected diameters compared.
Results
The novel reamer design was more accurate than the unused conventional reamer, using both whirlwind (0.1 mm (IQR 0–0.2) vs. 0.3 mm (IQR 0.3–0.4); p < 0.001) and straight techniques (0.3 mm (IQR 0.1–1.0) vs. 1.2 mm (IQR 1–1.6); p = 0.001). Whirlwind reaming was more accurate than straight reaming using both conventional (0.3 mm (IQR 0.3–0.4) vs. 1.2 mm (IQR 1–1.6); p < 0.0001) and single use reamers (0.1 mm (IQR 0–0.2) vs. 0.3 mm (IQR 0.1–1.0); p = 0.007). Reaming errors were higher in low-density bone compared to high-density bone, for both reamer types and reaming techniques tested (0.6 mm (IQR 0.3–1.5) vs. 0.3 mm (IQR 0.1–0.8); p = 0.005).
Conclusion
We present a novel reamer design that demonstrates superior accuracy to conventional reamers in achieving the desired reaming diameter. Improved reaming accuracy was also demonstrated using both devices and in both bone models, using a ‘whirlwind’ technique. We recommend the use of this novel reamer design employing a ‘whirlwind’ technique to optimize reaming accuracy. Particular attention should be paid toward patients with lower bone quality which may be more susceptible to higher inaccuracies.
... While static culture conditions exhibited some characteristics of bony adaptation to implantation, simulating physiological conditions with a bioreactor led to an accelerated response. KEYWORDS bone, mineralisation, osseointegration, preclinical, fixation, additive manufacturing, ex vivo, in vitro innovation, including new implant technologies such as additively manufactured porous structures (Brogini et al., 2021;Munford et al., 2022) nano coatings (Bai et al., 2021) and biophysical stimulation (Soares dos Santos et al., 2016;de Sousa et al., 2021), as well as novel approaches to design (van Arkel et al., 2018;Wang et al., 2021) and innovation in surgical technique (Doyle et al., 2019;Doyle et al., 2020). ...
Introduction: Preclinical assessment of bone remodelling onto, into or around novel implant technologies is underpinned by a large live animal testing burden. The aim of this study was to explore whether a lab-based bioreactor model could provide similar insight.
Method: Twelve ex vivo trabecular bone cylinders were extracted from porcine femora and were implanted with additively manufactured stochastic porous titanium implants. Half were cultured dynamically, in a bioreactor with continuous fluid flow and daily cyclic loading, and half in static well plates. Tissue ongrowth, ingrowth and remodelling around the implants were evaluated with imaging and mechanical testing.
Results: For both culture conditions, scanning electron microscopy (SEM) revealed bone ongrowth; widefield, backscatter SEM, micro computed tomography scanning, and histology revealed mineralisation inside the implant pores; and histology revealed woven bone formation and bone resorption around the implant. The imaging evidence of this tissue ongrowth, ingrowth and remodelling around the implant was greater for the dynamically cultured samples, and the mechanical testing revealed that the dynamically cultured samples had approximately three times greater push-through fixation strength (p < 0.05).
Discussion: Ex vivo bone models enable the analysis of tissue remodelling onto, into and around porous implants in the lab. While static culture conditions exhibited some characteristics of bony adaptation to implantation, simulating physiological conditions with a bioreactor led to an accelerated response.
... Direct relationships can be demonstrated between increased impaction energy (or force) and increased seating for various implants [14][15][16][17][18][19][20]. But excessive seating can cause periprosthetic fracture [5,6]. ...
... Reducing the applied energy and number of hits would reduce stresses but would also decrease seating ("surgeon" parameters). However, stresses decreased with increasing hammer diameter, length and density, which are all directly related [17]; Note3: This value results in a clinically measured impaction force [16]. Videos of the load transfer for the varied hammer-introducer stiffness (nominal, +/-order of magnitude) can be found as S1-S3 Files; Note4: Data for porous-coated stem in cadaveric femur [27]; Note5: from [16]. ...
... https://doi.org/10.1371/journal.pone.0268561.g009 PLOS ONE [14][15][16][17][18][19][20]. Generally, greater hammer energy is observed to increase implant stability [28][29][30], which is also reflected by the current model, but can also increase the risk of periprosthetic fracture [17]. ...
Press-fitted implants are implanted by impaction to ensure adequate seating, but without overloading the components, the surgeon, or the patient. To understand this interrelationship a uniaxial discretised model of the hammer/introducer/implant/bone/soft-tissues was developed. A parametric analysis of applied energy, component materials and geometry, and interactions between implant and bone and between bone and soft-tissues was performed, with implant seating and component stresses as outcome variables. To reduce the impaction effort (energy) required by the surgeon for implant seating and also reduce stresses in the hardware the following outcomes were observed: Reduce energy per hit with more hits / Increase hammer mass / Decrease introducer mass / Increase implant-bone resistance (eg stem roughness). Hardware stiffness and patient mechanics were found to be less important and soft tissue forces, due to inertial protection by the bone mass, were so low that their damage would be unlikely. This simple model provides a basic understanding of how stress waves travel through the impacted system, and an understanding of their relevance to implantation technique and component design.
... 16,[22][23][24] High impaction energies were shown to improve primary stability, while excessive impaction in terms of energy amount and number of strokes should be avoided. 25,26 An influence of the surrogate density on the impaction process has been demonstrated, 26 but the influence of the cup design has not yet been considered. ...
... Since the seating progress cannot be closely monitored during surgery, higher seating steps would facilitate the visible tracking of cup seating. The use of higher energies seems to have a positive effect on cup seating, but possibly increases the risk of bone damage.25 Cup implantation is also influenced by the acetabular cavity. ...
Insufficient primary stability of acetabular hip cups is a complication resulting in early cup loosening. Available cup designs vary in terms of wall thickness, potentially affecting implant fixation. This study investigated the influence of different wall thicknesses on the implantation process and the resulting primary stability using excised human acetabula. Implantations were performed using a powered impaction device providing consistent energy with each stroke. Two different wall thicknesses were compared in terms of seating progress, polar gap remaining after implantation, bone‐to‐implant contact area, cup deflection, and lever out moment. Thin‐walled cups showed higher lever out resistance (p < 0.001) and smaller polar gaps (p < 0.001) with larger bone contact toward the dome of the cup (p < 0.001) compared to thick‐walled cups. Small seating steps at the end of the impaction process were observed if a high number of strokes were needed to seat the cup (p = 0.045). A high number of strokes led to a strain release of the cup during the final strokes (p = 0.003). This strain release is indicative for over‐impaction of the cup associated with bone damage and reduced primary stability. Adequate cup seating can be achieved with thin‐walled cups with lower energy input in comparison to thicker ones. Thin‐walled cups showed improved primary stability and enable implantation with lower energy input, reducing the risk of over‐impaction and bone damage. Additional strokes should be avoided as soon as no further seating progress has been observed.
... Despite recent interest in orthopaedic impaction (13)(14)(15)(16)(17) there remains little understanding of the mechanism and little evidence-based information for the surgeon or the designers regarding technique or tools. ...
... In this study seating of a press-t femoral stem by impaction was modelled. Dynamic seating of orthopaedic implants has been documented experimentally (13)(14)(15)(16)(18)(19)(20) but little modelling exists, although publications exist in other elds, such as pile driving (21,22). The aim was to nd parameters that decreased introducer stresses without compromising seating. ...
... Nominal values for each parameter (red) and their variations. Note1: This value results in 1000 points representing the nominal applied force-time impaction impulse; Note2 from (14); Note3 :This value results in a clinically measured impaction force (13). Videos of the load transfer for the varied hammerintroducer stiffness (nominal, +/-order of magnitude) can be found as supplementary material; Note4: ...
Background
Press-fitted implants are implanted by impaction to ensure adequate seating, but without overloading the components, the surgeon, or the patient. To understand this interrelationship a uniaxial discretised model of the hammer/introducer/implant/bone/soft-tissues was developed. A parametric analysis of applied energy, component materials and geometry, and interaction between implant-bone and bone-soft-tissue was performed, with implant seating and component stresses as outcome variables. ResultsTo reduce stresses without compromising seating, the following outcomes were observed: Less energy per hit with more hits / Increase hammer mass / Decrease introducer mass / Increase implant-bone resistance (eg stem roughness). Material stiffness and patient mechanics were found to be less important.Conclusions
This simple model provides a basic understanding of how stress waves travel through the impacted system, and an understanding of their relevance to component design.
... It is hard for the surgeon to control the impaction strike precisely. High-energy strikes lead to a marginal increase in the pushout fixation but only a small decrease in the polar gap and thus should be avoided [29]. ...
Background:
Considering the excellent results already achieved in total hip arthroplasty (THA), new implants must be at least as safe as currently used implants and lead to longer survival. A new cementless femoral stem, SP-CL®, has been introduced. The aim of this study is to evaluate intraoperative complications and assess the risk factors of THA with the SP-CL® implant.
Materials and methods:
All THA patients who were operated on using the SP-CL® (LINK, Hamburg, Germany) implant between 2015 and 2018 were included in the analysis. Data were collected from medical records from national and hospital electronic databases. Radiological measurements were made from standard pre- and postoperative radiographs.
Results:
A total of 222 THA were performed using the SP-CL® implant. The average age of the patients was 56 years (14-77 years). There were 1 transient sciatic nerve injury, 1 acetabular fracture, and 11 (5.0%) intraoperative femoral fractures (IFF), of which 7 were treated with cerclage wire or titanium band during the operation while the other fractures were treated conservatively. None of the IFF patients were revised due to fracture during the follow-up period (one revision due to infection). The radiographic morphology of proximal femur was associated with increased risk of IFF (p = 0.02).
Conclusions:
The results of the current study demonstrate a 5% incidence of IFF when using the LINK SP-CL® femoral stem in THA. The radiographic morphology of the proximal femur was an important predictor of IFF and should be assessed when using SP-CL®.
Level of evidence:
Level 4.
... However, the natural acetabulum may have defects other than the lateral defect, such as an acetabular notch and an acetabular fossa, and it will also be necessary to examine their influence. [42][43][44] ...
Excellent primary stability of uncemented acetabular shells is essential to obtain successful clinical outcomes. However, in the case of developmental dysplasia of the hip (DDH), aseptic loosening may be induced by instability due to a decrease of the contact area between the acetabular shell and host bone. The aim of this study was to assess the primary stability of two commercially-available acetabular shells, hemispherical and hemielliptical, in normal and DDH models. Synthetic bone was reamed using appropriate surgical reamers for each reaming condition (normal acetabular model). The normal acetabular model was also cut diagonally at 40° to create a dysplasia model. Stability of the acetabular components was evaluated by the lever-out test. In the normal acetabular model conditions, the maximum primary stabilities of hemispherical and hemielliptical shells were observed in the 1-mm under- and 1-mm over-reamed conditions, respectively, and the resulting stabilities were comparable. The lateral defect in the dysplasia model had an adverse effect on the primary stabilities of the two designs. The lever-out moment of the hemielliptical acetabular shell was 1.4 times greater than that of the hemispherical acetabular shell in the dysplasia model. The hemispherical shell is useful for the normal acetabular condition, and the hemielliptical shell for the severe dysplasia condition, in the context of primary stability.
... Previous work has investigated the role of impaction energy or implantation force, both of which depend upon mallet mass and velocity, implant stability, and seating. 31 However the effect of number of impaction strikes remains unclear. As it can be difficult for the surgeon to accurately infer when a component is seated, 32 the effect of under-or over-impacting an acetabular component requires investigation. ...
... The details of the test setup and human cadaver validation have been described previously. 31,33 Expanded polyurethane foam (Model #1522 to 02 and #1522 to 04; Sawbones, Pacific Laboratories, Malmö, Sweden) was used as a repeatable synthetic bone substitute for the acetabulum: the high-density (30 PCF) foam replicated good-quality bone with a strong cortical rim while the low-density (15 PCF) foam replicated poorer quality bone, such as the exposed cancellous, subchondral bone seen in revision cases. [34][35][36][37][38] The bones were computer numerical control (CNC) milled to create a 53 mm diameter acetabular cavity, with a previously validated anatomically representative geometry, including two 'notches'. ...
... This location has previously been shown to experience the highest strain. 21,31 Strain gauge data were acquired for one second following each strike using a USB datalogger (NI9327; National Instruments, Budapest, Hungary) in quarter bridge configuration. Raw data were captured using Labview (National Instruments, 2014) and analyzed using MATLAB (Mathworks, Natick, Massachusetts, USA). ...
Aims
Cementless acetabular components rely on press-fit fixation for initial stability. In certain cases, initial stability is more difficult to obtain (such as during revision). No current study evaluates how a surgeon’s impaction technique (mallet mass, mallet velocity, and number of strikes) may affect component fixation. This study seeks to answer the following research questions: 1) how does impaction technique affect a) bone strain generation and deterioration (and hence implant stability) and b) seating in different density bones?; and 2) can an impaction technique be recommended to minimize risk of implant loosening while ensuring seating of the acetabular component?
Methods
A custom drop tower was used to simulate surgical strikes seating acetabular components into synthetic bone. Strike velocity and drop mass were varied. Synthetic bone strain was measured using strain gauges and stability was assessed via push-out tests. Polar gap was measured using optical trackers.
Results
A phenomenon of strain deterioration was identified if an excessive number of strikes was used to seat a component. This effect was most pronounced in low-density bone at high strike velocities. Polar gap was reduced with increasing strike mass and velocity.
Conclusion
A high mallet mass with low strike velocity resulted in satisfactory implant stability and polar gap, while minimizing the risk of losing stability due to over-striking. Extreme caution not to over-strike must be exercised when using high velocity strikes in low-density bone for any mallet mass. Cite this article: Bone Joint Res 2020;9(7):386–393.
