Summary Statement. A FEA model built from CT-data of frozen cadaver has been validated and used for under-reaming experiments. 1 mm under-reaming can provide contact surface and micromotions that are acceptable and within the clinical relevance without high impact force. Introduction. Long-term cup fixation and stability in total hip arthroplasty (THA) is directly related to the bone ingrowths between the porous cup and the acetabulum. To achieve the initial cup setting, 1 mm of under reaming is becoming the gold standard for cementless cup and what is at stake is usually the actual contact between cup and acetabulum wall. During impact and cup placement, friction forces are generated from the “not permanent” deformations of the acetabular wall that are translated into a gap between the reamed bone and the cup. Clinically the surgeon objective is to have the gap extended to a limited portion of the cup in order to improve bone ingrowth. Hence, the need arises from examining this cup bone stability interface by examining the selected “under reaming” conditions, the surface of contact between the acetabular cup and the bone and its relation to the impact force resulting from the hammering of the cup. Patients & Methods. A validated finite element model built from CT data of fresh frozen hip cadavers has been used for under-reaming mechanically testing experiment. The model was constrained at the sacral and pubic joints to mimic the exact fixation and potting of the pelvis used for testing, and an “impactor” model was used to force the cup into the acetabular reamed socket for both 1 and 2 mm under reaming conditions of the selected cup sizes. Three impact conditions were simulated by imposing cup displacements equivalent to 80, 100 and 120% of the initial distance between the cup apex and the bone. The corresponding reactions forces were evaluated as ideal insertion forces. After the loading phase, a relaxing phase was defined by the removal of load to determine the equilibrium position between the friction forces and the elastic deformation of the actabulum bone. In our last phase, the cup is loaded with a 1500N along the femoral mechanical axis following the same loading conditions of our cup-bone interface experimental setup. Results. The value of under-reaming plays a significant role in the hammering force due to cup placement and has a high correlation with the surface in contact in all cases of implantation, as well as the final stability of the cup throughout loading. When comparing the 2 mm with 1 mm of bone under-reaming we found that the higher degree of under-reaming resulted in slightly greater surface area of contact between the cup and bone as well as reduced micromotion at loading up to 1500 N. However, the impact force requirements for 2mm under reaming was found to be much higher in all three cases investigated. Discussion/Conclusion. Our results indicate that 1 mm under reaming can provide contact surface and micromotions that are both acceptable and within the clinical relevance of cup bone stability without the need of high impact force needed to insert the cup to its desired depth. High insertion forces may lead or cause risk of fracture

Aims. Metaphyseal tritanium cones can be used to manage the tibial bone loss commonly encountered at revision total knee arthroplasty (rTKA). Tibial stems provide additional fixation and are generally used in combination with cones. The aim of this study was to examine the role of the stems in the overall stability of tibial implants when metaphyseal cones are used for rTKA. Methods. This computational study investigates whether stems are required to augment metaphyseal cones at rTKA. Three cemented stem scenarios (no stem, 50 mm stem, and 100 mm stem) were investigated with 10 mm-deep uncontained posterior and medial tibial defects using four loading scenarios designed to mimic activities of daily living. Results. Small micromotions (mean < 12 µm) were found to occur at the bone-implant interface for all loading cases with or without a stem. Stem inclusion was associated with lower micromotion, however these reductions were too small to have any clinical significance. Peak interface micromotion, even when the cone is used without a stem, was too small to effect osseointegration. The maximum difference occurred with stair descent loading. Stress concentrations in the bone occurred around the inferior aspect of each implant, with the largest occurring at the end of the long stem; these may lead to end-of-stem pain. Stem use is also found to result in stress shielding in the bone along the stem. Conclusion. When a metaphyseal cone is used at rTKA to manage uncontained posterior or medial defects of up to 10 mm depth, stem use may not be necessary. Cite this article:Bone Joint Res. 2020;9(4):162–172

Reducing wear of endoprosthetic implants is still an important goal in order to increase the life time of the implant. Endoprosthesis failure can be caused by many different mechanisms, such as abrasive wear, corrosion, fretting or foreign body reactions due to wear accumulation. Especially, modular junctions exhibit high wear rates and corrosion due to micromotions at the connection of the individual components. The wear generation of cobalt-chromium-molybdenum alloys (CoCrMo) is strongly influenced by the microstructure. Therefore, the aim of this work is to investigate the subsurface phase transformation by deep rolling manufacturing processes in combination with a “sub-zero” cooling strategy. We analyzed the influence on the phase structure and the mechanical properties of wrought CoCr28Mo6 alloy (ISO 5832-12) by a deep rolling manufacturing process at various temperatures (+25°C,-10°C,-35°C) and different normal forces (700N and 1400N). Surface (S. a. ,S. z. ) and subsurface characteristics (residual stress) as well as biological behavior were investigated for a potential implant application. We showed that the microstructure of CoCr28Mo6 wrought alloy changes depending on applied force and temperature. The face centered cubic (fcc) phase could be transformed to a harder hexagonal-close-packed (hcp) phase structure in the subsurface. The surface could be smoothed (up to S. a. = 0.387 µm±0.185 µm) and hardened (≥ 700 HV 0.1) at the same time. The residual stress was increased by more than 600% (n=3). As a readout for metabolic activity of MonoMac (MM6) and osteosarcoma (SaOS-2) cells a WST assay (n=3) was used. The cells showed no significant negative effect of the sub-zero manufacturing process. We showed that deep rolling in combination with an innovative cooling strategy for the manufacturing process has a great potential to improve the mechanical properties of CoCr28Mo6 wrought alloy, by subsurface hardening and phase transformation for implant applications

Background. Fretting at modular junctions is thought to be a ‘mechanically assisted’ corrosion phenomenon, initiated by mechanical factors that lead to increased contact stresses and micromotions at the taper interface. We adopted a finite element approach to model the head-taper junction, to analyse the contact mechanics at the taper interface. We investigated the effect of assembly force and angle on contact pressures and micromotions, during loads commonly used to test hip implants, to demonstrate the importance of a good assembly during surgery. Methods. Models of the Bimetric taper and adaptor were created, with elastic-plastic material properties based on material tests with the actual implant alloy. FE contact conditions were validated against push-on and pull-off experiments. The models were loaded according to ISO 7206-4 and −6, after being assembled at 2-4-15kN, both axially and at a 30° angle. Average micromotions and contact pressures were analysed, and a wear score was calculated based on the contact pressures and micromotions. Results. The average contact pressure decreased when a higher assembly force was used, with loads being distributed over a larger contact area, but increased when tested at a 30° angle. Average micromotions reduced with a higher assembly load, except when assembled at a 30° angle. The wear score decreased with increasing assembly force, when applied perpendicularly, while when assembled at a 30° angle, the wear score did not reduce with assembly force. Conclusions. The location and patterns of micromotions were consistent with retrieved tapers and those generated in in-vitro test models. Increased impaction loads reduced the average amount of micromotion and fretting. We intend to apply more complex loading regimes in future analyses, enabling to study phenomena such as edge loading and frictional torque. Level of evidence. IIb - Experimental study. Disclosure. This study was financially supported by Biomet UK Healthcare Ltd

An increasingly used treatment for end-stage ankle osteoarthritis is total ankle replacement (TAR). However, implant loosening and subsidence are commonly reported complications, leading to relatively high TAR failure rates. Malalignment of the TAR has often been postulated as the main reason for the high incidence of these complications. It remains unclear to what extent malalignment of the TAR affects the stresses at the bone-implant interface. Therefore, this study aims to elucidate the effect of TAR malalignment on the contact stresses on the bone-implant interface, thereby gaining more understanding of the potential role of malalignment in TAR failure. FE models of the neutrally aligned as well as malaligned CCI Evolution TAR implant (Van Straten Medical) were developed. Separate models were developed for the tibial and talar segment, with the TAR components in neutral alignment and 5° and 10° varus, valgus, anterior and posterior malalignment, resulting in a total of 9 differently aligned TAR models. Loading conditions of the terminal stance phase of the gait cycle, when the force on the ankle joint is highest (5.2x body weight), were applied. Peak and mean contact pressure and shear stress at the bone-implant interface were analyzed. Also, stress distributions on the bone-implant interface were visualized. In the neutrally aligned tibial and talar TAR models, peak contact pressures of respectively 98.4 MPa and 68.2 MPa, and shear stresses of respectively 49.3 MPa and 39.0 MPa were found. TAR malalignment increases peak contact pressure and shear stress on the bone-implant interface. A maximum peak contact pressure of 177 MPa was found for the 10° valgus malaligned tibial component and the highest shear stress found was 98.5 MPa for the 10° posterior malaligned talar model. Upon TAR malalignment contact stresses increase substantially, suggesting that proper orientation of the TAR is needed to minimize peak stresses on the bone-implant interface. This is in line with previous studies, which state that malalignment considerably increases bone strains, micromotion, and internal TAR contact pressures, which might increase the risk of TAR failure. Further research is needed to investigate the relationship between increased contact stresses at the bone-implant interface and TAR failure

Abstract. Introduction. The long-term biological success of cementless orthopaedic prostheses is highly dependent on osteointegration. Pre-clinical testing of new cementless implant technology however, requires live animal testing, which has anatomical, loading, ethical and cost challenges. This proof-of-concept study aimed to develop an in vitro model to examine implant osteointegration under known loading/micromotion conditions. Methods. Fresh cancellous bone cylinders (n=8) were harvested from porcine femur and implanted with additive manufactured porous titanium implants (Ø4 × 15 mm). To simulate physiological conditions, n=3 bone cylinders were tested in a bioreactor system with a cyclic 30 µm displacement at 1Hz for 300 cycles every day for 15 days in a total of 21 days culture. The chamber was also perfused with culture medium using a peristaltic pump. Control bone cylinders were cultured under static conditions (n=5). Samples were calcein stained at day 7. Post-testing, bone cylinders were formalin fixed and bony ingrowth was measured via microscopy. Results. Viability of the freshly harvested ex vivo bone cylinders was maintained for up to 28 days. Two samples remain unanalysed due to COVID lockdown, one in each group. Similar to osteointegration seen in live animal models, evidence of bony ingrowth was seen more markedly at the bone-implant interface under dynamic conditions. This was evident by a greater intensity of calcein staining, confirming the deposition of new bone, at the bone-implant interface. In comparison, under static conditions, calcein staining was observed randomly all over the cylinder. Conclusion. This proof-of-concept study demonstrates that implant bony adaptation and ingrowth can be measured in vitro under known cyclic micromotion/loading conditions. This comparatively low cost, low ethical impact, controlled loading laboratory method has potential to accelerate the rate of implant development whilst conforming with the principles of NC3Rs. Declaration of Interest. (b) declare that there is no conflict of interest that could be perceived as prejudicing the impartiality of the research reported:I declare that there is no conflict of interest that could be perceived as prejudicing the impartiality of the research project

Summary. Micromotions between stem and neck adapter depend on prosthesis design and material coupling. Based on the results of this study, the amount of micromotion seems to reflect the risk of fretting-induced fatigue in vivo. Introduction. Bimodular hip prostheses were developed to allow surgeons an individual reconstruction of the hip joint by varying length, offset and anteversion in the operation theatre. Despite these advantages, the use of these systems led to a high rate of postoperative complications resulting in revision rates of up to 11% ten years after surgical intervention. During daily activities taper connections of modular hip implants are highly stressed regions and contain the potential of micromotions between adjacent components, fretting and corrosion. This might explain why an elevated number of fretting-induced neck fractures occurred in clinics. However, some bi-modular prostheses (e.g. Metha, Aesculap, Ti-Ti) are more often affected by those complications than others (e.g. H-Max M, Limacorporate, Ti-Ti or Metha, Ti-CoCr) implying that the design and the material coupling have an impact on this failure pattern. Therefore, the purpose of this study was to clarify whether clinical successful prostheses offer lower micromotions than those with an elevated number of in vivo fractures. Materials and Methods. Two different bimodular hip designs (Metha and H-Max M, n = 6 each) were tested in vitro. Embedded Ti6Al4V (Ti) stems were assembled with Ti or CoCr29Mo (CoCr) necks and sinusoidally loaded (f = 1 Hz, 10,000 cycles) ranging from 0.23 to 4.30 kN (peak to peak, represents going upstairs) using a servohydraulic testing machine (MiniBionix II, MTS). Based on the results of four eddy-current sensors, micromotions were assessed in the region of the crack origin of fractured prostheses (lateral radius). Due to the test set-up, the recorded displacement includes, beside the real micromotions, the elastic deformation between sensor holder and reflector. The amount of the elastic deformation was determined using the finite-element technique. For statistical analyses Twoway-ANOVAs were performed (α = 0.05). Results. The H-Max M prostheses exhibited significantly lower micromotions compared to Metha prostheses (1.8 ± 2.2 µm vs. 4.1 ± 3.2 µm, p = 0.03). For Ti-Ti couplings, Metha prostheses showed a trend towards higher micromotions compared to H-Max M (6.5 ± 1.6 µm vs. 3.6 ± 1.5 µm, p = 0.08). Independent of the design, prostheses with Ti neck adapters caused significantly higher micromotions than those with CoCr adapters (5.1 ± 2.1 µm vs. 0.8 ± 1.6 µm, p < 0.01). No differences between the clinically used Metha prostheses with CoCr neck adapters and H-Max M prostheses with Ti necks were found (2.6 ± 2.0 µm, p = 0.25). Discussion. Both, the material coupling and the design influence the interface micromotions. The magnitude of micromotions might explain why bimodular hip systems are susceptible to fretting-induced fractures; however, the threshold for critical micromotions is still not known. The results of this study indicate that the amount of micromotion at taper interfaces could be directly linked to the risk of clinical failure

Abstract. Objectives. Obesity is prevalent with nearly one third of the world's population being classified as obese. Total knee arthroplasty (TKA) is an effective treatment option for high BMI patients achieving similar outcomes to non-obese patients. However, increased rates of aseptic loosening in patients with a high BMI have been reported. In patients with high BMI/body mass there is an increase in strain placed on the implant fixation interfaces. As such component fixation is a potential concern when performing TKA in the obese patient. To address this concern the use of extended tibial stems in cemented implants or cementless fixation have been advocated. Extend tibial stems are thought to improve implant stability reducing the micromotion between interfaces and consequently the risk of aseptic loosening. Cementless implants, once biologic fixation is achieved, effectively integrate into bone eliminating an interface. This retrospective study compared the use of extended tibial stems and cementless implants to conventional cemented implants in high BMI patients. Methods. From a prospectively maintained database of 3239 primary Attune TKA (Depuy, Warsaw, Indiana), obese patients (body mass index (BMI) >30 kg/m²) were retrospectively reviewed. Two groups of patients 1) using a tibial stem extension [n=162] and 2) cementless fixation [n=163] were compared to 3) a control group (n=1426) with a standard tibial stem cemented implant. All operations were performed by or under the direct supervision of specialist arthroplasty surgeons. Analysis compared the groups with respect to class I, II, and III (BMI >30kg/m², >35 kg/m², >40 kg/m²) obesity. The primary outcome measures were all-cause revision, revision for aseptic loosening, and revision for tibial loosening. Kaplan-Meier survival analysis and Cox regression models were used to compare the primary outcomes between groups. Where radiographic images at greater than 3 months post-operatively were available, radiographs were examined to compare the presence of peri-implant radiolucent lines. Results. The mean follow-up of 4.8, 3.4, and 2.5 years for cemented, stemmed, and cementless groups respectively. In total there were 34 all-cause revisions across all the groups with revision rates of 4.55, 5.50, and 0.00 per 1000-implant-years for cemented, stemmed, and cementless groups respectively. Survival Analysis did not show any significant differences between the three groups for all-all cause revision. There were 6 revisions for aseptic loosening (5 tibial and 1 femoral); all of which were in the standard cemented implant group. In contrast there were no revisions in the stemmed or cementless implant groups, however, this was not significant on survival analysis. Analysis looking at class I, II, and III obesity also did not show any significant differences in survival for all cause revision or aseptic loosening. Conclusion. This retrospective analysis showed that there were no revisions required for aseptic loosening when either a cemented stemmed or cementless implant were used in obese patients. These findings are in line with other studies showing that cementless fixation or extended stem implants are a reasonable option in obese patients who represent an increasing cohort of patients requiring TKR. Declaration of Interest. (b) declare that there is no conflict of interest that could be perceived as prejudicing the impartiality of the research reported:I declare that there is no conflict of interest that could be perceived as prejudicing the impartiality of the research project

Summary Statement. The current biomecahnical study demonstrated that the stemless peripheral leg humeral component prototype and central screw humeral component prototype achieved similar initial fixation as stemmed Global Advantage humeral component in terms of resultant micromotion in total shoulder arthroplasty. Introduction. A stemless humeral component may offer a variety of advantages over its stemmed counterpart, e.g. easier implantation, preservation of humeral bone stock, fewer humeral complications, etc. However, the initial fixation of a stemless humeral component typically depends on cementless metaphyseal press-fit, which could pose some challenges to the initial stability. Long-term success of cementless implants is highly related to osseous integration, which is affected by initial implant-bone interface motion. 1. The purpose of the study was to biomechanically compare micromotion at the implant-bone interface of three humeral components in total shoulder arthroplasty. Patients & Methods. Three humeral components were evaluated: Global Advantage, a central screw prototype, and a peripheral leg prototype. All components were the smallest sizes available. Global Advantage is a stemmed design. Both central screw prototype and peripheral leg prototype are stemless designs. Five specimens were tested for each design. Composite analogue humeral models were utilized to simulate the humeral bone. The cortical wall had a thickness of 3 mm and a density of 481 kg/m. 3. , while the cancellous density was 80 kg/m. 3. The model was custom fabricated to accommodate 40 mm humeral component and had a 45° resected surface and a square base to facilitate test setup. Each humeral component was implanted per its surgical technique. The construct was clamped in a vise with the humeral shaft angled at 27°. A MTS test system was employed to conduct the test. A sinusoidal compressive load from 157 N to 1566 N (2BW) was applied to the humeral component at 1 Hz for 100 cycles. The implant-bone interface micromotion was measured with a digital image correlation system which had a resolution of less than 1 micron. The micromotion measurement was transformed to 2 components: 1 was parallel and the other perpendicular to the humeral resection surface. Peak-valley micromotion from the last 10 cycles were averaged and utilised for data analyses. A one-way ANOVA and post-hoc Tukey tests were performed to compare the micromotion of different designs (α=0.05). Results. Micromotion of Global Advantage parallel to the resection (X-Axis) was significantly less than that of central screw prototype and peripheral leg prototype. Micromotion of peripheral leg prototype perpendicular to the resection (Y-Axis) was significantly less than Global Advantage and central screw prototype. There was no significant difference between different designs in resultant micromotion. Discussion/Conclusion. Clinical studies have shown that current stemless shoulder prosthesis yielded encouraging results in mid-term follow-ups. Particularly, the stemless Arthrex Eclipse humeral component, a central screw design, has been reported to have a secure bony fixation and ingrowth at an average of 23 months postoperatively. 4. The current study demonstrated that the stemless peripheral leg prototype and central screw prototype achieved similar initial fixation as stemmed Global Advantage in terms of resultant micromotion, and provided biomechanical evidence that stemless humeral components could have comparable initial stability to stemmed counterparts

This study explored the relationship between the initial stability of the femoral component and penetration of cement into the graft bed following impaction allografting. Impaction allografting was carried out in human cadaveric femurs. In one group the cement was pressurised conventionally but in the other it was not pressurised. Migration and micromotion of the implant were measured under simulated walking loads. The specimens were then cross-sectioned and penetration of the cement measured. Around the distal half of the implant we found approximately 70% and 40% of contact of the cement with the endosteum in the pressure and no-pressure groups, respectively. The distal migration/micromotion, and valgus/varus migration were significantly higher in the no-pressure group than in that subjected to pressure. These motion components correlated negatively with the mean area of cement and its contact with the endosteum. The presence of cement at the endosteum appears to play an important role in the initial stability of the implant following impaction allografting

Summary Statement. In young, active patients cementless THR demonstrates excellent prosthetic stability by RSA and outstanding clinical outcomes at 5 years using a tapered titanium femoral stem, crosslinked polyethylene liners and either titanium or tantalum shells. Introduction. Early femoral implant stability is essential to long-term success in total hip replacement. Radiostereometric analysis (RSA) provides precise measurements of micromotion of the stem relative to the femur that are otherwise not detectable by routine radiographs. This study characterised micromotion of a tapered, cementless femoral stem and tantalum porous-coated vs. titanium acetabular shells in combination with highly cross-linked UHMWPE or conventional polyethylene liners using radiostereometric analysis (RSA) for 5 years following THR. Patients and Methods. This IRB-approved, prospective, double randomised, blinded study, involved 46 patients receiving a primary THR by a single surgeon. Each patient was randomised to receive a titanium (23) (Trilogy, Zimmer) or tantalum (23) (Modular Tantalum shell, Zimmer) uncemented hemispheric shell and either a highly-crosslinked or conventional polyethylene liner. Tantalum RSA markers were implanted in each patient. All patients had a Dorr A or B femoral canal and received a cementless, porous-coated titanium tapered stem (M/L Taper, Zimmer). All final femoral broaches were stable to rotational and longitudinal stress. RSA examinations, Harris Hip, UCLA, WOMAC, SF-12 scores were obtained at 10 days, 6 months, and annually through 5 years. Results. All patients demonstrated statistically significant improvement in Harris Hip, WOMAC, and SF-12 PCS scores post-operatively. Evaluation of polyethylene wear demonstrated that median penetration measurements were significantly greater in the conventional compared to the HXPLE liner cohorts at 1 year through 5 years follow-up (p<0.003). At 5 years, conventional liners showed 0.38 ± 0.05mm vertical wear whereas HXLPE liners showed 0.08 ± 0.02mm (p<0.003). Evaluation of the femoral stems demonstrated that the rate of subsidence was highest in the first 6 months (0.09mm/yr), with no other detectable motion through 5 years. Two outlying patients had significantly higher stem subsidence values at 6 months (0.7 mm and 1.0mm). One stem stabilised without further subsidence after 6 months (0.7mm), and the other stem stabilised at 1 year (1.5mm). Neither patient has clinical evidence of loosening. Evaluation of acetabular shells demonstrated less median vertical translation in tantalum than titanium shells at each time-point except at 3-years follow-up, however due to large standard errors, there was no significant difference between the two designs (p>0.05). These large standard errors were predominantly caused by two outliers, neither of which had clinical evidence of loosening. Discussion/Conclusion. In this RSA study of young THR patients, cementless tapered femoral stems, highly crosslinked polyethylene liners, and tantalum or titanium acetabular shells all demonstrated excellent performance through 5 years follow-up. Highly crosslinked polyethylene liners demonstrated significantly less wear than conventional liners. The femoral stem showed excellent stability through 5 years, with no clinical or radiologic episodes of failure. The small amount of micromotion seen is less than that previously reported for similar tapered, cementless stems and approaches the accuracy of RSA (0.05mm). Both acetabular shells demonstrated excellent stability with minimal micromotion at 5 years without significant differences in migration. All patients demonstrated significant clinical improvement in pain and function and additional RSA evaluation of these patients is planned

INTRODUCTION. Adequate osseointegration of knee resurfacing implants for the treatment of focal cartilage defects is an important prerequisite for good clinical outcomes. Inadequate initial fixation and sustained micromotion may lead to osteolysis and ultimately implant failure. PET/CT with the bone seeking tracer 18F-sodium fluoride (18F-NaF) allows for localisation and quantification of abnormalities in bone metabolism. 18F-NaF PET/CT has been shown to correlate with loosening of implants in the hip and spine. Here, we asses osseointegration of the knee resurfacing implants using micro-computed tomography (µCT) and correlate µCT parameters to 18F-NaF uptake on PET/CT scans taken 3 and 12 weeks after surgery. We hypothesize that 18F-NaF uptake at 12 weeks and its relative decrease between 3 and 12 weeks correlates with osseointegration at 12 weeks postoperatively. Polymer implants with Young”s moduli approximately equal to- and below the Young's modulus of bone, with- and without surface modification were used in this study next to a control metal implant. METHODS. Five different osteochondral implants were implanted bilaterally in critically-sized osteochondral defects in 16 goats. At 3 and 12 weeks postoperatively, a 10-minute static PET/CT-scan (Philips, Gemini TF PET/CT) was made 60 minutes after intravenous injection of 18F-NaF. Image processing resulted in an overall bone metabolism parameter, i.e. standardized uptake value (SUV). A cylindrical region of interest was drawn around each implant to obtain the maximum SUV (SUVmax). Bone quality parameters were quantified in a cylinder surrounding the implant using µCT after sacrifice as a measure for osseointegration. The in vivo 18F-NaF PET/CT uptake parameters were correlated to the bone quality parameters. RESULTS. Implant osseointegration strongly varied for the different implants. Some implant groups exhibited very poor osseointegration with clear signs of osteolysis, while titanium implants exhibited good osseointegration. A strong correlation was observed between bone quality parameters as determined using µCT and SUVmax at 12 weeks. The SUVmax of the implants with poor osseointegration remained high, while implants with good osseointegration showed a relative decrease in SUVmax between 3 and 12 weeks. CONCLUSION. This study suggests that the SUVmax of PET/CT 12 weeks after surgery correlates well for the quality of osseointegration assessed on µCT 12 weeks after surgery. De relative decrease of SUVmax between the given time points had a strong correlation with the degree of osseointegration. In this study, large differences in the quality of osseointegration were observed. The role of surface modification, elasticity and micromotion still remain to be determined as well as if 18F-NaF is sensitive enough to discriminate between smaller differences and what the optimum time point would be to predict the ultimate osseointegration

Study Aim. Femoral components used in total knee arthroplasty (TKA) are primarily designed on the basis of kinematics and ease of fixation. This study considers the stress-strain environment in the distal femur due to different implant internal geometry variations (based on current industry standards) using finite element (FE) analyses. Both two and three dimensional models are considered for a range of physiological loading scenarios – from full extension to deep flexion. Issues associated with micro-motion at the bone-implant interface are also considered. Materials and methods. Two (plane strain) and three dimensional finite element analyses were conducted to examine implant micro-motions and stability. The simple 2D models were used to examine the influence of anterior-posterior (AP) flange angle on implant stability. AP slopes of 3°, 7° and 11° were considered with contact between bone and implant interfaces being modeled using the standard coulomb friction model. The direction and region of loading was based on loading experienced at full extension, 90° flexion and 135° flexion. Three main model variations were created for the 3D analyses, the first model represented an intact distal femur, the second a primary implanted distal femur and the third a distal femur implanted with a posterior stabilising implant. Further each of the above 3D model sets were divided into two group, the first used a frictional interface between the bone and implant to characterise the behavior of uncemented implants post TKA and the second group assumed 100% osseointegration had already taken place and focused on examining the subsequent stress/strain environment in the femur with respect to different femoral component geometries relative the intact distal femur model. Results and Discussion. Analyses indicate a trend relating the slope of the anterior-posterior (AP) flange to implant loosening at high flexion angles for uncemented components. Once cemented, this becomes less important. Results from the 3D analyses show that the posterior stabilising implant causes stress concentrations which can lead to bicondylar fatigue fracture. All femoral components cause stress shielding in cancellous bone particularly when they are fully bonded. Investigations into implant micromotion show that revision implants with box sections provided more resistance to micromotion than the pegged primary implants. However for the gait cycle tested the maximum recorded micromotion of both implants was well within acceptable levels for osseointegration to occur

Summary Statement. Proximal femoral bony deficits present a surgical and biomechanical challenge to implant longevity in revision hip arthroplasty. This work finds comparable primary stability when a distally fixing tapered fluted stem was compared with a conical design in cadaveric tests. Introduction. Proximal bony deficits complicate revision hip surgery and compromise implant survival. Longer distally fixing stems which bypass such defects are therefore required to achieve stability compatible with bony ingrowth and implant longevity. Aims. It is hypothesised that a tapered stem will provide superior rotational stability to a conical design. This work therefore aims to compare the primary stability and biomechanical properties of a new design of tapered fluted modular femoral stem (Redapt®, Smith & Nephew) with that of a conical fluted stem (Restoration®, Stryker). Materials & Methods. 7 Pairs of cadaveric femora were obtained according to strict inclusion/exclusion criteria. Each underwent dual energy x-ray absorptiometry and calibration plain-film radiographs were taken. Digital templating was performed using TraumaCad (Voyant Health, Brainlab) to determine implant sizing. Both stems are fluted, modular and manufactured from titanium. The control stem (Restoration) featured a straight conical design and the investigation stem (Redapt) a straight tapered design. Implantation was performed by a revision arthroplasty surgeon familiar with both systems. Proximal bone deficiency was reproduced using an extended trochanteric osteotomy with removal of metaphyseal bone before reattaching the osteotomy. Primary stability in the axial, sagittal and coronal planes was assessed using micromotion transducers (HBM, Darmstadt, Germany) and also by Radiostereometric Analysis (RSA). RSA employs simultaneous biplanar radiographs to measure relative movement. Two 1mm tantalum beads were mounted on the prosthesis with the centre of the femoral head taken as the third reference point. Beads were placed proximally in the surrounding bone as rigid body markers. Each bone was potted according to the ISO standard for fatigue testing and cyclically loaded at 1Hz for at least 3 increments (750–350N, 1000–350N, 1500–350N) for 1000 cycles. RSA radiographs were taken at baseline and on completion of each cycle. A strain analysis was concurrently performed using a PhotoStress® (Vishay Precision Group, Raleigh, USA) photoelastic coating on the medial femoral cortex. Each bone was loaded intact and then with the prosthesis in-situ at 500N increments until strain fringes were identified. Once testing was completed, the stems were sectioned at the femoral isthmus and data is presented on the cross-sectional fit and fill observed. Results. Both stem designs showed comparable primary stability with all stems achieving clinically acceptable micromotion (<150 μm) when loaded at body weight. A larger proportion of the control stems remained stable as loading increased to x2-3 body weight. Transducer-recorded migration appeared greatest in the axial plane (y axis) with negligible distal movement in the coronal or sagittal planes. Point motion analysis (RSA) indicated most movement to be in the coronal plane (x-axis) whereas segment motion analysis showed rotation about the long axis of the prosthesis to be largest. Photoelastic strain patterns were transferred more distally in both designs, however substantial stress shielding was also observed. Discussion/Conclusion. Both designs achieved adequate distal fixation and primary stability under representative clinical loading conditions. This work supports the continued use of this novel stem design for revision surgery in the presence of extensive proximal bone loss

The stem and the rasp for cemented arthroplasty are typically designed to obtain a cement mantle 2–5 mm thick. However, sometimes a line-to-line cementation is preferred, where the femoral cavity is prepared with the same dimension as the actual stem. There are contrasting reports [1,2] about the suitability of this technique to withstand the long-term fatigue loads. While the theoretical geometry allows no space for the cement, a sort of cement mantle is formed as the cement penetrates in the spongy bone. The scopes of this study were: 1) developing a dedicated in vitro method to test line-to-line cementation; 2) assessing if a short, polished hip stem designed for a standard cementation can be safely cemented line-to-line. In order to perform long-term mechanical in vitro tests, composite bones must be used, as cadaveric bones cannot withstand millions of loading cycles [3]. For this study, the Sawbones Mod. 3406-4 were chosen: they feature an open-cell polyurethane core simulating low-density spongy bone. Post-implantation x-rays confirmed that a relevant cement-bone interdigitation was obtained. Four femurs were prepared with a CoreHip (Aesculap) with regular cement mantle (Regular). Another 4 femurs were rasped to the same rasp size, and implanted with line-to-line cementation with a larger stem (Line-to-line). The implanted femurs were subjected to an accelerated test derived from a validated protocol [3] which replicates the most demanding motor tasks of 24 years of patient activity. Implant elastic micromotions and permanent migrations were measured throughout the test. The implants were then sectioned and treated with dye penetrants to highlight the cement cracks. Elastic and permanent motions did not show any loosening trend, and never exceeded few micrometers. As expected, some damage was visible in the cement mantles after test completion, for both types of implantation (similar to retrieved cement mantles surrounding stable implants [3]. The cement damage was similar in all specimens. No sign of major disruption was visible, neither within the Regular nor in the Line-to-line specimens: in fact, the cracks were limited in length, did not seem to cross the entire mantle thickness, and did not result in any loose cement fragments. The cracks in the line-to-line implants showed the same position and distribution compared to those found in the regular implants, but were slightly longer in some specimens. This in vitro study confirmed the feasibility of simulating line-to-line cementation in vitro. Our results suggest that a stem designed for a regular cement mantle could induce slightly more damage when implanted line-to-line, but no significant trend toward loosening

The metal on metal implants was introduced without the proper stepwise introduction. The ASR resurfacing hip arthroplasty (RHA) withdrawn due to high clinical failure rates and the large diameter head THA (LDH-THA) are also widely abandoned. Early (2 year) radiostereometry studies does not support early instability as cause of failure but more likely metal wear products. A possible advantage may be maintenance of bone mineral density (BMD). We present 5 year prospective follow up from a randomized series, aiming to report changes from baseline and to investigate links between implant micromotion, Cr & Co ions and BMD. Patients eligible for an artificial hip were randomized to RHA, Biomet LDH-THA or standard Biometric THA. 19, 17 and 15 patients completed 5 year follow-up. All followed with BMD of the femur, acetabulum and for RHA the collum. RHA and THA with whole blood Co and Co. LDH-THA only at 5 year. RHA had marker based RSA of both components, cup only for LDH-THA. Translations were compiled to total translation (TT= √(x. 2. +y. 2. +z. 2. )). Data were collected at baseline, 8 weeks, 6 months, 1, 2 and 5 years. Statistical tests: ANCOVA for TT movement, Spearman's correlation for BMD, Cr, Co and BMI to TT at 5 years. RSA: The 5 year median (25%to75%) RHA cup translations were X=-0.00(−0.49 to 0.19) Y=0.15(−0.03 to 0.20), z=0.24(−0.42 to 0.37) and TT 0.58 (0.16 to 1.82) mm. For the LDH-THA X=−0.33(−0.90 to 0.20) Y=0.28(0.02 to 0.54), z=0.43(−1.12 to −0.19) and TT 1.06 (0.97 to 1.72) mm. The TT was statistically different (p<0.05) for the two cups. The RHA femoral component moved X=0.37(0.21 to 0.56) Y=0.02(−0.07 to 0.11), z=-0.01(−0.07 to 0.26) and TT 0.48 (0.29 to 0.60) mm at 5 years. There was no TT movement from year 2. The mean (SD) acetabular BMD was diminished to 93(90–97)% for RHA and 97(93–99.9)% for THA, but LDH-THA maintained 99(95–103)%. Overall femoral BMD was unchanged at 5 years for all interventions, but both stemmed implants lost 17% at the calcar. Median (25%to75%) whole-blood Cr peaked in the LDH-THA group with 1.7 (0.9 to 3.1) followed by RHA 1.2 (0.8 to 5.0) and THA with 0.5 (0.4 to 0.7)ppb. For Co the highest levels were found in RHA with 1.6(0.8 to 4.7) followed by LDH-THA 1.2 (0.7–1.7) and THA 0.2 (0.2 to 0.6) ppb. The only correlations above +/−0.3 for TT were the RHA femoral component with a correlation of 0.47 to BMI, 0.30 to Co and Cr. The ASR cup conversely had a negative correlation of −0.60 to BMI and again, the LDH-THA cup had a negative correlation of −0.37 to Cr. In contrast to registered revision rates, we found significantly larger movement for the Biomet cup than the ASR cup. The metal ion levels were similar. The LDH-THA cup maintained the acetabular BMD best at 5 years, but the difference was small, we are limited by small numbers and the correlations between TT and the covariates showed no clear pattern

Metal on metal press-fit acetabular cups are the worst performing acetabular cup type with severe failure consequences compared to cups made from more inert materials such as polyethylene or ceramic. The cause of failure of these cup types is widely acknowledged to be multi-factorial, therefore creating a complex scenario for analysis through clinical studies. A factorial analysis has been carried out using an experimentally validated finite element analysis to investigate the relative influence of four input factors associated with acetabular cup implantation on output parameters indicating potential failure of the implantation. These input factors were: cup material stiffness; cup inclination; cup version; cup seating; and level of press-fit. The output parameter failure indicators were: wear; tensile strains in the underlying bone; bone remodelling; and cup-bone micromotions. The factorial analysis concluded that the most significant influence was that of cup inclination on wear, and the second most significant was the influence of the level of press-fit on bone remodelling at the acetabular rim. Significant influence was also observed between version angle and wear, and cup-seating and micro-motion. The results demonstrated the clear multi-factorial nature of implant failure and highlighted the importance of correct implant positioning and fit

Summary Statement. Atypical femoral fractures consist of a thin fracture line extending through the lateral cortex. The adjacent bone is undergoing resorption and mechanical abrasion and is often replaced with woven bone. The mechanical environment seems to inhibit healing. Background. The pathophysiology behind bisphosphonate-associated atypical femoral fractures remains unclear. Histological findings at the fracture site itself might provide important clues. So far only one case describing the histological appearance of the fracture has been published. Methods. Between 2008 and 2013, bone biopsies comprising the fracture site were collected from 8 patients with 4 displaced and 4 undisplaced atypical femoral fractures. Seven female patients reported continuous bisphosphonate use for an average of 9.5 years. One patient was a man, not using bisphosphonates. The bone biopsies were evaluated histologically, with Fourier transformed infrared imaging (FTIR) and micro-computed tomography. Results. The 4 undisplaced fractures engaged the whole cortical thickness and comprised a 150 to 200 µm wide, meandering fracture gap filled with amorphous necrotic material. Von Kossa staining showed occasional mineralised elements with bony structure within the amorphic material. Active resorption and remodeling was common in the close vicinity of the fracture, but seldom reached into the fracture gap. In some areas, the bone adjacent to the gap appeared to undergo fragmentation and disintegration, possibly due to abrasion. Woven bone was common adjacent to the fracture gap, and appeared to have been formed in defects caused by abrasion or where resorption cavities had reached into the fracture gap. Periosteal and endosteal callus was found in all cases. Far away from the fracture, large areas of osteonal bone with only empty osteocyte lacunae were found in some samples. In one patient, the remodeling process bridged the fracture gap at some points. The fracture was otherwise similar to the other undisplaced fractures. This patient had suffered from thigh pain since her bisphosphonate treatment was discontinued 18 months earlier, when the atypical fracture was diagnosed. Discussion. Atypical femoral fractures show signs of increased remodeling in the vicinity of the fracture gap. The narrow width of the gap and its necrotic contents suggest that micromotion leads to strains between the fracture fragments that precludes survival of ingrowing cells. Moreover, there seemed to be continuous mechanical fragmentation of the bone at the crack, and replacement of fragmented areas with woven bone. Thus, it appears that the fracture line is not static, but moves in the bone over time, like the changes in the course of a meandering river

Bone growth into cementless prosthetic components is compromised by osteoporosis, by any gap between the implant and the bone, by micromotion, and after the revision of failed prostheses. Recombinant human transforming growth factor-β1 (rhTGF-β1) has recently been shown to be a potent stimulator of bone healing and bone formation in various models in vivo. We have investigated the potential of rhTGF-β1, adsorbed on to weight-loaded tricalcium phosphate (TCP) coated implants, to enhance bone ongrowth and mechanical fixation. We inserted cylindrical grit-blasted titanium alloy implants bilaterally into the weight-bearing part of the medial femoral condyles of ten skeletally mature dogs. The implants were mounted on special devices which ensured stable weight-loading during each gait cycle. All implants were initially surrounded by a 0.75 mm gap and were coated with TCP ceramic. Each animal received two implants, one with 0.3 μg rhTGF-β1 adsorbed on the ceramic surface and the other without growth factor. Histological analysis showed that bone ongrowth was significantly increased from 22 ± 5.6% bone-implant contact in the control group to 36 ± 2.9% in the rhTGF-β stimulated group, an increase of 59%. The volume of bone in the gap was increased by 16% in rhTGF-β1-stimulated TCP-coated implants, but this difference was not significant. Mechanical push-out tests showed no difference in fixation of the implant between the two groups. Our study suggests that rhTGF-β1 adsorbed on TCP-ceramic-coated implants can enhance bone ongrowth

Proponents of the biological theory of aseptic loosening have in recent years tended to concentrate on the production and distribution of particulate ultra-high-molecular-weight polyethylene (UHMWPE) debris around the potential joint space. However, mechanical loading of cemented implants with the differing elastic moduli of metal stems, polymethylmethacrylate (PMMA) cement and bone can result in relative micromotion, implying the potential for production of metal and PMMA particles from the stem-cement interface by fretting wear. In order to investigate the production and biological reactivity of debris from this interface, PMMA and metal particulate debris was produced by sliding wear of PMMA pins containing barium sulphate and zirconium dioxide against a Vaquasheened stainless steel counterface. This debris was characterised by SEM, energy-dispersive analysis by X-ray (EDAX) and image analysis, then added to cell cultures of a human monocytic cell line, U937, and stimulation of pro-osteolytic cytokines measured by ELISA. Large quantities of PMMA cement debris were generated by the sliding wear of PMMA pins against Vaquasheened stainless steel plates in the method developed for this study. Both cements stimulated the release of pro-osteolytic TNFα from the U937 monocytic cell line, in a dose-dependent fashion. There was a trend towards greater TNFα release with Palacos cement than CMW cement at the same dose. Palacos particles also caused significant release of IL-6, another pro-osteolytic cytokine, while CMW did not. The particulate cement debris produced did not stimulate the release of GM-CSF or IL1β from the U937 cells. These results may explain the cytokine pathway responsible for bone resorption caused by particulate PMMA debris. Radio-opaque additives are of value in surgical practice and clinical studies to quantify the relevance of these in vitro findings are required before the use of cement containing radio-opacifier is constrained