Objective

In ex vivo hip fracture studies femoral pairs are split to create two comparable test groups. When more than two groups are required, or if paired femurs cannot be obtained, group allocation according to bone mineral density (BMD) is sometimes performed. In this statistical experiment we explore how this affects experimental results and sample size considerations.

The clinical success of osteochondral autografts is heavily reliant on their mechanical stability, as grafts which protrude above or subside below the native cartilage can have a negative effect on the tribological properties of the joint [1]. Furthermore, high insertion forces have previously been shown to reduce chondrocyte viability [2]. Commercial grafting kits may include a dilation tool to increase the diameter of the recipient site prior to insertion. The aim of this study was to evaluate the influence of dilation on the primary stability of autografts. Six human cadaveric femurs were studied. For each femur, four 8.5 × 8mm autografts were harvested from the trochlear groove and implanted into the femoral condyles using a Smith & Nephew Osteochondral grafting kit. Two grafts were implanted into dilated recipient sites (n=12) and two were implanted with no dilation (n=12). Insertion force was measured by partially inserting the graft and applying a load at a rate of 1 mm/min, until the graft was flush with the surrounding cartilage. Push-in force was measured by applying the same load, until the graft had subsided 4mm below congruency. Significance was taken as (p<0.05). Average maximum insertion force of dilated grafts was significantly lower (p<0.001) than their non-dilated equivalent [28.2N & 176.7N respectively]. There was no significant difference between average maximum push-in force between the dilated and non-dilated groups [1062.8N & 1204.2N respectively]. This study demonstrated that significantly less force is required to insert dilated autografts, potentially minimising loss of chondrocyte viability. However, once inserted, the force required to displace the grafts below congruency remained similar, indicating a similar degree of graft stability between both groups

The aim of this scoping review is to understand the extent and type of evidence in relation to the use of guided growth for correcting rotational deformities of long bones. Guided growth is routinely used to correct angular deformities in long bones in children. It has also been proven to be a viable method to correct rotational deformities, but the concept is not yet fully examined. Databases searched include Medline, Embase, Cochrane Library, Web of Science and Google Scholar. All identified citations were uploaded into Rayyan.ai and screened by at least two reviewers. The search resulted in 3569 hits. 14 studies were included: 1 review, 3 clinical trials and 10 pre-clinical trials. Clinical trials: a total of 21 children (32 femurs and 5 tibiae) were included. Surgical methods were 2 canulated screws connected by cable, PediPlates obliquely oriented, and separated Hinge Plates connected by FiberTape. Rotation was achieved in all but 1 child. Adverse effects reported include limb length discrepancy (LLD), knee stiffness and rebound of rotation after removal of tethers. 2 pre-clinical studies were ex-vivo studies, 1 using 8-plates on Sawbones and 1 using a novel z-shaped plates on human cadaver femurs. There were 5 lapine studies (2 using femoral plates, 2 using tibial plates and 1 using an external device on tibia), 1 ovine (external device on tibia), 1 bovine (screws and cable on metacarp) and a case-report on a dog that had an external device spanning from femur to tibia. Rotation was achieved in all studies. Adverse effects reported include implant extrusions, LLD, articular deformities, joint stiffness and rebound. All included studies conclude that guided growth is a viable treatment for rotational deformities of long bones, but there is great variation in models and surgical methods used, and in reported adverse effects

Autologous osteochondral grafting has demonstrated positive outcomes for treating articular cartilage defects by replacing the damaged region with a cylindrical graft consisting of bone with a layer of cartilage, taken from a non-loadbearing region of the knee. Despite positive clinical use, factors that cause graft subsidence or poor integration are relatively unknown. The aim of this study was to develop finite element (FE) models of osteochondral grafts within a tibiofemoral joint and to investigate parameters affecting osteochondral graft stability. Initial experimental tests on cadaveric femurs were performed to calibrate the bone properties and graft-bone frictional forces for use in corresponding FE models, generated from µCT scan data. The effects of cartilage defects and osteochondral graft repair were measured by examining contact pressure changes using in vitro tests on a single cadaveric human tibiofemoral joint. Six defects were created in the femoral condyles which were subsequently treated with osteochondral autografts or metal pins. Matching µCT scan-based FE models were created, and the contact patches were compared. Sensitivity to graft bone properties was investigated. The bone material properties and graft-bone frictional forces were successfully calibrated from the initial tests with good resulting levels of agreement (CCC=0.87). The tibiofemoral joint experiment provided a range of cases to model. These cases were well captured experimentally and represented accurately in the FE models. Graft properties relative to host bone had large effects on immediate graft stability despite limited changes to resultant cartilage contact pressure. Model confidence was built through extensive validation and sensitivity testing, and demonstrated that specimen-specific properties were required to accurately represent graft behaviour. The results indicate that graft bone properties affect the immediate stability, which is important for the selection of allografts and design of future synthetic grafts. Acknowledgements. Supported by the EPSRC-EP/P001076

Range of Motion (ROM) assessments are routinely used during joint replacement to evaluate joint stability before, during and after surgery to ensure the effective restoration of patient biomechanics. This study aimed to quantify axial torque in the femur during ROM assessment in total hip arthroplasty to define performance criteria against which hip instruments can be verified. Longer term, this information may provide the ability to quantitatively assess joint stability, extending to quantitation of bone preparation and quality. Joint loads measured with strain-gaged instruments in five cadaveric femurs prepared using posterior approach were analysed. Variables such as surgeon-evaluator, trial offset and specimen leg and weight were used to define 13 individual setups and paired with surgeon appraisal of joint tension for each setup. Peak torque loads were then identified for specific motions within the ROM assessment. The largest torque measured in most setups was observed during maximum extension and external rotation of the joint, with a peak torque of 13Nm recorded in a specimen weighing 98kg. The largest torque range (19.4Nm) was also recorded in this specimen. Other motions within the trial reduction showed clear peaks in applied torque but with lower magnitude. Relationships between peak torque, torque range and specimen weight produced an R2 value greater than 0.65. The data indicated that key influencers of torsional loads during ROM were patient weight, joint tension and limb motion. This correlation with patient weight should be further investigated and highlights the need for population representation during cadaveric evaluation. Although this study considered a small sample size, consistent patterns were seen across several users and specimens. Follow-up studies should aim to increase the number of surgeon-evaluators and further vary specimen size and weight. Consideration should also be given to alternative surgical approaches such as the Direct Anterior Approach

The influence of the surgical process on implant loosening and periprosthetic fractures (PPF) as major complications in uncemented total hip arthroplasty (THA) have rarely been studied due to the difficult quantification. Meanwhile registry analyses have clearly shown a decrease in complications with increasing experience. The goal of this study was to determine the extent of variability in THA stem implantation between highly experienced surgeons with respect to implant-size, -position, press-fit, contact area, primary stability and the effect of using a powered impaction tool. Primary hip stems were implanted in 16 cadaveric femur pairs by three experienced surgeons using manual and powered impaction. Quantitative CTs were taken before and after each process step and stem tilt, canal-fill-ratio, pressfit and contact area between bone and implant determined. 11 femur pairs were additionally tested for primary stability under cyclic loading conditions. Higher variations in press-fit and contact area between the surgeons for manual impactions compared to powered were observed. Stem tilt and implant sizing varied between surgeons but not between impaction methods. Larger stems exhibited less micromotion compared to smaller stems. Larger implants may increase PPF risk, while smaller implants reduce primary stability. The reduced variation for powered impactions indicates that appropriate measures may promote a more standardized process. The observed variations between the experienced surgeons may represent the acceptable range for this specific stem design. Variability in the implantation process warrants further investigations since certain deviations e.g. a stem tilt towards varus, might increase bone stresses and PPF risk

Introduction. Polyetheretherketone (PEEK) has been proposed as an implant material for femoral total knee arthroplasty (TKA) components. Potential clinical advantages of PEEK over standard cobalt chrome alloys include modulus of elasticity and subsequently reduced stress shielding potentially eliminating osteolysis, thermal conduction properties allowing for a more natural soft tissue environment, and reduced weight enabling quicker quadriceps recovery. Manufacturing advantages include reduced manufacturing and sterilization time, lower cost, and improved quality control. Currently, no PEEK TKA implants exist on the market. Therefore, evaluation of mechanical properties in a pre-clinical phase is required to minimize patient risk. The objectives of this study include evaluation of implant fixation and determination of the potential for reduced stress shielding using the PEEK femoral TKA component. Methods and Materials. Experimental and computational analysis was performed to evaluate the biomechanical response of the femoral component (Freedom Knee, Maxx Orthopedics Inc., Plymouth Meeting, PA; Figure 1). Fixation strength of CoCr and PEEK components was evaluated in pull-off tests of cemented femoral components on cellular polyurethane foam blocks (Sawbones, Vashon Island, WA). Subsequent testing investigated the cemented fixation using cadaveric distal femurs. The reconstructions were subjected to 500,000 cycles of the peak load occurring during a standardized gait cycle (ISO 14243-1). The change from CoCr to PEEK on implant fixation was studied through computational analysis of stress distributions in the cement, implant, and the cement-implant interface. Reconstructions were analyzed when subjected to standardized gait and demanding squat loads. To investigate potentially reduced stress shielding when using a PEEK component, paired cadaveric femurs were used to measure local bone strains using digital image correlation (DIC). First, standardized gait load was applied, then the left and right femurs were implanted with CoCr and PEEK components, respectively, and subjected to the same load. To verify the validity of the computational methodology, the intact and reconstructed femurs were replicated in FEA models, based on CT scans. Results. The cyclic load phase of the pull-off experiments revealed minimal migration for both CoCr and PEEK components, although after construct sectioning, debonding at the implant-cement interface was observed for the PEEK implants. During pull-off from Sawbones the ultimate failure load of the PEEK and CoCr components averaged 2552N and 3814N respectively. FEA simulations indicated that under more physiological loading, such as walking or squatting, the PEEK component had no increased risk of loss of fixation when compared to the CoCr component. Finally, the DIC experiments and FEA simulations confirmed closer resemblance of pre-operative strain distribution using the PEEK component. Discussion. The biomechanical consequences of changing implant material from CoCr to PEEK on implant fixation was studied using experimental and computational testing of cemented reconstructions. The results indicate that, although changes occur in implant fixation, the PEEK component had a fixation strength comparable to CoCr. The advantage of long term bone preservation, as the more compliant PEEK implant is able to better replicate the physiological loads occurring in the intact femur, may reduce stress shielding around the distal femur, a common clinical cause of TKA failure. For any figures or tables, please contact the authors directly

It is common belief that consolidated intramedullary nailed trochanteric femur fractures can result in secondary midshaft or supracondylar fractures, involving the distal screws, when short or long nails are used, respectively. In addition, limited data exists in the literature to indicate when short or long nails should be selected for treatment. The aim of this biomechanical cadaveric study was to investigate short versus long Trochanteric Femoral Nail Advanced (TFNA) fixation in terms of construct stability and generation of secondary fracture pattern following trochanteric fracture consolidation. Eight intact human cadaveric femur pairs were assigned to 2 groups of 8 specimens each for nailing using either short or long TFNA with blade as head element. Each specimen was first biomechanically preloaded at 1 Hz over 2000 cycles in superimposed synchronous axial compression to 1800 N and internal rotation to 11.5 Nm. Following, internal rotation to failure was applied over an arc of 90° within 1 second under 700 N axial load. Torsional stiffness, torque at failure, angle at failure and energy at failure were evaluated. Fracture patterns were analyzed. Outcomes in the groups with short and long nails were 9.7±2.4 Nm/° and 10.2±2.9 Nm/° for torsional stiffness, 119.8±37.2 Nm and 128.5±46.7 Nm for torque at failure, 13.5±3.5° and 13.4±2.6° for angle at failure, and 887.5±416.9 Nm° and 928.3±461.0 Nm° for energy at failure, respectively, with no significant differences between them, P≥0.167. Fractures through the distal locking screw occurred in 5 and 6 femora instrumented with short and long nails, respectively. Fractures through the lateral entry site of the head element were detected in 3 specimens within each group. For short nails, fractures through the distal shaft region, not interfacing with the implant, were detected in 3 specimens. From biomechanical perspective, the risk of secondary peri-implant fracture after intramedullary nailed trochanteric fracture consolidation is similar when using short or long TFNA. Moreover, for both nail versions the fracture pattern does not unexceptionally involve the distal locking screw

Introduction: The objective of this study was to evaluate the biomechanical proprieties of a hip resurfacing system in terms of failure of the implant with different positioning of the prosthesis in cadaveric femurs. Materials and Methods: The study has been divided in 3 phases. First phase: Six-teen cadaveric femurs were tested to failure using a standard MTS device once the Conserve Plus (Wright Medical) system was implanted: 8 femurs after a 4mm notching of the neck and 8 contralateral without notching. Second phase: Six-teen cadaveric femurs were tested using a 210 Kg axial load: 8 with the Conserve Plus system implanted at 140° and 8 contralateral with 10° of varus. Third phase: Eight femurs were tested with the implant having 10 ° of excessive antiversion of the component and 8 with the implant having 10 ° of excessive retroversion. The control group was represented by 16 femurs having the system implanted following the natural version of the femoral neck. Results: An average of 4865 Newtons(N) was necessary for the failure of the implant after notching, compared to 7043 N without notching. The varus alignment of the implant showed a statistical different increase of the stress on the femoral neck: 15% postero-superiorly and 21% antero-superiorly. The neutral alignment at 140° showed a decrease of the overall stress on the femoral neck. Adding 10 ° of excessive anteversion or retroversion did not show any statistical difference in terms of failure of the implant when compared to the anatomical alignment. Conclusions: This biomechanical study showed that the correct positioning of the implant represents a fundamental requirement for the success of the hip resurfacing procedure. The notching of the neck decreases significantly the biomechanical proprieties of the implant, while the varus alignment increases the stress on the superior neck cortex

Objectives. Studies reporting specifically on squeaking in total hip arthroplasty have focused on cementless, and not on hybrid, fixation. We hypothesised that the cement mantle of the femur might have a damping effect on the sound transmitted through the metal stem. The objective of this study was to test the effect of cement on sound propagation along different stem designs and under different fixation conditions. Methods. An in vitro model for sound detection, composed of a mechanical suspension structure and a sound-registering electronic assembly, was designed. A pulse of sound in the audible range was propagated along bare stems and stems implanted in cadaveric bone femurs with and without cement. Two stems of different alloy and geometry were compared. Results. The magnitudes of the maximum amplitudes of the bare stem were in the range of 10.8 V to 11.8 V, whereas the amplitudes for the same stems with a cement mantle in a cadaveric bone decreased to 0.3 V to 0.7 V, implying a pulse-attenuation efficiency of greater than 97%. The same magnitude is close to 40% when the comparison is made against stems implanted in cadaveric bone femurs without cement. Conclusion. The in vitro model presented here has shown that the cement had a remarkable effect on sound attenuation and a strong energy absorption in cement mantle and bone. The visco-elastic properties of cement can contribute to the dissipation of vibro-acoustic energy, thus preventing hip prostheses from squeaking. This could explain, at least in part, the lack of reports of squeaking when hybrid fixation is used. Cite this article: F. J. Burgo, D. E. Mengelle, A. Ozols, C. Fernandez, C. M. Autorino. The damping effect of cement as a potential mitigation factor of squeaking in ceramic-on-ceramic total hip arthroplasty. Bone Joint Res 2016;5:531–537. DOI: 10.1302/2046-3758.511.BJR-2016-0058.R1

End caps are intended to prevent nail migration (push-out) in elastic stable intramedullary nailing. The aim of this study was to investigate the force at failure with and without end caps, and whether different insertion angles of nails and end caps would alter that force at failure. Simulated oblique fractures of the diaphysis were created in 15 artificial paediatric femurs. Titanium Elastic Nails with end caps were inserted at angles of 45°, 55° and 65° in five specimens for each angle to create three study groups. Biomechanical testing was performed with axial compression until failure. An identical fracture was created in four small adult cadaveric femurs harvested from two donors (both female, aged 81 and 85 years, height 149 cm and 156 cm, respectively). All femurs were tested without and subsequently with end caps inserted at 45°. In the artificial femurs, maximum force was not significantly different between the three groups (p = 0.613). Push-out force was significantly higher in the cadaveric specimens with the use of end caps by an up to sixfold load increase (830 N, standard deviation (SD) 280 vs 150 N, SD 120, respectively; p = 0.007). These results indicate that the nail and end cap insertion angle can be varied within 20° without altering construct stability and that the risk of elastic stable intramedullary nailing push–out can be effectively reduced by the use of end caps. Cite this article: Bone Joint J 2015;97-B:558–63

Prophylactic treatment is advised for metastatic bone disease patients with a high risk of fracture. Clinicians face the task of identifying these patients with high fracture risk and determining the optimal surgical treatment method. Subject-specific finite element (FE) models can aid in this decision process by predicting the mechanical effect of surgical treatment. In this study, we specifically evaluated the potential of FE models to simulate femoroplasty, as uncertainty remains whether this prophylactic procedure provides sufficient mechanical strengthening to the weight-bearing femur. In eight pairs of human cadaveric femurs artificial metastatic lesions were created. In each pair, an identical defect was milled in the left and right femur. Four pairs received a spherical lesion in the neck and the other four an ellipsoidal lesion in the intertrochanteric region, each at the medial, superior/lateral, anterior and posterior side, respectively. One femur of each pair was augmented with polymethylmethacrylate (5–10 ml), while the contralateral femur was left untreated. CT scans were made at three different time points: from the unaffected intact femurs, the defect femurs with lesion and the augmented femurs. Bone strength was measured by mechanical testing until failure in eight defect and eight augmented femurs. Nonlinear CT-based FE models were developed and validated against the experimentally measured bone strength. Subsequently, the validated FE model was applied to the available CT scans for the three different cases: intact (16 scans), defect (16) and augmented (8). The FE predicted strength was compared for the three different cases. The FE models predicted the experimental bone strength with a strong correspondence, both for the defect (R. 2. = 0.97, RMSE= 0.75 kN) and the augmented femurs (R. 2. = 0.90, RMSE = 0.98 kN). Although all lesions had a “moderate” to “high” risk for fracture according to the Mirels’ scoring system (score 7 or 8), three defect femurs did not fracture through the lesion (intertrochanteric anterior, lateral and posterior), indicating that these lesions did not act as a critical weak spot. In accordance with the experimental findings, the FE models indicated almost no reduction in strength between the intact and defect state for these femurs (0.02 ± 0.1%). For the remaining “critical” lesions, bone strength was reduced with 15.7% (± 14.9%) on average. The largest reduction was observed for lesions on the medial side (up to 43.1%). For the femurs with critical lesions, augmentation increased bone strength with 29.5% (± 29.7%) as compared to the defect cases, reaching strength values that were 2.5% (± 3.7%) higher than the intact bone strength. Our findings demonstrate that FE models can accurately predict the experimental bone strength before and after augmentation, thereby enabling to quantify the mechanical benefit of femoroplasty. This way FE models could aid in identifying suitable patients for whom femoroplasty provides sufficient increase in strength. For all lesions evaluated in this study, femoroplasty effectively restored the initial bone strength. Yet, additional studies on larger datasets with a wide variation of lesion types are required to confirm these results

Aims. The primary aim of this study was to define and quantify three new measurements to indicate the position of the greater trochanter. Secondary aims were to define ‘functional antetorsion’ as it relates to abductor function in populations both with and without torsional abnormality. Patients and Methods. Three new measurements, functional antetorsion, posterior tilt, and posterior translation of the greater trochanter, were assessed from 61 CT scans of cadaveric femurs, and their reliability determined. These measurements and their relationships were also evaluated in three groups of patients: a control group (n = 22), a ‘high-antetorsion’ group (n = 22) and a ‘low-antetorsion’ group (n = 10). Results. In the cadaver group, the mean anatomical antetorsion was 14.7° (. sd. 8.5; 0 to 36.5) and the functional antetorsion 21.5° (. sd. 8.1; 3.6 to 44.3): the posterior tilt was 73.3° (. sd. 10.8; 46.9 to 88.7) and the posterior translation 0.59 (. sd. 0.2; 0.2 to 0.9). These measurements had excellent intra and interobserver agreement with a range from 0.93 to 0.99. When the anatomical antetorsion decreased, the greater trochanter was more tilted and translated posteriorly in relation to the axis of the femoral neck, and the difference between functional and anatomical antetorsion increased. The results the three patient groups were similar to those of the cadaver group. Conclusion. The position of the greater trochanter and functional antetorsion varied with anatomical antetorsion. In the surgical management of femoral retrotorsion, subtrochanteric osteotomy can result in an excessively posterior position of the greater trochanter and an increase in functional antetorsion. Cite this article: Bone Joint J 2018;100-B:712–19

Introduction. The project of a modular, double-conicity stem is born from the need to obtain primary stability and correct osseointegration in patients with developmental hip dysplasia, or proximal femoral dysmorphisms requiring a femoral shortening osteotomy or presenting characteristics of non-adaptability to single-conicity or straight stems. Such an implant could also be employed in femoral nail failures, or lateral femoral neck fractures requiring prosthetic substitution. Aim of the study. To assess implantability of the new double-conicity stem in cadaver femurs, determining “fit and fill” and the behaviour of femoral cortical bone by means of Rx, CT and pre- and post-implantation mechanical testing. Methods. Seven double-conicity stems with anti-rotation fins were implanted in cadaver femurs of various sizes. All femurs underwent pre- and post-implantation radiological assessment for evaluation of fit and fill at the 2 levels corresponding to the 2 conicities, fins penetration, possible microfractures and stem positioning. Prior to implantation, templating was carried out to define the correct size of the stem to be implanted. Modular necks with cervico-diaphyseal angle of 125° or 135° (short or long) were implanted, to preserve the correct rotation center and femoral offset. In 2 femurs, mechanical testing was performed before and after implantation, in order to assess, by means of strain gauges, the variation of the tensional state of cortical bone under dynamic loading (gait cycle simulation). In 2 femurs, 3 cm chevron shortening osteotomies were performed and stabilized with the stem alone. Results. Implanted stems respected pre-operative planning. In the 2 cases in which shortening osteotomies were performed, the stem allowed for good meta-diaphyseal stability without the employment of fixation devices. Radiographic assessment evidenced a valid “fit and fill”. In 4 cases the stem was correctly aligned; in 2 cases it was positioned in 1° varus and in 1 case in 1° valgus. In the 2 osteotomy cases, penetration of the fins was good at the proximal level and slight distally. In the remaining 4 cases penetration at both levels ranged from slight to good. No microfractures, either intraoperative or following stress testing, were evidenced. Mechanical tests showed that stem implantation reduced deformation of the femoral cortical bone undergoing cyclic loading, in comparison with the pre-implantation situation. Conclusions. The double-conicity prosthetic stem showed good implantability, with the capacity to allow for stability in case of femoral shortening osteotomies without the use of plates or cerclage fixation. Mechanical testing also showed a correct load distribution, and a reduction of stress on femoral cortical bone in comparison with the state before implantation. Prospective clinical studies are necessary to assess efficacy and dependability from a clinical and radiographic viewpoint

A total of 20 pairs of fresh-frozen cadaver femurs were assigned to four alignment groups consisting of relative varus (10° and 20°) and relative valgus (10° and 20°), 75 composite femurs of two neck geometries were also used. In both the cadaver and the composite femurs, placing the component in 20° of valgus resulted in a significant increase in load to failure. Placing the component in 10° of valgus had no appreciable effect on increasing the load to failure except in the composite femurs with varus native femoral necks. Specimens in 10° of varus were significantly weaker than the neutrally-aligned specimens. The results suggest that retention of the intact proximal femoral strength occurs at an implant angulation of ≥ 142°. However, the benefit of extreme valgus alignment may be outweighed in clinical practice by the risk of superior femoral neck notching, which was avoided in this study

With the increasing use of 3D medical imaging, it is possible to analyze 3D patient anatomy to extract features, trends and population specific shape information. This is applied to the development of ‘standard implants’ targeted to specific population groups. INTRODUCTION. Human beings are diverse in their physical makeup while implants are often designed based on some key measurements taken from the literature or a limited sampling of patient data. The different implant sizes are often scaled versions of the ‘average’ implant, although in reality, the shape of anatomy changes as a function of the size of patient. The implant designs are often developed based on a certain demographic and ethnicity and then, simply applied to others, which can result in poor design fitment [1]. Today, with the increasing use of 3D medical imaging (e.g. CT or MRI), it is possible to analyze 3D patient anatomy to extract features, trends and population specific shape information. This can be applied to the development of new ‘standard implants’ targeted to a specific population group [2]. PATIENTS & METHODS. Our population analysis was performed by creating a Statistical Shape Model (SSM) [3] of the dataset. In this study, 40 full Chinese cadaver femurs and 100 full Caucasian cadaver femurs were segmented from CT scans using Mimics®. Two different SSMs, specific to each population, were built using in-house software tools. These SSMs were validated using leave-one-out experiments, and then analyzed and compared in order to enhance the two population shape differences. RESULTS. An SSM is typically represented by an average model and a few independent modes of variation that capture most of the inherent variations in the data. Based on these main modes of variations, the shape features, e.g. length, thickness, curvature neck angle and femoral version, presenting largest variations were determined, and correlations between these features were calculated. Figure 1 represents the Caucasian and Chinese average models, and shows that while the length of these two models was significantly different, the AP and ML dimensions were similar, indicating a difference of morphology (other than a scaling) between the two populations. Figure 2 represents the first mode of variation that illustrates the variation of Chinese femur shape with size. As an example, the neck angle increases of 26° with an increase of 139 mm in femur length, indicative of the effect of changes in loading conditions on geometry as a function of size. CONCLUSION. The advantage of using more advanced statistical analyses is that the 3D data are probed in an unbiased fashion, allowing the most important parameters of variation to be determined. These analyses are thus particularly effective to compare different populations, to evaluate how well existing implant designs fit specific populations, and to highlight the design parameters that need to be adapted for good fitment of specific populations

Purpose. The Birmingham Mid-Head Resection (BMHR) is a bone-conserving, short-stem alternative to hip resurfacing for patients with compromised femoral head anatomy. It is unclear, however, if an uncemented, metaphyseal fixed stem confers a mechanical advantage to that of a traditional hip resurfacing in which the femoral prosthesis is cemented to the prepared femoral head. Thus, we aimed to determine if a metaphyseal fixed, bone preserving femoral component provided superior mechanical strength in resisting neck fracture compared to a conventional hip resurfacing arthroplasty. Method. Sixteen matched pairs of human cadaveric femurs were divided evenly between specimens receiving a traditional epiphyseal fixed hip resurfacing arthroplasty (BHR) and those receiving a metaphyseal fixed BMHR. Pre-preparation scaled digital radiographs were taken of all specimens to determine anatomical parameters as well as planned stem-shaft angles and implant sizes. A minimum of 10 degrees of relative valgus alignment was planned for all implants and the planned stem-shaft angles and implant sizes were equal between femur pairs. Prior to preparation, bone mineral density scans of the femurs were obtained. Prepared specimens were potted, positioned in single-leg stance and tested to failure using a mechanical testing machine. Load-displacement curves were used to calculate construct stiffness, failure energy and ultimate failure load. Results. Human cadaveric femur pairs were well matched for anatomic parameters and BMD with no statistically significant differences in neck-shaft angle (p=0.110), neck width (p=0.173), femoral offset (p=0.224) or neck BMD (p=0.525). There was a statistically significant difference between failure loads for femurs prepared with a BHR and those prepared with a BMHR (p<0.001). Femurs prepared with a BHR (7012 N, SD 2619) failed at an average of 1578 N (SD 865) greater than paired femora prepared with a BMHR (5434 N, SD 2297), representing a 24% increase in failure load. Both construct stiffness and failure energy were not statistically different between groups (p>0.065). Transcervical vertical shear fractures accounted for 19 of 32 failures, the remaining 11 were subcapital fractures. There were no fractures observed at the base of the femoral neck for either implant. Conclusion. A metaphyseal fixed, bone conserving femoral implant does not provide superior mechanical strength nor increased resistance to femoral neck fracture compared to a conventional hip resurfacing arthroplasty

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

Introduction: Femoral neck fractures are common and percutaneous insertion of three cannulated screws is an accepted method of surgical treatment. The accuracy of surgical performance is highly correlated with the cut-out percentages of the screws. The conventional technique relies heavily on fiuoroscopy and could lead to inappropriate implant placement. Further, multiple guidewire passes might prolong the operation time and weaken the cancellous bone. A computer-assisted planning and navigation system based on 2D-fiuoroscopy has been developed for guidewire insertion in order to perform insertion of a guidewire to perform screw insertion. The image acquisition process was supported by a radiation-saving procedure called “Zero-dose C-arm navigation”. The purpose of this experimental study was to compare this technique with conventional C-arm fiuoroscopy with respect to the number of fiuoroscopic images, the number of drilling attempts and operation time. We used two operative settings, with sawbones and with cadavers. For the sawbone study, we also compared the femoral neck and head perforation and the neck-width coverage (the relative area of the femoral neck held by screws). Methods: Three cannulated hip screws were inserted into 12 femoral sawbones simulating femoral neck fractures and into 6 cadaveric femurs guided by the computer-based navigation. We compared them to the conventional fiuoroscopic technique also using 12 femoral sawbones and 6 cadaveric femurs. Results: The computer-assisted technique significantly reduced the amount of intraoperative fiuoroscopy (sawbone study: P< 0.001; cadaver study: P< 0.001) and the number of guidewire passes (sawbone study: P< 0.05; cadaver study: P< 0.05) in the sawbone and the cadaver setting. Operation time was significantly longer (sawbone study: P< 0.001; cadaver study: P< 0.05) in the navigation assisted group also in both settings. In the sawbone study, there was no significant difference in the femoral neck and head perforation, whereas the relative neck area held by the screws was significantly (P< 0.05) larger than that in the conventional group. Discussion: The addition of computer-assisted planning and surgical guidance supported by “Zero-dose C-arm navigation” may be useful for the fixation of femoral neck fractures by cannulated screws as it reduces the amount of intraoperative fiuoroscopy, requires fewer drill tracks and achieves a better neck coverage. Further studies with the goal of reducing the operation time by improving the learning curve are indispensable before integrating this navigation system into the clinical workfiow

Background: Resurfacing hip arthroplasty has re-emerged as an option in total hip arthroplasty and by 2008 these prostheses constituted 7.8% of the total number of primary hip replacements in Australia. In the Scandinavian countries the use of resurfacing prostheses is substantially less, reported from 0.6–2.8% in the different national arthroplasty registries. The resurfacing implant preserves proximal bone stock and is expected to retain a physiological load transfer in the proximal femur. Mid-term results for the resurfacing implants are promising, but periprosthetic neck fractures remains the most frequent complication. Finite element analyses have suggested increased strains in the femoral neck area after resurfacing arthroplasty. This has not yet been proved in a cadaver model. Purpose: This study compared the strain pattern of the femoral neck and the proximal femur in cadaver femurs before and after insertion of a resurfacing femoral component. Material and method: When load transfers trough the hip joint to the femur, the bone undergoes a deformation, which can be measured by strain gauges. In this study, ten strain gauge rosettes were distributed on the femoral neck and proximal femur of thirteen human cadaver femurs. The femurs were loaded in a hip simulator for single leg stance and stair climbing. Cortical strains were measured on the femoral neck and proximal femur before and after implantation of a resurfacing femoral component (DePuy ASRTM). Results: After resurfacing the mean tensile strain increased by 15 % (CI: 6 – 24%, p=0.003) on the lateral femoral neck, and mean compressive strain increased by 11 % (CI: 5 – 17%, p=0.002) on the medial femoral neck during single leg stance simulation. On the anterior side of the femoral neck the strain increased up to 16%, however this difference was not found statistically significant. On the proximal femur the deformation pattern remained similar to the strains measured on the unoperated femurs. Discussion: Both patient related factors such as female gender, obesity and high age, and surgical factors such as notching, lack of seating and varus-orientation of the implant have been associated with increased risk of neck fracture after resurfacing arthroplasty. We asked ourselves if there could be a biomechanical factor contributing to the risk of periprosthetic fracture. The small increase of strains in the neck area would probably not alone be sufficient to cause a neck fracture. Acting together with patient-specific and surgical factors it may however contribute to the risk of early periprosthetic fracture