Aims. Arthroplasty surgery of the knee and hip is performed in two to three million patients annually. Periprosthetic joint infections occur in 4% of these patients. Debridement, antibiotics, and implant retention (DAIR) surgery aimed at cleaning the infected prosthesis often fails, subsequently requiring invasive revision of the complete prosthetic reconstruction. Infection-specific imaging may help to guide DAIR. In this study, we evaluated a bacteria-specific hybrid tracer (. 99m. Tc-UBI. 29-41. -Cy5) and its ability to visualize the bacterial load on femoral implants using clinical-grade image guidance methods. Methods. 99m. Tc-UBI. 29-41. -Cy5 specificity for Stapylococcus aureus was assessed in vitro using fluorescence confocal imaging. Topical administration was used to highlight the location of S. aureus cultured on femoral prostheses using fluorescence imaging and freehand single photon emission CT (fhSPECT) scans. Gamma counting and fhSPECT were used to quantify the bacterial load and monitor cleaning with chlorhexidine. Microbiological culturing helped to relate the imaging findings with the number of (remaining) bacteria. Results. Bacteria could be effectively stained in vitro and on prostheses, irrespective of the presence of biofilm. Infected prostheses revealed bacterial presence on the transition zone between the head and neck, and in the screw hole. Qualitative 2D fluorescence images could be complemented with quantitative 3D fhSPECT scans. Despite thorough chlorhexidine treatments, 28% to 44% of the signal remained present in the locations of the infection that were identified using imaging, which included 500 to 2,000 viable bacteria. Conclusion. The hybrid tracer . 99m. Tc-UBI. 29-41. -Cy5 allowed effective bacterial staining. Qualitative real-time fluorescence guidance could be effectively combined with nuclear imaging that enables quantitative monitoring of the effectiveness of cleaning strategies. Cite this article: Bone Joint Res 2023;12(1):72–79

Purpose of the study: Hip resurfacing with a metal-on-metal bearing gives good mid-term clinical results. The design of the femoral piece has an effect on implant longevity, as does the vitality of the underlying cephalic bone. Computer-assisted surgery has been helpful in position the implant but the choice of the best position is still empirical. Prosthesis designers recommend valgus, but with too much there is a risk of a superolaterl notch which would weaken the neck. This leads the surgeon to use a larger femoral implant, and consequently to resect more acetabular bone. Anteversion is not evaluated. The purpose of this study was test mechanically different valgus/varus, anteversion/retroversion positions of the femoral implant. Material and methods: We implanted 15 femurs made of resin which were geometrically and mechanically identical. The following angles were tested: varus/valgus (−10°, neutral, +10°, +20°) and ante/retroversion (−10°, neutram, +10). A valgus notch (+20° and +10°) and a varus notch (−10°) were simulated. The femurs thus prepared were tested with Instron 8874. Load at failure was noted as well as the type of fracture: distance from the fracture line to the greater trochanter (FGT). Student’s t test was applied. Results: All of the femurs fractured at the neck. The fracture was closer to the implant (FGT: 11.0 mm) for the 20° valgus implantation (p< 0.05). The displacement was lesser with a valgus notch (mean 2.2 mm) then without a notch (mean 3.3 mm (p< 0.05). The varus notch had no effect. The failure load was lower for 20° valgus (1236 N, range 1117–1356N) then for the other angles (1664N, range 1142–2113 N) with near statistical significance (p=0.08). Retroversion had no effect. Anteversion allowed greater displacement (4.1 mm) and supported greater loading (1879 N) before failure. Discussion: This study, unlike clinical studies, did not demonstrate any static mechanical superiority of the valgus position for the femoral piece. Another study on cadaver bones is planned for confirmation. Clinical studies reflect the vitality of the trabecular bone supporting the implant, a vitality which could be stimulated by the valgus position

Metal-on-metal hip resurfacing arthroplasty has been reintroduced as an alternative to total hip replacement. Uncemented acetabular fixation is now the gold standard for this procedure. However, uncemented femoral component fixation is less common. We thus report our preliminary results of an uncemented, hydroxyapatite-coated femoral implant at resurfacing arthroplasty. Between June 2001 and July 2002 we undertook 70 uncemented resurfacings in 66 patients. The survival rate of the femoral implants after a minimum of two years’ follow-up was 98.6%. The mean Harris hip scores for pain and function pre-operatively were 12.0 (maximum possible score 44) and 28.3 (maximum possible score 47) respectively. Postoperatively, at final follow-up, these scores were 39.25 and 43.07 respectively (Z= −6.94, p< 0.0001 for function and Z= −7.19, p< 0.0001 for pain). There have been no femoral fractures, aseptic loosening or radiolucencies around the stem. Thinning of the femoral neck at the inferomedial cup-neck rim has been a frequent radiological finding but with no clinical implications so far. The cup-neck ratio immediately after surgery was a mean of 1.05 while at last follow-up was 1.1 and this difference was statistically significant (Z= −4.14, p< 0.0001). Increased height (p=0.02) seemed to protect patients against neck thinning, whereas increased weight (p=0.06) seemed to favour it. Our preliminary results with a hydroxyapatite-coated femoral implant in metal-on-metal hip resurfacing have been promising with excellent survival rates and clinical outcomes. Longer follow-up studies are needed, particularly to interpret the clinical significance of neck thinning

The success of a cementless Total Hip Arthroplasty (THA) depends not only on initial micromotion, but also on long-term failure mechanisms, e.g., implant-bone interface stresses and stress shielding. Any preclinical investigation aimed at designing femoral implant needs to account for temporal evolution of interfacial condition, while dealing with these failure mechanisms. The goal of the present multi-criteria optimization study was to search for optimum implant geometry by implementing a novel machine learning framework comprised of a neural network (NN), genetic algorithm (GA) and finite element (FE) analysis. The optimum implant model was subsequently evaluated based on evolutionary interface conditions. The optimization scheme of our earlier study [1] has been used here with an additional inclusion of an NN to predict the initial fixation of an implant model. The entire CAD based parameterization technique for the implant was described previously [1]. Three objective functions, the first two based on proximal resorbed Bone Mass Fraction (BMF) [1] and implant-bone interface failure index [1], respectively, and the other based on initial micromotion, were formulated to model the multi-criteria optimization problem. The first two objective functions, e.g., objectives f1 and f2, were calculated from the FE analysis (Ansys), whereas the third objective (f3) involved an NN developed for the purpose of predicting the post-operative micromotion based on the stem design parameters. Bonded interfacial condition was used to account for the effects of stress shielding and interface stresses, whereas a set of contact models were used to develop the NN for faster prediction of post-operative micromotion. A multi-criteria GA was executed up to a desired number of generations for optimization (Fig. 1). The final trade-off model was further evaluated using a combined remodelling and bone ingrowth simulation based on an evolutionary interface condition [2], and subsequently compared with a generic TriLock implant. The non-dominated solutions obtained from the GA execution were interpolated to determine the 3D nature of the Pareto-optimal surface (Fig. 2). The effects of all failure mechanisms were found to be minimized in these optimized solutions (Fig. 2). However, the most compromised solution, i.e., the trade-off stem geometry (TSG), was chosen for further assessment based on evolutionary interfacial condition. The simulation-based combined remodelling and bone ingrowth study predicted a faster ingrowth for TSG as compared to the generic design. The surface area with post-operative (i.e., iteration 1) ingrowth was found to be ∼50% for the TSG, while that for the TriLock model was ∼38% (Fig. 3). However, both designs predicted similar long-term ingrowth (∼89% surface area). The long-term proximal bone resorption (upto lesser trochanter) was found to be ∼30% for the TSG, as compared to ∼37% for the TriLock model. The TSG was found to be bone-preserving with prominent frontal wedge and rectangular proximal section for better rotational stability; features present in some recent designs. The optimization scheme, therefore, appears to be a quick and robust preclinical assessment tool for cementless femoral implant design. To view tables/figures, please contact authors directly

Purpose: The Exeter technique opens new perspectives for the treatment of femoral bone loss observed at revision hip arthroplasty. Early migration of the implant, considered by the advocates of the technique to be beneficial when limited, can, in the absence of secondary instability, weaken the cement shield leading to early revision. Several publications on this topic have examined the improvement in primary stability achieved by modifying the impaction technique or by searching for the ideal size of the grafts. The purpose of the present study was to examine the reproducibility of this method and its effect on transformation of the allograft. Material and methods: We performed a prospective analysis of outcome in 46 patients operated on since 1996. The Poste-Merle-d’Aubigné (PMA) clinical score and the Ling and Gie radiographic score as well as the SOFCOT score for substance loss were determined. We used frozen fragmented allografts without consideration of graft size. A standard sized femoral implant was used in all cases. Results: Mean follow-up was 3 years (range 12 – 66 months). Four patients were not followed beyond 9 months because of major complications requiring revision surgery (infection, fracture of the femur, malposition) or patient death (stroke). For the remaining 42 patients, loss of femoral stock was scored I in 6, II in 23, III in 13. The functional score improved from 9.13±3.9 preoperatively to 16.07±2.5 postoperatively. Radiographically, bone lines were observed in the graft in 36 patients, associated with bone remodelling in ten. In six patients, the allograft exhibited a heterogeneous aspect. Three implants migrated 4 mm. Defective distal sealing was noted in all three. One prosthesis implanted in a varus position worsened before stabilising. Discussion: This technique is a reliable method since primary stability of the implant was obtained in 90% of the cases and was maintained during long follow-up. This did not prevent graft remodelling

Negative remodelling of the femoral cortex in the form of calcar resorption due to stress-shielding, and femoral cortical hypertrophy at the level of the tip of the implant due to distal load transfer, is frequenly noted following cemented total hip replacement, most commonly with composite beam implants, but also with polished double tapered components. The C-stem polished femoral component was designed with a third taper running from lateral to medial across and along the entire length of the implant, with the aim of achieving more proximal and therefore more natural loading of the femur. The implant is designed to subside within the femoral cement mantle utilising the cement property of creep, generating hoop stresses, which are transferred more proximally to the femoral bone, starting at the level of the medial calcar. The intention is to load the proximal femur minimising stress-shielding and calcar resorption, as well as reducing distal load transfer as signified by the lack of distal femoral cortical hypertrophy. We present the results of a consecutive series of 500 total hip replacements using C-stem femoral components, performed between March 2000 and December 2005 at a single institution. Data was collected prospectively and all patients remain under annual follow-up by a Specialist Arthroplasty Practitioner. The operations were performed using a standard surgical technique with third generation cementing using Palacos-R antibiotic loaded cement. 500 arthroplasties were performed on 455 patients with an average age at the time of surgery of 68.3 years (23-92). There were 282 (62%) female and 173 (38%) male patients with osteoarthritis being the predominant diagnosis. 77 patients have died (73 hips) and the average duration of follow-up for the entire series is 81 months (52-124). Only 2 femoral implants have been revised - one for deep sepsis and the other as part of a revision procedure for a loose acetabulum, although the femoral component itself was not loose. One implant is currently loose following a periprosthetic fracture treated by internal fixation, but none of the remaining implants demonstrates any progressive radiolucencies in any Gruen zones or any features suggestive of current or future loosening. Calcar rounding has been observed, but there have been no cases with obvious loss of calcar height and no cases of distal femoral cortical hypertrophy. The C-stem femoral component has therefore performed well in clinical practice and the objective of eradicating negative bone remodelling has been achieved. The study is ongoing

Introduction. Ability to accommodate increased range of motion is a design objective of many modern TKA prostheses. One challenge that any “high-flex friendly” prosthesis has to overcome is to manage the femorotibial contact stress at higher flexion angle, especially in the polyethylene tibial insert. When knee flexion angle increases, the femorotibial contact area tends to decrease thus the contact stress increases. For a high-flex design, considerations should be taken to control the contact stress to reduce the risk of early damage or failure on the tibial insert. This study evaluated the effect of femoral implant design on high flexion contact stress. Two prostheses from a same TKA family were compared – one as a conventional design and the other as a high-flex design. Methods. Two cruciate retaining (CR) prostheses from a same TKA product family were included in this study. The first is a conventional design for up to 125° of flexion (Optetrak CR, Exactech, USA). The second is a high-flex design for up to 145° of flexion (Logic CR, Exactech, USA). The high-flex design has a femoral component which has modified posterior condyle geometry (Figure 1), with the intent to increase femorotibial contact area and decrease contact stress at high flexion. Three sizes (sizes 1, 3, and 5) from each prosthesis line were included to represent the commonly used size spectrum. Contact stress was evaluated at 135° of flexion using finite element analysis (FEA). The CAD models were simplified and finite element models were created assuming all materials as linear elastic (Figure 2). For comparison purpose, a compressive force of 20% body weight was applied to the femoral component. The average body masses of sizes 1, 3 and 5 patients are 69.6 kg, 89.9 kg, and 106.3 kg based on the manufacture's clinical database. A nonlinear FEA solver was used to solve the simulation. Von Mises stress in the tibial insert was examined and compared between the two prostheses. Results. The high-flex design demonstrated lower tibial insert stresses compared to the conventional design, and the stress reduction is consistent across different sizes (Figure 3). The peak von Mises stress of the high-flex design was 8.6 MPa, 10.8 MPa, and 11.9 MPa for sizes 1, 3 and 5, representing a 40% to 60% decrease compared to those of the conventional design (14.3 MPa, 26.5 MPa, and 25.6 MPa respectively). Discussion/Conclusion. One limitation of the study was that no material nonlinearity was considered in the FEA, thus stress values above the yield strength of polyethylene could be over-estimated. However, as a qualitative comparison, the analysis demonstrated the effectiveness of the high-flex design on reducing tibial insert contact stress. Although the actual flexion angle of a CR TKA patient is not fully defined by the prosthesis and largely affected by the patient's anatomy and pre-operative range of motion, a lower contact stress at high flexion indicates a more forgiving mechanical structure and less risk for polyethylene damage when the patient is able to perform high flexion activities

Introduction. Negative remodelling of the femoral cortex in the form of calcar resorption due to stress shielding and cortical hypertrophy at the level of the tip of the implant, due to distal load transfer, is frequently noted following cemented total hip replacement, most commonly with composite beam implants, but also with polished double tapers. The C-stem polished femoral component was designed with a third taper running from lateral to medial across and along the entire length of the implant, with the aim of achieving more proximal and therefore more natural loading of the femur. The hoop stresses generated in the cement mantle are transferred to the proximal bone starting at the calcar, which should theoretically minimise stress-shielding and calcar resorption, as well as reducing distal load transfer, as signified by the development of distal femoral cortical hypertrophy. Materials/Methods. We present the results of a consecutive series of 500 total hip replacements performed between March 2000 and December 2005 at a single institution, using a standard surgical technique and third generation cementing with Palacos-R antibiotic loaded cement. Data was collected prospectively and the patients remain under annual follow-up. 500 arthroplasties were performed on 455 patients with an average age of 68.3 years (23–92). 77 patients have died (73 arthroplasties) and the average duration of follow-up for the entire series is 81 months (52–124). Results. Only 2 femoral implants have been revised - one for deep sepsis and the other as part of a revision procedure for a loose acetabulum, although the femoral component itself was not loose. One implant is currently loose following a periprosthetic fracture treated by internal fixation, but none of the other remaining implants demonstrates any progressive radiolucencies in any Gruen zones, or any features suggestive of current or future loosening. Rounding of the calcar has been observed, but there have been no cases with obvious loss of calcar height and no cases of distal femoral cortical hypertrophy. Conclusion. The C-stem femoral component has therefore performed well in clinical practice and the objective of eradicating negative bone remodelling has been achieved. The study is ongoing

The authors report their preliminary experience with a minimum of one year follow –up of hydroxyapatite coating as the means of fixation of the femoral head in hip resurfacing. Between Dec 2003 and Dec 2004, of the 23 cases performed by the senior author,22 were available for follow up,15 were women (68.2%) and 7 were men (31.8). The femoral and acetabular components of the uncemented version of the CORMET 2000(Corin,Cire ncester,UK) were used. The surgical approach was the Hardinge approach in all cases. Patients were assessed pre-operatively for pain and function,using the Harris Hip Score. Post operatively they were assessed in clinic with x rays at 6 weeks,6 months and annually thereafter. X rays were evaluated for pre and post op neck shaft angle,giving an indication of varus or valgus placement of the head prosthesis. The lateral view was assessed to reveal anterior or posterior tilting of the prosthesis. Neck thinning was evaluated by measuring the ratio of the metal cup and bony neck diameters at the cup neck junction, recorded post op and at one year. None of the femoral implants were placed in varus. Only one case had inferior notching, which had remodelled at one year. In the lateral view none of the cups showed a displacement of more than ten degrees in the AP direction. There were no stem lucencies or signs of femoral implant migration in any of the cases. None of our cases showed neck thinning (change in ratio greater than 10%). Uncemented femoral implant in a metal on metal resurfacing hip replacement appears to perform well and shows no catastrophic problems at the short term one year follow up. Longer follow up studies are necessary

The measurement of bone mineral density in defined areas around metal implants has improved with the development of dual-energy X-ray absorptiometry. We used this technique to compare the bone mineral density adjacent to metal cementless femoral implants with that of identical regions of bone in normal proximal femora. We studied the anteroposterior views only of 72 femora which contained total hip implants and 34 non-operated femora. We compared the regional bone mineral density of bone adjacent to proximally porous-coated and distally porous-coated implants of one design, to measure the relative differences in the remodelling changes induced by different amounts of porous coating. We also measured differences in bone density with time and with variations in implant size (and therefore stiffness). The greatest decrease in bone mineral density (34.8%) occurred in the most proximal 1 cm of the medial femoral cortex around relatively stiff, extensively porous-coated implants. The next most severe decrease (20% to 25%) was in the next most proximal 6 cm of the medial femoral cortex. Small, progressive decreases in bone mineral density continued for five to seven years after implantation

Background

Thigh pain following a well-fixed total hip arthroplasty (THA) remains problematic and a source of patient dissatisfaction. The purpose of this study is to evaluate if the development of distal femoral cortical hypertrophy (DFCH) is associated with chronic postoperative thigh pain after THA with a short stem implant.

Femoral bone preservation is an important consideration in total hip replacement for those patients expected to outlive the success of their primary procedure. A clinical study was initiated to assess the performance of a new, ultra-short, cementless femoral implant that is sited in the region of the femoral neck. This two-centre study, conducted in Australia and Germany, was approved by the ethics committees and regulatory authorities in both countries. Patients aged between 25 and 65 with non-inflammatory arthritis were included subject to review against the detailed study selection criteria and the provision of written informed consent. Patients were assessed pre-operatively using the Harris Hip Score and Oxford Hip Score. These scores were repeated and standard radiographs taken at 3, 6, 12 and 24 months follow-up. Radiostereometric analysis (RSA) was employed to monitor the in-vivo femoral implant stability. The Oxford Hip was additionally collected at 36 and 48 months. Forty-one patients, 23 males and 18 females, received the SILENT. ™. femoral implant in primary total hip replacement surgery between January and November 2003. The mean age was 50.4 years (range 26–65) with an average BMI of 26.6 (Range 19–37). The diagnoses included osteoarthritis (68%), AVN (15%), DDH (7%), post-infection osteoarthritis (5%) and others (5%). The average Harris Hip Score increased from 54.3 (Range 26–80) pre-operatively to 95.0 (Range 46–100) at 24 months. This improvement was supported by the patient’s view with the mean Oxford Hip Score data changing from a pre-operative level of 38.9 (Range 19–52) to a 4-year average of 13.2 (Range 12–27). The radiographic performance is also positive with only one patient having evidence of a radiolucent line on the latest x-rays at 24 months however this is non-progressive and has been present since 6 months post-op. RSA data shows the mean values for the translations of the implant and distal tip in any of the three axes to be low out to 2 years follow-up indicating a high degree of stability in this critical post-operative period. No revisions of the SILENT. ™. implant have been undertaken to date. Early prosthetic stability is acknowledged as a critical success criterion for any new femoral implant being introduced into clinical practice. This has been demonstrated for a new, ultra-short, femoral implant thereby presenting a new solution for patients who could benefit from healthy bone preservation at the time of primary surgery

Background

Children suffering from primary bone cancer necessitating resection of growth plates, may suffer progressive leg length discrepancy, which can be attenuated with extendable prostheses. A serious complication is catastrophic implant failure. Over time, bone will remodel, altering the stress pattern in the implant. By using finite element analysis we can model different bone remodeling conditions to ascertain the effect that this will have on stress distribution and magnitude.

A finite element analysis was performed. Simplified computer generated models were designed of a cemented femoral Stanmore growing massive endoprosthesis. Three scenarios were designed, modelled on post-operative radiographs. Scenario 1 had a gap between the end of the femur and the implant collar, scenario 2 had no gap, but with no bone attachment into the collar, and scenario 3 had growth of the bone over the length of the collar with attachment. Physiological loading conditions were applied. The resultant stress in the implant for each scenario was measured, and compared to the strength of the material. Peak stresses were recorded at the stem-collar junction.

The maximum stress recorded in the implant in scenario 1 was 3104.2Mpa, compared to 1054.4Mpa in scenario 2, and 321.2Mpa in scenario 3.

The aim of this study was to assess whether a femoral component which retained the neck reduced the incidence of leg-length inequality following total hip arthroplasty. A retrospective review was undertaken of 130 consecutive primary total hip arthroplasties performed between April 1996 and April 2004 using such an implant. There were 102 suitable patients for the study. Standardised pre- and post-operative pelvic radiographs were measured by an independent investigator to the nearest millimetre.

The leg-length inequality was reduced from a mean pre-operative value of −0.71 cm to a mean of 0.11 cm post-operatively. Of the 102 patients 24 (23.5%) had an equal leg-length post-operatively, and 95 (93.1%) had a leg-length inequality between −1 cm and 1 cm.

Purpose: We report a prospective series of 70 explantations of the femoral pivot via a transfemoral approach required due to septic and aseptic loosening.

Material and methods: Aseptic loosening was observed in 61 cases, septic loosening in 9. The extended posterolateral approach was used to remove the implant in all cases and a femoral segment (Wagner method). Reconstruction of the femur was achieved with locked stems without cement (65 patients) or a long stem without cement (1 patient). Reimplantation was not attempted in four patients. Bone grafts were not used. Mean follow-up in this series was 3.5 years. The PMA score was used for clinical assessment. Radiographic assessment of segment healing and bone regrowth around the implant was done by measuring the cortical index.

Results: We observed a significant gain in the PMA score of more than 9 points. We had one intraoperative fracture of the femoral segment and two episodes of early dislocation. All femoral segments healed. Osteogenesis failed in three cases with fracture of the locking screw. There were also two cases of late fracture of the trochanter. At one year, bone regrowth measured from the cortical index was greater than 10% on the average.

Discussion: We discuss the characteristic features of this type of surgery in comparison with other solutions for femoral revision: operative time, blood loss, choice of implants, later weight bearing. We also found that this technique allows easier implant removal and more effective cleaning of the femoral shaft in the event of septic surgery with fewer cases of intraoperative accidents (malposition, femoral fractures). We were able to demonstrate that this method of femur reconstruction without bone graft provides a stimulation of osteogenesis in the floating segment. Stem locking provides primary stability in 100% of the cases. Secondary stability was achieved in 90% due to the quality of the newly formed bone.

Anterior positioning of a cephomedullary nail in the distal femur occurs in up to 88% of cases. This is considered to occur because of a mismatch between the radius of curvature of the femur and that of available implants. The hypothesis for this study was that the relative thicknesses of the cortices of the femur (referenced off the linea aspera) change with age and determine the final position of intramedullary implants.

This study used the data from CT scans undertaken as part of routine clinical practice in 919 patients with intact left femora (median age 66 years, 484 male and 435 female). The linea aspera and transverse intervals were plotted on a template femur between 25% – 60% femoral bone length (5% increments) and mapped automatically to all individual femora in the database with measurements taken in the plane of the linea aspera.

The linea aspera was found to be internally rotated as compared to the sagittal plane referenced off the posterior femoral condyles. An age related change in the posterior/anterior cortical thickness ratio was demonstrated. The >80 year old cohort shows a significantly disproportional posterior/anterior ratio increase of 70.0% from 25–50% bone length as compared to 48.1% for the <40 year old cohort (p<0.05).

This study has shown that assessment in the sagittal plane may be inaccurate because of rotational changes in the linea aspera. The centering influence of the corticies is lost with age with a relative thinning of the anterior cortex and thickening of the posterior cortex moving distally in the femur. This has a direct influence on the positioning of intramedullary implants explaining the preponderance of anterior malpositioning of intramedullary implants in the elderly.

Aims. Femoral revision component subsidence has been identified as predicting early failure in revision hip surgery. This comparative cohort study assessed the potential risk factors of subsidence in two commonly used femoral implant designs. Methods. A comparative cohort study was undertaken, analyzing a consecutive series of patients following revision total hip arthroplasties using either a tapered-modular (TM) fluted titanium or a porous-coated cylindrical modular (PCM) titanium femoral component, between April 2006 and May 2018. Clinical and radiological assessment was compared for both treatment cohorts. Risk factors for subsidence were assessed and compared. Results. In total, 65 TM and 35 PCM cases were included. At mean follow-up of seven years (1 to 13), subsidence was noted in both cohorts during the initial three months postoperatively (p < 0.001) then implants stabilized. Subsidence noted in 58.7% (38/65 cases) of the TM cohort (mean 2.3 mm, SD 3.5 mm) compared to 48.8% (17/35) of PCM cohort (mean 1.9 mm, SD 2.6 mm; p = 0.344). Subsidence of PCM cohort were significantly associated with extended trochanteric osteotomy (ETO) (p < 0.041). Although the ETO was used less frequently in PCM stem cohort (7/35), subsidence was noted in 85% (6/7) of them. Significant improvement of the final mean Oxford Hip Score (OHS) was reported in both treatment groups (p < 0.001). Conclusion. Both modular TM and PCM revision femoral components subsided within the femur. TM implants subsided more frequently than PCM components if the femur was intact but with no difference in clinical outcomes. However, if an ETO is performed then a PCM component will subside significantly more and suggests the use of a TM implant may be advisable. Cite this article: Bone Joint J 2020;102-B(6):709–715

Objectives/background: Flexion Stability and Patella tracking after Total Knee Replacement is mainly influenced from the rotational alignment of the femoral component. Different implant philosophies use different landmarks for rotational alignment, as the epicondylar line, the posterior condyles or the anteroposterior line. An individual variation of the different landmarks is known from manual implantation an cadaver and CT studies.

The purpose of this study was to measure the variation of three different lines for femoral rotational alignment to show the possible difference and check the so far used values in manual instrumentation technique.

Design/methods: Using the Navitrack Navigation system we performed 100 consecutive TKRs. The landmarks for the 3 most common lines for rotational alignment of the femoral component has been probed.

The software calculated the position of the lines and the 3-dimensional ankle between the lines. Intraoperative snapshots were taken to postoperative data analysis of the numeric data.

Results: The mean difference between the ECL and the PCL was –0,96 (SD 3,64; range −10.7 − 5,9). In varus knees −0,2 (−6 −4,5) in valgus knees 1,4 (–10,7 – 5,9). ECL to the APC was in mean 88,83 (SD 7,23; range 100,8 – 71,9). In varus knees 91,3 (99 – 76,2) in valgus knees 83,8 (100,8 – 71,9).

Conclusions: Using a navigation system it is easy to perform an individual, intraoperative measurement of the relationship of different anatomical landmarks for rotational alignment of the femoral component. But the range of values shows that in the manual technique with fixed rotational alignment given by the instruments, there is a high risk for femoral rotational malalignment. The results depended on preoperative deformity could only be seen as a bias for higher variance in valgus knees. For the navigation procedures there is not one universal landmark which can be used. Furthermore the systems must be developed for intraoperative functional analysis, with integration of soft tissue balancing, to improve functional and long-term outcome in TKR.

Introduction. Conventional implant designs in total knee arthroplasty (TKA) are based on metal on UHMWPE bearing couples. Although this procedure is quite successful, early loosening is still a matter of concern. One of the causes for early failure is stress shielding, leading to loss of bone stock, periprosthetic bone fractures and eventually aseptic loosening of the component. The introduction of a polyetheretherketone (PEEK) on UHMWPE bearing couple could address this problem. With mechanical properties more similar to distal (cortical) bone it could allow stresses to be distributed more naturally in the distal femur. A potential adverse effect, however, is that the femoral component and the underlying cement mantle may be at risk of fracturing. Therefore, we analyzed the effect of a PEEK-Optima® femoral component on stress shielding and the integrity of the component and cement mantle, compared to a conventional Cobalt-Chromium (CoCr) alloy implant. Methods. We created a Finite Element (FE) model of a reconstructed knee in gait, based on the ISO-14243-1 standard. The model consisted of an existing cemented cruciate retaining TKA design implanted on a distal femur, and a tibial load applicator, which together with the bone cement layer and the tibial implant is referred to as the tibial construct. The knee flexion angle was controlled by the femoral construct, consisting of the femoral implant, the bone cement and the distal femur. The tibial construct was loaded with an axial force, anterior-posterior (AP) force and a rotational torque, representing the ground reaction force, soft tissue constraints and internal/external rotation of the tibia, respectively. The integrity of the femoral component and cement mantle were expressed as a percentage of their yield stress. Stress shielding in the periprosthetic femur was evaluated by the strain energy (density) in the bone and compared to a model replicating an intact knee joint. Results. Considering implant durability, the CoCr and PEEK-Optima® femoral components performed equally well, with peak stresses reaching only 12–18 percent of their respective yield stresses (Figure 1(A)). The bone cement experienced higher loads in the reconstruction with the PEEK-Optima® implant, but the principal stresses were within a safe range, with a maximum of 20 percent of the ultimate compressive load (Figure 1(B)). As anticipated, the more compliant polymer implant resulted in a strain energy magnitude and distribution similar to that of an intact knee (Figure 2,3), which could prevent the loss of bone stock on the longer term. Discussion. Our simulations indicate that the femoral implant and cement mantle are not at risk of failure during gait. Moreover, the hypothesis that stress shielding can be reduced by a polymer implant is corroborated by this model. ISO loads can be considered an underestimation and so we intend to expand the model with more comprehensive loading regimes, based on musculoskeletal simulations of gait as well as more arduous physical activities. We plan to include activities like squatting or stair ascending as they are likely to be more detrimental to the implant performance

The effects of metal ion release and wear particle debris in metal-on-metal articulation warrants an investigation of alternative material, like ceramics, as a low-wear bearing couple [1]. Short-stem resurfacing femoral implant, with a stem-tip located at the centre of the femoral head, appears to provide a better physiological load transfer within the femoral head and therefore seems to be a promising alternative to the long-stem design [2]. The objective of this study was to investigate the effect of evolutionary bone adaptation on load transfer and interfacial failure in cemented metallic and ceramic resurfacing implant. Bone geometry and material properties of 3D finite element (FE) models (intact, short-stem metallic and ceramic resurfaced femurs of 44 mm head diameter) were derived from the CT scan data. The FE models consisted of 170352 quadratic tetrahedral elements and 238111 nodes with frictional contact at the implant-cement (μ = 0.3) and stem-bone interfaces (μ = 0.4) and fully bonded cement-bone interface. Normal walking and stair climbing were considered as two different loading conditions. A time-dependant “site specific” bone remodelling simulation was based on the strain energy density and internal free surface area of bone [3]. The variable time-step was determined after each remodelling iteration. The Hoffman failure criterion was used to assess cement-bone interfacial failure. Predicted change in bone density due to bone remodelling was very much similar in both the metallic and ceramic resurfaced femurs (Fig. 1). Both the metallic and ceramic implant resulted in strain reduction in the proximal regions (Region of interest, ROI 2 and 4) and subsequent bone resorption, average bone density reduction by 72% (Fig. 1). Higher strains were generated in ROI 5 and 7, which caused bone apposition, an average increase in bone density of 145% (Fig. 1). The tensile stresses in the resurfacing implants increased with change in bone density; a maximum stress of 83 MPa and 63 MPa were observed in the ceramic and the metallic implants, respectively. The tensile stress in the cement mantle also increased with bone remodelling. Although the cement-bone interface was secure against interface debonding in the post-operative situation, calculations of Hoffman number indicated that risk of cement-bone interfacial failure was increased with peri-prosthetic bone adaptation. During the remodelling simulation, maximum tensile stress in the implant and the cement was far below its strength. However, with bone adaptation greater volume of cement mantle was exposed to higher stresses which, in-turn, resulted in greater risk of interfacial failure around the periphery of the cement mantle. Both the short-stem ceramic and metallic resurfacing component, under debonded stem-bone interface, resulted in more physiological stress distribution across the femoral head. Based on these results, short-stem ceramic resurfacing component appears to be a viable alternative to the metallic design