Aims. Cemented hemiarthroplasty is an effective form of treatment for most patients with an intracapsular fracture of the hip. However, it remains unclear whether there are subgroups of patients who may benefit from the alternative operation of a modern uncemented hemiarthroplasty – the aim of this study was to investigate this issue. Knowledge about the heterogeneity of treatment effects is important for surgeons in order to target operations towards specific subgroups who would benefit the most. Methods. We used causal forest analysis to compare subgroup- and individual-level treatment effects between cemented and modern uncemented hemiarthroplasty in patients aged > 60 years with an intracapsular fracture of the hip, using data from the World Hip Trauma Evaluation 5 (WHiTE 5) multicentre randomized clinical trial. EuroQol five-dimension index scores were used to measure health-related quality of life at one, four, and 12 months postoperatively. Results. Our analysis revealed a complex landscape of responses to the use of a cemented hemiarthroplasty in the 12 months after surgery. There was heterogeneity of effects with regard to baseline characteristics, including age, pre-injury health status, and lifestyle factors such as alcohol consumption. This heterogeneity was greater at the one-month mark than at subsequent follow-up timepoints, with particular regard to subgroups based on age. However, for all subgroups, the effect estimates for quality of life lay within the confidence intervals derived from the analysis of all patients. Conclusion. The use of a cemented hemiarthroplasty is expected to increase health-related quality of life compared with modern uncemented hemiarthroplasty for all subgroups of patients aged > 60 years with a displaced intracapsular fracture of the hip. Cite this article: Bone Joint J 2024;106-B(7):656–661

In the UK, multidisciplinary teamwork for patients with hip fracture has been shown to reduce mortality and improves health-related quality of life for patients, while also reducing hospital bed days and associated healthcare costs. However, despite rapidly increasing numbers of fragility fractures, multidisciplinary shared care is rare in low- and middle-income countries around the world. The HIPCARE trial will test the introduction of multidisciplinary care pathways in five low- and middle-income countries in South and Southeast Asia, with the aim to improve patients’ quality of life and reduce healthcare costs. Cite this article: Bone Joint J 2024;106-B(12):1369–1371

Aims

Periprosthetic fractures (PPFs) following hip arthroplasty are complex injuries. This study evaluates patient demographic characteristics, management, outcomes, and risk factors associated with PPF subtypes over a decade.

Aims. A fracture of the hip is the most common serious orthopaedic injury, and surgical site infection (SSI) is one of the most significant complications, resulting in increased mortality, prolonged hospital stay and often the need for further surgery. Our aim was to determine whether high dose dual antibiotic impregnated bone cement decreases the rate of infection. Patients and Methods. A quasi-randomised study of 848 patients with an intracapsular fracture of the hip was conducted in one large teaching hospital on two sites. All were treated with a hemiarthroplasty. A total of 448 patients received low dose single-antibiotic impregnated cement (control group) and 400 patients received high dose dual-antibiotic impregnated cement (intervention group). The primary outcome measure was deep SSI at one year after surgery. Results. The rate of deep SSI was 3.5% in the control group and 1.1% in the intervention group (p = 0.041; logistic regression adjusting for age and gender). The overall rate of non-infective surgical complications did not differ between the two groups (unadjusted chi-squared test; p > 0.999). Conclusion. The use of high dose dual-antibiotic impregnated cement in these patients significantly reduces the rate of SSI compared with standard low dose single antibiotic loaded bone cement. Cite this article: Bone Joint J 2016;98-B:1534–1541

Purpose of the study: Few data are available concerning the proper management of patients with a periprosthetic fracture of the hip who presents biological signs of inflammation (increased WBC, sedimentation rate, or C-reactive protein). The purpose of this work was to determine the prevalence of elevated biological markers in this type of patient and to determine the reliability of such markers for the diagnosis of periprosthetic infection. Material and methods: A periprosthetic hip fracture was diagnosed in 204 patients from 2000 to 2006. The WBC count, the sedimentation rate and the serum CRP level were noted at admission to the emergency ward. The diagnosis of infection was confirmed by at least two positive bacteriological samples of tissue biopsy and/or joint fluid collected at surgery. A statistical analysis was conducted to determine the prevalence of elevated biological markers of inflammation, the sensitivity, their specificity and their positive predictive value for deep infection. Results: Twenty-one patients (11.6%) developed a periprosthetic infection. Among the 204 patients, the WBC count increased in 16.2%, sedimentation rate in 33.3% and CRP in 50.5%. The sensitivity was 24% (WBC), 50% (sedimentation rate) and 83% (CRP). The specificity was 85% (WBC), 69% (sedimentation rate) and 56% (CRP). The positive predictive value was low (18, 21 and 29% respectively). Discussion: Markers of inflammation are frequently ordered before surgery to search for infection but can be elevated for various reasons. Most often, these markers are elevated because of the patient’s general status and are thus related to other co-morbid conditions and/or reaction to the new fracture. In this population, the WBC count did not contribute to the diagnosis of infection as only 24% of the infected patients had a high count. CRP and sedimentation rate and the WBC count had low positive predictive values. Conclusion: This study shows that an isolated elevation of biological markers of inflammation in a patient with a periprosthetic fracture is not a good indicator of infection

Aim: Hip fracture is the most devastating outcome of osteoporosis with high early mortality. Less is known about men in terms of long-term survival and fracture risk, information of outmost importance in terms of strategies for fracture prevention. The aim of this study was to evaluate long-term survival, new fractures and residual life time risk of fracture in a cohort of men with hip fracture in different ages. This is the first study with a follow-up above 10 years. Methods: All men above 20 yrs of age suffering a hip fracture 1984–1985 in Malmö, Sweden were identified and followed up to 22 years or death. All new radiographic examinations related to musculoskeletal trauma with or without fracture were individually registered. Survival and fractures were evaluated in 5-year age bands and age-groups (< 75, 75–84 and ≥85 years). Kaplan Meier survival analyses were used to evaluate mortality and fracture risk. Results: 263 men (74.2 yrs, range 33–101) with an index hip fracture due to low energy trauma were identified. 56% had cervical fractures and 44% trochanteric with 6% having concomitant fractures. 10 % had suffered a previous hip fracture. After 22 years 94% were dead; 32 % within 1 yr, 62% within 5 yrs and 79% within 10yrs. Mean age at death was 80.1 yr (range 41–101), equal to a mean of 5.8 yrs above the mean age for fracture. The 50% survival in respectively age groups < 75, 75–84 and ≥ 85 years was 7 yrs, 2 yrs and 3 months. 74/263 (28%) suffered totally 131 fractures (1.8, range 1–7 fractures/patient) at 121 occasions. The majority suffered only a new fracture at one occasion (n=48, 65%). 14% of the fracture occasions occurred within 1 yr and half of the fractures occurred within 3.2 yrs. Mortality adjusted life time risk of fracture was 62% and 10-year risk of fracture was 47%. Conclusion: In this study we report fracture risk and mortality in a residual life time perspective in men after hip fracture. Men suffer hip fractures earlier in life and have, compared to women from the same cohort, higher early mortality (32% resp 21% (1 yr)) and lower residual lifetime risk of fracture (28% resp 45%). 1. The high early mortality probably mirrors a higher morbidity among male hip fracture patients. The consequence is that fracture preventing strategies need to consider both gender, age and mortality

Aims. Surgical treatment of hip fracture is challenging; the bone is porotic and fixation failure can be catastrophic. Novel implants are available which may yield superior clinical outcomes. This study compared the clinical effectiveness of the novel X-Bolt Hip System (XHS) with the sliding hip screw (SHS) for the treatment of fragility hip fractures. Methods. We conducted a multicentre, superiority, randomized controlled trial. Patients aged 60 years and older with a trochanteric hip fracture were recruited in ten acute UK NHS hospitals. Participants were randomly allocated to fixation of their fracture with XHS or SHS. A total of 1,128 participants were randomized with 564 participants allocated to each group. Participants and outcome assessors were blind to treatment allocation. The primary outcome was the EuroQol five-dimension five-level health status (EQ-5D-5L) utility at four months. The minimum clinically important difference in utility was pre-specified at 0.075. Secondary outcomes were EQ-5D-5L utility at 12 months, mortality, residential status, mobility, revision surgery, and radiological measures. Results. Overall, 437 and 443 participants were analyzed in the primary intention-to-treat analysis in XHS and SHS treatment groups respectively. There was a mean difference of 0.029 in adjusted utility index in favour of XHS with no evidence of a difference between treatment groups (95% confidence interval -0.013 to 0.070; p = 0.175). There was no evidence of any differences between treatment groups in any of the secondary outcomes. The pattern and overall risk of adverse events associated with both treatments was similar. Conclusion. Any difference in four-month health-related quality of life between the XHS and SHS is small and not clinically important. There was no evidence of a difference in the safety profile of the two treatments; both were associated with lower risks of revision surgery than previously reported. Cite this article: Bone Joint J 2021;103-B(2):256–263

Introduction: Hip resurfacing is a good conservative option for young patients with arthritis. Resurfacings risk two unique failure mechanisms that do not occur in THA, i.e. femoral neck fracture and femoral head collapse. Old age, osteopaenia, alcohol abuse, and large cysts are risk factors for fractures. It has been suggested that performing a bilateral resurfacing puts the first side at risk of fracture from the force used in implanting the second resurfacing. Is this a true risk or a sampling error?. Methods: Out of 2576 consecutive resurfacings performed by the senior author (July 1997 – May 2005), 191 patients (382 hips, 14.8% of all resurfacings) presented with bilateral arthritis and had both hips operated in the same hospital admission. 133 patients had the two operations a week apart and 58 had both the same day. A posterior approach was used in all cases with the patient in the lateral position on the contralateral side. Results: Of the 382 resurfacings, only two failed from a femoral neck fracture. Both had the second operation a week after the first. A 35-year lady (rheumatoid arthritis) sustained a femoral neck fracture of the first hip following a fall nine weeks after the operation. A 57-year man (osteoarthritis) fractured his femoral neck at 3.5 months. He fractured the side operated second. Discussion: The incidence of femoral neck fracture in the author’s series of 2576 resurfacings is 0.4%. Patients who present with bilateral severe arthritis are more likely to have non-primary OA such as inflammatory arthritis. It is difficult to conclude if such bilateral cases are more predisposed to a fracture by virtue of the pathology itself. The low incidence of fractures (2/382, 0.5%) in this bilateral resurfacing series does not support the view that there is an increased risk of fracture from a bilateral procedure

Femoral neck fracture is a common short-term hip resurfacing failure mode, but later term fractures are starting to be reported. The fracture pattern may indicate whether etiology is primarily mechanical or biological¹. This study evaluated fracture patterns in conjunction with histology to determine etiology in a varied group of hip resurfacings.

Central 3mm thick coronal slices were cut from each of 50 cemented and 2 cementless fractured femoral components (27 males, 25 females). Fracture patterns were grouped as: “edge to edge”, “inside head”, “outside” and “edge to outside”¹. Sections were decalcified and processed for routine histology to examine viability and remodelling. Bone viability was judged on the presence of osteocyte nuclei. Components were judged to be unseated if the cement mantle was more than twice the manufacturers recommended thickness. Histological and clinical data were correlated with fracture pattern.

Overall average time to fracture was 6 months (1–85 months). There were 25 “edge to edge”, 12 “inside head”, 4 “outside” and 11 “edge to outside” fractures, which occurred after a median of 2.0, 13, 1.5, and 2.0 months respectively. The majority of the heads were viable, and the fractures occurred through a region of healing bone involving one or both edges. Fifteen heads with a substantial proximal avascular segment fractured at the interface between necrotic and viable bone, typically inside the component. Eleven implants (21%) were considered unseated. All 4 “outside” fractures were found to be unseated. All “inside head” fractures were seated, but 83% (10/12) of them were found to be avascular. The latest failure (85 months) occurred in association with wear-induced osteolysis. Both cementless components fractured early with an “edge to outside” pattern and were found to be substantially avascular.

Avascular heads failed from one month to four years, usually inside the component. Viable heads tended to fracture early through an area of healing bone at or below the rim. Most fractures were technical failure-sand might be avoided with better patient selection and surgical technique.

Aims

The risk of mechanical failure of modular revision hip stems is frequently mentioned in the literature, but little is currently known about the actual clinical failure rates of this type of prosthesis. The current retrospective long-term analysis examines the distal and modular failure patterns of the Prevision hip stem from 18 years of clinical use. A design improvement of the modular taper was introduced in 2008, and the data could also be used to compare the original and the current design of the modular connection.

Metal-on-metal hip resurfacing prostheses are a relatively recent intervention for relieving the symptoms of common musculoskeletal diseases such as osteoarthritis. While some short term clinical studies have offered positive results, in a minority of cases there is a recognised issue of femoral fracture, which commonly occurs in the first few months following the operation. This problem has been explained by a surgeon's learning curve and notching of the femur but, to date, studies of explanted early fracture components have been limited.

Tribological analysis was carried out on fourteen retrieved femoral components of which twelve were revised after femoral fracture and two for avascular necrosis (AVN). Eight samples were Durom (Zimmer, Indiana, USA) devices and six were Articular Surface Replacements (ASR, DePuy, Leeds, United Kingdom). One AVN retrieval was a Durom, the other an ASR. The mean time to fracture was 3.4 months. The AVNs were retrieved after 16 months (Durom) and 38 months (ASR).

Volumetric wear rates were determined using a Mitutoyo Legex 322 co-ordinate measuring machine (scanning accuracy within 1 micron) and a bespoke computer program. The method was validated against gravimetric calculations for volumetric wear using a sample femoral head that was artificially worn in vitro. At 5mm3, 10mm3, and 15mm3 of material removal, the method was accurate to within 0.5mm3. Surface roughness data was collected using a Zygo NewView500 interferometer (resolution 1nm).

Mean wear rates of 17.74mm3/year were measured from the fracture components. Wear rates for the AVN retrievals were 0.43mm3/year and 3.45mm3/year. Mean roughness values of the fracture retrievals (PV = 0.754nm, RMS = 0.027nm) were similar to the AVNs (PV = 0.621nm, RMS = 0.030nm), though the AVNs had been in vivo for significantly longer.

Theoretical lubrication calculations were carried out which found that in both AVN retrievals and in seven of the twelve cases of femoral fracture the roughening was sufficient to change the lubrication regime from fluid film to mixed. Three of these surfaces were bordering on the boundary lubrication regime. The results show that even before the femoral fracture, wear rates and roughness values were high and the implants were performing poorly.

Introduction

Austin Moore cervicocephalic prostheses have been a therapeutical option for femoral neck fractures in patients with a reduced general condition for many years. Since treatments other than total hip arthroplasties have also been included in National arthroplasty registers during the last decade, adequate reference data for comparative analyses have recently become available.

Metal-on-metal hip resurfacing prostheses are a relatively recent intervention for relieving the symptoms of common musculoskeletal diseases such as osteoarthritis. While some short term clinical studies have offered positive results, in a minority of cases there is a recognised issue of femoral fracture, which commonly occurs in the first few months following the operation. This problem has been explained by a surgeon's learning curve and notching of the femur but, to date, studies of explanted early fracture components have been limited.

Tribological analysis was carried out on fourteen retrieved femoral components of which twelve were revised after femoral fracture and two for avascular necrosis (AVN). Eight samples were Durom (Zimmer, Indiana, USA) devices and six were Articular Surface Replacements (ASR, DePuy, Leeds, United Kingdom). One AVN retrieval was a Durom, the other an ASR. The mean time to fracture was 3.4 months. The AVNs were retrieved after 16 months (Durom) and 38 months (ASR).

Volumetric wear rates were determined using a Mitutoyo Legex 322 co-ordinate measuring machine (scanning accuracy within 1 micron) and a bespoke computer program. The method was validated against gravimetric calculations for volumetric wear using a sample femoral head that was artificially worn in vitro. At 5mm³, 10mm³, and 15mm³ of material removal, the method was accurate to within 0.5mm³. Surface roughness data was collected using a Zygo NewView500 interferometer (resolution 1nm).

Mean wear rates of 17.74mm³/year were measured from the fracture components. Wear rates for the AVN retrievals were 0.43mm³/year and 3.45mm³/year. Mean roughness values of the fracture retrievals (PV = 0.754, RMS = 0.027) were similar to the AVNs (PV = 0.621, RMS = 0.030), though the AVNs had been in vivo for significantly longer.

Theoretical lubrication calculations were carried out which found that in both AVN retrievals and in seven of the twelve cases of femoral fracture the roughening was sufficient to change the lubrication regime from fluid film to mixed. Three of these surfaces were bordering on the boundary lubrication regime. The results show that even before the femoral fracture, wear rates and roughness values were high and the implants were performing poorly.

Introduction: Previous studies have demonstrated the value of the tip-apex distance (TAD) and the location of the screw in the femoral head in predicting cut-out. Similarly surgeons’ volume has been shown to affect mortality and morbidity in various surgical specialties, including in trauma and orthopaedics. Aim: To determine whether re-operation due to cut out at six month can be predicted using TAD, location of the screw and fracture type; and whether the experience of the surgeon is important. Methods: Logistic regression was used to analyse data collected retrospectively from 241 patients with extracapsular fractures (Jensen’s modification of Evans’ classification: Class I – 90, Class II – 93 and Class III – 58), treated with a dynamic hip screw, classic hip screw or intramedullary hip screw from April 2005 to October 2007. Results: There were 7 cut outs (2.5%) requiring re-operation within 6 months – 1 in the consultant group and 6 in the trainee group,. The model used was statistically significant (X2=23.6 [13df], p< 0.05). The tip-apex distance was a strong predictor (p< 0.05) of cut-out requiring re-operation at six months. The odds of the patient requiring re-operation due to cut out increases by a factor of 1.2 for each millimetre increase in the TAD. Location of the hip screw and fracture type were however not significant predictors. The first surgeon was a consultant in 54 cases and trainee in 187 cases. There was no statistically significant difference in re-operation rate due to cut out between patients operated on by consultants compared to trainees. Conclusion: The TAD is a strong predictor of cut out requiring re-operation at 6 months. No difference was found in our series in re-operation rate due to cut out among cases performed by consultants compared to trainees

Introduction and Aims: Severe central fracture dislocations of the hip in the elderly can be catastrophic events. Conservative treatment yields poor results with stiff painful hips. We assessed the results of three patients treated with a total hip replacement for a central fracture dislocation of the hip, using ante-protrusio supports and bone grafts. Method: Three elderly patients with central fracture dislocations were treated with early total hip replacement utilising ante-protrusio supports. Bone grafting was used to re-establish acetabular bone stock. Intra and post-operatively these patients had no more complications than a comparable group undergoing hip replacement for femoral neck fractures. The surgical times were longer than for routine hip replacment, and blood replacement requirements was slightly higher. Patients were mobilised early and aggressively. Results: All became independent walkers. All regained a good range of movement. Radiologically the acetabular/pelvic fractures united and good bone-implant interfaces were obtained. There was no excessive heterotrophic bone formation. The economic assessment indicated that it was more cost-effective to treat these patients with a hip replacement than with alternative methods. Conclusion: We regard total hip replacements in the management of acetabular fractures in the elderly as a reasonable approach, enabling our patients to mobilise early and keeping morbidity to an acceptable level. The procedure is also more cost-effective than internal fixation and delayed arthroplasty

Introduction: Among numerous international studies on hip fractures only few were dealing with the occurrence and risk of a subsequent hip fracture. Some studies contain information identifying patients at risk of subsequent hip fractures as well as the risk of a hip fracture following another osteoporotic fracture, others on outcome following the subsequent fracture. Material and methods: The Funen County Hip Fracture Register contains information on every consecutive hip fracture in the county of Funen since January 1st 996. The register contains general information about the patient i.e.: type of fracture, operative treatment, complications, living conditions, ADL, as well as information from 4 and 12 month out-patient visit and if necessary re-surgery. A maximum of 155 variables can be recorded about every patient. The register has been subjected to a complete revision and validation (4.660 patient files was checked) and contained a total number of 7.457 hip fractures from January 1st 1996 to December 31st 2003. Incidence numbers were calculated based on risk of fracture from the first fracture since January 1st 1996 to death or December 31st 2003. Results: In the period January 1st 1996 to December 31st 2003, 7,457 fractures were registered. Of these, 261 patients were registered with a second fracture, the primary fracture occurring before the period and thus excluded. Within the period 6,676 primary fractures were registered, and of these 520 patients (7.5 %) experienced a subsequent fracture. The median time from primary to subsequent fracture was 8 months (range 0–75 months) in males and 14 months (range 0–82 months) in females, the overall median was 13.5 months (range 0–82 months). In males the risk of dying after the primary hip fracture was 10 times higher than the risk of sustaining a subsequent hip fracture, in females it was five times higher. Conclusion: Only few patients with a hip fracture will experience a subsequent hip fracture and with the short time frame presented, any intervention should have immediate impact

Femoral head fractures i.e. Pipkin fractures are uncommon injuries and there are very few large series in literature with reported outcomes. There remain many controversies regarding diagnosis and management. This study, which is the largest single surgeon experience, is an attempt to get answers to some of these controversies.

This series is an analysis of 51 patients with femoral head fractures. There were 44 males and seven females. The right side was involved in 36 and left in 16 patients. According to Pipkin classification these were 13 Pipkin-I, 27 Pipkin-11, three Pipkin-111 and eight Pipkin-IV fractures. Thirty-two patients were managed by surgical intervention. The surgical approach was posterior in Pipkin-I and in seven cases of Pipkin-II fractures. Another eight Pipkin II cases were managed surgically by anterior Smith-Peterson approach while another eight fractures were accessed by posterior approach with flip osteotomy. The Pipkin III and IV cases were managed using surgical approaches that varied depending on the pattern of associated acetabular injury. The fractured fragment, if small, was excised and, if large, was re-fixed using small fragment partially threaded cancellous screw. Follow-up of two to eight years was available in 39 cases.

Using Thompson and Epstein criteria, 26 patients were rated as having good results, eight fair and five poor results. Early osteoarthritic changes were seen in five patients, avascular necrosis of the femoral head in three patients and one patient had re-fracture in same hip during an epileptic fit with subsequent fixation problems. Of four patients with sciatic nerve injury, two had persisting motor deficit. There was one case of heterotopic ossification.

Most Pipkin-I fractures can be managed by closed reduction, Pipkin-II fractures usually require ORIF. The best results have been obtained by a Smith-Peterson approach if the hip has already been reduced, but posterior approach with flip osteotomy offers the best exposure if the hip is still unreduced. Pipkin III patients need hip replacement if presentation is late, while ORIF gives acceptable outcome in Pipkin IV fractures.

We aimed to establish if radiological parameters, dual energy x-ray absorbtiometry (DEXA) and quantitative CT (qCT) could predict the risk of sustaining a femoral neck fracture following hip resurfacing.

Twenty-one unilateral fresh frozen femurs were used. Each femur had a plain AP radiograph, DEXA scan and quantitative CT scan. Femurs were then prepared for a Birmingham Hip Resurfacing femoral component with the stem shaft angle equal to the native neck shaft angle. The femoral component was then cemented onto the prepared femoral head. No notching of the femoral neck occurred in any specimens. A repeat radiograph was performed to confirm the stem shaft angle. The femurs were then potted in a position of single leg stance and tested in the axial direction to failure using an Instron mechanical tester. The load to failure was then analysed with the radiological, DEXA and qCT parameters using multiple regression.

The strongest correlation with the load to failure values was the total mineral content of the femoral neck at the head/neck junction using qCT r= 0.74 (p< 0.001). This improved to r=0.76 (p< 0.001) when neck width was included in the analysis. The total bone mineral density measurement from the DEXA scan showed a correlation with the load to failure of r=0.69 (p< 0.001). Radiological parameters only moderately correlated with the load to failure values; neck width (r=0.55), head diameter (r= 0.49) and femoral off-set (r=0.3).

This study suggests that a patient’s risk of femoral neck fracture following hip resurfacing is most strongly correlated with total mineral content at the head/neck junction and bone mineral density. This biomechanical data suggests that the risk of post-operative femoral neck fracture may be most accurately identified with a pre-operative quantitative CT scan through the head/neck junction combined with the femoral neck width.

We aimed to establish if radiological parameters, dual energy x-ray absorbtiometry (DEXA) and quantitative CT (qCT) could predict the risk of sustaining a femoral neck fracture following hip resurfacing. 21 unilateral fresh frozen femurs were used. Each femur had a plain AP radiograph, DEXA scan and quantitative CT scan. Femurs were then prepared for a Birmingham Hip Resurfacing femoral component with the stem shaft angle equal to the native neck shaft angle. The femoral component was then cemented onto the prepared femoral head. No notching of the femoral neck occurred in any specimens. A repeat radiograph was performed to confirm the stem shaft angle. The femurs were then potted in a position of single leg stance and tested in the axial direction to failure using an Instron mechanical tester. The load to failure was then analysed with the radiological, DEXA and qCT parameters using multiple regression. The strongest correlation with the load to failure values was the total mineral content of the femoral neck at the head/neck junction using qCT r= 0.74 (p< 0.001). This improved to r=0.76 (p< 0.001) when neck width was included in the analysis. The total bone mineral density measurement from the DEXA scan showed a correlation with the load to failure of r=0.69 (p< 0.001). Radiological parameters only moderately correlated with the load to failure values; neck width (r=0.55), head diameter (r= 0.49) and femoral off-set (r=0.3). This study suggests that a patient’s risk of femoral neck fracture following hip resurfacing is most strongly correlated with total mineral content at the head/neck junction and bone mineral density. This biomechanical data suggests that the risk of post-operative femoral neck fracture may be most accurately identified with a pre-operative quantitative CT scan through the head/neck junction combined with the femoral neck width.

Introduction: A unique failure mode of hip resurfacing is femoral neck fracture. These tend to occur early after surgery during normal activities. One theory regarding fracture occurrence includes the introduction of stress magnifiers in the form of notches on the superior neck. The presence of a notch can arise from reaming or from removal of osteophytes during surgery. The aim of the present study was to investigate the effect of notching the femoral neck, following resurfacing by using a finite element (FE) model.

Methods: A physiological load case was simulated in the FE model of a femur, implanted with a cemented hip resurfacing system. Twelve implant alignments were modelled: an ideal implant alignment with no notch, and a 1 mm, 3 mm, 5 mm and 7 mm superior notch; 5° anteversion, 5° and 10° degrees retroversion; 5° and 10° degrees in varus and valgus. These models were compared to that of an intact femur for baseline analysis.

The intact femur geometry was derived from a CT dataset of a cadaveric femur and CT numbers were converted into a realistic distribution of material properties. The FE intact mesh was based on an experimentally validated mesh of a human femur. The femur was segmented into 22 neck sections.

The loading condition was modelled to represent an instant at 10% of gait where all muscle forces were included. The femoral neck regions were compared between the models to evaluate the effect of notch sizes on stress distribution. Maximum tensile stresses were compared to the ultimate tensile stress (UTS) of cortical and cancellous bone.

Results: As the notch size increased the peak and average 1st (tensile) and 3rd (compressive) principal stress increased along the superior portion of the femoral neck. For the 5 mm superior notch, the maximum 1st principal stress increased by 283% and 154% when compared to that of the ideally aligned implant and the intact femur respectively. The largest increase of tensile stress was observed when the implant was mal-aligned in 10° of varus; this resulted in a 768% increase in stress compared to the ideally implanted model.

Discussion: The introduction of a superior notch causes a stress concentration on the femoral neck. Although the stress concentration is pronounced, a notch on the superior aspect of the femoral neck may not lead to fracture following resurfacing; the UTS of cortical bone is 100MPa, and the UTS of cancellous bone is between 2MPa and 20MPa. Peak stresses in the model are well below the UTS of cortical bone, and for damage to accumulate in cancellous bone, energy absorption in the ‘honey-comb’ structure of trabecular bone must be considered. Varus mal-alignment resulted in the largest increase in tensile stress on the superior aspect of the neck, and has been associated with femoral neck fracture; this type of mal-alignment may be critical when considering femoral neck fractures.