Risk Factors Affecting Outcome of Metal-on-Metal Surface Arthroplasty of the Hip:

State of the art in hard-on-hard bearings: how did we get here and what have we achieved?

Total hip arthroplasty has shown excellent results in decreasing pain and improving function in patients with degenerative disease of the hip. Improvements in prosthetic materials, designs and implant fixation have now resulted in wear of the bearing surface being the limitation of this technology, and a number of hard-on-hard couples have been introduced to address this concern. The purpose of this article is to review the origins, development, survival rates and potential advantages and disadvantages of the following hard-on-hard bearings for total hip arthroplasty: metal-on-metal standard total hip arthroplasty; metal-on-metal hip resurfacing arthroplasty, ceramic-on-ceramic total hip arthroplasty; and ceramic-on-metal bearings. Improvements in the manufacturing of metal-on-metal bearings over the past 50 years have resulted in implants that provide low wear rates and allow for the use of large femoral heads. However, concerns remain regarding elevated serum metal ion levels, potential teratogenic effects and potentially devastating adverse local tissue reactions, whose incidence and pathogenesis remains unclear. Modern total hip resurfacing has shown excellent outcomes over 10 years in the hands of experienced surgeons. Current ceramic-on-ceramic bearings have demonstrated excellent survival with exceptionally low wear rates and virtually no local adverse effects. Concerns remain for insertional chipping, in vivo fracture and the variable incidence of squeaking. Contemporary ceramic-on-metal interfaces are in the early stages of clinical use, with little data reported to date. Hard-on-hard bearings for total hip arthroplasty have improved dramatically over the past 50 years. As bearing designs continue to improve with new and modified materials and improved manufacturing techniques, it is likely that the use of hard-on-hard bearings will continue to increase, especially in young and active patients.

Recovery in mechanical muscle strength following resurfacing vs standard total hip arthroplasty - a randomised clinical trial

OBJECTIVES

To evaluate the effect of resurfacing vs standard total hip replacement on post-surgery hip and knee muscle strength recovery in a prospective randomised controlled trial at the Department of Orthopaedics, University Hospital, Odense, Denmark.

METHODS

Forty-three patients were randomised into (A) standard total hip arthroplasty (S-THA) and (B) resurfacing total hip arthroplasty (R-THA). Pre-surgery assessment and follow-up were conducted (8, 26 and 52 wks). Maximal isometric muscle strength (Nm) and between-limb asymmetry for the knee extensors/flexors, hip adductors/abductors, hip extensors/flexors were analysed.

RESULTS

Maximal knee extensor and hip abductor strength were higher in S-THA than R-THA at 52 wks post-surgery (P ≤ 0.05) and hip extensors tended to be higher in S-THA at 52 wks (P = 0.06). All muscle groups showed substantial between-limb strength asymmetry (7-29%) with the affected side being weakest (P ≤ 0.05) and hip flexors being most affected. Asymmetry was present in half of the muscle groups at 26 wks (P ≤ 0.05), and remained present for the hip flexors and hip adductors at 52 wks (P ≤ 0.05).

CONCLUSIONS

R-THA patients showed an attenuated and delayed recovery in maximal lower limb muscle strength (in 2/6 muscle groups) compared to S-THA. Notably, the attenuated strength recovery following R-THA was most markedly manifested in the late phase (1 yr) of post-surgical recovery, and appeared to be due to the detachment of the lower half of the gluteus maximus muscle rather than implant design per se. Thus, the present data failed to support the hypothesis that R-THA would result in an enhanced strength rehabilitation compared to S-THA. Further, between-limb asymmetry remained present for hip flexors and adductors after 52 wks.

TRIAL REGISTRATION

NCT01229293.

Hip resurfacing arthroplasty: a series of 140 consecutive hips with a minimum five year follow-up. A clinical, radiological and histological analysis

We reviewed the clinical and radiological outcome at a minimum of five years of 140 consecutive metal-on-metal hip resurfacing (HR) arthroplasties in 132 patients. The mean follow-up was 73 months (62 to 105). Revision of either component was defined as failure. The average Harris hip score (HHS) was 58.6 (25 to 88) preoperatively and 94.4 (60 to 100) at the latest follow-up (p<0.0005). Average University of California Los Angeles (UCLA) activity score was 3.1 (1 to 9) pre-operatively and 6.7 (2 to 10) post-operatively (p<0.0005). The survival after 6 years was 97.8% overall and 98.5% (excluding a post traumatic femoral neck fracture). These good medium-term results suggest that HR is an effective procedure in young and active patients.

Prevalence of dysplasia as the source of worse outcome in young female patients after hip resurfacing arthroplasty

PURPOSE

Smaller femoral component size has been implicated as underlying the risk factor that explains the higher failure rate in women who have a hip resurfacing arthroplasty (HRA). We suspect that the diagnosis of dysplasia may be a more important causative risk factor than either small component size or female gender.

METHODS

From January 2002 to July 2008, a total of 1,216 HRA cases, 1,082 with the primary diagnosis of osteoarthritis and 134 with dysplasia, were included in this study. Of them, 867 cases were performed in men and 349 performed in women. The average femoral component size was 51 ± 4 mm. Cox proportional hazard regression models were used to evaluate the significance of each variable and determine the causative risk factors for failure.

RESULTS

The average follow-up was 5 ± 2 years. Thirty-nine cases failed (20 in men vs. 19 in women). The failure rate for the whole group was 3.2% (2.3% in men vs. 5.4% in women; P = 0.01). Dysplasia (P = 0.05) was identified as the only significant risk factor in our multi-variable analysis; small femoral component size (P = 0.09) and gender (P = 0.76) were not significant risk factors. Women with the primary diagnosis of dysplasia had a survivorship rate of only 75% compared to 93% for the entire group at eight-year follow-up post-operatively.

CONCLUSIONS

In our study, we found that the high incidence of dysplasia in young women undergoing HRA was the reason that women had a higher failure rate after HRA. In dysplasia, 70% of failures were due to acetabular problems, of which 50% were due to failure of fixation and 20% due to adverse wear.

Silent soft tissue pathology is common with a modern metal-on-metal hip arthroplasty

BACKGROUND AND PURPOSE

Adverse reactions to metal debris have been reported to be a cause of pain in metal-on-metal hip arthroplasty. We assessed the incidence of both symptomatic and asymptomatic adverse reactions in a consecutive series of patients with a modern large-head metal-on-metal hip arthroplasty.

METHODS

We studied the early clinical results and results of routine metal artifact-reduction MRI screening in a series of 79 large-head metal-on-metal hip arthroplasties (ASR; DePuy, Leeds, UK) in 68 patients. 75 hips were MRI scanned at mean 31 (12-52) months after surgery.

RESULTS

27 of 75 hips had MRI-detected metal debris-related abnormalities, of which 5 were mild, 18 moderate, and 4 severe. 8 of these hips have been revised, 6 of which were revised for an adverse reaction to metal debris, diagnosed preoperatively with MRI and confirmed histologically. The mean Oxford hip score (OHS) for the whole cohort was 21. It was mean 23 for patients with no MRI-based evidence of adverse reactions and 19 for those with adverse reactions detected by MRI. 6 of 12 patients with a best possible OHS of 12 had MRI-based evidence of an adverse reaction.

INTERPRETATION

We have found a high early revision rate with a modern, large-head metal-on-metal hip arthroplasty. MRI-detected adverse rections to metal debris was common and often clinically "silent". We recommend that patients with this implant should be closely followed up and undergo routine metal artifact-reduction MRI screening.

A survey on the prevalence of pseudotumors with metal-on-metal hip resurfacing in Canadian academic centers

BACKGROUND

Metal-on-metal bearings for hip arthroplasty have been in clinical use for over twenty years with excellent clinical results reported worldwide. A small percentage (<1%) of patients have developed an inflammatory response, and a more severe inflammatory response termed pseudotumor has been more recently reported. The primary purpose of this study was to determine the prevalence of pseudotumor following metal-on-metal hip resurfacing in Canadian academic centers.

METHODS

Nine of the fourteen centers that perform metal-on-metal hip resurfacings were surveyed. The number of metal-on-metal hip resurfacing arthroplasties performed at each center was determined, as was the number of patients who presented with a pseudotumor and subsequently required revision hip surgery between 2002 and December 2008.

RESULTS

At the nine centers, 3432 hip resurfacing arthroplasties were performed; 76.9% of the patients were male, the mean age was 51.2 years (range, sixteen to eighty-three years), and the mean body-mass index was 28.1 (range, 17 to 55). The mean length of follow-up was 3.4 years (range, two to nine years). A pseudotumor developed after four of the 3432 arthroplasties, for a prevalence of 0.10%.

CONCLUSIONS

Although pseudotumors remain a concern after metal-on-metal hip resurfacing, the prevalence at short to midterm follow-up is very low in this multicenter survey. Continued close monitoring is required to determine what clinical factors are involved with the uncommon pseudotumor formation.

Evolution in hip resurfacing design and contemporary experience with an uncemented device

The concepts of surface replacement of the hip and metal-on-metal articulation date back to the 1930s, and recent hip resurfacing designs have been more successful than their predecessors. Experience with the Cormet device followed initial collaboration with Mr. Derek McMinn. Both hybrid implants (a cementless cup and a cemented head) and entirely cementless implants, inserted with use of a variety of surgical approaches, yielded good results, with the cementless option increasing in popularity. The indications for hip resurfacing have become better understood, with the procedure considered most suitable for young and middle-aged males with a high activity profile. In addition, revision surgery, if necessary, has been associated in most cases with bone and soft-tissue conservation. Caution should be exercised when treating small individuals (especially females) and individuals with accompanying diagnoses other than osteoarthritis (such as hip dysplasia), for whom other bone-conserving options may be more appropriate to avoid an adverse reaction to metal debris. Correct implant placement during hip resurfacing is of critical importance.

Radiographic changes of the femoral neck after total hip resurfacing

INTRODUCTION

Significant femoral neck narrowing following hip resurfacing arthroplasty has been observed. Several factors contributing to the physiopathology of femoral neck narrowing have been suggested. The aim of this study was to evaluate the femoral neck radiographic changes observed after hip resurfacing at a minimum follow-up period of 5 years and to determine their causes.

PATIENTS AND METHODS

We conducted a prospective study of 57 hip resurfacing arthroplasties performed in 53 patients (30 men, 23 women) of mean age 49.2 years (32-65) at surgery. These patients were clinically reviewed (inguinal pain during walking, WOMAC and UCLA scores) at 2 years and radiographically examined at 1, 2 and 5 postoperative years. The accuracy of our computer-aided measurement method was 1mm. Measurement of femoral neck to implant ratio was performed to assess the amount of neck thinning at the femoral neck-implant junction (N/H) and midway between the implant and the inter-trochanteric line (N(1/2)H) on an AP radiograph. Neck-thinning greater than 10% was considered as significant. Any other radiographic morphologic change in the femoral neck was investigated. Metallic ion concentration in blood was measured. A uni- and multivariate analysis was performed to determine the correlation with radiographic changes.

RESULTS

In one third of the patients, femoral neck narrowing was greater than 1mm at 2 and 5 postoperative years. Such result corresponds to a mean decrease in neck to implant ratio (N/H) of 5.9% (range, 2.3 to 9.4) at 2 years and 8.3% (range, 2.5 to 23.8) at 5 years. At 5 postoperative years, an overall neck thinning greater than 10% was reported in 3 patients (with a 10- to 17-% increase in femoral neck narrowing between the 2nd and the 5th postoperative year). In one case, neck thinning was associated with fracture of the femoral stem managed with revision surgery during which femoral neck necrosis was confirmed. Neck thinning was, in these cases, circumferential to the neck-implant junction. There was no significant negative impact on clinical scores and no relationship could be established between neck thinning and factors such as BMI or patient activity. Moreover, neck thinning greater than 10% was reported in two cases after 2 postoperative years through the appearance of a localized femoral neck notching which was absent in the postoperative period, secondary to a femoroacetabular impingement.

DISCUSSION-CONCLUSION

Femoral neck narrowing used to be a common phenomenon after HR when polyethylene acetabular bearings were implanted thus inducing osteolysis secondary to PE wear debris. The incidence of such phenomenon has decreased but still occurs after HR when using a metal-on-metal bearing surface. It has an early occurence but stabilizes after 2 postoperative years. Changes in mechanical stress distribution in the neck region after hip resurfacing have been hypothesized to be a cause of neck thinning. Other aetiologies may be suggested. An overall evolutive femoral neck narrowing after 2 postoperative years should raise the suspicion of necrosis leading to a risk of loosening, fracture or implant failure. Therefore, radiographic monitoring should be conducted. The presence of femoral neck notching secondary to femoroacetabular impingement represents a differential diagnosis which conservative treatment is advocated in the absence of any associated symptoms.

Unsatisfactory surgical learning curve with hip resurfacing

BACKGROUND

Hip resurfacing is considered by many to be a conservative alternative to conventional total hip arthroplasty. There are advantages and drawbacks to any procedure, and there is a learning curve associated with the introduction of any new technology. The purpose of this study is to report the complication rate, types of complications, and outcomes of hip resurfacing during the early experience of two high-volume hip surgeons.

METHODS

Seventy-three hip resurfacing procedures were performed in sixty-four patients between September 2006 and March 2009. These procedures represented 6% of all of the primary hip arthroplasty procedures performed by the two surgeons.

RESULTS

After an average duration of follow-up of twenty-five months, there were six revisions--i.e., an early failure rate of 8%. These revisions were performed to treat two deep infections, two femoral neck fractures, one case of femoral implant loosening, and one failure of an acetabular implant.

CONCLUSIONS

Because of a high early failure rate, we have reduced the utilization of hip resurfacing in our patients who are candidates for hip arthroplasty.

Failure modes of 433 metal-on-metal hip implants: how, why, and wear

Metal-on-metal total hip replacements (THRs) and hip resurfacings are coming under increasing scrutiny in light of concerns that they fail because of high wear and elevated metal ions. The aim of this study was to investigate the modes of failure in a collection of 433 metal-on-metal THRs and hip resurfacings and to examine the correlations between the reasons for revision and a range of patient and implant variables considered relevant to implant wear.

The effect of patient selection and surgical technique on the results of Conserve® Plus hip resurfacing--3.5- to 14-year follow-up

The results of metal-on-metal hip Conserve® Plus resurfacings with up to 14 years of follow-up with and without risk factors of small component size and/or large femoral defects were compared as performed with either first- or second-generation surgical techniques. There was a 99.7% survivorship at ten years for ideal hips (large components and small defects) and a 95.3% survivorship for hips with risk factors optimized technique has measurably improved durability in patients with risk factors at the 8-year mark. The lessons learned can help offset the observed learning curve of resurfacing.

Thirty-year follow-up after Wagner resurfacing hip arthroplasty: Case report

Wagner hip arthroplasty has been used as a resurfacing and thereby bone-preserving method for the treatment of disabling osteoarthritis particularly in younger individuals. The underlying rationale was to replace exclusively diseased tissue, to restore anatomy and function and to optimize range of motion and stress transfer to the proximal femur. Wagner's approach was designed to reduce the risk of infection and to make later revisions easier. The technique was however associated with a high revision rate due to early aseptic wear induced component loosening and neck fractures. Nevertheless, we report a case of a 30 years follow-up of a Wagner resurfacing hip arthroplasty.

Indications and results of hip resurfacing

The best indication for hip resurfacing is a young active patient with severe hip arthritis, good hip morphology and reasonable bone quality. With revision of either component for any reason as the endpoint, there were 68 revisions in our series of 3,095 consecutive Birmingham Hip Resurfacings (BHR) (1997-2009), including all diagnoses in all ages. This equates to a revision rate of 2.2% and survivorships of 99, 97 and 96% at five, ten and 13 years, respectively. In patients under 55 years with osteoarthritis, the survivorship is 99 and 98% at ten and 13 years. These results provide medium-term evidence that BHR when performed well in properly selected patients offers excellent outcomes and implant survivorship. Small changes to implant materials and design can affect joint function and survivorship significantly as seen from the withdrawal of certain resurfacing devices recently from clinical use. The clinical history of one device cannot be extrapolated to other devices.

Metal-on-metal hip resurfacing: a critical review

In this article, a concise review of the current literature on metal-on-metal hip resurfacing (MoMHR) is given. In contrast to conventional total hip arthroplasty, older age, female sex and small femoral head sizes predispose to failure. Neck fracture and metal wear-related complications account for the most frequent reasons for re-operations. Although the long-term consequences of metal ion release remain unknown, the increasing prevalence of soft tissue related problems with potentially devastating functional consequences in this younger patient group are of concern. Outcome after revision for metal wear related failure of MoMHR is poor. In our opinion, patients with this device should be managed in dedicated centers with facilities for data collection and monitoring. The majority of proposed advantages of MoMHR cannot be supported by the published evidence.

The Birmingham hip resurfacing prosthesis: an independent single surgeon's experience at 7-year follow-up

An independent single surgeon's 7-year experience with Birmingham hip resurfacing is presented. The study also involved investigation of the significance of pedestal sign in patients requiring revision. A consecutive 117 hips in 101 patients (59 male and 42 female patients) operated on by the senior author (VGJ) were assessed at a mean follow-up of 7 years (range, 5-9.4 years). Mean age at surgery was 54 years (range, 20-74 years). Seventy-three hips had a preoperative diagnosis of primary osteoarthritis, and secondary osteoarthritis was seen in 44 hips. Failure was defined as revision for any reason. Revision of the femoral component alone was undertaken in 8 hips (6.8%): 5 within first year for periprosthetic fracture neck of femur and in 3 hips after 5 years of follow-up. In 2 patients who were known to have osteonecrosis of the femoral head preoperatively, the femoral component progressively collapsed into varus after 5 years of follow-up. Pedestal sign was the earliest radiologic sign noted in these 2 patients and progressed rapidly within 1 year on serial radiographs well before the onset of clinical symptoms. Kaplan-Meier survival with revision as end point at 7 years was 91.5% (95% confidence interval, 97.6%-85.4%).

What happens to femoral neck bone mineral density after hip resurfacing surgery?

The major advantage of hip resurfacing is the decreased amount of bone resection compared with a standard total hip replacement. Fracture of the femoral neck is the most common early complication and poor bone quality is a major risk factor. We undertook a prospective consecutive case control study examining the effect of bone mineral density changes in patients undergoing hip resurfacing surgery. A total of 423 patients were recruited with a mean age of 54 years (24 to 87). Recruitment for this study was dependent on pre-operative bilateral femoral bone mineral density results not being osteoporotic. The operated and non-operated hips were assessed. Bone mineral density studies were repeated over a two-year period. The results showed no significant deterioration in the bone mineral density in the superolateral region in the femoral neck, during that period.

These findings were in the presence of a markedly increased level of physical activity, as measured by the short-form 36 health survey physical function score.

Clinical and radiographic results of metal-on-metal hip resurfacing with a minimum ten-year follow-up

BACKGROUND

There was a need for information about the long-term performance of the modern generation of hip resurfacing implants. A retrospective review of the first 100 hips that had implantation of one resurfacing design and had been followed for a minimum of ten years was performed.

METHODS

Between 1996 and 1998, 100 CONSERVE PLUS hip resurfacing devices were implanted by a single surgeon in eighty-nine patients. The mean age of the patients was 49.1 years, and fifty-nine patients were male. Primary osteoarthritis was the etiology for sixty-four hips. All patients were assessed clinically and radiographically.

RESULTS

The mean duration of follow-up was 11.7 years (range, 10.8 to 12.9 years). Two patients were lost to follow-up, and five patients died of causes unrelated to the surgery. Eleven hips had conversion to total hip arthroplasty because of loosening of the femoral component (eight), a femoral neck fracture (one), recurrent subluxation (one), and late infection (one). The Kaplan-Meier survivorship was 88.5% at ten years. None of the resurfacing arthroplasties failed in the twenty-eight hips that had a femoral component of >46 mm and no femoral head cystic or necrotic defects of >1 cm. Five hips had narrowing of the femoral neck, three had radiolucent zones interpreted as osteolysis, and twenty had signs of neck-socket impingement. Five hips had radiolucencies around the metaphyseal stem (two partial and three complete) that had been stable for 7.8 to 10.2 years. The mean scores on the University of California at Los Angeles (UCLA) system at the time of the latest follow-up were 9.5 points for pain, 9.3 points for walking, 8.9 points for function, and 6.8 points for activity; the mean scores on the physical and mental components of the Short Form-12 (SF-12) were 47.3 and 50.5 points, respectively; and the mean Harris hip score was 90 points.

CONCLUSIONS

The results of the present series constitute a reference point to which subsequent series should be compared. These ten-year results in a group of young patients are satisfactory, and the low rate of osteolysis is encouraging, but longer follow-up is required for comparison with conventional total hip arthroplasty.

Cortical strut allograft as an adjunct to plate fixation for periprosthetic fractures of the femur

The use of cortical strut allografts in the treatment of periprosthetic femoral fractures remain controversial. Complications such as infection and the potential transmission of disease remain concerns. A retrospective review at a tertiary-care hospital was completed of 21 patients who had sustained a periprosthetic femoral fracture and who were treated using a plate and a deep-frozen cortical strut allograft, between 1996 and 2007. The average age at the time of surgery was 80.3 years old and included 16 women and 5 men. Three patients were lost to follow-up and four died within a few weeks of discharge. The remaining 14 patients were evaluated clinically and radiographically with a mean follow-up of 3.2 years. Fracture union was observed in 13 patients, and integration of the graft occurred in 12 patients. One of the 14 patients developed a deep infection with Coagulase-Negative Staphylococcus, with a satisfactory outcome after surgical debridement and antibiotic treatment. There were no cases of fixation failure or plate rupture. At the final evaluation, the mean EQ-5D VAS score was 64 (ranging from 40-90 points) and the mean EQ-5D health state index adapted to Spanish value sets was 0.57. The mean Oxford Hip Score was 31.2. The results support the use of cortical allograft for these fractures to increase the likelihood of fracture healing and to improve the bone stock. We consider that cortical strut grafting is specially indicated for B1 and C fractures in which decreased bone density is present.

A comparison of clinical results of hip resurfacing arthroplasty and 28 mm metal on metal total hip arthroplasty: a randomised trial with 3-6 years follow-up

Two hundred and nine hips were randomised to receive either a 28 mm total hip athroplasty (THA, 100 hips) or hybrid hip resurfacing (HR, 109 hips). At 1 and 2 years post-operatively, patients with HR achieved statistically significantly better WOMAC functional scores. However, differences in scores were of slight clinical relevance with a difference of 2.2/100 and 3.3/100, at 1 and 2 years respectively (p=0.007). After an average follow-up of 56 months (range 36-72) there were similar re-operation rates 7/100 THA and 6/109 HR (p=0.655) and revision rates 2/100 THA and 4/109 HR (p=0.470). However, the types of complications were different. Higher early aseptic loosening rate was found in HR and long-term survival analysis of both patient cohorts is necessary to determine whether the potential bone preservation advantage offers by HR will overcome its earlier higher failure rate.

Femoral component loosening after hip resurfacing arthroplasty

OBJECTIVE

Before the re-introduction of the current generation of total hip resurfacing arthroplasty, component loosening and osteolysis were of great concern to the orthopaedic community. Early, mid- and long-term clinical results are encouraging, but component loosening still exists.

MATERIALS AND METHODS

Macroscopic, contact radiographic and histopathological analyses after undecalcified preparation of bone tissue specimens were performed. To investigate the frequency and morphological patterns of the loosening of the femoral component, we analysed a series of 190 retrieved femoral remnants that were revised for aseptic failures.

RESULTS

Thirty-five (18.4%) hips were revised for clinical and/or radiographic loosening of the femoral component. Pseudoarthrosis (n = 17; median in situ time: 16 weeks, interquartile range [IQR]: 9 to 34), collapsed osteonecrosis (n = 5; median in situ time: 79 weeks, IQR: 63 to 97), cement-socket debonding (n = 3; median in situ time: 89 weeks, IQR: 54 to 97) and at later follow-up bone-cement loosening (n = 10; median in situ time: 175 weeks; IQR 112 to 198; p =0.005) were distinct patterns of the femoral remnant-implant loosening. Fibrocartilaginous metaplasia of interface bone trabeculae (n = 38; median in situ time: 61 weeks, IQR: 32 to 138) was strongly associated with femoral component loosening (p = 0.009). Both the trabecular hyperosteoidosis (n = 32; median in situ time: 71 weeks, IQR 50 to 129) and excessive intraosseous lymphocyte infiltration (n = 12; median in situ time: 75 weeks, IQR 51 to 98) at the bone-cement interface correlated strongly with fibrocartilaginous metaplasia (p = 0.001 and p = 0.016 respectively) and all three lesions were associated with the female gender (p = 0.021, p = 0.009, and p = 0.051).

CONCLUSION

Femoral component loosening at early follow-up was mostly caused by pathological changes of the femoral remnant bone tissue: pseudoarthrosis and collapsed osteonecrosis. Fibrocartilaginous metaplasia was frequently observed in hips with femoral component loosening. The potential role of interface hyperosteoidosis as a precursor lesion of bone-cement loosening and its possible association with delayed type hypersensitivity reaction are discussed.

Influence of bone density on the cement fixation of femoral hip resurfacing components

In clinical outcome studies, small component sizes, female gender, femoral shape, focal bone defects, bad bone quality, and biomechanics have been associated with failures of resurfacing arthroplasties. We used a well-established experimental setup and human bone specimens to analyze the effects of bone density on cement fixation of femoral hip resurfacing components. Thirty-one fresh frozen femora were prepared for resurfacing using the original instruments. ASR resurfacing prostheses were implanted after dual-energy X-ray densitometer scans. Real-time measurements of pressure and temperature during implantation, analyses of cement penetration, and measurements of micro motions under torque application were performed. The associations of bone density and measurement data were examined calculating regression lines and multiple correlation coefficients; acceptability was tested with ANOVA. We found significant relations between bone density and micro motion, cement penetration, cement mantle thickness, cement pressure, and interface temperature. Mean bone density of the femora was 0.82 +/- 0.13 g/cm(2), t-score was -0.7 +/- 1.0, and mean micro motion between bone and femoral resurfacing component was 17.5 +/- 9.1 microm/Nm. The regression line between bone density and micro motion was equal to -56.7 x bone density + 63.8, R = 0.815 (p < 0.001). Bone density scans are most helpful for patient selection in hip resurfacing, and a better bone quality leads to higher initial component stability. A sophisticated cementing technique is recommended to avoid vigorous impaction and incomplete seating, since increasing bone density also results in higher cement pressures, lower cement penetration, lower interface temperatures, and thicker cement mantles.

Recent developments in total hip replacements: cementation, articulation, minimal-invasion and navigation

Total hip replacement is a commonly performed procedure with good results. The implants could be cemented or cementless, and there has been a resurgence of resurfacing procedures. It is important that special consideration is given to the choice of the material used at the bearing surfaces. There have been many developments in recent years that influence our choice of implant and have shaped our practice, including minimally invasive surgery and computer-assisted surgery. This article aims to provide an overview of these developments.

Sports activity after total hip resurfacing

BACKGROUND

Little is known about sports activity after total hip resurfacing.

HYPOTHESIS

Patients undergoing total hip resurfacing can have a high level of sports activity.

STUDY DESIGN

Case series; Level of evidence, 4.

METHODS

The authors evaluated the level of sports activities with a standardized questionnaire in 138 consecutive patients (152 hips) 2 years after total hip resurfacing. Range of motion, Harris hip score, and Oxford score were assessed, and radiological analysis was performed.

RESULTS

Preoperatively, 98% of all patients participated in sports activities. Two years postoperatively, 98% of the patients participated in at least 1 sports activity. The level of sports activity decreased after surgery. The number of sports activities per patient decreased from 3.6 preoperatively to 3.2 postoperatively. Intermediate- and high-impact sports, especially tennis, soccer, jogging, squash, and volleyball, showed a significant decrease while the low-impact sports (stationary cycling, Nordic walking, and fitness/weight training) showed a significant increase. Physical activity level at the time of follow-up as measured by the Grimby scale was significantly higher than in the year before surgery. Duration of sports participation per week increased significantly after surgery. Men had a significantly higher sport level than women before and after surgery. Eighty-two percent felt no restriction while performing sports. One-third missed certain sports activities such as jogging, soccer, tennis, and downhill skiing. The Harris hip and Oxford scores showed a significant increase postoperatively.

CONCLUSION

The results of this short-term follow-up study show that sports activity after total hip resurfacing surgery is still possible. Physical activity level increased with a shift toward low-impact sports. Duration of sports participation increased. High-impact sports activities decreased. These findings can be important for the decision-making process for hip surgery and should be communicated to the patient.

The influence of the size of the component on the outcome of resurfacing arthroplasty of the hip

The survivorship of contemporary resurfacing arthroplasty of the hip using metal-on-metal bearings is better than that of first generation designs, but short-term failures still occur. The most common reasons for failure are fracture of the femoral neck, loosening of the component, osteonecrosis of the femoral head, reaction to metal debris and malpositioning of the component. In 2008 the Australian National Joint Registry reported an inverse relationship between the size of the head component and the risk of revision in resurfacing hip arthroplasty. Hips with a femoral component size of ≤ 44 mm have a fivefold increased risk of revision than those with femoral components of ≥ 55 mm irrespective of gender. We have reviewed the literature to explore this observation and to identify possible reasons including the design of the implant, loading of the femoral neck, the orientation of the component, the production of wear debris and the effects of metal ions, penetration of cement and vascularity of the femoral head. Our conclusion is that although multifactorial, the most important contributors to failure in resurfacing arthroplasty of the hip are likely to be the design and geometry of the component and the orientation of the acetabular component.

Hip resurfacing arthroplasty: a review of the evidence for surgical technique, outcome, and complications

Hip resurfacing arthroplasty has reemerged as a valid reconstruction option for the osteoarthritic hip. Patient selection is critical for excellent surgical outcomes, especially when compared with total hip arthroplasty. However, concerns regarding surgical technique and postsurgical complications persist. The authors review the evidence for surgical technique, outcomes, and complications related to modern metal-on-metal hip resurfacing arthroplasty.

No superiority of cemented metal-on-metal over metal-on-polyethylene THA in a randomized controlled trial at 10-year follow-up

In a randomized controlled trial, 102 cemented Stanmore 28-mm metal-on-metal total hip arthroplasties (THAs) were compared to 98 metal-on-polyethylene THAs in 195 patients. At a mean follow-up of 10 years, 11 patients (11 hips) were lost to follow-up, 53 patients (55 hips) died, and 6 patients (6 hips) underwent revision. Average age of the surviving patients was 79 years. Harris Hip Scores and Oxford Hip Scores had increased significantly in both groups (P=.000). Ten years postoperatively, mean Harris Hip Score was 86 in the metal-on-metal patients and 87 in the metal-on-polyethylene patients (P=.441); Oxford Hip Scores were 27 and 24, respectively (P=.494). Wear was present in 30 of 52 polyethylene cups. Periprosthetic radiolucencies were seen in 57% of the metal-on-metal patients and in 52% of the metal-on-polyethylene patients (P=.680); they were mainly seen in DeLee & Charnley's zones 1 and 2. Serum cobalt and chromium concentration were higher in the metal-on-metal group (cobalt 1.1, chromium 1.0 vs 0.5 and 0.5 mug/L, respectively; P<.001). Patients with high ion levels (maximum 9.5 and 11 mug/L, respectively) all showed high Harris Hip Scores and few or no periprosthetic radiolucencies, and none were revised. Ten-year survival was 95.5% in the metal-on-metal group (4 revisions) and 96.8% in the metal-on-polyethylene group (2 revisions; P=.402). All revisions were indicated for aseptic loosening. One case of aseptic lymphocytic vasculitis-associated lesions and no pseudotumors were observed. The absence of clinical superiority of the cemented metal-on-metal bearing and the concerns over their biological effects have led us to favor the cemented metal-on-polyethylene THA.

Increased strain in the femoral neck following insertion of a resurfacing femoral prosthesis

The cortical strains on the femoral neck and proximal femur were measured before and after implantation of a resurfacing femoral component in 13 femurs from human cadavers. These were loaded into a hip simulator for single-leg stance and stair-climbing. After resurfacing, the mean tensile strain increased by 15% (95% confidence interval (CI) 6 to 24, p = 0.003) on the lateral femoral neck and the mean compressive strain increased by 11% (95% CI 5 to 17, p = 0.002) on the medial femoral neck during stimulation of single-leg stance. On the proximal femur the deformation pattern remained similar to that of the unoperated femurs.

The small increase of strains in the neck area alone would probably not be sufficient to cause fracture of the neck However, with patient-related and surgical factors these strain changes may contribute to the risk of early periprosthetic fracture.

Outcome of primary resurfacing hip replacement: evaluation of risk factors for early revision

BACKGROUND AND PURPOSE

The outcome of modern resurfacing remains to be determined. The Australian Orthopaedic Association National Joint Replacement Registry (AOANJRR) started collection of data on hip resurfacing at a time when modern resurfacing was started in Australia. The rate of resurfacing has been higher in Australia than in many other countries. As a result, the AOANJRR has one of the largest series of resurfacing procedures. This study was undertaken to determine the results of this series and the risk factors associated with revision.

PATIENTS AND METHODS

Data from the AOANJRR were used to analyze the survivorship of 12,093 primary resurfacing hip replacements reported to the Joint Replacement Registry between September 1999 and December 2008. This was compared to the results of primary conventional total hip replacement reported during the same period. The Kaplan-Meier method and proportional hazards models were used to determine risk factors such as age, sex, femoral component size, primary diagnosis, and implant design.

RESULTS

Female patients had a higher revision rate than males; however, after adjusting for head size, the revision rates were similar. Prostheses with head sizes of less than 50 mm had a higher revision rate than those with head sizes of 50 mm or more. At 8 years, the cumulative per cent revision of hip resurfacing was 5.3 (4.6-6.2), as compared to 4.0 (3.8-4.2) for total hip replacement. However, in osteoarthritis patients aged less than 55 years with head sizes of 50 mm or more, the 7-year cumulative per cent revision for hip resurfacing was 3.0 (2.2-4.2). Also, hips with dysplasia and some implant designs had an increased risk of revision.

INTERPRETATION

Risk factors for revision of resurfacing were older patients, smaller femoral head size, patients with developmental dysplasia, and certain implant designs. These results highlight the importance of patient and prosthesis selection in optimizing the outcome of hip resurfacing.

Internal fixation after subtrochanteric femoral fracture after hip resurfacing arthroplasty

Periprosthetic fractures around total hip arthroplasty create surgical challenges with many described techniques of either fixation or revision. The increasing popularity of hip resurfacing arthroplasty poses different problems especially if there is a desire to retain the prosthesis rather than converting to a total hip arthroplasty. We describe a previously unreported technique of fixation for a comminuted, proximal femoral fracture, beneath a hip resurfacing.

Morphologic analysis of periprosthetic fractures after hip resurfacing arthroplasty

BACKGROUND

Periprosthetic fractures have long been recognized as one of the major complications of hip resurfacing arthroplasty. The objective of this study was to develop a systematic and morphologic classification of the fracture mode based on pathogenesis.

METHODS

One hundred and seven retrieved specimens consisting of the femoral remnant and the femoral component of a total hip resurfacing arthroplasty that had failed as a result of a periprosthetic fracture were analyzed with regard to the morphologic failure mode. The location of the fracture line was used to differentiate the fractures. The fractures were also classified histopathologically as acute biomechanical, acute postnecrotic, or chronic biomechanical.

RESULTS

Fifty-nine percent (sixty-three) of the fractures occurred within the bone inside the femoral component. Fifty-one percent (fifty-five) of the fractures were classified morphologically as acute postnecrotic; 40% (forty-three), as chronic biomechanical; and 8% (nine), as acute biomechanical. Acute biomechanical fractures were found exclusively in the femoral neck and occurred earlier (mean time [and standard deviation] between implantation and revision, 41 +/- 57 days) than acute postnecrotic fractures (mean time between implantation and revision, 149 +/- 168 days; p = 0.002) or chronic biomechanical fractures (mean time between implantation and revision, 179 +/- 165 days; p = 0.001). The latter two fracture types both occurred predominantly in the bone inside the femoral component.

CONCLUSIONS

Three distinct fracture modes were characterized morphologically. Osteonecrosis was the most frequent cause of fracture-related failures. We suggest that an intraoperative mechanical injury of the femoral neck such as notching and/or malpositioning of the femoral component might lead to changes in the loading pattern or in the resistance to fracture of the femoral neck and may result in both acute and chronic biomechanical femoral neck fractures. These findings may serve as feedback information for the surgeon and possibly influence future therapeutic strategies.

Articular Surface Replacement of the hip: a prospective single-surgeon series

We present the early clinical and radiological results of Articular Surface Replacement (ASR) resurfacings in 214 hips (192 patients) with a mean follow-up of 43 months (30 to 57). The mean age of the patients was 56 years (28 to 74) and 85 hips (40%) were in 78 women.

The mean Harris hip score improved from 52 (11 to 81) to 95 (27 to 100) at two years and the mean University of California, Los Angeles activity score from 3.9 (1 to 10) to 7.4 (2 to 10) in the same period. Narrowing of the neck (to a maximum of 9%) was noted in 124 of 209 hips (60%). There were 12 revisions (5.6%) involving four (1.9%) early fractures of the femoral neck and two (0.9%) episodes of collapse of the femoral head secondary to avascular necrosis. Six patients (2.8%) had failure related to metal wear debris. The overall survival for our series was 93% (95% confidence interval 80 to 98) and 89% (95% confidence interval 82 to 96) for hips with acetabular components smaller than 56 mm in diameter.

The ASR implant has a lower diametrical clearance and a subhemispherical acetabular component when compared with other more frequently implanted metal-on-metal hip resurfacings. These changes may contribute to the higher failure rate than in other series, compared with other designs. Given our poor results with the small components we are no longer implanting the smaller size.

Metal-on-metal hip resurfacing in patients with pigmented villonodular synovitis: a report of two cases

Pigmented villonodular synovitis (PVNS) of the hip joint is a rare and benign tumor of the synovia. This local, aggressive, proliferative disorder of the joint synovial membrane can lead to secondary osteoarthritis and represents a small percentage of all patients undergoing total hip replacement (THR). Because of the usually young age of the patients undergoing THR for PVNS, a resurfacing arthroplasty of the hip appears as a beneficial treatment option due to its bone-conserving nature, good joint stability, and ability to easily convert to a THR if needed. This article describes 2 cases of metal-on-metal hip resurfacing in patients with pigmented villonodular synovitis. In patient 1, PVNS was suspected on radiographs but confirmed only after removal of a mass of thick, grey-brown spotted synovia. A complete synovectomy was performed prior to hip resurfacing. Seven years postoperatively, radiographs show secure fixation of the components with no radiolucencies. In patient 2, arthroscopy of the hip joint had been performed 3 months prior, but PVNS had not been diagnosed. Pigmented villonodular synovitis was confirmed during the operation when incising a yellowish nodular mass protruding from the capsule. Granuloma was also found in the inferior and anterior part of the acetabulum. Four years postoperatively, the patient exhibits excellent clinical and radiographic results. Complete surgical removal of all tissue affected with PVNS is the key to a successful resurfacing, which is otherwise technically similar to resurfacing in patients with other etiologies. The mid-term results of the 2 presented cases are satisfying and show the potential of the resurfacing technique for young patients with PVNS of the hip.

Evaluation of a new fluoroscopy-based navigation system in the placement of the femoral component in hip resurfacing

Prosthesis-specific mechanical alignment instruments for the precise and reproducible positioning of the femoral component constitute one of the major improvements in modern hip resurfacing prostheses. However, mechanical failure of the femoral component is mostly attributable to the surgical technique, and in particular to notching of the femoral neck. In order to evaluate a novel computer-assisted fluoroscopy-based planning and navigation system, six DUROMTM hip resurfacing prostheses were implanted into artificial femurs by means of computer-assisted fluoroscopy-based navigation and prosthesis-specific mechanical alignment instruments. Subsequently, the planning and navigation system was tested within the scope of a cadaver study on three fixed whole-body preparations (six femurs). The average difference between planned and actual angle of the prosthesis was 0±0.7° for fluoroscopy-based navigation versus 6.5±7.8° for the in-vitro use of the prosthesis-specific mechanical alignment instruments, and 1±1.4° for fluoroscopic navigation in the cadaver study. The average discrepancy between planned and actual anterior offset was −1.2±1.2 mm versus 0.8±4 mm, and 0.3±2.2 mm in the cadaver study, and the time required for the total of five planning and navigation steps was 17.2±1.5 min versus 14±0.8 min and 20.2±2.5 min respectively. No notching of the femoral neck occurred under fluoroscopy nor under conventional treatment. During in-vitro studies, use of the computer-assisted fluoroscopy-based planning and navigation system resulted in enhanced accuracy compared with conventional prosthesis-specific mechanical alignment instruments. The system has yielded initial promising results within the scope of the cadaver study.

Imageless computer navigation without pre-operative templating may lead to malpreparation of the femoral head in hip resurfacing

The computed neck-shaft angle and the size of the femoral component were recorded in 100 consecutive hip resurfacings using imageless computer-navigation and compared with the angle measured before operation and with actual component implanted. The reliability of the registration was further analysed using ten cadaver femora. The mean absolute difference between the measured and navigated neck-shaft angle was 16.3° (0° to 52°). Navigation underestimated the measured neck-shaft angle in 38 patients and the correct implant size in 11. Registration of the cadaver femora tended to overestimate the correct implant size and provided a low level of repeatability in computing the neck-shaft angle.

Prudent pre-operative planning is advisable for use in conjunction with imageless navigation since misleading information may be registered intraoperatively, which could lead to inappropriate sizing and positioning of the femoral component in hip resurfacing.

Learning from the learning curve in total hip resurfacing: a radiographic analysis

BACKGROUND

Operation of hip resurfacing prosthesis is a technically demanding procedure accompanied by a learning curve. To our knowledge no objective data on this learning curve are available in the literature.

METHODS

For the first 40 resurfacing hip prostheses implanted by a single-surgeon radiographic 'learning curve' analysis was performed. Optimal implant positioning on preoperative digital templating was compared with the eventual implant position postoperatively, measured by six establishes radiographic parameters and compared for four chronological cohorts of patients.

RESULTS

A learning curve was clearly present and an optimal result was established in the last cohort. Pitfalls were a relatively steep cup position initially and a stem position in the posterior 1/3 of the collum. Besides marginal medialization a fully anatomic reconstruction of the center of rotation was achieved.

CONCLUSION

In total hip resurfacing one should recognize the presence of a learning curve. This learning curve appears to be acceptable and a reproducible optimal implant positioning can be achieved quickly.

Hip resurfacing after failed free vascularized fibular graft

Metal-on-metal resurfacing of the hip is a bone sparing arthroplasty that may be an option when a head-sparing nonarthroplasty option fails. We present the first published report of 5 cases of failed free vascularized fibular graft treated with modern hip resurfacing arthroplasty. This selected group of patients had avascular necrosis with less than 20% head involvement and cysts less than 1 cm in diameter. Follow-up ranging from 2 to 5 years (mean, 38 months) showed improvement in hip function without evidence of prosthesis loosening. There were no femoral neck fractures or revisions. A vascularized fibular bone graft does not prevent good early results with hip resurfacing but may add technical complexity owing to its position within the femoral head and neck.

Clinical experience of Ganz surgical dislocation approach for metal-on-metal hip resurfacing

Although the posterior approach is the most commonly used for hip resurfacing, concerns remain in terms of risk of femoral neck fracture secondary to an osteonecrotic event. The purpose of this study was to look at the short-term results of metal-on-metal hip resurfacing done by the vascular-preserving surgical approach as developed by Ganz in 116 hip resurfacing arthroplasties performed in 106 patients (86 men, 20 women; mean age, 46.5 years; range, 19-62). At a mean follow-up of 38.3 months (range, 12-84), Harris Hip Scores improved significantly from 53.1 to 90.16 (P < .001). There were 10 nonunions (8.7%) and 21 hips (18.3%) requiring screw removal for painful bursitis. Two hips underwent conversion to total hip arthroplasty: one at 18 months for femoral loosening and one at 7 years for acetabular loosening. Although the trochanteric slide approach as developed by Ganz provides excellent exposure to the hip joint and preserves femoral head vascularity, it does carry some inherent morbidity in regard to the greater trochanter.

Cementless femoral components in young patients: review and meta-analysis of total hip arthroplasty and hip resurfacing

The study purpose was to analyze current results of modern cementless femoral components in young patients having total hip arthroplasty (THA) or hip resurfacing. Twenty-two studies (n = 5907; hips = 6408) evaluating modern cementless THA in young patients and 15 studies evaluating hip resurfacing (n = 3002; hips = 3269) were included. Meta-analysis techniques were used to pool failure rates. The pooled failure rate for THA using femoral revision for mechanical failure as an end point was 1.3% (95% confidence interval [CI], 1.0%-1.7%) at a mean 8.4 years of follow-up. At a mean of 3.9 years of follow-up, the pooled mechanical failure rate of the femoral component for hip resurfacing was 2.6% (95% CI, 2.0-3.4). In conclusion, the enthusiasm for hip resurfacing should be tempered by these data. Longer follow-up and direct comparison trials are required to confirm these findings.

Leg length and offset following hip resurfacing and hip replacement

We measured and compared critical parameters on antero-posterior radiographs from 28 patients who had undergone hybrid hip replacement (CPS/EPF), with 28 patients who had undergone cemented hip resurfacing (Cormet). All operations were performed by a single surgeon or under his supervision. We measured the femoral offset, acetabular offset, cup height and leg length on pre and post operative radiographs. The mean difference in femoral offset post-operatively was 3.52 mm (95% CI: -1.10 to 8.14 mm) in the hybrid group and -1.30 mm (95%CI: -2.88 to 0.29 mm) in the resurfacing group. Using the independent sample t test (two-tailed), the difference between these means was significant, test statistic t 2.025, p<0.05. This suggests that resurfacing restored the femoral offset more accurately than hybrid hip replacement. The mean difference in leg length post-operatively was 11.91 mm (95% CI: 8.21 to 15.62 mm) in the hybrid group and 4.87 mm (95% CI: 3.32 to 6.42 mm) in the resurfacing group. Using the independent sample t test (two-tailed), the difference between the means was significant, test statistic t 3.597, p<0.001. This suggests that resurfacing produced less change in leg length post-operatively than hybrid hip replacement. We found no statistically significant difference in ideal pre and post operative centre of rotation in the two groups. Proximal femoral anatomy was restored during hip resurfacing by resecting bone of a thickness determined by corresponding preoperative templating and implant thickness rather than relying on placement of the cutting ring at the head-neck junction. No femoral neck fractures occurred in the resurfacing group.

No superiority of cemented metal-on-metal vs metal-on-polyethylene THA at 5-year follow-up

A randomized controlled trial was performed to compare the cemented Stanmore metal-on-metal (Biomet, Warsaw, Indiana) total hip arthroplasty (THA; 102 hips) to the cemented Stanmore metal-on-polyethylene (Biomet) THA (98 hips). The primary outcome was clinical performance. Radiological performance, serum cobalt analysis, and prosthetic survival were secondary outcome measures. At a mean follow-up of 5.6 years, 5 patients were lost to follow-up, 18 died, and 4 were revised (3 metal-on- metal, 1 metal-on-polyethylene). Harris Hip Scores improved from 48 to 90 in the metal-on-metal patients (P<.001) and from 46 to 87 in the metal-on-polyethylene patients (P<.001). Oxford Hip Scores changed from 40 to 19 in the metal-on-metal group (P<.001) and from 40 to 18 in the metal-on-polyethylene group (P<.001). For both Harris and Oxford Hip Scores, there was no significant difference between the 2 groups. Five-year survival with revision for any reason was 97% (95% CI 93%-100%) in the metal-on-metal group and 99% (95% CI 97%-100%) in the metal-on-polyethylene group. All revisions were indicated for aseptic loosening (metal-on-metal: 3 cup revisions; metal-on-polyethylene: 1 total revision). At 5-year follow-up, cemented metal-on-metal THA showed no clinical superiority over metal-on-polyethylene THA.

Hueter anterior approach for hip resurfacing: assessment of the learning curve

The results of metal-on-metal hip resurfacing arthroplasty have been very encouraging. However, extensile approaches such as the posterior have been recommended to ensure proper component placement. This article evaluates the safety and the learning curve with the less invasive Hueter hip resurfacing using an anterior approach on an orthopedic traction table. The first 50 hip resurfacings using this approach are compared with the previous 50 procedures performed through a surgical dislocation approach. The authors conclude that it is a reasonable alternative to more extensile surgical approaches for a high-volume resurfacing arthroplasty surgeon. Further long-term studies and comparisons to other approaches will determine if the anterior approach provides advantages in terms of patient function and time to recovery.

Femoral neck fractures after hip resurfacing

Femoral neck fracture is an important early complication after hip resurfacing. Our aims were firstly to determine the incidence of fracture in an independent series and secondly, in a case control study, to investigate potential risk factors. Fifteen femoral neck fractures occurred in a series of 842 procedures, representing an incidence of 1.8%. No relationship existed between age, sex, and fracture incidence. Mechanical factors such as notching, femoral neck lengthening, and varus alignment of the femoral component were found to have a similar incidence in both fracture and control groups. The proportion of patients that had at least 1 mechanical risk factor was not different between the 2 groups (fracture group, 50%; control group, 41%). Established avascular necrosis of the femoral head was evident in all retrieved femoral heads (n = 9) of patients who sustained postoperative fracture; in none of these patients was avascular necrosis the initial diagnosis. This study suggests that in our practice, mechanical factors, such as neck notching, neck lengthening, or varus angulations, are not the primary cause of femoral neck fractures.

Outcome of hip resurfacing arthroplasty in patients with developmental hip dysplasia

Patients with osteoarthritis secondary to developmental dysplasia of the hip (DDH) typically are young and active, which might affect functional ratings or failure rates after resurfacing arthroplasty. We therefore evaluated 24 patients (32 hips; mean age, 44.2 years) after hip resurfacing performed for osteoarthritis secondary to DDH. We used the Harris hip score (HHS), the University of California, Los Angeles (UCLA) activity scale, and a sports and activity questionnaire. A radiographic analysis also was performed. We followed patients a minimum of 28 months (mean, 43 months; range 28-60 months). The HHS improved from a mean of 54.7 to 97.3 and UCLA activity levels increased from a mean of 5.3 to 8.6. All patients returned to sports activity at a mean of 11 weeks after surface replacement. There were no major differences in preoperative and postoperative participation in the most common sports and activities. Two of the 32 replacements (6%) failed. We detected femoral radiolucencies in 10 of the remaining 30 hips. Despite satisfactory outcomes in clinical scores, return to sports, and hip biomechanics, the failure rate of 6% was disappointing. Additional followup is important to assess if failure rates increase in these young, active patients.

LEVEL OF EVIDENCE

Level IV, therapeutic study. See the Guidelines for Authors for a complete description of levels of evidence.

Femoral component positioning in hip resurfacing with and without navigation

Early failures after hip resurfacing often are the result of technical errors in placing the femoral component. We asked whether image-free computer navigation decreased the number of outliers compared with the conventional nonnavigated technique. We retrospectively compared 51 consecutive hip resurfacings performed using image-free computer navigation with 88 consecutive hip resurfacings performed without navigation. Patient demographics were similar. There were no differences in the average native femoral neck-shaft angles, planned stem-shaft angles, or postoperative stem-shaft angles. However, when the postoperative stem-shaft angle was compared with the planned stem-shaft angle, there were 33 patients (38%) in the nonnavigated group with a deviation greater than 5 degrees in contrast to none in the navigated group. Notching was present in four patients in the nonnavigated group and none in the navigated group. The average operative time was 111 minutes for the navigated group and 105 minutes for the nonnavigated group. Image-free navigation decreased the number of patients with potentially undesirable implant placements.

LEVEL OF EVIDENCE

Level III, therapeutic study. See the Guidelines for Authors for a complete description of levels of evidence.

Is a valgus position of the femoral component in hip resurfacing protective against spontaneous fracture of the femoral neck?: a biomechanical study

The aim of our study was to investigate whether placing of the femoral component of a hip resurfacing in valgus protected against spontaneous fracture of the femoral neck. We performed a hip resurfacing in 20 pairs of embalmed femora. The femoral component was implanted at the natural neck-shaft angle in the left femur and with a 10 degrees valgus angle on the right. The bone mineral density of each femur was measured and CT was performed. Each femur was evaluated in a materials testing machine using increasing cyclical loads. In specimens with good bone quality, the 10 degrees valgus placement of the femoral component had a protective effect against fractures of the femoral neck. An adverse effect was detected in osteoporotic specimens. When resurfacing the hip a valgus position of the femoral component should be achieved in order to prevent fracture of the femoral neck. Patient selection remains absolutely imperative. In borderline cases, measurement of bone mineral density may be indicated.

Comparison of acetabular reamings during hip resurfacing versus uncemented total hip arthroplasty

PURPOSE

To compare the quantity of bone removed from the acetabulum during resurfacing hip arthroplasty versus uncemented total hip arthroplasty (THA).

METHODS

62 consecutive patients with osteoarthritis of the hip were prospectively studied. 24 men and 7 women aged 40 to 86 (mean, 59) years underwent Birmingham hip resurfacing. 13 men and 18 women aged 34 to 88 (mean, 61) years underwent uncemented THA using the trident acetabular cup. Obese elderly women at risk of femoral neck fracture and patients with large subchondral pseudocysts or a history of avascular necrosis of the femoral head were assigned to uncemented THA. Acetabular reamings were collected; marginal osteophytes were not included. The reamings were dehydrated, defatted, and weighed.

RESULTS

The mean weight of acetabular reamings was not significantly different between patients undergoing hip resurfacing and uncemented THA (p=0.57).

CONCLUSION

In hip resurfacing, the use of an appropriately small femoral component avoids oversizing the acetabular component and removal of excessive bone stock.