We assessed the orientation of the acetabular component in 1070 primary total hip arthroplasties with hard-on-soft, small diameter bearings, aiming to determine the size and site of the target zone that optimises outcome. Outcome measures included complications, dislocations, revisions and ΔOHS (the difference between the Oxford Hip Scores pre-operatively and five years post-operatively). A wide scatter of orientation was observed (2sd 15°). Placing the component within Lewinnek’s zone was not associated withimproved outcome. Of the different zone sizes tested (± 5°, ± 10° and ± 15°), only ± 15° was associated with a decreased rate of dislocation. The dislocation rate with acetabular components inside an inclination/anteversion zone of 40°/15° ± 15° was four times lower than those outside. The only zone size associated with statistically significant and clinically important improvement in OHS was ± 5°. The best outcomes (ΔOHS > 26) were achieved with a 45°/25° ± 5° zone.

This study demonstrated that with traditional technology surgeons can only reliably achieve a target zone of ±15°. As the optimal zone to diminish the risk of dislocation is also ±15°, surgeons should be able to achieve this. This is the first study to demonstrate that optimal orientation of the acetabular component improves the functional outcome. However, the target zone is small (± 5°) and cannot, with current technology, be consistently achieved.

Cite this article: Bone Joint J 2015;97-B:164–72.

Inflammatory pseudotumours occasionally occur after metal-on-metal hip resurfacing and often lead to revision. Our aim was to determine the severity of this complication by assessing the outcome of revision in these circumstances and by comparing this with the outcome of other metal-on-metal hip resurfacing revisions as well as that of matched primary total hip replacements.

We identified 53 hips which had undergone metal-on-metal hip resurfacing and required revision at a mean of 1.59 years (0.01 to 6.69) after operation. Of these, 16 were revised for pseudotumours, 21 for fracture and 16 for other reasons. These were matched by age, gender and diagnosis with 103 patients undergoing primary total hip replacement with the Exeter implant.

At a mean follow-up of three years (0.8 to 7.2) the outcome of metal-on-metal hip resurfacing revision for pseudotumour was poor with a mean Oxford hip score of 20.9 (sd 9.3) and was significantly worse (p < 0.001) than the outcome for fracture with a mean Oxford hip score of 40.2 (sd 9.2) or that for other causes with a mean Oxford hip score of 37.8 (sd 9.4). The clinical outcome of revision for pseudotumour was also significantly worse (p < 0.001) than the outcome of matched primary total hip replacements. By contrast, the outcome for fracture and other causes was not significantly different from that of matched primary total hip replacements (p = 0.065). After revision for pseudotumour there were three cases of recurrent dislocation, three of palsy of the femoral nerve, one of stenosis of the femoral artery and two of loosening of the component. Five hips required further revision. In three of these there was evidence of recurrent pseudotumour, and one is currently awaiting further revision. The incidence of major complications after revision for pseudotumour (50%) was significantly higher (p = 0.018) than that after revision for other causes (14%).

The outcome of revision for pseudotumour is poor and consideration should be given to early revision to limit the extent of the soft-tissue destruction. The outcome of resurfacing revision for other causes is good.

A prospective, multi-centre study was carried out on 1421 total hip replacements between January 1999 and July 2007 to examine if obesity has an effect on clinical outcomes.

The patients were categorised into three groups: non-obese (body mass index (BMI) < 30 kg/m²), obese (BMI 30 to 40 kg/m²) and morbidly obese (BMI > 40 kg/m²). The primary outcome measure was the change in Oxford hip score at five years. Secondary outcome measures included dislocation and revision rates, increased haemorrhage, deep infection, deep-vein thrombosis and pulmonary embolism, mean operating time and length of hospital stay. Radiological analysis assessing heterotopic ossification, femoral osteolysis and femoral stem positioning was performed. Data were incomplete for 362 hips (25.5%)

There was no difference in the change in the Oxford hip score, complication rates or radiological changes at five years between the groups. The morbidly obese group was significantly younger and required a significantly longer operating time. Obese and morbidly obese patients have as much to gain from total hip replacement as non-obese patients.

Few independent studies have reported the outcome of resurfacing arthroplasty of the hip. The aim of this study was to report the five-year clinical outcome and seven-year survival of an independent series.

A total of 610 Birmingham Hip Resurfacing arthroplasties were performed in 532 patients with a mean age of 51.8 years (16.5 to 81.6). They were followed for between two and eight years; 107 patients (120 hips) had been followed up for more than five years. Two patients were lost to follow-up. At a minimum of five years’ follow-up, 79 of 85 hips (93%) had an excellent or good outcome according to the Harris hip score. The mean Oxford hip score was 16.1 points (sd 7.7) and the mean University of California Los Angeles activity score was 6.6 points (sd 1.9). There were no patients with definite radiological evidence of loosening or of narrowing of the femoral neck exceeding 10% of its width. There were 23 revisions (3.8%), giving an overall survival of 95% (95% confidence interval 85.3 to 99.2) at seven years. Fractured neck of femur in 12 hips was the most common indication for revision, followed by aseptic loosening in four. In three hips (three patients) (0.5%), failure was possibly related to metal debris.

Considering that these patients are young and active these results are good, and support the use of resurfacing. Further study is needed to address the early failures, particularly those related to fracture and metal debris.

We performed a clinical and radiological study to determine the rate of failure of the Charnley Elite-Plus femoral component. Our aim was to confirm or refute the predictions of a previous roentgen stereophotogrammetric analysis study in which 20% of the Charnley Elite-Plus stems had shown rapid posterior head migration. It was predicted that this device would have a high early rate of failure.

We examined 118 patients at a mean of nine years after hip replacement, including the 19 patients from the original roentgen stereophotogrammetric study. The number of revision procedures was recorded and clinical and radiological examinations were performed.

The rate of survival of the femoral stems at ten years was 83% when revision alone was considered to be a failure. It decreased to 59% when a radiologically loose stem was also considered to be a failure. All the patients previously shown in the roentgen stereophotogrammetric study to have high posterior head migration went on to failure. There was a highly significant difference (p = 0.002) in posterior head migration measured at two years after operation between failed and non-failed femoral stems, but there was no significant difference in subsidence between these two groups.

Our study has shown that the Charnley Elite-Plus femoral component has an unacceptably high rate of failure. It confirms that early evaluation of new components is important and that roentgen stereophotogrammetric is a good tool for this. Our findings have also shown that rapid posterior head migration is predictive of premature loosening and a better predictor than subsidence.

We inserted an electrode up the femoral neck into the femoral head of ten patients undergoing a metal-on-metal hip resurfacing arthroplasty through a posterior surgical approach and measured the oxygen concentration during the operation. In every patient the blood flow was compromised during surgery, but the extent varied. In three patients, the oxygen concentration was zero at the end of the procedure. The surgical approach caused a mean 60% drop (p < 0.005) in oxygen concentration while component insertion led to a further 20% drop (p < 0.04). The oxygen concentration did not improve significantly on wound closure. This study demonstrates that during hip resurfacing arthroplasty, patients experience some compromise to their femoral head blood supply and some have complete disruption.

Polished, tapered stems are now widely used for cemented total hip replacement and many such designs have been introduced. However, a change in stem geometry may have a profound influence on stability. Stems with a wide, rectangular proximal section may be more stable than those which are narrower proximally. We examined the influence of proximal geometry on stability by comparing the two-year migration of the Exeter stem with a more recent design, the CPS-Plus, which has a wider shoulder and a more rectangular cross-section. The hypothesis was that these design features would increase rotational stability.

Both stems subsided approximately 1 mm relative to the femur during the first two years after implantation. The Exeter stem was found to rotate into valgus (mean 0.2°, sd 0.42°) and internally rotate (mean 1.28°, sd 0.99°). The CPS-Plus showed no significant valgus rotation (mean 0.2°, sd 0.42°) or internal rotation (mean −0.03°, sd 0.75°). A wider, more rectangular cross-section improves rotational stability and may have a better long-term outcome.