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.

Objectives

The number of surgical procedures performed each year to treat femoroacetabular impingement (FAI) continues to rise. Although there is evidence that surgery can improve symptoms in the short-term, there is no evidence that it slows the development of osteoarthritis (OA). We performed a feasibility study to determine whether patient and surgeon opinion was permissive for a Randomised Controlled Trial (RCT) comparing operative with non-operative treatment for FAI.

Femoral stem varus has been associated with poorer results. We report the incidence of varus/valgus malalignment of the Exeter polished, double taper design in a multicentre prospective study. The surgical outcomes at a minimum of five year and complication rates are also reported.

A multicentre prospective study of 987 total hip replacements was undertaken to investigate whether there is an association between surgical outcome and femoral stem malalignment. The primary outcome measure was the change in the Oxford hip score (OHS) at five years. Secondary outcomes included the rate of dislocation and revision.

The incidence of varus and valgus malignment were 7.1% and 2.6% respectively. There was no significant difference in OHS between neutral and malaligned femoral stems at 5 years (neutral, mean = 40.2; varus, mean 39.3, p = 0.465; valgus, mean = 40.9, p = 0.605). There was no significant difference in dislocation rate between the groups (p = 0.66). There was also no significant difference in revision rate (p = 0.34).

This study provides evidence that the Exeter stem is extremely tolerant of varus and valgus malalignment, both in terms of outcome and complication rate.