RISK FACTORS FOR DISLOCATION AFTER PRIMARY TOTAL HIP ARTHROPLASTY VIA THE POSTERO-LATERAL APPROACH

Abstract

Dislocation remains a common complication following total hip arthroplasty, second only to aseptic loosening as a cause of revision. Factors thought to play a role in dislocation include cup and stem alignment, soft tissue tension, surgical approach, patient factors, and design features of the prosthesis, including femoral head size.

We analysed all consecutive total hip replacements at one institution over a 17 year period. Criteria for study inclusion were hips replaced due to primary osteoarthritis with no previous surgery, femoral head sizes of 28mm and 32mm only, and at least one year from date of surgery. 3682 hips fulfilled these criteria. All procedures were carried out using a posterolateral approach with enhanced posterior repair, and a standard method of intraoperative soft tissue balance assessment.

The rate of dislocation was 1.6%. 32mm femoral head size was associated with a statistically significant lower rate of dislocation. However, after controlling for different follow-up times between 28mm and 32mm heads, this difference was no longer observed. Older age at time of surgery and decreased cup anteversion were shown to be significantly associated with an increased risk of dislocation. Ceramic on ceramic bearing surface was significantly associated with a decreased risk of dislocation, after controlling for age, bearing wear and time from surgery. Cup inclination, gender, BMI, and preoperative hip score were not related to dislocation risk.

Our dislocation rate may reflect current dislocation rates of surgeons using the posterolateral approach with posterior capsule and external rotator repair. The risk factors identified and excluded in this study are likely to be relevant to all surgeons who utilise this approach in total hip arthroplasty.