The cumulative mid- to long-term risk of dislocation following total hip arthroplasty is considerably greater than has been reported in short-term studies. We retrospectively investigated the epidemiology of first-time dislocation following total hip arthroplasty using 28-mm heads through the direct anterior approach in patients with hip dysplasia who were followed up for more than 5 years.
The operative records of 871 hips in 790 consecutive patients were reviewed to determine the incidence of postoperative first-time dislocation.
The mean follow-up duration was 7.8 (range, 5.6-11.7) years. The direct anterior approach was used for all hips. Postoperative dislocation was observed in 8 hips (0.92%) in 8 patients. First-time dislocation occurred during the first 3 weeks in 6 hips (75%). The cumulative risk of postoperative dislocation was 0.69% at 1 month, 0.80% at 1 year, and 0.93% at 5 years. One patient underwent revision surgery for recurrent dislocation within the first month due to malalignment of the cup.
Our findings demonstrated that the direct anterior approach limits the time of dislocation to the very early postoperative period; that is, the risk of a first-time dislocation after the first month is considerably low. Preserving muscular structures may contribute to continuous dynamic stability of the hip, which could explain the slight increase in the cumulative risk of first-time dislocation.