Effect of femoral head size and abductors on dislocation after revision THA.

Dislocation is a common complication after revision total hip arthroplasty, particularly if the abductor mechanism is deficient. Use of a large femoral head may reduce the incidence of dislocation. However, it is not clear if the large femoral head is effective in controlling dislocation when the abductor mechanism is deficient. We separated 230 patients who underwent revision total hip arthroplasty into four groups: Group 1 (159 patients) had an intact abductor mechanism and a 28-mm femoral head, Group 2 (20 patients) had an absent abductor mechanism (trochanteric nonunion or complete segmental proximal femoral bone loss) and a 28-mm femoral head, Group 3 (42 patients) had an intact abductor mechanism and a 36-mm femoral head, and Group 4 (nine patients) had an absent abductor mechanism and a 36-mm femoral head. The minimum followup was 6 months (mean, 27 months; range, 6 months to 7 years). A 36-mm head was associated with a lower dislocation rate after revision total hip arthroplasty than a 28-mm head with an intact abductor mechanism; the rate of dislocation was 12.7% for Group 1, 40.0% for Group 2, 0% for Group 3, and 33.3% for Group 4. However, the use of a large-diameter head does not reduce the rate of dislocation if the abductor mechanism is absent.