[Apropos of 87 dislocations of total hip prostheses].

Eighty seven dislocations were seen in 1571 consecutive total hip replacements, mostly performed through a posterior approach. Nine occurred immediately after operation and most of the remainder within 5 weeks. In 26 cases further dislocation occurred, and in 11 patients another operation was required. The 87 dislocated hips have been compared with the remaining 1484. Factors predisposing to dislocation included revision operations, the experience of the surgeon and proper reconstruction of the abductor musculature. When the hip was deemed unstable at the end of an operation, dislocation occurred on 18 occasions out of 20 such cases. The position of the components in the dislocated hips was compared with that in 100 stable prostheses chosen by random sampling. A vertical acetabular prosthesis, and retroversion of the acetabular and femoral components all favoured dislocation. In 331 replacements with a 22 mm diameter head 29 dislocations were seen (8.7%), whereas in 168 replacements with 32 mm heads, 5 dislocations occurred (2.9%).