We studied the risk of recurrent dislocation in 121 primary and 39 revision Charnley or Charnley hybrid total hip arthroplasties which had been treated for a primary dislocation between 1979 and 1995. Only 35% of these hips had no further dislocation or a revision for instability within one year. The rates of survival gradually declined with time or if a second, third or fourth dislocation occurred. The risk of recurrence was greater in men, but was not related to age, diagnosis, time of the first dislocation or whether the index operation had been a primary or a revision procedure.

Operative treatment included 15 reoperations leaving intact components, 50 revisions, and permanent removal of the femoral stem in seven patients. The operation was successful in four patients with reoperations and in 36 who had an exchange procedure within two years. Treatment was successful in 35 of 49 hips in which it was possible to correct a technical error compared with 5 out of 16 hips in which malposition of the components was not seen (p = 0.007).

We studied the effect of surgical experience on the dislocation rate after 4230 primary total hip arthroplasties (THAs) all performed using the posterior approach at three orthopaedic centres at major county hospitals. There were 129 postoperative (3%) dislocations.

Twice the number of dislocations were registered for inexperienced surgeons as for their more experienced colleagues. This frequency of dislocation levelled off with increasing numbers of operations and remained constant after approximately 30. For every ten primary THAs performed annually, the risk of dislocation decreased by 50%.