Computed tomographic evaluation of component position on dislocation after total hip arthroplasty.

True proper position after total hip arthroplasty was determined by measuring the cup and stem anteversion using computed tomography. We compared 20 dislocated hips (14 posterior and 6 anterior) with 18 non-dislocated hips. Both the cup anteversion and the stem anteversion showed no differences among the groups. The sum of cup and stem anteversion in posterior dislocated hips was significantly lesser than that in non-dislocated hips and the sum in anterior dislocated hips was significantly greater than that in non-dislocated hips. These results suggested even if the cup alone or the stemalone is at proper position, dislocation might occur.