Effect of femoral head diameter and operative approach on risk of dislocation after primary total hip arthroplasty.

TLDR: In total hip arthroplasty, a larger femoral head diameter was associated with a lower long-term cumulative risk of dislocation and was greatest in association with the posterolateral approach.

Abstract: Background: It has been postulated that use of a larger femoral head could reduce the risk of dislocation after total hip arthroplasty, but only limited clinical data have been presented as proof of this hypothesis Methods: From 1969 to 1999, 21,047 primary total hip arthroplasties with varying femoral head sizes were performed at one institution Patients routinely were followed at defined intervals and were specifically queried about dislocation The operative approach was anterolateral in 9155 arthroplasties, posterolateral in 3646, and transtrochanteric in 8246 The femoral head diameter was 22 mm in 8691 of the procedures, 28 mm in 8797, and 32 mm in 3559 Results: One or more dislocations occurred in 868 of the 21,047 hips The cumulative risk of first-time dislocation was 22% at one year, 30% at five years, 38% at ten years, and 60% at twenty years The cumulative ten-year rate of dislocation was 31% following anterolateral approaches, 34% following transtrochanteric approaches, and 69% following posterolateral approaches The cumulative ten-year rate of dislocation was 38% for 22-mm-diameter femoral heads, 30% for 28-mm heads, and 24% for 32-mm heads in hips treated with an anterolateral approach; 35% for 22-mm heads, 35% for 28-mm heads, and 28% for 32-mm heads in hips treated with a transtrochanteric approach; and 121% for 22-mm heads, 69% for 28-mm heads, and 38% for 32-mm heads in hips treated with a posterolateral approach Multivariate analysis showed the relative risk of dislocation to be 17 for 22-mm compared with 32-mm heads and 13 for 28-mm compared with 32-mm heads Conclusions: In total hip arthroplasty, a larger femoral head diameter was associated with a lower long-term cumulative risk of dislocation The femoral head diameter had an effect in association with all operative approaches, but the effect was greatest in association with the posterolateral approach Level of Evidence: Therapeutic Level III See Instructions to Authors for a complete description of levels of evidence