Stem design and dislocation after revision total hip arthroplasty: Clinical results and computer modeling
Robert L. Barrack; R. Allen Butler; Daniel R. Laster; Pamela AndrewsHip
The effect of the size and shape of the neck and the taper of the femoral stem on dislocation rate after revision total hip arthroplasty was examined. Design I had a large (14/16), long taper with a circular neck cross-section; a fixed 42-mm offset; and a neck that was anteverted relative to the stem. Design II was characterized by a smaller (12/14), shorter taper; a trapezoidal neck cross-section; a progressive (40-50 mm) offset; and no neck anteversion relative to the stem. The stems were digitized and placed through a range of motion using virtual reality software, and the cross-sectional area of the neck, length of the taper, and total arc of motion before impingement between the neck and liner were compared. The dislocation rate at a minimum of 2 years’ follow-up was 15.4% (8 of 52) for design I compared with 4.3% (2 of 46) for design II. This finding was consistent with the results of computer modeling, which showed that design I had a cross-sectional area that was 32% greater and a total arc of motion that was 76% less compared with design II. The results suggest that neck and taper design may be an important factor in dislocation after revision total hip arthroplasty.
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