Proximal displacement of the femoral head after Chiari pelvic osteotomy for coxarthrosis with dysplastic acetabulum

Proximal displacement of the femoral head can been seen sometimes after Chiari pelvic osteotomy. In order to clarify the causes of the displacement, a quantification analysis was performed to evaluate the factors of this osteotomy. The statistical analysis showed that 54% of the causes could be explained as being due to the angle of osteotomy, obesity ratio, the variation of the acetabular trochanteric distance, and other three factors. Paying attention to get good results: 1) making the angle of osteotomy from 11 degrees to 20 degrees, 2) keeping the variation of the acetabular trochanteric distance within 20mm, 3) the improvement of the lever arm ratio within 15%, and 4) the approximate acetabular index above 30%. In a case with the greater trochanter pulled down, a computer simulation showed that the centripetal force of the femoral head was decreased, and the displacement was increased.