[Biomechanics of the Chiari pelvic osteotomy]

We have reviewed our findings on 476 hip joints that underwent a Chiari pelvic osteotomy (Chiari) between June 1983 and March 1990, employing computer simulation using non-linear analysis based on the rigid-body spring model (RBSM) proposed by Kawai. We further made estimates of the changes in the hip abduction force resulting from the Chiari. The abduction force was measured by a Cybex II machine, before and after Chiari, and they were compared with those from simulation modeling (using the abduction muscle model: ABMM) for the power change expected by Chiari. According to the results in the RBSM, the resultant force, the abduction force, deviation of the pelvis, and the joint stress improved outcome after Chiari. Chiari had a positive effect on the peak torque of the hip abduction, though the abduction force was not fully restored clinically. The simulation by ABMM, showed similar results with the abduction force decreasing with increasing degree of hip abduction. From these results, we have developed and established a new technique for the reattachment of the greater trochanter in Chiari.