Three-dimensional displacement of the hip joint after triple pelvic osteotomy - A postmortem radiostereometric study

Triple pelvic osteotomy reorients the acetabulum relative to the pelvis in order to improve acetabular coverage of the femoral head in cases of acetab ular dysplasia. We undertook a radiostereometric analysis (RSA) on 6 osteot omized cadaver hips to determine the actual three-dimensional reorientation obtained. The centers of the femoral head were all translated posteriorly between 11 and 41 mm, and distally up to 13 mm. 4 were lateralized up to 8 mm, and 2 w ere medialized up to 5 mm. All acetabuli rotated anteriorly about the later al to medial axis (X-axis), and 4 rotated outwards around the distal to pro ximal axis (Y-axis). The correlations between measurements performed on con ventional anteroposterior radiographs and the RSA measurements were poor: v ariations in the lateral-medial direction ranged from -16 to +6 mm, and in the distal-proximal direction between -10 and +12 mm. The changes in orientations measured will significantly affect the load acr oss the hip joint, since the dimensions of the pelvis change and the moment arms of the muscles, their lengths and lines of action are changed as well . We conclude that, with the procedures presently performed, the loads acro ss the hip joint are bound to change, and that the reorientation can hardly be checked with conventional radiographs.