A computer simulation of rotational acetabular osteotomy for dysplastic hip joint: does the optimal transposition of the acetabular fragment exist?

For young patients who have early signs of coxarthrosis resulting from acetabular dysplasia, periace- tabular osteotomies for correcting abnormal stress distribution can be useful for preventing the progression of the disease. However, it is difficult to confirm the optimal transposition of the osteotomized acetabular fragment. To deal with this problem, we devised a computer program to support preoperative planning. Hip images obtained by computed tomography were loaded into our program, and a threedimensional voxel model was created. Then, osteotomy was simulated and the pressure distribution was analyzed with a rigid-body spring analysis (computational nonlinear mechanical analysis). The three-dimensional pressure distributions in seven dysplastic hips were evaluated before and after virtual rotational acetabular osteotomy. A peak pressure was calculated for every 5° of rotation of the acetabular fragment. The peak pressure decreased gradually and increased again afterward, indicating the optimal transposition of the acetabular fragment. The postoperative peak pressure decreased to about 40% in the most improved case. This program allows the hip joint mechanics to be evaluated easily so that the advantages and disadvantages of various surgical methods can be examined biomechanically prior to surgery.