Three-dimensional kinetic simulation before and after rotational acetabular osteotomy

Some reports indicate that one of major causes of clinical failure after periacetabular osteotomy is development of secondary femoroacetabular impingement (FAI). To assess the impact of range of motion (ROM) on the increase in FAI following rotational acetabular osteotomy (RAO), we performed FAI simulations before and after RAO. We evaluated 12 hips that had undergone RAO (study group), and 12 normal hips (control group). The study group was evaluated before and after surgery. Morphological parameters were evaluated to assess acetabular coverage. The acetabular anteversion angle, anterior CE angle, alpha angle, and combined anteversion angle were also measured. Impingement simulations were performed using 3D-CT. The ROM which causes bone-to-bone impingement was evaluated in flexion (flex), abduction, external rotation at 0A degrees flexion, and internal rotation at 90A degrees flexion. The lesions caused by impingement were evaluated. Radiographic measurements indicated improved postoperative acetabular coverage in the study group. The crossover sign was recognized pre- and postoperatively in every case in the study group and in no cases in the control group. In the simulation study, flexion, abduction, and internal rotation at 90A degrees flexion decreased postoperatively. Impingement occurred within 45A degrees internal rotation at 90A degrees flexion in two preoperative and nine postoperative cases. The impingement lesions were anterosuperior of the acetabulum in all cases. There were correlations between anterior CE angle, CE angle, acetabular anteversion angle, and hip flexion angle. There were also correlations between the anterior CE angle, combined anteversion angle, and angle of internal rotation at 90A degrees flexion. In the postoperative simulation, there was a tendency to reduce the ROM in flexion, abduction, and internal rotation at 90A degrees flexion due to impingement. Since there were more cases which caused impingement within 45A degrees internal rotation at 90A degrees flexion after RAO, we consider there is a potential for increased FAI after RAO.