Outcome of periacetabular osteotomy: Joint contact pressure calculation using standing AP radiographs, 12 patients followed for average 2 years

AP radiographs are the most common imaging technique used for patients with hip dysplasia. While pelvic AP and oblique radiographs are used for preoperative planning before periacetabular osteotomy, the diagnosis and follow-up routines are usually based on AP radiographs showing both hip joints (Sibenrock et al. 1999). The AP views are standardized using a standing (weight-bearing) posture to improve the assessment of joint-space (Turula et al. 1985). Because a pelvic AP view is taken of every patient with dysplasia, independent of the treatment, these views can be used to compare patient outcomes. Klaue et al. (1988) introduced the use of CT for preoperative planning based on 3D imaging of the pelvis. Our work comparing the alignment between normal and dysplastic joints simplified the practical application of this technique (Lepisto et al. 1998). Presently, our institution which uses this method as a standard surgical planning tool for hip dysplasia. Diagnosis and follow-up, however, is still based on AP pelvic radiographs. Since the structure of dysplastic hips varies markedly, it is difficult to establish general guidelines for surgery. Pelvic osteotomy is performed to relieve pain and avoid joint subluxation by improving the contact pressure distribution and the femoral head coverage. Because the contact pressure distribution following surgery cannot be characterized from the preoperative plan, surgeons typically try to reproduce the joint coverage seen in normal hips. The characteristics of correct alignment for the contact surface have been sought by comparing the contact pressure distribution for the normal and dysplastic hips, both computationally (Genda et al. 1995, Hipp et al. 1999) and experimentally (Michaeli et al. 1997). Previous studies have lacked information about the influence of anatomical variations between patients on the contact pressure distribution, however. In order to evaluate how effectively pelvic osteotomy procedures improve the contact pressure distribution in dysplastic hips, we performed a mechanical study of patients treated with a pelvic osteotomy. Our hypothesis was that the radiographically measured parameters used to assess the alignment of the joint surface do not necessarily correlate with the mechanical goals of periacetabular osteotomy.