Research On The Optimization Of Prosthetic Replacement For Developmental Hip Dysplasia By 3-D Reconstruction

Adult acetebular dysplasia of the hip is the most common underlying condition leading to secondary osteoarthritis (OA) of the hip, many patients ultimately progress to having total hip arthroplasty (THA). Although arthroplasty often is the only definitive way of restoring the normal biomechanics of the dysplastic joint, these procedures often are challenging, primarily because of the associated bony deformities. Typically, the dysplastic joint consists of a subluxed or even dislocated femur with a straight, narrow canal and a short excessively anteverted neck, and a shallow, vertically-inclined acetabulum. The increased surgical demands of the dysplastic joint often result in inferior results after total hip replacement (THR) with an increased incidence of loosening and dislocation at long-term followup.These procedures also are associated with an increased prevalence of intraoperative complications, and most notably cortical fracture because of the difficulties of inserting conventional prostheses into canals of distorted shape and version.Three-dimensional computerized tomography scans of a patient who had a acetebular dysplasia of the hip. Based on the results of the current study, we think that greater attention should be given to the morphologic characteristics of normal and dysplastic acetabulum and femurs in the patients. Lateral oblique view of the hip. The hypoplastic true acetabulum, triangular in shape, has segmental deficiency of the entire acetabular rim, a narrow opening, and inadequate depth. The femoral head is small, there is increased anteversion of the femoral neck, and the diaphysis has a thin cortex and a narrow canal. Lateral oblique view of the defective acetabulum after removal of the femoral head. Bone stock at the level of the true acetabulum is mainly superoposterior. The anterior acetabular wall is defective. The entire iliac bone is in increased anteversion. The hollow in the iliac wing represents the false articulation of the dislocated femoral head.This anatomic observation has several important clinical implications. Orthopaedic surgeons appreciate the fact that, during radiographic examination of the hip, the neck-shaft angle of the femur and the medial offset of the femoral head only are depicted accurately if the femoral neck is oriented parallel to the xray cassette. In the case of the dysplastic femur, in which anteversion is exaggerated, rotational orientation dramatically affects not only the appearance of the proximal femur, but the size and shape of the canal. Moreover, as the canal is twisted, the elliptical shape of the canal at the isthmus, does not lie in the plane of the neck, but rather at 30°to 60°to the sagittal and coronal planes. Consequently, the minor axis of the isthmus appears on neither the AP nor the lateral radiograph and so measurements of canal size taken from the AP radiograph overestimate the minimum canal diameter by as much as 2 mm. This explains why it often is difficult to select prostheses to fit the dysplastic canal during THR, and why surgeons have favored the use of undersized cemented components that allow greater latitude intraoperatively.These findings and those of earlier studies indicated that prosthetic devices primarily designed for individuals of larger anatomy do not fit the femora of patients, or patients with dysplasia. Furthermore, in cases with excessive anteversion, the concomitant twist of the femoral canal makes joint replacement doubly difficult. Hopefully, the knowledge gained through this study will provide greater insight into the morphologic characteristics of the dysplastic acetabulum and femur and the challenges confronting the joint replacement surgeon.