Pathomorphologic characteristics of posttraumatic acetabular dysplasia.

OBJECTIVES: The pathomorphology of posttraumatic acetabular dysplasia differs fundamentally from the classic developmental dysplasia of the adolescent. The aim of this report is to qualify and quantify the pathomorphologic characteristics of the posttraumatic acetabular dysplasia and to define the requirements for adequate corrective surgery in this type of dysplasia.

DESIGN AND MATERIAL: Retrospective review of the anteroposterior (AP) radiographs of ten patients with symptomatic posttraumatic acetabular dysplasia. In five cases, false profile views and in five cases computed tomography (CT) scans were also available for investigation. Measurements of distances and angles on radiographs and CT scans were made by pencil and goniometer.

RESULTS: On the AP radiographs, posttraumatic acetabular dysplasia shows uniformly deformed true pelvis with an angular deformation of the innominate bone averaging 20 degrees in the region of the acetabular fossa that causes the concavity of the pelvic brim to increase in direction of the involved acetabulum and creates both a lateral and a caudal displacement of the acetabulum, averaging twenty-three millimeters and nine millimeters, respectively. The increased width of the inner wall of the acetabulum, measuring an average of eleven millimeters, makes lateralization of the center of the femoral head reach a mean of forty-three millimeters. The acetabular deformity in all cases shows a pronounced lateral deficiency. Ventral deficiency is moderate. All ten posttraumatic dysplastic acetabuli show marked retroversion averaging 27 degrees. In contrast, the contralateral acetabuli shows a mean anteversion of 23 degrees.

CONCLUSIONS: The morphology of this kind of acetabular dysplasia is uniform and differs significantly from that seen in classic developmental dysplasia of the hip. For reconstructive surgery of such a hip, the challenge to abolish the lateralization of the hip joint to restore normal body weight lever arm is imperative. Because acetabular retroversion is a reproductive feature of posttraumatic dysplasia, it is important to avoid further reduction of the posterolateral containment of the femoral head and augmentation of the anterior acetabular wall, increasing the risk of anterior impingement.