DIRECT COMPARISON OF CONTACT AREAS, CONTACT STRESS AND SUBCHONDRAL MINERALIZATION IN HUMAN HIP-JOINT SPECIMENS

X-ray densitometric and CT osteoabsorptiometric findings suggest that in the human hip subchondral mineralization patterns change from bicen tric to monocentric as a function of age. It has been hypothesized tha t these changes indicate an alteration in the geometric configuration of the joint from incongruous to congruous, possibly associated with t he onset of osteoarthrosis. The purpose of this study was therefore to directly compare contact areas, contact stress and subchondral minera lization in the hip joint. Twelve specimens without cartilage lesions (ages 34-86 years) were investigated. Simulating the mid-stance phase, the contact areas were determined by polyether casting and the contac t stress with Fuji film. The distribution of subchondral mineralizatio n Was assessed non-invasively with CT osteoabsorptiometry. At small lo ads the load-bearing areas were located at the periphery of the lunate surface. In some joints they were found in the acetabular roof and ex panded, with higher loads, to the center of the lunate surface and the anterior and posterior horns. In other joints, the contact areas were recorded at lower loads in the anterior and posterior horns, and only at higher forces they merged in the acetabular roof. The maximal cont act stress ranged from 8 to 9 MPa at 300% body weight. Maxima of subch ondral mineralization were recorded in the acetabular roof, in the ant erior and posterior horns, or in all three locations. There was no cle ar correlation between the distribution of contact and pressure, and t he pattern of subchondral bone density. Incongruity is shown to strong ly affect the distribution of contact and pressure in the human hip jo int. However, the pattern of subchondral mineralization cannot be read ily explained in terms of the contact areas and contact stress during mid-stance. Incongruity may give rise to tensile stresses in the subch ondral bone, and the construction of the pelvis as a whole may play an important role in subchondral bone loads and adaptation.