Comparative study of the intrinsic mechanical properties of the human acetabular and femoral head cartilage

Using the biphasic creep indentation methodology and our new automated indentation apparatus, we obtained the intrinsic material properties and thickness of normal articular cartilage in ten human hip joints. The results indicate that significant differences exist in these properties topographically in the acetabulum and femoral head, and between these two anatomical structures. Articular cartilage in the area below the fovea has the smallest compressive modulus. Cartilage in the supero-medial aspect of the femoral head has the largest compressive modulus. In the anatomical position, the significantly stiffer supero-medial portion of the femoral head articulates with the supero-medial portion of the acetabulum. During sitting, the inferior portion of the femoral head is in contact with the significantly stiffer anterior acetabulum. These findings corroborate the clinical observation that the inferior portion of the femoral head and the superior portion of the acetabulum degenerate more frequently. This may be due to mismatch in their compressive modulus with that of their opposing surfaces.