COMPARATIVE-STUDY OF THE INTRINSIC MECHANICAL-PROPERTIES OF THE HUMANACETABULAR AND FEMORAL-HEAD CARTILAGE

Biphasic creep indentation methodology and an automated indentation ap paratus were used to measure the aggregate modulus, Poisson's ratio, p ermeability, thickness, creep and recovery equilibrium times, and perc entage of recovery of normal articular cartilage in 10 human hip joint s. These properties were mapped regionally to examine the mechanical f actors involved in the development of site-specific degenerative lesio ns in the acetabulum and femoral head. The results indicate that there are significant differences between these properties regionally in th e acetabulum and femoral head and between the two anatomical structure s. Specifically, it was found that cartilage in the superomedial aspec t of the femoral head has a 41% larger aggregate modulus than its anat omically corresponding articulating surface in the acetabulum. In addi tion, the superomedial aspect of the femoral head has the greatest agg regate modulus (1.816 MPa) within the hip joint. During sitting, the i nferior portion of the femoral head is in contact with the anterior ac etabulum, and the anterior acetabulum has a 53% greater aggregate modu lus than the inferior femoral head. This area below the fovea on the f emoral head has the least aggregate modulus (0.814 MPa) within the hip joint. These mismatches in the compressive modulus of opposing articu lating surfaces may contribute to degeneration of cartilage in the sup eromedial acetabulum and the inferior femoral head. Our findings suppo rt the clinical observation that these areas are frequent sites of ear ly degeneration.