The 'instantaneous' compressive modulus of human articular cartilage in joints of the lower limb

The instantaneous compressive modulus of articular cartilage was surveyed in 11 sets of human lower limb joints obtained from the ipsilateral side. The average modulus for the entire joint surface of each joint and the topographical variations in the modulus within each joint were examined for all 11 sets, and subjected to statistical analysis. Within each set of joints (hip, knee and ankle), the ankle always had a significantly greater mean compressive modulus than the hip and knee (P < 0.001-P < 0.05). In seven sets of joints, there was no significant difference between the mean compressive moduli of the knee and hip joints. In three sets of joints, the compressive modulus of the knee was significantly greater than that of the hip (P < 0.001-P < 0.01), while in only one set of joints was the compressive modulus of the hip significantly greater than that of the knee (P < 0.01). The topographical variations in the cartilage instantaneous compressive modulus over the surfaces of the lower limb joints were matched by differences in the stresses occurring in different areas of each joint. The results of the present study corroborate previous findings and show that the site-specific stresses and corresponding values of the instantaneous cartilage compressive modulus over the surfaces of lower limb joints were correlated (r = 0.82 at P < 0.01), thus adding credence to the conditioning hypothesis of cartilage by prevalent stress.