BIOMECHANICAL TOPOGRAPHY OF HUMAN ANKLE CARTILAGE

The material properties of normal cadaveric human cartilage in the ank le mortice (tibiotalar articulation) were evaluated to determine a pos sible etiologic mechanism of cartilage injury of the ankle when an obv ious traumatic episode is not present. Using an automated indentation apparatus and the biphasic creep indentation methodology, creep indent ation experiments were performed in five sites in the distal tibia, on e site in the distal fibula, and eight sites in the proximal talus of 14 human ankles (seven pairs). Results showed significant differences in the mechanical properties of specific human ankle cartilage regions . Topographically, tibial cartilage is stiffer (1.19 MPa) than talar c artilage (1.06 MPa). Cartilage in the anterior medial portion of the t ibia has the largest aggregate modulus (H-A = 1.34 MPa), whereas the s oftest tissue was found to be in the posterior lateral (0.92 MPa) and the posterior medial (0.92 MPa) regions of the talus. The posterior la teral ridge of the talus was the thickest (1.45 mm) and the distal fib ula was the thinnest (0.95 mm) articular cartilage. The largest Poisso n's ratio was found in the distal fibula (0.08). The lowest and highes t permeability were found in the anterior lateral regions of the astra galus (0.80 x 10(-15) m(4)N(-1)sec(-1)) and the posterior medial regio n of the tibia (1.79 x 10(-15) m(4)N(-1)sec(-1)), respectively. The an terior and posterior regions of the lateral and medial sites of the ti bia were found to be 18-37% stiffer than the anatomically correspondin g sites in the talus. The biomechanical results may explain clinically observed talar dome osteochondral lesions when no obvious traumatic e vent is present. Cartilage lesions in a repetitive overuse process in the ankle joint may be related to a disparity of mechanical properties between the articulating surfaces of the tibial and talar regions.