Biomechanical topography of human ankle cartilage

Abstract

The material properties of normal cadaveric human cartilage in the ankle mortice (tibiotalar articulation) were evaluated to determine a possible etiologic mechanism of cartilage injury of the ankle when an obvious traumatic episode is not present. Using an automated indentation apparatus and the biphasic creep indentation methodology, creep indentation experiments were performed in five sites in the distal tibia, one 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 cartilage (1.06 MPa). Cartilage in the anterior medial portion of the tibia has the largest aggregate modulus (HA = 1.34 MPa), whereas the softest 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 lateral ridge of the talus was the thickest (1.45 mm) and the distal fibula was the thinnest (0.95 mm) articular cartilage. The largest Poisson's ratio was found in the distal fibula (0.08). The lowest and highest permeability were found in the anterior lateral regions of the astragalus (0.80 x 10(-15) m4N-1sec-1) and the posterior medial region of the tibia (1.79 x 10(-15) m4N-1sec-1), respectively. The anterior and posterior regions of the lateral and medial sites of the tibia were found to be 18-37% stiffer than the anatomically corresponding sites in the talus. The biomechanical results may explain clinically observed talar dome osteochondral lesions when no obvious traumatic event 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.

Topographic Variations in Biomechanical and Biochemical Properties in the Ankle Joint: An In Vitro Bovine Study Evaluating Native and Engineered Cartilage

“…This testing approach represents a validated method for evaluating biomechanical and biochemical properties of cartilage. 13,24,25 For engineered neocartilage construct formation, chondrocytes were isolated from 7 cadaveric ankle and knee joints, as previously described. 23 In brief, tissue from the tibial plafond, distal fibula, and talar dome, using the femoral condyle as a control, was collected separately and minced into 1-mm pieces, followed by digestion in 0.2% type II collagenase (Worthington, Lakewood, NJ) for 18 hours, as previously described.…”

“…28 Samples were tested as previously described 26 using a semi-analytical, semi-numeric, biphasic model 29 and finite-element optimization. 13 Each sample's aggregate modulus and shear modulus were analyzed. In choosing parameters for comparing different tissues, compression and tensile moduli were assayed because they are intrinsic mechanical properties.…”

“…As intrinsic properties, tensile and compressive moduli are commonly measured to inform the mechanical quality of cartilage. Thus both tensile and compressive tests were performed such that we would be able to compare our data with the literature values 13 ; the value of the shear modulus was also calculated.…”

“…11,12 Significant topographic variations in the cartilage material properties have been described that may be related to the increased risk of degeneration. 13 In addition, variations in the biochemical properties of the extracellular matrix and the metabolic activity of the chondrocytes between the ankle and the knee joint have been reported. 14,15 This suggests that biomechanical and biological factors may be involved in the pathogenesis of chondral lesions.…”

Composition and transport properties of human ankle and knee cartilage

“…25 Sulfated glycosaminoglycans (S-GAG) were quantified as a measure of proteoglycan content using the 1,9-dimethylmethylene blue (DMMB) assay. 26 Standards were prepared from chondroitin 4-sulfate at concentrations of 10,20,30,40,60,80, and 100 mg/mL. Samples were diluted with papain until the values lay within the standard curve.…”