Comparison of biomechanical and biochemical properties of cartilage from human knee and ankle pairs

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Abstract
Cartilage was obtained from eight matched knee (tibiofemoral and femoropatellar) and ankle (talocrural) joints of five different donors (both left and right from donors 14, 22, and 38 years of age, and left only from donors 31 and 45 years of age) within 24 hours of death. All cartilage was graded as normal by the macroscopic visual Collins' scale and the histological Mankin scale. Cylindrical disks of cartilage were harvested from 10 sites within the tibiofemoral and femoropatellar joint surfaces and four sites within the talocrural joint, and uniaxial confined compression measurements were performed to quantify a spectrum of physical properties including the equilibrium modulus, hydraulic permeability, dynamic stiffness, streaming potential, electrokinetic coupling coefficient, and electrical conductivity. Matched specimens from the same 14 sites were used for complementary measurements of biochemical composition and molecular interaction, including water content, hypotonic swelling behavior, and sulfated glycosaminoglycan and collagen contents. In comparison of the top 1‐mm slices of talar cartilage with the top 1‐mm of tibiofemoral cartilage, the talar cartilage appeared denser with a higher sulfated glycosaminoglycan content, lower water content, higher equilibrium modulus and dynamic stiffness, and lower hydraulic permeability. The equilibrium modulus increased with increasing sulfated glycosaminoglycans per wet weight and decreased with increasing water content for all joint surfaces. Multiple linear regression showed that greater than 80% of the variation in the equilibrium modulus could be accounted for by variations in the biochemical parameters (water content, sulfated glycosaminoglycans/wet weight, and hydroxyproline content/wet weight) for each joint surface. Nonhomogeneous depth‐dependent changes in the physical properties and biochemical composition of full‐thickness distal femoral cartilage were consistent with previous reports. Since the compressive deformation of cartilage during cyclic loading is confined to the more superficial regions, the differences in properties of the upper regions of the talar compared with tibiofemoral or femoropatellar cartilage may be important in the etiology of osteoarthritis.