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

Cartilage was obtained from eight matched knee (tibiofemoral and femoropate llar) 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 3 1 and 45 years of age) within 24 hours of death. All cartilage was graded a s normal by the macroscopic visual Collins' scale and the histological Mank in scale. Cylindrical disks of cartilage were harvested from 10 sites withi n the tibiofemoral and femoropatellar joint surfaces and four sites within the talocrural joint, and uniaxial confined compression measurements were p erformed to quantify a spectrum of physical properties including the equili brium modulus, hydraulic permeability, dynamic stiffness, streaming potenti al, electrokinetic coupling coefficient, and electrical conductivity. Match ed specimens from the same 14 sites were used for complementary measurement s of biochemical composition and molecular interaction, including water con tent, hypotonic swelling behavior, and sulfated glycosaminoglycan and colla gen contents. In comparison of the top I-mm slices of talar cartilage with the top l-mm of tibiofemoral cartilage, the talar cartilage appeared denser with a higher sulfated glycosaminoglycan content, lower water content, hig her equilibrium modulus and dynamic stiffness, and lower hydraulic permeabi lity. The equilibrium modulus increased with increasing sulfated glycosamin oglycans 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 variati ons in the biochemical parameters (water content, sulfated glycosaminoglyca ns/wet weight, and hydroxyproline content/wet weight) for each joint surfac e. Nonhomogeneous depth-dependent changes in the physical properties and bi ochemical composition of full-thickness distal femoral cartilage were consi stent with previous reports. Since the compressive deformation of cartilage during cyclic loading is confined to the more superficial regions, the dif ferences in properties of the upper regions of the talar compared with tibi ofemoral or femoropatellar cartilage may be important in the etiology of os teoarthritis.