Some aspects of the biomechanics of articular cartilage repair

The sensitivity of the affects of indenter radius, defect depth, cartilage permeability and flow boundary conditions, on the indentation testing of a repairing osteochondral defect was investigated. Since the boundary condition on the flow across the cartilage repair-subchondral bone interface is not known, the effects of two different conditions were investigated: free-flow and no-flow. A poroelastic finite element model of an osteochondral defect at different stages of the repair process was developed using dimensions typical of the rabbit knee. Results showed when the radius of the indenter was much less than the thickness of the cartilage the sensitivity of the indentation displacement to flow boundary conditions decreased. Simulated indentation displacement was insensitive to bone regeneration up to 50% of the initial defect depth, which suggests that only the properties of the material in the upper half of the defect are being evaluated. Small variations in permeability had little affect on the simulated indentation. In a fully repaired defect, the simulated indentation is independent of the boundary condition. It was concluded that the boundary condition on the repair-subchondral bone interface must be known in all cases except when the defect approaches full repair, if accurate estimates of material properties are to be obtained from indentation.; Little is known of the mechanical environment in osteochondral defects that are being developed to repair areas of damaged cartilage. Since the mechanical environment in a repair cannot be measured, a finite element model of joint contact with an osteochondral defect was developed and used for this purpose. The stress and strain distributions at several stages of tissue repair were evaluated. Variations of normal and radial stresses and strains were greatly increased as the stage of repair increased. The large differences between 0% repair and 100% repair suggest that the initial mechanical environment in a repairing osteochondral defect is vastly different from that in a normal cartilage layer.; Hydrostatic pressure of the interstitial fluid is considered to be an important mechanical determinant by resisting compressive force applied on the cartilage surface. An existing hydrostatic pressure system was evaluated, redesigned as needed and validated. The redesigned pressure chamber was able to reach a maximum pressure of 11.2 MPa and is capable of applying different levels, durations, and frequencies of compression.