Depth Dependent Strain Analysis of Articular Cartilage Under Impaction Loading

Lesions in the cartilage of the knee can lead to degenerative arthritis of the joint. Therefore, procedures such as osteochondral grafting are used to repair the cartilage. Osteochondral grafting procedures are of interest, because the lesion is replaced with true hyaline cartilage. This procedure involves press-fitting a cylindrical bone-cartilage plug by impaction to repair the damaged cartilage area. Recently, it has been shown that impact insertion of osteochondral grafts generates damaging loads that cause chondrocyte death, particularly in the superficial zone [1]. Using high speed video analysis, it has been shown that the highest local deformations occur within the superficial zone of the osteochondral plug [2,3]. However, the exact strain condition of the tissue during impaction and any depth dependent strain differences remain unknown. Assuming uniaxial load conditions of an ideal cylinder exposed to high strain rates, the stress-strain response of cartilage plugs during the impaction process is reported in this study. We hypothesized that the highest strain levels would occur in the superficial zone. Based on the experimental results, the fundamental material effects substantial for the load case under consideration can be studied. Consequently, suitable material models for subsequent numerical simulations can be established.