Dynamic response of femoral cartilage in knees with unicompartmental osteoarthritis

Abstract

The objective of the present work was to determine the dynamic indentation response, stiffness and relaxation curves for the shear and the bulk modulus of femoral knee cartilage with no visual damage in cases under unicompartmental osteoarthritis. A cyclic displacement of 0.5 mm in axial direction was applied with a 3 mm plane-ended cylindrical indenter at specific points in the femoral knee cartilage specimens of seven patients with unicompartmental osteoarthritis (UOA). The indentation force over time was recorded and next the maximum stiffness in all cycles was obtained and compared. Also, the relaxation curves for the shear and the bulk modulus of cartilage were obtained in this work. A decrease in the maximum indentation force was observed comparing between indentation cycles; it was of 6.75 ± 0.71% from cycle 1 to cycle 2 and 4.70 ± 0.31% for cycle 2 to cycle 3. Stiffness values changed with a mean of 3.35 ± 0.39% from cycle 1 to cycle 2 and 1.40 ± 0.71% from cycle 2 to cycle 3. Moreover, relaxation curves for the shear modulus and the bulk modulus showed the nonlinear behavior of articular cartilage with UOA. Our results showed that cartilage specimens with no visual damage in UOA preserve a nonlinear viscoelastic behavior and its stiffness increases through the loading cycles. Our work provides experimental values for generating a more realistic cartilage behavior than those currently used in computer cartilage models for the study of UOA.