SIMULTANEOUS MEASUREMENT OF STIFFNESS AND ENERGY ABSORPTIVE PROPERTIES OF ARTICULAR-CARTILAGE AND SUBCHONDRAL TRABECULAR BONE

The purpose of this study was to develop a method for simultaneous mea surement of the mechanical properties of articular cartilage and under lying trabecular bone. Cylindrical bone-cartilage specimens from human cadaver knees were tested under non-destructive axial compression. Th e specimens were mounted in a cage by three screws fixed to the subcho ndral bone plate to create a reference plane between the cartilage and the bone. Each test was carried out as a single test cycle between a 0.12 MPa (4 N) pre-stress and 0.5 per cent bone strain. Twenty conditi oning cycles were performed prior to each test cycle. In order to dete rmine the reproducibility of the test method, the test procedure was r epeated after turning the cage through 90 degrees. The specimens were then kept at + 5 degrees C for 24 hours, and the procedure was repeate d. The normalized stiffness and energy absorptive properties were calc ulated from each test cycle. No significant difference was found betwe en the results obtained on the first and on the second day. Both days the stiffness of cartilage was significantly larger during the second test, indicating that 20 conditioning cycles may not provide a viscoel astic steady state.