DYNAMIC STIFFNESS OF ARTICULAR CARTILAGE BY SINGLE IMPACT MICRO-INDENTATION (SIMI)

Fresh pig cadaver knees (6 mt old) were used. A SIMI device [2] was mounted on a load-cell attached to the adjustable crosshead of a rigid frame (Fig. 1) to provide control of pre-load. A mechanical stage and laser were used to position samples under the 1 mm indenter. The dynamic fall/rebound path of the indenter is captured by an electric coil. SIMI software uses an indentation model to determine aggregate modulus and loss angle. On 8 specimens, 16 indentations were made at 1 min. intervals--in the load bearing aerias of the patella, trochlea and the medial and lateral femoral condyles. The SIMI impulse load parameters are similar to those observed during rapid gait—i.e. the strain rate is somewhat higher than in walking