Indentation instrument for the measurement of cartilage stiffness under arthroscopic control.

Changes in the biomechanical properties of articular cartilage are one of the first signs of the tissue degeneration. We have developed a small size indentation instrument for the quantification of cartilage stiffness under arthroscopic control. During measurement, the indenter imposes a constant deformation on the cartilage and the maximal indenter force, by which the cartilage resists the deformation, is used as a measure for cartilage stiffness. The instrument has been tested in laboratory conditions with elastomer and cadaver knee joint cartilage samples. A linear relationship was found between indenter force and elastomer stiffness (r = 0.990, n = 14) as well as between indenter force and cartilage shear modulus obtained by a reference device (r = 0.879, n = 22). Also, the correlation between two repeated measurements at the measurement sites, used to evaluate the reproducibility, was linear (r = 0.953, n = 16). Quantitative detection of cartilage stiffness is possible with the instrument.