The change in tissue impedance due to the change in the extracellular
matrix that results from the degradation of cartilage is utilized to
detect degradation of articular cartilage. A probe includes electrodes
that apply a current to the articular cartilage which results in a current
distribution and electric field within the cartilage, along with an
associated voltage drop across the electrodes. The amplitude of this
voltage drop is then measured and divided by the current applied to
determine the tissue impedance. By measuring the impedance of patient
tissue and comparing the detected patient impedance to a normal value for
the tissue from clinically normal tissue, a determination of whether the
patient tissue is degraded, and a determination of the extent of
degradation is possible. Preferably, the impedance is measured using a
probe with interdigitated electrodes. By changing which electrodes are
utilized, the wavelength of the current distribution changes, allowing the
probe to image depth dependent focal lesions.
