Quantitation and localization of cartilage degeneration following the induction of osteoarthritis in the rabbit knee

Objective: To develop and apply a new video imaging technique to quantify and localize Indian ink staining of cartilage of the rabbit femorotibial joint after the induction of osteoarthritis by unilateral transection of the anterior cruciate ligament (ACLT). Methods: Nine weeks after surgery, femora and tibiae from 11 ACLT and contralateral control knees were harvested and positioned to obtain calibrated gray-scale images of the ink-painted articular cartilage surfaces that are opposed with the knee in 90 degrees flexion. Images were processed so that areas of normal cartilage gave a relatively high reflectance score, whereas ink-stained fibrillated cartilage and exposed bone gave low scores. Results: Comparison of the medial and lateral femoral condyles and tibial plateaus (MFC, LFC, MTP, LTP) of control and ACLT knees showed that the area of the MTP not covered by the meniscus had a significantly lower reflectance score (P < 0.001) than other areas. ACLT led to an 11% decrease (P < 0.001) in the overall reflectance score. The reflectance score decreased as a traditional morphological grading of degeneration increased. ACLT-induced degeneration had a predilection for the posteromedial aspects of the joint, and to a lesser extent, the anterolateral aspects. In the tibial plateaus, ACLT caused significant degeneration in the covered, but not the uncovered, areas. Image scores of opposing cartilage surfaces (i.e., MFC vs MTP and LFC vs LTP) were significantly (R=0.56-0.70, P < 0.001) correlated in ACLT and control knees. Discussion: Identification and characterization of cartilage areas prone to degeneration may be particularly useful for further analysis of biochemical and biomechanical mechanisms in osteoarthritis, as well as the efficacy of therapeutic interventions.