Experimental validation of arthroscopic cartilage stiffness measurement using enzymatically degraded cartilage samples

In order to evaluate the ability of the arthroscopic indentation instrument , originally developed for the measurement of cartilage stiffness during ar throscopy, to detect cartilage degeneration, we compared changes in the sti ffness with the structural and constitutional alterations induced by enzyme s on the tissue in vitro. The culturing of osteochondral plugs on Petri dis hes was initiated in Minimum Essential Medium with Earle's salts and the ba seline stiffness was measured. Then, the experimental specimens were digest ed using 50 mu g ml(-1) trypsin for 24 h, 0.1 U ml(-1) chondroitinase ABC o r 30 U ml-(1) purified collagenase (type VII) for 24 h or 48 h (n = 8-15 pe r group). The control specimens were incubated in the medium. After the enz yme digestion, the end-point stiffness was measured and the specimens for t he microscopic analyses were processed. The proteoglycan (PG) distribution was analysed using quantitative microspectrophotometry and the quantitative evaluation of the collagen network was made using a computer-based polariz ed light microscopy analysis. Decrease (p < 0.05) of cartilage stiffness wa s found after 24 h trypsin (36%) and 48 h chondroitinase ABC (24%) digestio n corresponding to a decrease (p < 0.01) of up to 80% and up to 30% in the PG content respectively. Decrease of the superficial zone collagen content or arrangement (78%, p < 0.001) after 48 h collagenase digestion also induc ed a decrease (30%, p < 0.001) in cartilage stiffness. We conclude that our instrument is capable of detecting early structural and compositional chan ges related to cartilage degeneration.