Collagenase degradation decreases collagen fibril diameters--an in vitro study of the rabbit medial collateral ligament.

Based on the similarity of fibril diameters in healing and grafted ligaments, it has been speculated that all small fibrils represent newly synthesized collagen. Alternatively, small fibrils in grafts could be due to enzymatic degradation of endogenous large fibrils. This study examined the effect of collagenase on collagen fibril diameters in normal NZW rabbit MCLs. Midsubstance MCL slivers were incubated in buffer for 72 or 144 h for comparison with slivers incubated in buffer containing 4 units/ml bacterial collagenase. The samples were examined under TEM for fibril diameter analysis. Mean fibril diameters of 3-day and 6-day collagenase-treated MCLs were significantly reduced, resembling 40-week scar values. These results suggest that collagenase treatment can alter collagen fibril diameter and shape in normal rabbit MCL, thus it is possible that despite their similarity to ligament scars, that at least some small fibrils in ligament grafts may be enzymatically reduced endogenous fibrils.