Metabolism and composition of the canine anterior cruciate ligament relate to differences in knee joint mechanics and predisposition to ligament rupture

Purpose: The objective of this study was to determine whether differences in the composition and metabolism of the extracellular matrix (ECM) in canine anterior cruciate ligaments (ACLs) might relate to mechanical properties of the canine knee. Variations in ACL biochemistry and knee mechanics could account for divergent predispositions to ligament rupture. Methods: Eleven knee joints were obtained from both cadaveric Labrador Retrievers (rupture predisposed) and ex-racing Greyhounds (non-rupture predisposed). Anterioposterior laxity and tensile testing determined mechanical properties of the knee joints and ACL samples respectively. The thermal properties of the collagenous matrix were determined by differential scanning calorimetry (DSC) and the biochemical properties by measuring collagen content, collagen cross-links, glycosaminoglycan (GAG) levels, matrix metalloproteinase-2 (MMP-2), tissue inhibitors of metalloproteinase (TIMP). Results: The anterioposterior laxity was significantly greater ( p=0.04) in the Labrador Retriever knee joints, and their ACLs tended to be weaker ( p=0.06). Greater collagen turnover was demonstrated by significantly higher ( p=0.02) concentrations of pro-MMP-2, and lower enthalpy of denaturation ( p=0.05) in Labrador Retriever ACLs. Conclusions: The different metabolism of the collagenous matrix in the ACLs of dogs predisposed to rupture was related to greater knee joint laxity and lower ligament material properties (ultimate tensile stress). This may be suggestive of a link between ligament rupture and eventual knee osteoarthritis in both dogs and humans.