ABNORMAL JOINT MECHANICS AND THE PROTEOGLYCAN COMPOSITION OF NORMAL AND HEALING RABBIT MEDIAL COLLATERAL LIGAMENT

Objective: This study investigated the influence that abnormal joint m echanics may have upon the biochemical composition of the joint's own soft tissue holding elements. Design: The investigation used an animal model of ligament injury, the rabbit medial collateral ligament (MCL) . The proteoglycan component of the ligament extracellular matrix was extracted, purified and characterized. Interventions: The experimental groups consisted of: a) a control group consisting of the MCL from bo th right and left knees of six animals that had not undergone surgery; b) a group (healing gap injury) of six MCL from right knees in which a segment of tissue had been excised from the anterior cruciate and th e MCL of the right knee 3 wk prior to sacrifice; and c) a third group (contralateral gap injury) comprised of the MCL from the six left knee s of the same gap injury animals. Outcome Measures: The MCL water cont ent, total proteoglycan content, hexose and hexuronate-containing prot eoglycan and proteoglycan electrophoretic mobility were determined for each group studied. Results: The healing gap injury MCL was found to have a higher water content, a higher total proteoglycan content and a higher proportion of aggregating proteoglycan than MCL from control a nimals. The nonaggregating proteoglycan fraction from the contralatera l MCL (group 3) had a greater electrophoretic mobility and probably, t herefore, a smaller molecular weight than that found in the MCL from t he same knee of control animals. Conclusions: Since MCL healing took p lace in an abnormal mechanical environment, these results suggest that Joint biomechanics may be an important factor in mediating connective tissue proteoglycan composition.