OBJECTIVE: This study investigated the influence that abnormal joint mechanics 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 both 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 the 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 knees of the same gap injury animals.

OUTCOME MEASURES: The MCL water content, total proteoglycan content, hexose and hexuronate-containing proteoglycan 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 animals. The nonaggregating proteoglycan fraction from the contralateral MCL (group 3) had a greater electrophoretic mobility and probably, therefore, a smaller molecular weight than that found in the MCL from the same knee of control animals.

CONCLUSIONS: Since MCL healing took place in an abnormal mechanical environment, these results suggest that joint biomechanics may be an important factor in mediating connective tissue proteoglycan composition.

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