OBJECTIVES To investigate the effects of collagen induced arthritis (CIA) on the tensile properties of rat anterior cruciate ligament (ACL).

RESULTS The tensile strength of the ACL unit was significantly lower in the rats with CIA at 10 weeks after immunisation (ultimate failure load, 74.9% of the control; stiffness, 62.0% of the control). The major mode of failure was femoral avulsion, and the BMD was significantly lower in the rats with CIA. A histological examination of the ligament insertion in rats with CIA showed resorption of the cortical bone beneath the ACL insertion and an enlarged mineralised fibrocartilage zone.

CONCLUSIONS These findings indicate that the decrease in tensile strength of ACL units correlated with histological changes in the ligament-bone attachment, such as bone resorption beneath the ligament insertion site and an enlargement of the mineralised fibrocartilage zone.