The effects of immobilization on the maturation of the anterior cruciate ligament of the rabbit knee.

Immobilization-induced alterations occurred in young anterior cruciate ligament (ACL) samples, including the loss of the rounded appearance of the cells. The mature ACL was minimally altered by immobilization at the light microscopy level. In the immobilized young ACL the fibroblasts became elongated and there was loss of the normal pericellular matrix. The immobilized mature ACL differed from controls primarily in the intracellular composition, as there was significantly more rough endoplasmic reticulum (RER) present. Collagen concentrations were reduced only in young immobilized ACL, while no differences were observed in the mature ACL. The collagen synthesis rate in the mature ACL increased with immobilization, although no significant change was observed in the young ACL. The increase in the rate of synthesis of the stress deprived ACL in the mature animals reflected an increase in collagen turnover rather than an increase in accumulation of collagen.