Ultrastructural changes in knee ligaments following immobilization.

Anterior cruciate (ACL) and medial collateral (MCL) ligaments from control and immobilized rabbit knee joints were examined using transmission electron microscopy. The fibroblasts of these two tissues were distinct in control ligaments, but these differences in fibroblast morphology were less obvious after immobilization. The most drastic changes took place in the ACL; the ACL fibroblasts from control ligaments were ovoid-shaped, while after immobilization they were spindle-shaped with extensive cytoplasmic extensions. These cellular changes corroborate previously demonstrated changes in the mechanical properties of these ligaments seen following immobilization, and are consistent with biochemical studies.