Effect of immobilization of the knee joint on mechanoreceptors in anterior cruciate ligament of the rabbit

We investigated the morphologic distribution of mechanoreceptors in the anterior cruciate ligament of the knee in rabbits and the effects of immobilization of the knee joint, and evaluated the qualitative and quantitative morphologic changes of the mechanoreceptors after resumption of movement of the knee joint. There was no significant difference in the total number of mechanoreceptors present after 4-week immobilization compared with the number of mechanoreceptors on the unfixed control side. However, there was a significant increase in Pacinian corpuscles and Ruffini receptors with an atypical morphology. When immobilization was performed for 6 weeks, the total number of mechanoreceptors, including typical and atypical ones, showed a significant decrease compared to the control. After 12 and 24 weeks of remobilization, the total number of mechanoreceptors had returned to a level not significantly different from that on the control side, but typical mechanoreceptors were still significantly decreased and the atypical mechanoreceptors had increased. These results suggest that immobilization brings about morphologic changes and a reduction in the number of mechanoreceptors. The total number of mechanoreceptors recovers after re-mobilization, but the typical mechanoreceptors do not return, and the number of atypical mechanoreceptors increas. These changes are thought to be irreversible.