To clarify the morphologic and quantitative changes of mechanoreceptors of the human ACL with degenerative arthritis.

Eleven fresh specimens of anterior cruciate ligament (ACL) were obtained from patients with degenerative arthritis during TKA. As a control, two fresh specimens were taken from healthy men at the time of a traumatic above knee amputation. The whole ligaments were serially frozen and sectioned at a thickness of 40 mum. After immunohistochemical staining, the mechanoreceptors were observed under a light microscope. The ratios of sections showing mechanoreceptors were calculated. Statistical analyses were performed using the chi-square test.

In the two control specimens, nineteen mechanoreceptors were found, evenly distributed at the femoral and tibial ends. However, the average number of mechanoreceptors was 1.4 (total 15) in the arthritic ligaments (p<0.05), and these were located near the femoral side rather than the tibial end. The percentage of sections showing mechanorecptors was 8.3% in the arthritic group and 40.2% in the control group (p<0.05). All receptors were round or fusiform shaped Ruffini corpuscles; Pacinian corpuscles could not be found in either group. Nine of 15 mechanoreceptors in the arthritic groups were “necrotic” in shape.

Mechanoreceptors in arthritic ACL were significantly reduced in number and mainly necrotic in shape. Our findings suggest that the numerical and morphological changes of mechanoreceptors are closely related with reduced proprioception in degenerative arthritis.