A Morphologic and Quantitative Study of Mechanoreceptors in the Remnant Stump of the Human Anterior Cruciate Ligament

Purpose: To investigate the morphology and quantity of mechanoreceptors in the remnant stumps of injured anterior cruciate ligaments (ACLs) and the association of the number of mechanoreceptors with the time from injury to surgery. Methods: Complete ACL stump specimens were collected from 40 volunteer patients who underwent arthroscopic ACL reconstruction surgery. Serial sections, 20 mm in thickness, were prepared from each specimen. After H&E staining and immunohistochemical labeling, the morphology, type, size, and quantity of the mechanoreceptors were observed under an optical microscope. Results: A total of 176 Ruffini corpuscles, 61 pacinian corpuscles, 15 Golgi-like tendon organs, and 66 atypical mechanoreceptors were observed. Free nerve endings were commonly present in the specimens. The time from injury to surgery (log(10) days) was negatively correlated with the number of total mechanoreceptors (r = -0.43, P < .006), Ruffini corpuscles (r = -0.45, P < .003), and the volume of the ACL stump (r = -0.52, P < .01), and these correlations were independent of age, gender, injury side, and career. Conclusions: The number of mechanoreceptors in an ACL stump and the volume of the stump decreased with the time from injury to surgery.