Immunohistochemical analysis of sensory nerve endings in ankle ligaments: a cadaver study.

BACKGROUND The aim of this study was to analyze the pattern and types of sensory nerve endings in ankle ligaments using immunohistochemical techniques, in order to gain more insight into functional ankle stability. METHODS One hundred forty ligaments from 10 cadaver feet were included: the calcaneofibular and anterior/posterior talofibular ligaments from the lateral complex; inferior extensor retinaculum complex, talocalcaneal oblique and canalis tarsi ligaments from the sinus tarsi; deltoid ligament with its individual portions from the medial complex, and anterior tibiofibular ligament (ATiFL) from the syndesmosis. Mechanoreceptors were classified according to Freeman and Wyke [Acta Anat (Basel) 1967;68:321-333] after staining with hematoxylin-eosin, low-affinity neurotrophin receptor p75, protein gene product 9.5, and S-100 protein. RESULTS Free nerve endings were the predominant sensory endings in all four complexes, with the greatest density in the lateral and medial complexes; followed by Ruffini endings, unclassifiable corpuscles, Pacini corpuscles, and Golgi-like endings. Ruffini endings were significantly more prevalent in the ATiFL than in the medial complex, and more common than Pacini corpuscles and Golgi-like endings in the lateral, medial, and sinus tarsi complexes. A greater number of blood vessels correlated with a greater number of free nerve endings. There was a negative correlation between the number of Ruffini endings, unclassifiable corpuscles, and age. CONCLUSIONS Free nerve endings are the dominant mechanoreceptor type in the ankle ligaments, followed by Ruffini endings. The ligaments of the lateral and medial ankle complexes are more innervated than the sinus tarsi ligaments.