Immunohistochemical Analysis of Sensory Nerve Endings in Ankle Ligaments: A Cadaver Study

Abstract

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.

Immunohistochemical Mapping of Sensory Nerve Endings in the Human Triangular Fibrocartilage Complex

“…Free nerve endings were the predominant mechanoreceptor type in all of the examined structures of the triangular fibrocartilage complex, which is in accordance with a previous study [24] and studies of the human ankle [21], fat tissue in the human sinus tarsi [23], and the human knee capsule [12]. The predominance of free nerve endings indicates an important role in perceiving noxious, chemical, mechanical, and inflammatory stimuli.…”

“…Ruffini endings were the third most common mechanoreceptors closely followed by Golgi-like endings and Pacini corpuscles. A study on ligaments at the ankle revealed higher amounts of Ruffini endings followed by Pacini corpuscles and Golgilike endings with the following ratios: Ruffini: Pacini = 4.7:1; Ruffini: Golgi = 15.5:1, and Pacini: Golgi = 3.3:1 [21]. The more equal relationships among Ruffini, Pacini, and Golgi-like endings in the current study (Table 2) indicate that the ulnocarpal and distal radioulnar joints require a homogenous distribution of proprioceptive qualities.…”

“…Blood vessels were investigated using antihuman smooth muscle-actin (working dilution: 1:750; Code: M 0851; DakoCytomation). Details regarding the immunohistochemical protocol, a description of antibodies, and control stainings performed were discussed in a previous study [21]. …”

“…microscopy, which does not permit a complete representation of the whole mechanoreceptor [21]. Nevertheless, even three-dimensional reconstructions of multiple levels of ligaments have revealed a large portion of unclassifiable corpuscles in wrist ligaments [26].…”

“…Joint stability relies on fine interactions of mechanical and dynamic components. Although static joint stability is constituted by osseous and ligamentous integrity, the dynamic elements of joint stability concern proprioceptive control of the compressive and directional muscular forces acting on the joint [3,21]. The core of the distal radioulnar joint stability is best described with the concept of ''tensegrity,'' which entails stability through a synergy of ligament tensile and joint compressive forces [11].…”