Structural and Distribution Analysis of Mechanoreceptors and Free Nerve Endings in the Annular Pulleys of the Flexor Tendons of the Hand

Abstract

Background: The hand is essential in enabling physical interaction with the environment, with the annular pulleys playing a key role in its functionality. These fibrocartilaginous structures, located along the flexor tendons, are vascularized and may contain nerve endings and mechanoreceptors, aligning tendons with the bones to optimize finger flexion. However, their innervation remains poorly understood, limiting therapeutic advancements for flexor tendon conditions, such as stenosing tenosynovitis (trigger finger). This study aims to analyze the presence and distribution of mechanoreceptors and free nerve endings in the A1 annular pulley to provide insights for improved surgical and therapeutic approaches.

Methods: Twenty A1 pulleys from the ring fingers were obtained from fresh-frozen cadavers. The pulleys were submitted to cryostat sectioning. The sections were subjected to immunofluorescence with the PGP 9.5 (protein gene product 9.5) and confocal microscopy analysis.

Results: The analysis revealed the presence of type I mechanoreceptors (Ruffini corpuscles) in a subset of samples, while type IV free nerve endings were consistently found in all specimens. Both types of neural structures were primarily located at the medial and lateral fibrocartilaginous insertions of the A1 pulley, highlighting specific areas of sensory innervation within the structure.

Conclusion: This study contributes to the anatomical characterization of the A1 pulley, highlighting the presence and distribution of mechanoreceptors and free nerve endings. While the clinical implications of these findings remain uncertain, they may serve as a basis for future research on proprioception, sensory feedback, and potential surgical considerations.

Keywords: fibrocartilage; hand diseases; immunofluorescence; mechanoreceptors; trigger finger.

Figure 1.

A1 pulley resection. (a) Incision in the skin and exposure of the flexor pulleys of the fourth finger of the right hand. (b) Resection of pulley A1. (c) Images after removal of sectioned pulley A1.

Figure 2.

Microscopic analysis of A1 pulley. Note. (a) Hematoxylin-eosin staining of a slide to check the quality of slides and determine other histological and cytological structures. (b) Overview in confocal microscopy of free nerve endings. Immunofluorescence obtained with PGP 9.5 (protein gene product 9.5) (primary antibody) and Alexa Fluor 488 (secondary antibody). (c) Multiple forms of free nerve endings. (d) type I mechanoreceptor (Ruffini).