Distribution of Nerve Endings in the Human Proximal Interphalangeal Joint and Surrounding Structures

Abstract

To examine the distribution of encapsulated nerve endings called mechanoreceptors in the human proximal interphalangeal (PIP) joint and surrounding structures. We processed 12 right index finger PIP joints and surrounding structures from fresh and dissecting-room cadavers for immunohistochemistry of the anti-protein gene product 9.5 and silver staining to detect encapsulated nerve endings. Serial transverse sections were cut throughout the whole specimen and divided into 3 regions along the longitudinal axis: distal, middle, and proximal. Each of the transverse sections was partitioned into dorsal capsule (DC), radial capsule (RC), ulnar capsule (UC), volar plate (VP), radial assemblage nuclei (RAN), and ulnar assemblage nuclei (UAN); the RAN and UAN are located on the radial and ulnar side of the VP. The C1 pulley contained the proximal region of the RAN and UAN, whereas the A3 pulley contained the middle and distal regions. The accessory collateral ligament contained all the regions of the RAN and UAN. The densities of encapsulated nerve endings in these 18 different regions were analyzed and compared. According to the modified Freeman and Wyke classification, type I (Ruffini-like endings) and type II (Pacini-like endings) nerve endings were identified. The density of type I nerve endings in the proximal region of the VP was substantially higher than that in the proximal region of the RAN, UAN, RC, UC, and DC. The density of type II nerve endings in the proximal region of the RAN and UAN was substantially higher than that in the proximal region of the VP, RC, UC and DC, and that in the proximal region of the VP and DC, respectively. Our examination of the distribution of type I and type II nerve endings provides information on the sensory systems of the PIP joints and surrounding structures.