Distribution of nerve endings in human distal interphalangeal joint and surrounding structures

Purpose: To examine the distribution of encapsulated nerve endings called mechanoreceptors in the human distal interphalangeal (DIP) joint and surrounding structures. Methods: We processed 12 right index finger DIP joints and surrounding structures from fresh cadavers for immunohistochemistry of the anti-protein gene product 9.5 (PGP9.5) 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), and radial and ulnar assemblage nuclei (RAN and UAN); the RAN and UAN are located on both the radial and ulnar side of the VP. The C3 pulley contained the proximal region of the RAN and UAN, whereas the A5 pulley contained the middle and distal. The accessory collateral ligament contained all the regions of the RAN and UAN. We analyzed and compared the density of encapsulated nerve endings among the 18 different regions. Results: According to the modified Freeman and Wyke classification, we identified type I (eg, Ruffini-like endings) and type II (eg, Pacini-like endings) nerve endings. The density of type II nerve endings in the proximal region of the RAN and UAN was considerably higher than that in the proximal region of the VP, RC, UC and DC, and that in the proximal region of the VP, RC, UC, and DC, respectively. Conclusions: Our examination of the distribution of type I and type II nerve endings provides new information on the sensory systems of the DIP joints and surrounding structures.