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

Objective: The aim of this study is to quantitatively analyze the distribution of nerve endings in the thumb interphalangeal joint capsule to better understand the neurophysiological functions of the thumb joint. Method: In this study, the right hand thumbs of 5 fresh frozen cadavers (5 males) were dissected. The average age of the cadavers at the time of death was 63.4 years (55-73). There was no injury or deformation of the fingers. After the hands were fixed in anatomical position, the skin of the thumb was removed and the thumb IP joint was stripped from the surrounding structures, leaving only the joint capsule (tendon, A2 pulley). The IP joint capsule was removed dorsally and volarly. It was divided into proximal and distal regions in 2 equal parts. Then, transverse serial sections were taken from all samples at 5 µm intervals. These sections were stained with PGP9.5 antibody immunohistochemically and hematoxylin-eosin (HE) staining for detection of nerve endings. Results: According to the data we obtained, Ruffini-like nerve endings were found statistically more in the proximal parts of both volar and dorsal parts (p <0.05). No statistical difference was found between regions in terms of paccini and Golgi nerve endings. It was determined that the presence of Ruffini like nerve endings in the volar part of the capsule was 1.5 times more than the dorsal region and paccini like nerve endings were 4.4 times more in the dorsal part. Golgi-like nerve endings were found to have similar values in the dorsal and volar regions. Conclusion: According to the results of this study, Ruffini like nerve endings were observed at a higher rate in both volar and proximal parts of the dorsal joint capsule. Therefore, the proximal and distal parts of the thumb interphalangeal joint capsule may have different functions during joint movement. In addition, type 3 nerve terminations were observed in the thumb IP joint. We believe that our study should be taken into consideration by researchers for a better understanding of thumb physiology, and new studies should be conducted to better understand this issue.