Comparative Anatomy of the Subsynovial Connective Tissue in the Carpal Tunnel of the Rat, Rabbit, Dog, Baboon, and Human

Abstract

The tenosynovium in the human carpal tunnel is connected to the flexor tendons and the median nerve by the subsynovial connective tissue (SSCT). The most common histological finding in carpal tunnel syndrome (CTS), a compression neuropathy of the median nerve, is noninflammatory fibrosis of the SSCT. The relationship, if any, between the fibrosis and nerve pathology is unknown, although some have speculated that a change in the SSCT volume or stiffness might be the source of the compression. Yet, while animal models have been used to study the physiology of nerve compression, so far none have been used to study the relationship of the SSCT pathology to the neurophysiological abnormalities. The purpose of this study was to identify animal models that might be appropriate to study the interaction of SSCT and nerve function in the development of CTS. The front paws of a rat, rabbit, dog, and baboon were dissected. The carpal tunnel anatomy and SSCT of these animals were also examined by light and scanning microscopy and compared to the relevant human anatomy and ultrastructure. The carpal tunnel anatomy and contents of the baboon and rabbit are similar to humans. The canine carpal tunnel lacks the superficial flexor tendons and the rat carpal tunnel is very small. The human, baboon, and rabbit specimens had very similar organization of the SSCT, and content of the carpal canal. We conclude that, while both the baboon and rabbit would be good animal models to study the relationship of the SSCT to CTS, the rabbit is likely to be more practical, in terms of cost and animal care concerns.

Magnetic resonance (MR) imaging of the carpal tunnel and related structures in New Zealand Rabbit (Oryctolagus cuniculus): An anatomic and radiologic evaluation on an animal model

“…The carpal tunnel anatomy of the rabbit has been reported by several authors and it is similar to man regarding the osseous and connective tissue formations in this region (3,10,13,18). The carpal joint of rabbit consists of four bones in the proximal row, radial, intermediate, ulnar, and a small accessory carpal bone and another four in the distal row, the carpal bones from 1 st to 4 th , which are attached to each metacarpal except the fifth (10).…”

“…The carpal joint of rabbit consists of four bones in the proximal row, radial, intermediate, ulnar, and a small accessory carpal bone and another four in the distal row, the carpal bones from 1 st to 4 th , which are attached to each metacarpal except the fifth (10). The only dissimilarity to human wrist is the central carpal bone in between the 2 nd and 3 th carpal bones (18).…”

“…The only dissimilarity to human wrist is the central carpal bone in between the 2 nd and 3 th carpal bones (18). The median artery and the median nerve pass through the carpal tunnel together with the tendons of deep and superficial digital flexor muscles (7,10,18). The flexor pollicis longus of the rabbit is also within the carpal tunnel.…”

Tendon Injury Produces Changes in SSCT and Nerve Physiology Similar to Carpal Tunnel Syndrome in an in Vivo Rabbit Model

“…Rats, while also commonly used [10], do not have an SSCT [3]; in dogs, the FDS tendons are outside the tunnel [3]. While primate species would of course be even closer to humans and thus would be appropriate as a CTS model [11], they were not available to us.…”

The mechanical properties of the rabbit carpal tunnel subsynovial connective tissue

“…Recently, the carpal tunnel anatomy and SSCT of animals were also examined by light and scanning microscopy and compared to the relevant human anatomy and ultrastructure (Ettema et al, 2006b rabbit anatomy had very similar organization of the SSCT and content of the carpal canal. The purpose of this study was to present a method to measure the mechanical properties of the rabbit SSCT in response to shear stress.…”