Immunohistochemical Mapping of Sensory Nerve Endings in the Human Triangular Fibrocartilage Complex

Background: The triangular fibrocartilage complex (TFCC) is the main stabilizer of the distal radioulnar joint (DRUJ). While static joint stability is constituted by osseous and ligamentous integrity, the dynamic aspects of joint stability chiefly concern proprioceptive control of the compressive and directional muscular forces acting on the joint.

Questions/Purposes: We aimed to (1) analyze the general distribution of sensory nerve endings and blood vessels; (2) compare the number and types of mechanoreceptors in each part; and (3) analyze intrastructural distribution of nerve endings at different tissue depth.

Methods: The extensor carpi ulnaris (ECU) subsheath, the meniscoid, the articular disk, the distal and volar radioulnar ligaments, and ulnolunate and ulnotriquetral ligaments were dissected from 11 human cadaver wrists. Sensory nerve endings were counted in five levels/specimen as total cell amount/cm² after staining with p75, PGP 9.5, and S-100 protein and thereafter classified according to Freeman and Wyke.

Results: All types of sensory corpuscles were found in the various structures of the TFCC with the exception of the ulnolunate ligament, which contained no Ruffini or Pacini receptors, and the articular disk, which had only free nerve endings. Free nerve endings were the predominant sensory nerve ending and were more prevalent than all other types of mechanoreceptors. The articular disk contained fewer free nerve endings and fewer blood vessels than all other structures of the TFCC (p ≤ 0.001) except the ulnolunate ligament. The intrastructural analysis showed a homogenous distribution of nerve endings in all seven parts of the TFCC.

Conclusions: Nociception has a primary proprioceptive role in the neuromuscular stability of the DRUJ. The articular disk and ulnolunate ligament rarely are innervated, which implies mainly mechanical functions, whereas all other structures have pronounced proprioceptive qualities.

Clinical Relevance: TFCC lesions affect both the mechanical and proprioceptive stability of the DRUJ, and surgical reconstruction in instances of radioulnar ligament injury is important. Arthroscopic thermal shrinkage should be used with caution and limited to articular disk tears to avoid undesirable side effects of denervating ligaments that contribute to dynamic stability of the DRUJ.