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

Abstract

Background: The triangular fibrocartilage complex is the main stabilizer of the distal radioulnar joint. 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. Therefore, an investigation of the pattern and types of sensory nerve endings gives more insight in dynamic distal radioulnar joint stability.

Questions/purposes: We aimed to (1) analyze the general distribution of sensory nerve endings and blood vessels; (2) examine interstructural distribution of sensory nerve endings and blood vessels; (3) compare the number and types of mechanoreceptors in each part; and (4) analyze intrastructural distribution of nerve endings at different tissue depth.

Methods: The subsheath of the extensor carpi ulnaris tendon sheath, the ulnocarpal meniscoid, the articular disc, the dorsal and volar radioulnar ligaments, and the ulnolunate and ulnotriquetral ligaments were dissected from 11 human cadaver wrists. Sensory nerve endings were counted in five levels per specimen as total cell amount/cm(2) after staining with low-affinity neurotrophin receptor p75, protein gene product 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 triangular fibrocartilage complex with the exception of the ulnolunate ligament, which contained only Golgi-like endings, free nerve endings, and unclassifiable corpuscles. The articular disc had only free nerve endings. Furthermore, free nerve endings were the predominant sensory nerve ending (median, 72.6/cm(2); range, 0-469.4/cm(2)) and more prevalent than all other types of mechanoreceptors: Ruffini (median, 0; range, 0-5.6/cm(2); difference of medians, 72.6; p < 0.001), Pacini (median, 0; range, 0-3.8/cm(2); difference of medians, 72.6; p < 0.001), Golgi-like (median, 0; range, 0-2.1/cm(2); difference of medians, 72.6; p < 0.001), and unclassifiable corpuscles (median, 0; range, 0-2.5/cm(2); difference of medians, 72.6; p < 0.001). The articular disc contained fewer free nerve endings (median, 1.8; range, 0-17.8/cm(2)) and fewer blood vessels (median, 29.8; range, 0-112.2/cm(2); difference of medians: 255.9) than all other structures of the triangular fibrocartilage complex (p ≤ 0.001, respectively) except the ulnolunate ligament. More blood vessels were seen in the volar radioulnar ligament (median, 363.62; range, 117.8-871.8/cm(2)) compared with the ulnolunate ligament (median, 107.7; range, 15.9-410.3/cm(2); difference of medians: 255.91; p = 0.002) and the dorsal radioulnar ligament (median, 116.2; range, 53.9-185.1/cm(2); difference of medians: 247.47; p = 0.001). Free nerve endings were obtained in each structure more often than all other types of sensory nerve endings (p < 0.001, respectively). The intrastructural analysis revealed no differences in mechanoreceptor distribution in all investigated specimens with the numbers available, showing a homogenous distribution of proprioceptive qualities in all seven parts of the triangular fibrocartilage complex.

Conclusions: Nociception has a primary proprioceptive role in the neuromuscular stability of the distal radioulnar joint. The articular disc and ulnolunate ligament rarely are innervated, which implies mainly mechanical functions, whereas all other structures have pronounced proprioceptive qualities, prerequisite for dynamic joint stability.

Clinical relevance: Lesions of the volar and dorsal radioulnar ligaments have immense consequences not only for mechanical but also for dynamic stability of the distal radioulnar joint, and surgical reconstruction in instances of radioulnar ligament injury is important.

Fig. 1A–E

(A) The triangular fibrocartilage complex consists of seven separate structures, namely the subsheath of the extensor carpi ulnaris tendon sheath (1 = SS-ECU), the articular disc (2 = AD), the volar radioulnar ligament (3 = VRUL), the dorsal radioulnar ligament (4 = DRUL), the ulnolunate ligament (5 = UL), the ulnotriquetral ligament (6 = UTq), and the ulnocarpal meniscoid (7 = UCM). (B) The subsheath of the extensor ulnaris tendon sheath is seen after removal of the extensor retinaculum. (C) Parts 2 through 6 of the triangular fibrocartilage complex are seen after removal of the carpal bones from the sagittal plane. (D) The ulnotriquetral ligament (6) inserts at the volar aspect of the triquetrum and originates on the radiovolar base of the ulna styloid. The ulnolunate ligament (5) inserts at the volar aspect of the lunate and originates mainly on the volar border of the articular disc (2). The dorsal radioulnar (4) and volar radioulnar (arrow 3) ligaments begin at the dorsoulnar or ulnovolar margin of the radius at the sigmoid notch and run toward the ulnar styloid. (E) A close-up view shows the ulnocarpal meniscoid (7).

Fig. 2A–D

Immunohistochemical staining of the sensory nerve endings using low-affinity nerve growth factor receptor p75 are shown. (A) The Ruffini ending is characterized by p75 immunoreactive dendritic nerve endings (arrowhead), a clearly visible, but non-immunoreactive central axon (white arrow), and a thin, at times partial encapsulation of the corpuscle (black arrow). (B) In contrast, the Pacini corpuscle has an onion-layered p75 immunoreactive capsule (black arrow) and central axon (white arrow). (C) The Golgi-like ending is larger with an afferent nerve fascicle (white arrow) coursing to the center of the corpuscle. Typically smaller corpuscles in the Golgi-like ending are seen (arrowheads). (D) Free nerve endings (arrowhead) are p75 immunoreactive (original magnification, ×400).

Fig. 3

The general distributions of sensory nerve endings are shown as medians with minimum and maximum. There were no significant differences between all sensory corpuscles. * = values, which are more than 1.5-fold away from minimum or maximum; o = values, which are more than threefold away from minimum or maximum.

Fig. 4

The general distributions of free nerve endings and blood vessels are shown as medians with minimum and maximum. There were significantly more blood vessels than free nerve endings (p < 0.001). o = values, which are more than threefold away from minimum or maximum.

Fig. 5

Medians with minimum and maximum for the sensory nerve endings are shown for each part of the triangular fibrocartilage complex. The subsheath of the extensor carpi ulnaris (SS-ECU) and the ulnocarpal meniscoid (UCM) had significantly more unclassifiable corpuscles than the articular disc (AD) (^#p = 0.002). All other comparisons of the sensory nerve endings between the seven different structures of the triangular fibrocartilage complex were not statistically significant. UTq = ulnotriquetral ligament; UL = ulnolunate ligament; VRUL = volar radioulnar ligament; DRUL = dorsal radioulnar ligament; * = values, which are more than 1.5-fold away from minimum or maximum; o = values, which are more than threefold away from minimum or maximum.

Fig. 6

The distributions of free nerve endings and blood vessels are seen as medians with minimum and maximum. The subsheath of the extensor carpi ulnaris (SS-ECU), ulnocarpal meniscoid (UCM), ulnotriquetral ligament (UTq), and volar (VRUL) and dorsal radioulnar ligaments (DRUL) had significantly more free nerve endings and blood vessels than the articular disc (AD) (*p < 0.001, respectively). Furthermore, the volar radioulnar ligament contained significantly more blood vessels than the ulnolunate (^§p = 0.002) and dorsal radioulnar ligaments (^#p = 0.001). * = values, which are more than 1.5-fold away from minimum or maximum; o = values, which are more than threefold away from minimum or maximum.