Macroscopic and microscopic analysis of the thumb carpometacarpal ligaments: a cadaveric study of ligament anatomy and histology

Abstract

Background: Stability and mobility represent the paradoxical demands of the human thumb carpometacarpal joint, yet the structural origin of each functional demand is poorly defined. As many as sixteen and as few as four ligaments have been described as primary stabilizers, but controversy exists as to which ligaments are most important. We hypothesized that a comparative macroscopic and microscopic analysis of the ligaments of the thumb carpometacarpal joint would further define their role in joint stability.

Methods: Thirty cadaveric hands (ten fresh-frozen and twenty embalmed) from nineteen cadavers (eight female and eleven male; average age at the time of death, seventy-six years) were dissected, and the supporting ligaments of the thumb carpometacarpal joint were identified. Ligament width, length, and thickness were recorded for morphometric analysis and were compared with use of the Student t test. The dorsal and volar ligaments were excised from the fresh-frozen specimens and were stained with use of a triple-staining immunofluorescent technique and underwent semiquantitative analysis of sensory innervation; half of these specimens were additionally analyzed for histomorphometric data. Mixed-effects linear regression was used to estimate differences between ligaments.

Results: Seven principal ligaments of the thumb carpometacarpal joint were identified: three dorsal deltoid-shaped ligaments (dorsal radial, dorsal central, posterior oblique), two volar ligaments (anterior oblique and ulnar collateral), and two ulnar ligaments (dorsal trapeziometacarpal and intermetacarpal). The dorsal ligaments were significantly thicker (p < 0.001) than the volar ligaments, with a significantly greater cellularity and greater sensory innervation compared with the anterior oblique ligament (p < 0.001). The anterior oblique ligament was consistently a thin structure with a histologic appearance of capsular tissue with low cellularity.

Conclusions: The dorsal deltoid ligament complex is uniformly stout and robust; this ligament complex is the thickest morphometrically, has the highest cellularity histologically, and shows the greatest degree of sensory nerve endings. The hypocellular anterior oblique ligament is thin, is variable in its location, and is more structurally consistent with a capsular structure than a proper ligament.

Figures

Fig. 1

Diagrams showing the topography of the distal trapezial joint surface, as redrawn from computed tomography (CT) surface rendering of a normal right hand. The thumb carpometacarpal joint motion arcs of the metacarpal on the trapezium are flexion-extension and abduction-adduction. Pronation-supination represents composite rotation and translation of this joint based on morphology and muscular activity. The thumb position in relation to the fingers represents a completion of the carpal arch, which places the thumb carpometacarpal joint oblique to the adjacent fingers. The arcs of motion thus are out of phase with the fingers, depending on the thumb’s position in space.

Fig. 2

Photographs showing the dorsal thumb carpometacarpal ligaments as seen from the dorsal aspect of the thumb (Fig. 2-A) and from a volar view within the joint (Fig. 2-B), illustrating the three ligaments of the stout dorsal deltoid ligament complex, including the dorsal radial ligament (DRL), the dorsal central ligament (DCL), and the posterior oblique ligament (POL). The deltoid ligament complex emanates from the tubercle (*) of the dorsal trapezium (Tz) and inserts fan-shaped onto the dorsal base of the first metacarpal (MC1). Also seen is the insertion of the abductor pollicis longus (APL) and the dorsal aspect of the second metacarpal (MC2).

Fig. 3

Photographs showing the thin volar ligaments of the thumb carpometacarpal joint. The diaphanous anterior oblique ligament (AOL) and ulnar collateral ligament (UCL) (also known as the first volar trapeziometacarpal ligament [VTM-1]) are noted with the thumb carpometacarpal joint in extension (Fig. 3-A) and flexion (Fig. 3-B). The abductor pollicis longus (APL) is reflected distally. In this specimen, a capsular structure seen deep to the ulnar collateral ligament is interpreted as the deep anterior oblique (arrows). Tz = trapezium, MC1 = first metacarpal, and MC2 = second metacarpal.

Fig. 4

Photograph showing the ulnar thumb carpometacarpal ligaments from the dorsal view, with the thumb in abduction. The first dorsal trapeziometacarpal ligament (DTM-1) stabilizes the thumb carpometacarpal joint in abduction, pronation, and flexion, whereas the intermetacarpal ligament (IML) stabilizes the joint in abduction and supination. The dorsal deltoid ligament complex is also seen in this view (1, 2, and 3). * = dorsal tubercle of the trapezium, 1 = dorsal radial ligament, 2 = dorsal central ligament, 3 = posterior oblique ligament, MC1 first metacarpal, and MC2 = second metacarpal.

Fig. 5

Histological appearance of the dorsal radial ligament (Figs. 5-A and 5-C) and the anterior oblique ligament (Figs. 5-B and 5-D) as stained with hematoxylin and eosin (Figs. 5-A and 5-B) and DAPI (Figs. 5-C and 5-D). The dorsal radial ligament demonstrates distinct collagen bundles with both stains, with the nuclei of the fibrocytes in the collagen visualized with DAPI (Fig. 5-C); the circle indicates a cluster of nuclei. In contrast, the anterior oblique ligament has the appearance of disorganized connective tissue, with no apparent collagenous structure (Fig. 5-B) or cellularity (Fig. 5-D).

Fig. 6

Line graph showing the distribution of mean ligament cell counts in each of the five carpometacarpal ligaments from five specimens. AOL = anterior oblique ligament, UCL = ulnar collateral ligament, POL = posterior oblique ligament, DCL = dorsal central ligament, DRL = dorsal radial ligament.

Fig. 7

Mixed-effects linear regression with simultaneous pairwise comparisons of the mean differences in ligament cellularity between the five carpometacarpal ligaments. The dorsal radial ligament (DRL), dorsal central ligament (DCL), and posterior oblique ligament (POL) were significantly (p

Fig. 8

Overview of the ligament composition in a dorsal radial ligament sample as seen with use of a triple-staining immunofluorescence technique. A mechanoreceptor (R) with distinct p75 immunofluorescence (Fig. 8-A) and PGP9.5 immunofluorescence (Fig. 8-B) is seen in close proximity to the arteriole. The parent axon (arrows) is seen leading up to the receptor (Figs. 8-A and 8-B). A large arteriole (Fig. 8-A) is identified with the DAPI stain (Fig. 8-C), and the innervation in the vessel wall shows PGP9.5 immunofluorescence (Fig. 8-B). The last image (Fig. 8-D) shows the p75, PGP9.5, and DAPI stains imaged simultaneously for a coherent understanding of the ligament topography. Median nerve specimens at the wrist level from two hands were used for control.