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Introduction: Ligamentous anatomy and injury contributes to the pathology of many joints including the thumb CMC.  Radiopaque markers and paint have been used to determine the precise anatomy of knee and ankle ligaments. We hypothesize that the spatial relationships of the surrounding thumb CMC joint structures - ligaments, tendons, and bony prominences – may be demonstrated on plain radiographs (x-rays) using radiopaque and digitized markers.

Methods: In 12 cadaveric hands, the soft tissue and bony landmarks around the thumb CMC joint were identified using 3 modalities: 1) Tantalum Beads: Gross dissection identified the dorsal and volar ligamentous anatomy in 4 specimens; 2 hands were dedicated to the dorsal ligaments (dorsal radial, dorsal central  and posterior oblique ligaments) and 2 hands to the volar ligaments (anterior oblique  and ulnar collateral ligaments).  The ligaments were identified from origin to insertion, outlined using 4 tantalum beads per ligament, and imaged with AP, lateral, and Robert's view x-rays. 2) Tantalum Paint: The abductor pollicis longus, extensor pollicis longus, extensor pollicis brevis and flexor carpi radialis tendons were painted with tantalum in 4 cadavers to highlight their position around the CMC.  The same x-ray views were obtained. 3) Micro-CT Simulated X-ray:  The volar metacarpal beak, trapezoidal groove for the flexor carpi radialis, dorsal radial tubercle, and dorsal ulnar tubercle were digitally marked on 3-D micro-CT images of 4 hands. Software volume rendering with intensity adjustment simulated plain x-rays.

Results: The, ligaments, tendons, and bony prominences may be visualized and identified with plain x-rays.  

Ligament Locations:  The 3 dorsal ligaments and 2 volar ligaments were outlined by tantalum beads on x-ray, demonstrating the oblique orientation of both sets of ligaments, and a fanning array of the dorsal ligaments (Figure 1).

Tendon Course:  The 4 tendons crossing the CMC joint were identified with tantalum paint demonstrating the precise spatial relationship of the tendon to superficial and deep structures; we found paint inferior to tantalum beads in the challenge of application (Figure 2).

Bony Landmarks: The dorsal ulnar and radial tubercles, trapezial ridge, and metacarpal volar beak were all identified, with the best correlation seen on the simulated Robert's view projection (Figure 3).  

Discussion and Conclusion: The ligaments, tendons, and bony prominences surrounding the CMC joint were identified on plain and simulated x-rays. These radiographic landmarks may provide clinically relevant information for imaging this complex joint with especial relevance to unstable fractures and CMC arthritis.