Arthroscopic visualization of the thumb carpometacarpal joint: introduction and evaluation of a new radial portal.

PURPOSE: The goal of this study is to describe a new radial portal for improving the view of the carpometacarpal (CMC) joint of the thumb without increasing the risk of neurovascular or ligament injuries. A further goal is to define the anatomic relationships of the portals to extra- and intra-articular structures. TYPE OF STUDY: Cadaver study.
METHODS: Six fresh-frozen adult cadaver hands were studied. The ulnar portal (UP) was marked just ulnar to the extensor pollicis brevis (EPB) tendon at the level of the joint. The new radial portal (RP) was marked just distal to the oblique ridge of the trapezium following a line referencing the radial edge of the flexor carpi radialis tendon. A 2.7-mm arthroscope was used. After the endoscopic procedure, the CMC joint was dissected. The distances from the superficial radial nerve (SRN) to the EPB tendon, to the abductor pollicis longus (APL) tendon at the level of the joint, and to both portals were measured. The distances between the radial artery and the EPB tendon and both portals were also documented. The dissected ligaments were inspected endoscopically again. Finally, the joint was hinged on the dorsal side to see the inner structures.
RESULTS: The UP passed radial to the radial artery, between the dorsal radial ligament (DRL) and the posterior oblique ligament (POL). The RP passed through the capsular window radial to the anterior oblique ligament. It allowed a better assessment of the DRL and POL, and a complete view of the lateral side of the joint. The SRN was within a range of 4 to 8 mm (mean, 6.3 mm) to the UP, and 4 to 12 mm (mean, 7.8 mm) to the RP. The shortest distance from the SRN to the RP was the longest distance from the nerve to the APL tendon (landmark for the standard RP). In 3 hands, the radial nerve crossed over the APL tendon. The mean distance from the ulnar edge of the UP to the radial artery was 2.7 mm (range, 2-3.5 mm). The distance was shorter when the metacarpal dorsal tubercle or the DRL was wider. The radial artery was in proximity to the RP in 2 specimens with radiopalmar variations, located at 10 and 15 mm, respectively, from this portal.
CONCLUSIONS: The arthroscopic technique with the new radial portal allowed a better triangulation and a complete assessment of the lateral side of the joint, with no neurovascular or ligament injuries. The shape of the DRL and bones determined the true distance from the radial artery to the ulnar portal. The least safe area was between the POL and the intermetacarpal ligament, where the branches of the artery were closest to the joint.