High Resolution Motion Analysis for Identification of Primary Trapeziometacarpal Joint Stabilizers during Grip Motions

Introduction Joint hypermobility/subluxation due to ligamentous laxity has been implicated as a factor in the development and subsequent progression of trapeziometacarpal (TMC) osteoarthritis. Five ligaments have been reported as primary stabilizers of the TMC joint: the dorsal radial ligament (DRL), posterior oblique ligament (POL), anterior oblique ligament (AOL), ulnar collateral ligament (UCL), and the intermetacarpal ligament (IML). Using a high-resolution motion-tracking system in a cadaver model, we analyzed relative displacement of the joint when subjected to sequential sectioning of these ligaments during four sizes of grip motion. We hypothesized that the dorsal radial ligament would have the greatest effect on stability of the TMC joint when subject to all motions.

Materials and Methods Eleven fresh-frozen cadaveric hands/forearms were used for this analysis. A single lateral exposure extended from 2 mm proximal to the trapezium, 15 mm distally along the first metacarpal. The forearm was restrained with its medial surface coincident to the fixture base. The fingers were held in a flexed position using a dorsal blocking splint. Infrared markers were placed in bone at the trapezium and base of the first metacarpal (1st MCB). Surface markers were placed on the radius, second metacarpal, and proximal first metacarpal for reference. To produce motions of grip, the flexor pollicis longus (FPL), abductor pollicis brevis (APB), adductor pollicis (ADD), flexor pollicis brevis (FPB), and opponens pollicis (OPP) were exposed and suture tagged near the bone/tendon surface. A series of pulleys allowed for loading along muscle trajectories. The tendons were loaded with a combined 3kg-force. L-shaped polymer pipes were placed between the thumb and fingers in ½-, 1-, 1½-, and 2-inch sizes (Fig. 1). Six high resolution cameras (690fps; 1/10,000 mm resolution) were positioned to capture six degrees of motion. Following intact testing, each specimen was subjected to sequential sectioning of the ligament assigned to this specimen by raising the ligament off the base of the first metacarpal. Loading and capture were repeated. Greater than 2 mm relative displacement between sectioned and intact motion was selected as a clinically significant difference.

Results Trapezium Motion. For ½-inch grip, the DRL increased dorsal displacement (2.1 mm). For 1½-inch grip, the IML decreased dorsal displacement (2.7mm). 1st MCB Motion. For ½-inch grip, the IML caused a shift from dorsal to volar displacement (4.1 mm), but the DRL caused a shift from volar to dorsal displacement (5.6 mm). For 1-inch grip, POL decreased dorsal displacement (2.6 mm), but the DRL caused a shift from volar to dorsal displacement (5.5 mm). For 1½-inch, IML release decreased dorsal displacement (3.4 mm).

Conclusion The DRL has the greatest effect on stability of the trapezium and first metacarpal during small grip motions (½ and 1 inch) in a small sample of cadaveric hands. The IML has the greatest effect on the trapezium and 1MCB during large grip motion (1½ inch).

Fig. 1 Specimen subject to grip motions: (a) ½-inch grip; (b) 1-inch grip; (c) 1½-inch grip; (d) 2-inch grip.