Material properties of the trapezial and trapeziometacarpal ligaments.

Destabilization of the trapezium from its normal orientation with respect to the trapezoid, second metacarpal, and thumb metacarpal leads to incongruity at the trapeziometacarpal (TMC) joint. Abnormal shear forces may eventually result in TMC joint arthritis. By determining the relative stiffness and strength of the ligaments that stabilize this joint, one may infer their role in providing stability to the TMC joint. This study addresses the material properties of the ligaments stabilizing the trapezium and TMC joint to better understand the mechanics and kinematics of this joint. Fresh-frozen cadaveric hands (10 males and 10 females) were used to obtain bone-ligament-bone complexes from the dorsal and volar trapeziotrapezoid ligaments, dorsal and volar trapezio-second metacarpal ligaments, anterior oblique ligament, dorsoradial ligament, and trapezio-third metacarpal (T-III MC) ligament. The following material properties were derived from our data: ultimate load, ultimate stress (normalized failure load), ultimate strain (percent elongation), stiffness, toughness (energy to failure), and hysteresis. The dorsoradial ligament demonstrated the greatest ultimate load and toughness (energy to failure). The T-III MC ligament demonstrated the greatest ultimate stress (normalized failure load) and stiffness. The anterior oblique ligament demonstrated the least stiffness and the greatest hysteresis. The material properties of capsuloligamentous structures may be a good indicator of their importance to joint stability. Using these criteria we conclude that the T-III MC and dorsoradial ligaments are important stabilizers of the trapezium and TMC joint, respectively. These two ligaments were found to be the strongest, stiffest, and toughest ligaments, while the anterior oblique ligament was relatively weak and compliant. The dorsal trapezio-second metacarpal, volar trapezio-second metacarpal, and T-III MC ligaments were all relatively strong and are anatomically aligned to function as tension bands to restrain the trapezium against cantilever bending forces applied to it by the thumb during key or tip pinch.