Structural properties of 6 forearm ligaments.

Purpose: To first determine the structural properties of 6 forearm ligaments and then to create linear and nonlinear analytical models of each ligament from these properties.

Methods: We nondestructively tested the annular ligament, dorsal and palmar radioulnar ligaments, and the distal, central, and proximal bands of the interosseous ligament from 7 fresh cadaver forearms in a servohydraulic testing apparatus. We performed testing with the bone-ligament-bone constructs positioned corresponding to neutral forearm rotation as well as in 45° of supination and 45° of pronation. Based on a mechanical creep test of each ligament, we computed a linear and nonlinear ligament stiffness value for each ligament. We then compared these computed analytical responses to loading with loading data when each ligament was tested at 1.0 and 0.05 mm/s. We analyzed differences among ligaments and forearm positions using 1-way and 2-way analyses of variance.

Results: The stiffnesses for the distal band and the dorsal radioulnar ligament were statistically less when the constructs were positioned in supination compared with neutral forearm rotation. At all forearm positions, the linear stiffness of the central band was greater than that for the distal band of the interosseous ligament, the proximal band of the interosseous ligament, and the dorsal radioulnar and palmar radioulnar ligaments. In neutral forearm rotation, the linear stiffness of the central band was statistically greater than the annular ligament. The experimental loading behavior of each ligament was better modeled by a nonlinear stiffness than a linear one.

Conclusions: The central band of the interosseous membrane is the stiffest stabilizing structure of the forearm. Any structure used to replace the central band or other forearm ligaments should demonstrate a nonlinear response to loading.

Clinical Relevance: In considering a reconstruction for the forearm, the graft used should have a nonlinear response to loading and be one that is similar to the normal, original ligament.