BIOMECHANICAL ANALYSIS OF THE ANKLE ANTERIOR DRAWER TEST FOR ANTERIORTALOFIBULAR LIGAMENT INJURIES

The effect of sectioning the anterior talofibular ligament on the load -displacement behavior of the ankle was evaluated in vitro during the anterior drawer test using the flexibility approach. Controlled forces were applied across the ankle joint in the anterior-posterior directi on, and the resulting displacements were measured at four flexion angl es (10 degrees of dorsiflexion, neutral, and 10 degrees and 20 degrees of plantar flexion). The anterior talofibular ligament then was secti oned, and the anterior-posterior loadings were repeated at the four fl exion angles. Two parameters were developed to describe the nonlinear load-displacement response of the ankle joint: neutral zone laxity (jo int displacement between +/-2.5 N) and flexibility (a measure of the n onlinear load-displacement response of the ankle between 10 and 50 N o f anterior drawer loading). After sectioning the anterior talofibular ligament, significant increases in neutral zone laxity were observed a t all angles of ankle flexion. The largest increases in neutral zone l axity were found with the ankle in 10 degrees of plantar flexion (76.3 % increase) and 20 degrees of plantar flexion (89.7% increase). After sectioning the ligament, a significant increase (19.3%) in flexibility of the ankle was observed at 10 degrees of dorsiflexion, but no chang e in flexibility was observed with the ankle in the neutral and planta r flexed positions. These findings indicate that anterior drawer testi ng of the anterior talofibular ligament-deficient ankle between 10 deg rees and 20 degrees of plantar flexion results in the largest increase in neutral zone laxity compared with the normal ankle with intact lig aments. They also suggest that an excessive magnitude of force during clinical application of the anterior drawer examination may not be nee ded to diagnose disruption of the anterior talofibular ligament.