Peak passive resistive torque at maximum inversion range of motion in subjects with recurrent ankle inversion sprains

Although a number of mechanical and neuromuscular processes have been identified, the primary mechanisms underlying residual functional instability of the ankle remain unclear. Understanding such mechanisms will help physical therapists identify where to focus treatment efforts, ultimately leading to more effective rehabilitation. In the present investigation, resistive torque at maximum ankle inversion was evaluated to determine if lateral ankle structures demonstrated mechanical laxity. Thirty subjects with a history of unilateral recurrent inversion sprains were tested bilaterally. A custom-made apparatus provided a stress to the lateral ankle in a method that was similar to the inversion stress test. Two measures of laxity were used: maximum passive inversion range of motion and peak passive resistive torque. Differences between the involved and uninvolved ankles were determined using analysis of covariance procedures. There were no significant differences between involved and uninvolved ankles for maximum inversion range of motion and for peak passive resistive torque. Post hoc testing confirmed adequate statistical power. The results support previous investigations, which suggest that functional instability can exist in the absence of mechanical lateral ankle laxity.