The effects of thigh soft-tissue stiffness on the control of anterior tibial displacement by functional knee orthoses.

Using three soft-tissue analogs of variable compliances, four custom functional knee orthoses were evaluated for their abilities to control anterior tibial displacement (ATD) using an anterior cruciate ligament (ACL)-deficient surrogate knee model with applied forces from 25 to 250 N. These analogs had stiffnesses (compliance) ranging from 2.18 N/mm to 4.6 N/mm, simulating the range in the thigh soft-tissue compliances found in subjects ranging from sedentary individuals to competitive athletes. Significant differences in the ATDs allowed were observed between the soft-tissue analogs, orthoses, and the force applied. At low forces, soft-tissue compliance did not play an important role in the reduction of ATD; however, at high forces ATD was directly related to the soft-tissue compliance.