The ACL-deficient knee demonstrates an increase in both tibial rotation and translation that can lead to progressive degeneration within the knee joint. Functional Knee Braces (FKBs) have often been prescribed as an integral part of treatment programmes for such patients. However, the ability of a FKB to increase the stability of the ACL-deficient knee by controlling tibial translation has yet to be confirmed. In addition the athlete with ACL deficiency frequently asks if he/she can use a treadmill as a safe indoor exercise tool.

A prospective study was carried out on 15 pre-operative ACL-deficient patients and 15 fully matched subjects as controls. A gait analysis study was designed using the CODA mpx30 gait analysis system with electromyography (EMGs). The study was carried out using 3 gait situations - simple level walking and treadmill walking (3.6 km/h) both representing low physical activity and treadmill running (10 km/h) representing high physical activity. The tempero-spatial parameters, total range of motion (ROM), joint positions and EMGs were recorded with and without the FKB and the results were compared with the baseline data of both the patients and the data derived from the control subjects.

ACL-deficient subjects had significantly lower speed, shorter stride length and consequently longer double support time while walking on level ground (p< 0.05). None of these variables changed following bracing. The ACL-deficient subjects showed more knee flexion at heel strike and mid-stance which was assumed to be a compensatory reaction to the ligament deficient knee. The FKB significantly reduced ROM in the ACL-deficient subjects at all gait activity levels (p< 0.05). It also reduced peak knee flexion during swing while walking on level ground, but increased maximum knee flexion in swing while walking on the treadmill. Walking on the treadmill reduced hip ROM but running on the treadmill increased ankle ROM in both groups of subjects. No significant angulatory kinematic changes were found during running on the treadmill either before or after bracing. The ACL-deficient subjects showed more knee rotation than the controls during all the trials. Neither the quadriceps nor hamstring muscles showed significant differences between the ACL-deficient and control subjects. The gastrocnemius muscle however was found to have a principal role in the ACL-deficient subjects. FKBs caused the gastrocnemius to be activated earlier (P=0.0001) and showed a positive effect during low force activities. As treadmill walking or running was always accompanied by an increased ankle plantar flexion, it always decreased the gastrocnemius onset activation time that may be a compensatory reaction to stabilise the injured knee. No significant differences were found between the ACL-deficient and the control subjects in terms of kinematics or EMG findings during running on the treadmill.

We have identified beneficial biomechanical changes following the use of FKBs on ACL-deficient knees but only during walking trials. The brace was as effective for walking on the treadmill as walking on the ground. The FKBs led the deficient knees into a safer kinematics and EMG pattern. The ACL-deficient subjects ran as normally as the control subjects and no effects of the FKBs were found during running in our studies.