Functional knee bracing provides protection to the anterior cruciate ligament in response to rotatory loads

The aim of the study was to quantify the effect of functional knee bracing on native knee kinematics and the in-situ force in the ACL in response to external loading.

A robotic testing system was used to apply three external loads from full extension to 60° of flexion to eight fresh frozen human cadaveric knees: 1) a 134 N anterior load, 2) a combined 5-Nm internal rotation +5-Nm valgus torque, and 3) a combined 5-Nm external rotation +5-Nm valgus torque. For native and braced states, kinematics were recorded and the in-situ force in the ACL was determined.

In response to the combined internal + valgus torque, ideal bracing significantly reduced internal rotation at each flexion angle and valgus rotation at 60° of flexion and reduced the in-situ force in the ACL at full extension and 30° of flexion. In response to the combined external + valgus torque, ideal bracing significantly reduced external rotation at each flexion angle and the in-situ force in the ACL at full extension. Ideal bracing had no effect on kinematics in the other degrees of freedom or on the in-situ force in the ACL in response to a 134 N anterior load.

Ideal knee bracing provided a protective effect on the ACL in response to a combined 5-Nm internal rotation +5-Nm valgus torque but had minimal impact in response to anterior loading and valgus torque. Therefore, ideal functional knee bracing may improve rotatory stability and provide protection to the ACL.