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

Background: 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. Methods: A robotic testing system was used to apply three external loads from full extension to 60 degrees 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. Findings: In response to the combined internal + valgus torque, ideal bracing significantly reduced internal rotation at each flexion angle and valgus rotation at 60 degrees of flexion and reduced the in-situ force in the ACL at full extension and 30 degrees 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. Interpretation: 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.