The effect of knee brace misalignment on the anterior cruciate ligament

Abstract

Protective knee braces are used for rehabilitation or prevention. Due to poor patient compliance or slippage, the brace might be misaligned with the knee axis. Does a misaligned knee brace stress the anterior cruciate ligament? It is an experimental study. A strain sensor was implanted on the anterior cruciate ligament in eight limbs. The limbs were mounted in a knee simulator, muscle forces were applied and a cyclic motion from 10° to 60° flexion was performed under three conditions: unbraced, braced and with a misaligned brace. The outcome measures were anterior cruciate ligament strain and three-dimensional kinematics of the knee joint. The correctly aligned brace significantly reduced the anterior cruciate ligament strain at 10° compared to the unbraced condition from 0% to -1.54% (standard deviation = 1.4). The misaligned brace neutralised the effect of bracing to -0.06% (standard deviation = 1.1) anterior cruciate ligament strain. At 60° flexion angle, bracing had no statistically significant effect on the anterior cruciate ligament strain compared to the unbraced knee: -2.58% (standard deviation = 0.8) versus -1.64% (standard deviation = 1.0). The anterior cruciate ligament in the misaligned braced knee at 60° flexion with a strain of -1.1% (standard deviation = 0.9) was significantly more stressed than in the correctly aligned condition. An effect of bracing on knee kinematics was not detected. A correctly aligned knee brace reduced anterior cruciate ligament strain. By contrast, a misaligned brace tended to increase the anterior cruciate ligament strain compared to the unbraced knee. The correct alignment of the brace was identified as a key factor decisively influencing the effectiveness of bracing.