BACKGROUND: 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. OBJECTIVES: Does a misaligned knee brace stress the anterior cruciate ligament? STUDY DESIGN: It is an experimental study. METHODS: 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. OUTCOME MEASURES: The outcome measures were anterior cruciate ligament strain and three-dimensional kinematics of the knee joint. RESULTS: 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. CONCLUSION: 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. CLINICAL RELEVANCE: The correct alignment of the brace was identified as a key factor decisively influencing the effectiveness of bracing.
BACKGROUND: 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. OBJECTIVES: Does a misaligned knee brace stress the anterior cruciate ligament? STUDY DESIGN: It is an experimental study. METHODS: 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. OUTCOME MEASURES: The outcome measures were anterior cruciate ligament strain and three-dimensional kinematics of the knee joint. RESULTS: 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. CONCLUSION: 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. CLINICAL RELEVANCE: The correct alignment of the brace was identified as a key factor decisively influencing the effectiveness of bracing.