The effect of knee brace misalignment on the anterior cruciate ligament

Abstract

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.

Assessing effects of exoskeleton misalignment on knee joint load during swing using an instrumented leg simulator

“…In those studies, the braces were worn by human subjects and not actuated through any external force application. A cadaver study found that while the well-aligned brace reduced the strain on the anterior cruciate ligament, the misaligned situation showed an increased strain compared to the unbraced knee [ 16 ]. Despite the difference in research question and approach, with the present study using this passive knee brace to simulate a powered exoskeleton, the findings of the cadaver study are along similar lines as our outcome of an increasing joint load with increasing misalignment.…”

Safety first in rehabilitation robots! Investigating how safety-related physical human-robot interaction ca be assessed

“…In those studies, the braces were worn by human subjects and not actuated through any external force application. A cadaver study found that while the well-aligned brace reduced the strain on the anterior cruciate ligament, the misaligned situation showed an increased strain compared to the unbraced knee [208]. Despite the difference in research question and approach, with the present study using this passive knee brace to simulate a powered exoskeleton, the findings of the cadaver study are along similar lines as our outcome of an increasing joint load with increasing misalignment.…”

“…Cadaver studies can also be a means to assess effects of physical human-robot interaction on biological structures such as ligaments. Limitations of such an approach can be the limited muscle forces and different behavior of tissues compared to living human tissue [208].…”

Return to Sport After an Anterior Cruciate Ligament Tear: Bridging the Gap Between Research and Practice

“…Some nonsurgical options include the usage of a brace to increase knee stability and physical therapy to rehabilitate knee function and strength (39). Evidence indicates that ACL strains can be minimized with the use of a correctly positioned knee brace in comparison with an unbraced knee; a misplaced brace seems to increase the risk of ACL strain (39). Current functional bracing solutions do not sufficiently restore normal biomechanics to the ACL-deficient knee, protect the restored ACL, or enhance long-term patient outcomes, according to biomechanical and clinical research (81).…”