The Effect of Anterior Cruciate Ligament Deficiency and Functional Bracing on Translation of the Tibia Relative to the Femur During Nonweightbearing and Weightbearing

Background: Much of what is known about functional bracing is derived from studies of the knee during unweighted or weightbearing conditions, whereas little is known about the transition between these postures. Hypothesis: Bracing the anterior cruciate ligament-deficient knee during nonweightbearing, throughout the transition to weightbearing, and during weightbearing reduces the abnormal translations of the tibia relative to the femur to within the limits of normal. Study Design: Controlled laboratory study. Methods: Subjects with chronic anterior cruciate ligament tears were studied with and without braces. Anteroposterior shear and compressive loads were applied to the knee, and translations of the tibia relative to the femur were measured while subjects were nonweightbearing, throughout the transition to weightbearing, and during weightbearing. Results: Bracing the anterior cruciate ligament-deficient knee resulted in a significant reduction of anteroposterior laxity values, to a level within the limits of the normal knee during nonweightbearing and weightbearing postures. In contrast, when the anterior cruciate ligament-deficient knees transitioned from nonweightbearing to weightbearing, the anterior translation of the tibia relative to the femur was 3.5 times greater than in the normal knee, and bracing did not reduce this to within the limits of normal. Conclusions: Bracing a knee with a chronic anterior cruciate ligament tear was effective in reducing abnormal anteroposterior laxity during nonweightbearing and weightbearing; however, braces were not effective in reducing the abnormal anterior translations produced by the change between these postures. Clinical Relevance: This study explains why subjects with anterior cruciate ligament tears gain partial control of pathologic anteroposterior laxity with the use of a brace but may continue to experience abnormal translations during activity.