Effect of muscle loads and torque applied to the tibia on the strain behavior of the anterior cruciate ligament: An in vitro investigation

Background: Very little is known about the effects of applied torque about the long axis of the tibia in combination with muscle loads on anterior cruciate ligament biomechanics. The purpose of this study was to determine the effect of muscle contraction and tibial torques applied about the long axis of the tibia on anterior cruciate ligament strain behavior. Methods: Six cadaver knee specimens were used to measure the strain behavior of the anterior cruciate ligament. Internal and external axial torques were applied to the tibia when the knee was between 30 degrees and 120 degrees of flexion in combination with the conditions of no muscle load, isolated quadriceps load, and simultaneous quadriceps and hamstring loading. Findings: The highest anterior cruciate ligament strain values were measured when the muscles were not loaded, when the knee was at 120 degrees of flexion, and when internal tibial torques were applied to the knee. During muscle loading the highest anterior cruciate ligament strain values were measured at 30 degrees of flexion and then the strain values gradually decreased with increase in knee flexion. During co-contraction of the quadriceps and hamstring muscles the anterior cruciate ligament was unstrained or minimally strained at 60 degrees, 90 degrees and 120 degrees of knee flexion. Interpretation: This study suggests that quadriceps and hamstring muscle co-contraction has a potential role in reducing the anterior cruciate ligament strain values when the knee is in deep flexion. These results can be used to gain insight into anterior cruciate ligament injury mechanisms and to design rehabilitation regimens. (C) 2011 Elsevier Ltd. All rights reserved.