Non‐uniform strain distribution in anterolateral capsule of knee: Implications for surgical repair

The existence of a ligamentous structure within the anterolateral capsule, which can be injured in combination with the anterior cruciate ligament, has been debated. Therefore, the purpose of this study was to determine the magnitude and direction of the strain in the anterolateral capsule in response to external loads applied to the knee. The anterolateral capsule was hypothesized to not function like a traditional ligament. A 6‐degree‐of‐freedom robotic testing system was used to apply ten external loads to human cadaveric knees (n = 7) in the intact and anterior cruciate ligament (ACL) deficient states. The position of strain markers was recorded on the midsubstance of the anterolateral capsule during the resulting joint kinematics to determine the magnitude and direction of the maximum principal strain. The peak maximum principal strain ranged from 22% to 52% depending on the loading condition. When histograms of strain magnitude values were analyzed to determine strain uniformity, the mean kurtosis was 1.296 ± 0.955, lower than a typical ligament, and the mean variance was 0.015 ± 0.008, higher than a typical ligament. The mean angles of the strain direction vectors compared to the proposed ligament ranged between 38° and 130° (p < 0.05). The magnitude of the maximum principal strain in the anterolateral capsule is much larger than a typical ligament and does not demonstrate a uniform strain distribution. The direction of strain is also not aligned with the proposed ligament. Clinical Significance: Reconstruction methods using tendons will not produce normal joint function due to replacement of a multi‐axial structure with a uni‐axial structure. © 2019 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res