The Role of the Peripheral Passive Rotation Stabilizers of the Knee With Intact Collateral and Cruciate Ligaments: A Biomechanical Study

Background: A subset of patients have clinical internal and/or external knee rotational instability despite no apparent injury to the cruciate or collateral ligaments. Purpose/Hypothesis: The purpose of this study was to assess the effect of sequentially cutting the posterolateral, anterolateral, posteromedial, and anteromedial structures of the knee on rotational stability in the setting of intact cruciate and collateral ligaments. It was hypothesized that cutting of the iliotibial band (ITB), anterolateral ligament and lateral capsule (ALL/LC), posterior oblique ligament (POL), and posteromedial capsule (PMC) would significantly increase internal rotation, while sectioning of the anteromedial capsule (AMC) and the popliteus tendon and popliteofibular ligament (PLT/PFL) would lead to a significant increase in external knee rotation. Study Design: Controlled laboratory study. Methods: Ten pairs (N = 20) of cadaveric knees were assigned to 2 sequential cutting groups (group 1: posterolateral-to-posteromedial [PL -> PM] and group 2: posteromedial-to-posterolateral [PM -> PL]). Specimens were subjected to applied 5-N.m internal and external rotation torques at knee flexion angles of 0 degrees, 30 degrees, 60 degrees, and 90 degrees while intact and after each cut state. Rotational changes were measured and compared with the intact and previous cut states. Results: Sectioning of the ITB significantly increased internal rotation at 60 degrees and 90 degrees by 5.4 degrees and 6.2 degrees in group 1 (PL -> PM) and 3.5 degrees and 3.8 degrees in group 2 (PM -> PL). PLT/PFL complex sectioning significantly increased external rotation at 60 degrees and 90 degrees by 2.7 degrees and 2.9 degrees in group 1 (PL -> PM). At 60 degrees and 90 degrees in group 2 (PM -> PL), ALL/LC sectioning produced significant increases in internal rotation of 3.1 degrees and 3.5 degrees, respectively. In group 2 (PM -> PL), POL sectioning produced a significant increase in internal rotation of 2.0 degrees at 0 degrees. AMC sectioning significantly increased external rotation at 30 degrees to 90 degrees of flexion with a magnitude of change of <1 degrees in both groups 1 (PL -> PM) and 2 (PM -> PL). Conclusion: Collectively, the anterolateral corner structures provided primary internal rotation control of the knee from 60 degrees to 90 degrees of knee flexion in knees with intact cruciate and collateral ligaments. The ITB was the most significant primary stabilizer of internal rotation. The POL had a primary role for internal rotational stability at full extension. The PLT/PFL complex was a primary stabilizer for external rotation of the knee at 60 degrees and 90 degrees. Clinical Relevance: This study delineates the primary and secondary roles of the ITB, ALL/LC, POL, and PLT/PFL to rotatory stability of the knee and provides new information to understand knee rotational instabilities.