Behavior of the anterolateral structures of the knee during internal rotation.

INTRODUCTION Since the recent descriptions of the anterolateral ligament (ALL), the role played by the anterolateral peripheral structures in the rotational control of the knee is again being debated. The objective of this study was to identify the structures during internal tibial rotation and then to define their anatomical characteristics. We hypothesized that internal rotation would tighten several anatomical formations, both superficial and deep, with the ALL one part of these structures. MATERIAL AND METHODS Nine fresh-frozen cadaver knee specimens were studied. The anterolateral structures tightened were identified from superficial to deep at 30° of flexion. Each was selectively dissected, identifying its insertions and orientations, and measuring its size. The length variations of the ALL during internal tibial rotation were measured by applying a 30-N force using a dynamometric torque wrench at the tibiofibular mortise. RESULTS The superficial structures tightened were the iliotibial tract and the Kaplan fibers. In internal tibial rotation, the Kaplan fibers held the iliotibial tract against the lateral epicondyle, allowing it to play the role of a stabilizing ligament. The Kaplan fibers were 73.11±19.09mm long (range, 63-82mm) and at their femoral insertion they were 12.1±1.61mm wide (range, 10-15mm). The deep structures tightened covered a triangular area including the ALL and the anterolateral capsule. The ALL was 39.11±3.4mm long (range, 35-46mm) in neutral rotation and 49.88±5.3mm long (range, 42-58mm) in internal rotation (p<0.005). Its femoral insertion area was narrow at 5.27±1.06mm (range, 3.5-7mm) and was mainly proximal and posterior at the lateral epicondyle. Its tibial insertion zone was wide, with a clearly differentiated anterior limit but a posterior limit confused with the joint capsule. In the vertical plane, this insertion was located 6.44±2.37mm (range, 2-9) below the joint space. DISCUSSION This study demonstrates two distinct anterolateral tissue planes tightened during internal rotation of the tibia: a superficial plane represented by the iliotibial tract and the Kaplan fibers, which acts as a ligament structure, and a deep plane represented by a triangular capsular ligament complex within which the ALL and the anterolateral capsule are recruited. LEVEL OF EVIDENCE Descriptive cadaver study IV.