Anatomy of Secondary Restraints of ACL

Due to a lack of any mechanical bone constraint, knee stability is almost exclusively provided by the knee ligaments, which have a very complex functional anatomy. Knee ligaments can be divided into three compartments: the medial compartment, the lateral compartment, and the central pivot. A detailed comprehension of these structures is essential, as the pattern of knee instability is strictly related to injuries of the anterior cruciate ligament (ACL) and secondary restraints. In the last century, many authors have studied the anatomy of the anterolateral compartment, whose lesion is associated with increased rotatory instability of the knee. However, the anatomical descriptions were often conflicting, and the existence of a true anterolateral capsular ligament was questioned. In 2013, Claes published a very detailed anatomical study, identifying the anterolateral ligament (ALL), originating close to the lateral femoral epicondyle, inserting into the lateral tibial plateau midway between Gerdy’s tubercle and the tip of the fibular head. This finding had a great mediatic impact on the scientific community, refocusing attention on the secondary restraints of the knee, which were forgotten by most surgeons worldwide. Since then, many anatomical, microscopic, and biomechanical studies have supported the existence of the ALL. It is currently reasonably accepted that the ALL is the main structure of the so-called anterolateral complex, which also includes the deep portion of the fascia lata and the posterior horn of the lateral meniscus.