The Anterolateral Ligament (ALL): A Comprehensive Study Encompassing Anatomic and Radiographic Landmarks and Native Structural Properties

OBJECTIVES: Recent publications have described significant variability in the femoral attachment and overall anatomy of the anterolateral ligament (ALL). Additionally, there is a paucity of data on its structural properties. The purpose of this comprehensive investigation was to provide quantitative data characterizing the anatomic and radiographic locations, and structural properties of the ALL to assist in the development of an evidence-based approach to anterolateral ligament reconstructions. METHODS: In this descriptive laboratory study, identification of the ALL was performed by a combined outside-in and inside-out anatomic dissection of 15 nonpaired cadaveric knees. Quantitative anatomic relationships were made using a three-dimensional coordinate measuring device. The ALL attachments and additional structures were marked with radiopaque markers prior to obtaining true anteroposterior (AP) and lateral radiographs. Radiographic distances were subsequently made using a picture archiving and communications system program. Structural properties were characterized during a single pull-to-failure test in line with the ALL fibers using a tensile testing machine. Ultimate failure strength (N), stiffness (N/mm), and mechanism of failure were recorded for each specimen. All anatomic, radiographic, and biomechanical measurements were reported as mean values and 95% confidence intervals (95% Confidence interval (CI), Lower bound, Upper bound). RESULTS: Anatomy. The ALL was identified as a thickening of the lateral capsule coming under tension with an applied internal rotation at 30° of flexion. Its femoral attachment was consistently located posterior and proximal to the lateral epicondyle (LE), 4.7 mm posterior and proximal to the fibular collateral ligament (FCL) attachment. The ALL coursed anterodistally to its anterolateral tibial attachment approximately midway between Gerdy's tubercle and the anterior margin of the fibular head, located 24.7 mm (95% CI, 23.3, 26.2) and 26.1 mm (95% CI, 23.9, 28.3) from each structure respectively. Radiography. On the AP view, the ALL originated on the femur 22.3 mm (95% CI, 20.7, 23.9) proximal to the joint line and inserted on the tibia 13.1 mm (95% CI, 12.3, 13.9) distal to the lateral tibial plateau. On the lateral view, the femoral attachment was 8.4 mm (95% CI, 6.8, 10.0) posterior and proximal from the lateral epicondyle. The tibial attachment was 19.0 mm (95% CI, 17.1, 20.9) posterior and superior from Gerdy's Tubercle. Structural Properties. The average maximum load during pull-to-failure was 175 N (95% CI, 139, 211) and the stiffness was 20 N/mm (95% CI, 16, 25). Failure occurred by four distinct mechanisms: ligamentous tear at the femoral (n=4) or tibial attachment (n=1), midsubstance tear (n=4) and bony avulsion of the tibial attachment (Segond fracture; n=6). CONCLUSION: In conclusion, the ALL was observed as a capsular thickening of the lateral knee, primarily coursing from an attachment posterior and proximal to the lateral femoral epicondyle to the anterolateral tibia which was confirmed by anatomic, radiographic and structural property methods. Failure mechanisms of the ALL included tearing at the femoral origin, intrasubstance tears, and bony avulsions of its tibial attachment (Segond fractures). If necessary, the ALL can be adequately reconstructed using most soft tissue grafts.