Radiographic Landmarks for Locating the Femoral Origin and Tibial Insertion of the Knee Anterolateral Ligament

Background: Recent anatomic studies have confirmed the presence of a true ligament structure, the anterolateral ligament (ALL), in the anterolateral region of the knee. This structure is involved in the rotatory instability of the knee and might explain why some isolated reconstructions of the anterior cruciate ligament result in a residual pivot shift. Therefore, when considering the least invasive method for reconstruction of this structure, it is important to identify the corresponding bony landmarks on radiographic images. Purpose: To establish radiographic femoral and tibial landmarks for the ALL in frontal and lateral views. Study Design: Descriptive laboratory study. Methods: Ten unpaired cadaver knees were dissected. The attachments of the ALL were isolated and its anatomic parameters were quantified. Its origin and insertion were marked with a 2-mm-diameter metallic sphere, and radiographs were taken from frontal and lateral views. The obtained images were analyzed and the ALL parameters established. Results: The origin of the ALL in the lateral view was found at a point an average SD of 47.5% 4.3% from the anterior edge of the femoral condyle and about 3.7 +/- 1.1 mm below the Blumensaat line. In the frontal view, the origin was about 15.8 +/- 1.9 mm from the distal condyle line. The ALL insertion was an average of 53.2% +/- 5.8% from the anterior edge of the lateral tibial plateau in the lateral view and 7.0 +/- 0.5 mm below the lateral tibial plateau in the frontal view. In anatomic dissections, the origin of the ALL was 1.9 +/- 1.4 mm anterior and 4.1 +/- 1.1 mm distal to the lateral collateral ligament, and the insertion was 4.4 +/- 0.8 mm below the lateral tibial plateau cartilage. Conclusion: The ALL origin on an absolute lateral radiograph of the knee is approximately 47% of the anterior-posterior size of the condyle and 3.7 mm caudal to the Blumensaat line. In a frontal radiograph, the ALL is 15.8 mm from the posterior bicondyle line. The ALL insertion is approximately 53.2% of the anterior-posterior size of the plateau in the lateral view and 7.0 mm below the articular line in the frontal view. Clinical Relevance: Knowledge of the anatomic landmarks of the ALL on radiography will permit minimally invasive surgical reconstruction with lower morbidity.