The Relationship Between Lateral Femoral Anatomic Structures and the Femoral Tunnel Outlet in Anterior Cruciate Ligament Reconstruction Using the Transportal Technique: A 3-Dimensional Simulation Analysis

BACKGROUND: The relationship between the lateral femoral anatomic structures and femoral tunnel outlet according to changes in knee flexion and transverse drill angle during femoral tunnel creation in anterior cruciate ligament (ACL) reconstruction remains unclear. PURPOSE: To investigate the relationships between the lateral femoral anatomic structures and femoral tunnel outlet according to various knee flexion and transverse drill angles and to determine appropriate angles at which to minimize possible damage to the lateral femoral anatomic structures. STUDY DESIGN: Controlled laboratory study. METHODS: Simulation of ACL reconstruction was conducted using a 3-dimensional reconstructed knee model from the knees of 30 patients. Femoral tunnels were created using combinations of 4 knee flexion and 3 transverse drill angles. Distances between the femoral tunnel outlet and lateral femoral anatomic structures (minimum safe distance, 12 mm), tunnel length, and tunnel wall breakage were assessed. RESULTS: Knee flexion and transverse drill angles independently affected distances between the femoral tunnel outlet and lateral femoral anatomic structures. As knee flexion angle increased, the distance to the lateral collateral ligament, lateral epicondyle, and popliteal tendon decreased, whereas the distance to the lateral head of the gastrocnemius increased (P < .001). As the transverse drill angle decreased, distances to all lateral femoral anatomic structures increased (P < .001). Considering safe distance, 120°, 130°, or 140° of knee flexion and maximum transverse drill angle (MTA) could damage the lateral collateral ligament; 130° or 140° of knee flexion and MTA could damage the lateral epicondyle; and 110° or 120° of knee flexion and MTA could damage the lateral head of the gastrocnemius. Tunnel wall breakage occurred under the conditions of MTA – 10° or MTA – 20° with 110° of knee flexion and MTA – 20° with 120° of knee flexion. CONCLUSION: Approximately 120° of knee flexion with MTA – 10° and 130° or 140° of knee flexion with MTA – 20° or MTA – 10° could be recommended to prevent damage to the lateral femoral anatomic structures, secure adequate tunnel length, and avoid tunnel wall breakage. CLINICAL RELEVANCE: Knee flexion angle and transverse drill angle may affect femoral tunnel creation, but thorough studies are lacking. Our findings may help surgeons obtain a stable femoral tunnel while preventing damage to the lateral femoral anatomic structures.