Influence of knee flexion angle and transverse drill angle on creation of femoral tunnels in double bundle ACL reconstruction using transportal technique : 3D CT simulation analysis

Abstract

There has been no previous study on double bundle reconstruction dealing with the characteristics of femoral tunnel which change according to the combined effect of various flexion angles of knee and transverse drill angles. The purpose of the study was to find appropriate conditions of knee flexion angle and transverse drill angle for optimal femoral tunnels of anteromedial (AM) bundle and posterolateral (PL) bundle which include sufficient tunnel length without wall breakage, an obtuse graft-tunnel angle, an ellipsoidal tunnel aperture and no communication between two tunnels in double bundle ACL reconstruction using transportal technique. Three-dimensional reconstructed knee models were developed using customized software from computed tomography images of 30 patients. On the transepicondylar axis, the knee flexion angles were altered from 100º to 130º at intervals of 10º. Three transverse drill angles were set up according to the maximum transverse drill angle (MTA) in contact with medial femoral condyle and maximum angle minus 10° and 20° by moving drill laterally. Twelve different femoral tunnels determined by four flexion angles and three transverse drill angles were created for AM bundle and PL bundle, respectively. Following variables of femoral tunnels were assessed: (1) tunnel length; (2) tunnel wall breakage; (3) communication between tunnels of AM and PL bundle; (4) graft-tunnel angle; (5) length of long axis of femoral tunnel aperture. The mean length of tunnel of AM bundle was more than 30mm at 120° and 130° of flexion in all transverse drill angles. The mean length of tunnel of PL bundle was more than 30mm during every condition. There was no case of wall breakage of tunnel in creating PL bundle during every condition, but there were one or more cases of wall breakage except for 120° of flexion and MTA and 130° of flexion and MTA in creating AM bundle. Considering gap length of more than 2mm between two tunnels as having no communication, combination of AM bundle created at 120° of flexion and MTA with PL bundle created at 120° of flexion and MTA (gap length = 2.12±0.93mm), 130° of flexion and MTA (gap length = 2.08±1.17mm) and 130° of flexion and MTA-10° (gap length = 2.03±1.14mm) and combination of AM bundle created at 130° of flexion and MTA with PL bundle created at 120° of flexion and MTA (gap length = 2.48±1.11mm), 130° of flexion and MTA (gap length = 2.35±1.20mm) and 130° of flexion and MTA- 10° (gap length = 2.29±1.16mm) were optimal conditions. Among these combinations, 120° of flexion and MTA was the most optimal conditions for both AM and PL bundles considering graft-femoral tunnel angle and tunnel aperture morphology. Flexion angle of knee and transverse drill angle had a combined effect on the characteristics of femoral tunnel in double bundle ACL reconstruction using transportal technique. Achieving a flexion angle of 120° and transverse drill angle close to the cartilage of medial femoral condyle could be recommended for optimal tunnels of both AM and PL bundles.