The effects of extra-articular starting point and transtibial femoral drilling on the intra-articular aperture of the tibial tunnel in ACL reconstruction

Abstract

Background: The recent emphasis on more horizontal femoral tunnel placement for single-bundle anterior cruciate ligament (ACL) reconstructions requires placing a femoral tunnel lower on the lateral wall of the notch. Some surgeons have advocated moving the starting point of the tibial tunnel farther medial to achieve this more horizontal tunnel.

Purpose: To compare tibial tunnel aperture changes with transtibial femoral tunnel drilling.

Study design: Controlled laboratory study.

Methods: Twenty match-paired cadaveric knees (10 specimens) were randomized into 2 groups with equal right and left knee distribution. Ten of the knees underwent tibial tunnel drilling from a medial starting point (group 1), and the corresponding opposite knee of each cadaveric specimen had the tibial tunnel drilled from a central starting point (group 2). Computerized tomography (CT) with thin slices and 3-dimensional reconstruction was used to obtain the dimensions of the apertures, area of the apertures, angles of the tunnels, and location of the starting point and ending point of the tunnels. We also determined the location of the femoral tunnels in the notch for each of the groups. The 10 knees with medial starting points underwent transtibial femoral tunnel drilling and were restudied with CT to evaluate changes in tibial tunnel characteristics. The 10 knees with central starting points underwent femoral drilling from an anteromedial arthroscopic portal.

Results: Central tibial tunnels were slightly larger than medial tibial tunnels before femoral drilling (106.3 mm(3) vs 92.4 mm(3)). After femoral drilling through the medial tunnels, the apertures were larger than the central tibial apertures (118.6 mm(3) vs 106.3 mm(3)). Medial tibial tunnels resulted in an intra-articular aperture that was farther from the tibial tubercle (43.1 mm vs 16.3 mm), farther from the medial tibial plateau (38.3 mm vs 32.2 mm), and more acute in the coronal plane (50.4 degrees vs 79.3 degrees ). Medial tibial tunnels resulted in an intra-articular aperture that was closer to the anterior edge of the tibia (22.6 mm vs 29.6 mm) but with a less acute sagittal plane angle (82.5 degrees vs 54.5 degrees ). The average clock-face measurement on the femur was 10:40 (+/-14 minutes) for the medial starting point and 10:14 (+/-14 minutes) for the central starting point (drilled from an anteromedial arthroscopic portal) (P = .0016).

Conclusion: We observed significantly increased tibial aperture size and shape after transtibial femoral drilling with a medial tibial starting point. Medial tibial tunnels, compared with more central tunnels, resulted in a more acute tibial tunnel in the coronal plane and less acute tibial tunnels relative to the sagittal plane. Medial tibial tunnels started farther from the tibial tubercle but ended farther from the medial joint line and closer to the anterior edge of the tibia in comparison to central tunnels Clinical Relevance Femoral tunnel placements may be best accomplished using a technique other than transtibial drilling through a medial tibial tunnel. Tibial tunnel angle, intra-articular position, and femoral tunnel placement are affected by the choice of extra-articular starting position.