Effect of tibial tunnel diameter on femoral tunnel placement in transtibial single bundle ACL reconstruction

Purpose The purpose of this study was to identify the impact of tibial reamer size and placement on the position of femoral tunnel placement via a transtibial approach for anterior cruciate ligament (ACL) reconstruction. Methods Eight cadaveric knee specimens were fixed to a stationary table at 90° of flexion and neutral rotation. After removing the anterior capsule and patella, native joint anatomy was recorded with a digitizer (MicroScribe™; CNC Services, Amherst, VA) accurate to 0.05 mm. Tibial and femoral tunnels were drilled via a transtibial ACLR technique using the optimal tibial starting point described by Piasecki et al. On the tibial side, tunnels were drilled progressively with 6-, 7-, 8-, 9-, 10-, and 11-mm reamers. After each reaming, a beath pin was placed in the posterior aspect of the tibial tunnel, positioned relative to the native anatomic ACL femoral footprint, and digitized. Rhino software (McNeel, Seattle, WA) was used to geometrically determine the center of the native femoral footprint and measure in millimeters the relationship of this point with the femoral position achieved using a 7-mm offset femoral guide with each tibial tunnel size. The surface areas of each tibial and femoral insertion were measured using the insertional periphery data recorded with the digitizer. Statistical analysis of continuous variable data was performed with t tests; P values below 0.05 were deemed significant. Results The center of the femoral ACL footprint was reached with a 9-mm tibial tunnel in six knees, and with an 8-mm tunnel in two knees. A 6- or 7-mm tibial tunnel did not allow for anatomic positioning in any specimen, with femoral positioning significantly more superior than that achieved with a 9-, 10-, or 11-mm tibial tunnel ( P < 0.01). The 6- and 7-mm tunnels produced errors of 4.6 ± 1.6 and 2.9 ± 0.5 mm, respectively. After use of the 11-mm tibial reamer, the average tibial tunnel length was 32.1 ± 2.6 mm. Conclusions Limitations of a transtibial ACLR technique may result in non-anatomic femoral tunnel placement with tibial tunnel sizes smaller than 9 mm. However, tibial tunnels placed in the proximal entry position with at least a 9-mm tunnel size allowed anatomic femoral tunnel placement via a transtibial approach.