Anatomical limitations of transtibial drilling in anterior cruciate ligament reconstruction

Background: Recommended techniques for transtibial drilling in anterior cruciate ligament reconstruction are based on strategies to prevent graft impingement and preserve tibial tunnel length. The limitations of this drilling technique may restrict the ability to centralize tunnels in the anterior cruciate ligament footprints. Hypothesis: A transtibial drilling starting point to centralize the tibial and femoral tunnels in their respective footprints can be identified, but it will result in a short tibial tunnel. Study Design: Descriptive laboratory study. Methods: The femoral and tibial attachments of the anterior cruciate ligament were characterized in 12 fresh-frozen cadaveric knees. Knees were secured in 700 and 900 of flexion. A guide pin was drilled antegrade through the central femoral and proximal anterior cruciate ligament attachment sites through the central tibia] anterior cruciate ligament attachment site to exit on the anterior tibia. Results: In 901 of flexion using the central femoral and tibial attachment sites, the exit point of the pin on the anterior tibia was 14.1 mm from the tibial joint line and 20.9 mm anterior to the superficial medial collateral ligament. The length of the pin in the tibia was 30.6 mm. Extending the knee to 70 degrees or directing the pin through the proximal femoral anterior cruciate ligament attachment moved the starting point less than 4 mm from this point. Conclusion: The transtibial technique can produce tunnels centered in the anterior cruciate ligament footprints, but a starting point close to the tibial joint line is required. This will result in a relatively short tibial tunnel. Clinical Relevance: If tunnels centered in the anterior cruciate ligament attachment sites are desired with the transtibial drilling technique, then a short tibial tunnel is necessary. A short tibial tunnel may compromise graft fixation and graft incorporation, or it may result in a tunnel length-graft length mismatch. An alternative drilling strategy might be employed.