Anatomic Tunnel Drilling in ACL Reconstruction
Is there a preferred drilling technique for tunnel placement when reconstructing a torn anterior cruciate ligament?
Michael B. Banffy, MD
The author has no disclosures relevant to this article.
Ultimately, the goal of anterior cruciate ligament (ACL) reconstruction is to restore normal knee kinematics in a patient with an ACL-deficient knee. It is hypothesized that abnormal joint forces will occur during activity in an ACL-deficient knee, which could lead to the development of osteoarthritis. [1,2]
The ACL plays an important role in both anterior tibial translation and rotation with respect to the femur. This stability is conferred through a ligament that takes the proper anatomical load.
During ACL reconstruction, the femoral tunnel can be drilled in either a transtibial or an independent drilling technique. Several studies have documented that the transtibial technique leads to a vertical non-anatomic position of the ACL on the femur. [3-7] Independent tunnel drilling through a two incision technique, or now more commonly through an anteromedial portal, more consistently reproduces the normal anatomic footprint on the femur. [4,5]
One reason for failure after ACL reconstruction is persistent rotational instability. Biomechanically, a graft placed in the non-anatomic position will have decreased rotational stability. [8,9] Drilling from an anteromedial portal allows the surgeon to place the single-bundle ACL at the center of the anatomic footprint, ideally leading to anatomic rotational and translational restraints.
It is possible that a graft placed in the non-anatomic position will be unable to reproduce the physiologic restraint provided by the normal ACL, leading to this persistent instability. Xu et al  showed that a non-anatomic position of the ACL leads to decreased loads conferred by the reconstructed ligament.
Despite the biomechanical evidence, there is little clinical evidence comparing the outcomes of transtibial versus anatomic femoral tunnel drilling in ACL reconstruction. A recent article by Duffee et al  presents the outcomes for a large cohort of patients comparing transtibial to anteromedial tunnel drilling. The authors found a statistically significant increase in repeat ipsilateral knee surgery in patients treated with the transtibial technique. These surgeries ranged from revision ACL reconstruction to meniscal and cartilage procedures, suggesting recurrent instability in those patients with non-anatomic grafts. Although a robust study, there clearly needs to be more clinical data supporting the use of independent drilling.
Overall, ACL reconstruction has an excellent, 80% success rate. Cadaveric and radiologic studies have shown that anteromedial and two-incision techniques better recreate the anatomical femoral footprint. With new data supporting anatomic placement of the femoral tunnel and increased utilization of independent drilling techniques, it is possible that the success of ACL reconstruction may further improve.
Biomechanical and now clinical studies show that anatomic grafts lead to improved rotational stability and decreased revision surgeries. Further clinical evidence will likely continue to support the use of anatomic femoral tunnel drilling.
Michael B. Banffy, MD, is an orthopaedic surgeon with Kerlan-Jobe Orthopaedic Clinic in Los Angeles, California. He specializes in sports medicine, joint preservation, and joint reconstruction.
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- Kondo E, Merican AM, Yasuda K, et al. Biomechanical comparison of anatomic double bundle, anatomic single bundle, and nonanatomic single bundle anterior cruciate ligament reconstructions. Am J Sports Med. 2011;39(2):279-88.
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- Duffee A, Magnussen R, Pedroza A, et al. Transtibial ACL Femoral Tunnel Preparation Increases Odds of Repeat Ipsilateral Knee Surgery. JBJS. 2013;29:2035-42.