Tibial Tunnel Coronal Plane Angle Also a Factor for ACL Reconstruction
Abstract & Commentary
Synopsis: Vertically placed tunnels, with a starting point close to midline, are associated with greater loss of flexion and anterior laxity. This study recommends drilling the tibial tunnel at an angle of 65-70° in the coronal plane to reduce the incidence of this problem.
Source: Howell SM, et al. The relationship between the angle of the tibial tunnel in the coronal plane and anterior laxity after anterior cruciate ligament reconstruction. Am J Sports Med. 2001;29(5):567-574.
Howell has taught us all the importance of the location of the tibial tunnel in the sagittal plane. Now he emphasizes that we should also consider tibial tunnel location in the coronal plane. In a series of articles published previously by Howell, he demonstrated that the tibial tunnel must lie posterior to the intercondylar roof. Although several authors have suggested that a more medial starting point allows better access for femoral tunnel drilling, there has been little in the literature suggesting that the coronal angle of the tibial tunnel could affect clinical results.
In a prospective study, 5 surgeons performed hamstring ACL reconstructions on 119 patients who were followed for 4 months postoperatively. Howell and colleagues then measured all of the radiographs and collected all clinical data on the patients at that point. The sagittal radiograph was checked for roof impingement, and the AP radiograph was analyzed to determine if the tibial tunnel was contained between the tibial eminences and to measure the angle the tibial tunnel formed with the medial joint line. They found that loss of flexion and anterior laxity increased with more vertical tibial tunnel angles. The critical threshold appeared to be at angles greater than 75°. They also noted a wide degree of variability among surgeons. In order to drill at these less vertical angles, it is necessary to partially violate the fibers of the medial collateral ligament.
Comment by Mark D. Miller, MD
Howell et al have once again introduced some potentially important technical concepts regarding the optimum way to perform ACL reconstruction. It is amazing that despite not being aware of this, and potentially many other issues, how successful many of us have been with ACL reconstruction. I have always been taught, and continue to teach others, that the starting point for the tibial tunnel should be located midway between the tibial tubercle and the posteromedial aspect of the tibia. I am not aware of what angle of the tibial tunnel in the coronal plane will result from this starting point, but I suspect that it would fall within Howell’s safe zone in most cases. Howell has developed another guide, or at least an attachment to his existing guide, to help in the measurement of the coronal angle. It is not explicitly clear from the article, but if Howell was indeed "Surgeon A" in the paper, then his angle variance was 9° with the modified guide. This is an interesting paper, and offers much food for thought and possibilities for further research.
Dr. Miller, Associate Professor, University of Virginia Health System, Department of Orthopaedic Surgery, Charlottesville, is Associate Editor of Sports Medicine Reports.