ACL Tibial Tunnel Landmarks—Have We Been Given a Black Pearl?’
Abstract & Commentary
Synopsis: Landmarks that reference from the existing PCL position were most reliable for tunnel placement in ACL reconstruction.
Source: Hutchinson MR, Bae TS. Reproducibility of anatomic tibial landmarks for anterior cruciate ligament reconstructions. Am J Sports Med. 2001;29:777-780.
Recommendations for ACL tibial tunnel placement, published in the mid 1990s by both Jackson1 and Morgan,2 have been widely adapted, but never challenged—until now. Recommended landmarks included placement of the tibial guide pin: 1) in the posteromedial aspect of the native ACL footprint; 2) adjacent to the apex of the medial eminence; 3) along a line extended from the posterior border of the anterior horn of the lateral meniscus; and 4) 7 mm in front of the PCL. Hutchinson and Bae dissected and studied 42 pairs of cadaveric knees to critically evaluate these recommendations. They carefully exposed the ACL and PCL and then studied the relationship of the ACL to Jackson and Morgan’s recommended landmarks. Although it is difficult to determine from their materials and methods, it appears that the posterior border of the native ACL was used as the main reference to these landmarks. They determined that the PCL and the so-called "over the back position" (a depression in the tibial plateau at the anterior aspect of the PCL insertion described by McGuire3) were the most consistent landmarks, with a standard deviation of only 1.2 mm in cadavers of various sizes and shapes. They recommended use of the old ACL stump and 10-11 (not 7) mm in front of the PCL (or over the back position) as the primary landmarks for ACL reconstruction.
Comment by Mark D. Miller, MD
Add this study to the growing list of articles challenging "classic" recommendations for ACL reconstruction. It’s a wonder that any of our reconstructions are successful, let alone 90% or more! Although this present study presents some potentially important information, several issues must be considered before completely throwing out the recommendations of Jackson and Morgan. Perhaps the most important consideration is not where the existing ACL footprint lies, but where the ideal ACL tibial tunnel should lie. We have become increasingly aware that this location may be different for a 7-mm hamstring graft and an 11-mm patellar tendon graft. The cross-sectional area of hamstring and patellar tendon grafts is different as well, and this may influence recommended tunnel placement. A variety of other factors are also important such as considerations in revision ACL surgery, multiple ligament injuries, and extra-articular tunnel location.
It is important to point out that even though the standard deviation of measurements (1.2 mm) from PCL-based landmarks to the ACL footprint yielded the lowest values, the range of these measurements was more than 6 mm! A difference of 1.2 mm is probably of no clinical significance, but 6 mm would likely make a big difference. In conclusion, I think it is safe to rely more on the PCL based measurements, but don’t completely discard the others!
Dr. Miller, Associate Professor, UVA Health System, Department of Orthopaedic Surgery, Charlottesville, VA, is Associate Editor of Sports Medicine Reports.
References
1. Jackson DW, Gasser SI. Tibial tunnel placement in ACL reconstruction. Arthroscopy. 1994;10:124-131.
2. Morgan CD, et al. Definitive landmarks for reproducible tibial tunnel placement in anterior cruciate ligament reconstruction. Arthroscopy. 1995;11:275-288.
3. McGuire DA, et al. The relationship between anterior cruciate ligament reconstruction tibial tunnel location and the anterior aspect of the posterior cruciate ligament insertion. Arthroscopy. 1997;13:465-473.
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