PCL Inlay Has Less Stress
Abstract & Commentary
Synopsis: This cadaver study demonstrated the PCL inlay grafts have less stress than grafts placed anterior to posterior (trans-tibial). PCL inlay grafts avoid the "killer turn" and may have less graft attrition than traditional techniques.
Source: Markolf KL. Cyclic loading of posterior cruciate ligament replacements fixed with tibial tunnel and tibial inlay methods. J Bone Joint Surg Am. 2002;84-A:518-524.
Although posterior cruciate ligament (PCL) injuries and reconstruction are less common than that of the ACL, there is still much controversy regarding the treatment of these knee problems. Traditional PCL techniques include an anterior-to-posterior trans-tibial tunnel. This can be technically challenging, risk key neurovascular structures, and requires the graft to negotiate a steep angle at the superior margin of the tunnel (killer turn). Proponents of this technique have downplayed the significance of this turn, but others believe this may be the etiology of late PCL laxity following reconstruction with this technique. An alternative technique, first developed in Europe and then reported in the United States in the mid-1990s, obviates this turn by inlaying (not onlaying) this graft into a trough made in the back of the tibia at the PCL origin.
In the present study, Markolf and colleagues chose to compare these techniques in a cadaver model with cyclic loading. Thirty-one trans-tibial and 31 inlay PCL reconstructions were accomplished and the knees were subjected to 2000 cycles of 50-300 Newtons. Graft elongation and changes in graft thickness were measured following testing. An alarming 10 of 31 trans-tibial grafts failed (no inlay grafts failed). Changes in thickness of these grafts averaged 40.6% reduction compared to a 12.5% reduction in the inlay grafts. Graft elongation was 9.8 mm with the trans-tibial grafts and 5.9 mm with the inlay grafts. All of these measurements were statistically significant.
Comment by Mark D. Miller, MD
This study, much like the smaller study recently published by Bergfeld and colleagues from the Cleveland Clinic,1 raises serious concerns about the long-term durability of traditional PCL reconstruction techniques. I have long been a proponent of PCL inlay techniques2 because of concerns with the "killer turn." I believe that this issue is even more important than the raging debate over whether 1 or 2 femoral tunnels provides the best biomechanical advantage. As Markolf et al point out in this study, both techniques are associated with graft elongation. This tended to occur relatively early in the testing. Therefore, regardless of technique, it is critical to cyclically load the graft prior to fixation. I have found this to be true in clinical practice as well, and will often note that the graft will elongate with cycling the knee several times before graft fixation. The present study is a cadaver study, and only time will tell whether these concerns are important clinically. I would submit, however, that the lack of clinical success with trans-tibial techniques might be at least in part attributable to the killer turn. This study lends credence to this possibility.
Dr. Miller, Associate Professor, UVA Health System, Department of Orthopaedic Surgery, Charlottesville, VA, is Associate Editor of Sports Medicine Reports.
References
1. Bergfeld JA, et al. A biomechanical comparison of posterior cruciate ligament reconstruction techniques. Am J Sports Med. 2001;29(2):129-136.
2. Markolf KL, Zemanovic JR, McAllister DR. Cyclic loading of posterior cruciate ligament replacements fixed with tibial tunnel and tibial inlay methods. J Bone Joint Surg Am. 2002;84A(4):518-524.
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