JBJS Classics: ACL Graft Strength and Stiffness
Each month during the coming year, OrthoBuzz will bring you a current commentary on a “classic” article from The Journal of Bone & Joint Surgery. These articles have been selected by the Editor-in-Chief and Deputy Editors of The Journal because of their long-standing significance to the orthopaedic community and the many citations they receive in the literature. Our OrthoBuzz commentators will highlight the impact that these JBJS articles have had on the practice of orthopaedics. Please feel free to join the conversation about these classics by clicking on the “Leave a Comment” button in the box to the left.
In the classic article, “Biomechanical analysis of human ligament grafts used in knee-ligament repairs and reconstructions” (J Bone Joint Surg Am 1984; 66:344–352), now 30 years old, Noyes and colleagues studied the mechanical properties of several anterior cruciate ligament (ACL) grafts that were used at that time. Using young donors, they found that the bone-patellar tendon-bone (BPTB) graft was the only graft studied that had a maximum load in excess of the native ACL. Many of the grafts they studied—including iliotibial tract, fascia lata, and quadriceps retinaculum—had exceedingly poor strengths, which is probably why they are no longer used.
Unfortunately, the authors did not double their hamstring grafts (as is commonly done clinically) for testing, and they also used 14-mm BPTB grafts, which are much wider than commonly used clinically, so some of their comparisons may have limited clinical applicability. The authors did note several limitations to their study, including that graft strength is only one of many factors for successful ACL reconstruction, that gripping was sometimes a problem during testing, and that they only performed uni-axial testing. Nevertheless, this article set the stage for critically analyzing graft choice based upon mechanical properties.
Subsequent studies, including those by Woo, Cooper, Howell, Brown, and others, now suggest that several grafts are available that are stronger and stiffer than the native ACL, including BPTB, quadrupled hamstring (strongest and stiffest of all grafts studied), quadriceps tendon, tibialis anterior tendon, and posterior tibial tendon:
|Graft Type||Ultimate Strength(N)||Stiffness (KN/m)|
Of course, many other ACL reconstruction controversies continue to be debated, including technique, fixation, and autograft vs. allograft. But graft strength and stiffness will continue to be one of many important factors for the ACL surgeon to consider, especially if future options such as ACL augmentation and the use of synthetics and biologics become available. We welcome comments from JBJS readers.
Mark D. Miller, MD
JBJS Deputy Editor for Sports Medicine