Poster presentation evaluates five graft preparation techniques

“The all-inside technique for knee cruciate ligament reconstruction has gained popularity in recent years,” explained Jacqueline M. Brady, MD. “Various techniques for graft preparation have been described, but little research has been conducted to compare those techniques. We performed a biomechanical comparison of five graft preparation techniques—including two quadrupled techniques and three alternative methods—that can be used when the available tendon is not long enough to be quadrupled.” Dr. Brady is an orthopaedic sports surgeon at Oregon Health & Science University in Portland, Ore. and a coauthor of Scientific Poster P422, “A Biomechanical Comparison of All-Inside Anterior and Posterior Cruciate Ligament Graft Preparation Techniques,” which was on display during the AAOS Annual Meeting. A popular approach
According to Dr. Brady, use of the all-inside technique for cruciate ligament reconstruction has grown for the following reasons:

• It has the potential to solve the problem of graft size for anterior cruciate ligament (ACL) reconstruction. Graft size, in the form of tendon width, has been shown to correlate with outcomes following ACL reconstruction, and when using a traditional technique with autograft, sometimes the semitendinosus and gracilis tendons are unacceptably small when doubled (ie, the conventional method). Quadrupling both tendons can thus create a thicker graft, saving the patient the cost of adding an allograft tendon, or added morbidity of harvesting a contralateral autograft tendon.
• If size is not an issue, the patient can keep one of the hamstring tendons rather than having both harvested: if the semitendinosus tendon is sufficiently large when quadrupled, the gracilis can be spared when using the all-inside technique.
• When compared to violation of the tibial cortex required with a full tibial tunnel, use of a tibial socket has been found by some to reduce pain.
• Creation of a socket also reduces the communication of the knee joint to the incision to a small guide pin hole. This smaller hole reduces the fluid loss and subsequent issues with arthroscopic visualization that can occur with a full tibial tunnel. This factor may be especially helpful with posterior cruciate ligament (PCL) reconstruction. As the tibial socket/tunnel is very posterior, visualization is key to avoid injury to the neurovascular structures behind the knee.
• In skeletally immature patients, the ability to avoid a full tunnel creation may help protect the growing physis.

However, Dr. Brady notes that graft length can sometimes be insufficient to quadruple the tendon and retain enough soft tissue within the bony socket for incorporation.

“You need the graft to traverse the knee joint,” she said, “and based on the available literature, you need at least 20 mm of soft tissue within each socket to ensure adequate strength and incorporation. So clinicians have developed various ways of compensating for a too-short graft.” The research team conducted a randomized study using fresh frozen porcine extensor tendons. Overall, 10 specimens were prepared for each of the following techniques:

• quadrupled, using 2 different techniques
• two grafts, doubled
• folded
• tripled

Tendons subsequently underwent preconditioning (10 loading cycles from 20–50N at 0.1 Hz), cyclic loading (500 loading cycles from 50–250N at 1.0 Hz) and load-to-failure (load applied at 20 mm/min). The displacement (mm) and force (N) were measured throughout testing. Cyclic displacement, cyclic stiffness, and ultimate failure load were the primary endpoints for comparing graft types.

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Dr. Brady and her colleagues found no significant differences in cyclic displacement, ultimate failure load, or cyclic stiffness between the two quadrupled techniques. The three alternative methods displayed no significant difference in cyclic stiffness, but differed significantly in both cyclic displacement and ultimate failure load. The tripled group had the smallest cyclic displacement, followed by the folded group. The two-doubled group had the greatest cyclic displacement. “We were delighted to find no significant differences between the two methods of quadrupling the graft, as both techniques are widely utilized,” said Dr Brady. “Most importantly, we found that the tripled technique was clearly superior when quadrupling was not an option. “However, I did not expect the dramatic inferiority of the most expensive option: the two grafts doubled,” she continued. “As the grafts are still draped over the heavy suture on one end, I expected it to be roughly equivalent to the other constructs. However, it turns out that the folding of the graft over the suspensory device on both ends (not just one) may be an important component of the time-zero strength of the construct. This has implications for the use of quadriceps tendon (not tested in our study), in which a single limb of graft is secured at both ends by suture to the suspensory construct. If the tendon is not wrapped around the suspensory suture, the graft preparation technique appears to be significantly weakened.” According to Dr. Brady, when surgeons must select an alternative graft preparation technique due to a short available tendon, the tripled technique is recommended over the folded technique. “The two-doubled group showed more than double the displacement of the folded and tripled groups with cyclic loading and is not recommended for use in all-inside cruciate ligament reconstruction,” she said. Dr. Brady concludes that, given a graft of insufficient length for quadrupling, tripling the graft is a viable alternative, assuming the size is acceptable. She states that quadrupled graft constructs remain the preferred method of preparation, but either technique of quadrupling can be utilized without concern for compromising the graft. “If the all-inside technique for PCL reconstruction using allograft becomes widely popular, we may realistically develop a national shortage of tendons long enough for use in quadrupled form,” she said. “This is perhaps the most pressing concern. The PCL is a very long ligament, and not many people donate 36 cm tendons! Knowing our options with regard to alternative methods of graft preparation is important when striving to optimize patient outcomes after cruciate ligament reconstruction.”                    Dr. Brady's coauthors are Colter Wichern, MS; Kathryn C. Skoglund, BS; Joseph G. O'Sullivan, BS; Anora K. Burwell, MS, DPT; Joseph T. Nguyen, MPH; and Andrea Herzka, MD. Details of the authors' disclosure as submitted to the Orthopaedic Disclosure Program can be found in the Final Program; the most current disclosure information may be accessed electronically at www.aaos.org/disclosure Peter Pollack is the electronic content specialist for AAOS Now. He can be reached at ppollack@aaos.org

Bottom Line

• Researchers investigated various techniques for cruciate ligament graft preparation using a porcine model.
• They found no significant difference in cyclic displacement, ultimate failure load, or cyclic stiffness between the two quadrupled techniques.
• Regarding alternative techniques, the tripled group had the smallest cyclic displacement, followed by the folded group. The two-doubled group had the greatest cyclic displacement, and is not recommended for use in all-inside cruciate ligament reconstruction.