ACL Reconstruction: Rupture Risk Calculator Guides Management

Heidi Splete

July 07, 2021

An autograft risk calculator based on patient traits accurately predicted the odds of graft rupture in young, active individuals who underwent anterior cruciate ligament reconstructions with hamstring tendon or bone-patellar tendon-bone grafts.

Anterior cruciate ligament reconstructions (ACLR) have historically high failure rates in younger patients, wrote Hama Marmura, PhD candidate at Western University, London, Ontario, Canada, and colleagues.

"Failure of ACLR is multifactorial and can be associated with traumatic reinjury, poor biological healing, insufficient rehabilitation, and surgical technique," the researchers wrote. Of these, surgical technique is one risk factor surgeons can modify to improve postprocedure prognosis, and "graft type is arguably the most significant component of surgical technique for ACLR," they wrote. However, data on optimal graft choices, especially for younger patients, are lacking, they added.

To help guide shared decision-making and graft choice, the Multicenter Orthopaedic Outcomes Network (MOON) knee group developed an algorithm based on patient characteristics and lifestyle that are usually collected at an initial surgical consult. These factors included age, sex, body mass index, sport played at the time of injury, Marx Activity Scale, preoperative knee laxity, and graft choice of hamstring tendon (HT) or bone-patellar tendon-bone (BPTB).

In a study published in the American Journal of Sports Medicine, the researchers used the MOON calculator to assess 839 patients aged 14-22 years who received HT or BPTB grafts. They conducted an external validation by comparing outcomes with those of 618 patients aged 25 years and younger in STABILITY 1, a randomized clinical trial in which patients received hamstring tendon grafts with or without lateral extra-articular tenodesis (LET).

Overall, the calculator was acceptably predictive, with an area under the curve of 0.73. "This suggests that the model correctly predicts which patient will experience a graft rupture first in any given pair approximately 73% of the time," the researchers said. The sensitivity and specificity of the MOON risk calculator were 47% and 85%, respectively.

For calibration, the Brier score was 0.07, which reinforces the accuracy of the model, the researchers noted.

In the MOON cohort, patients who received HT grafts were approximately twice as likely to experience a rupture than those who received BPTB. By comparison, patients in the STABILITY trial who received HT only were more than three times as likely to suffer a rupture compared to those who received HT plus LET, the researchers said. The results confirm that BPTP and HT plus LET are more protective against rupture in young, active ACLR patients compared to HT alone, and that use of HT alone should be avoided in this population, if possible, they added.

Higher-grade preoperative knee laxity and age in the 14-22-years range were confirmed as significant predictors of increased graft rupture risk.

The calculator, while not perfectly accurate, "can help standardize surgeons' decision-making practices to ensure that individual patient characteristics, rather than surgeon preference or industry trends, are driving graft choice," the researchers wrote.

The study findings were limited by several factors, including the differences in graft selection and differences in follow-up times between the MOON and STABILITY studies, the researchers noted. Although the model rarely predicted the odds of rupture as greater than 10%, this range reflects other studies of young and active patients, they added.

Despite these limitations, the results provide strong external validation for the MOON knee group ACLR risk calculator, the researchers said. "However, there is room for additional work to provide an increased level of certainty," they noted. In particular, "An impact analysis is required to understand how use of the prediction model in clinical practice influences patient rupture rates," they concluded.

Data Reflect Challenges in Young Patients

As the competitive level of sports participation increases in young athletes, there will continue to be many young surgical patients with ACL injuries, said Kyle Hammond, MD, an orthopedic surgeon at Emory University, Atlanta, in an interview.

"Understanding modifiable surgical factors that may decrease the risk of re-injury in a young population can improve quality-adjusted life years going forward for our patients," he said.

Dr Kyle Hammond

Hammond, who was not involved in the study, said that he was not surprised by its findings. "I have always utilized either a quadriceps or patellar tendon autograft for my young ACL patients over the last 10 years," he said. "I have seen anecdotally and through research papers observed that hamstring autografts and allografts have a higher failure rate in the young, athletic population and I do not utilize them in this patient population," he noted.

"LET surgical techniques have a historical relevance and now have made a comeback in their potential clinical relevance as an addition to modern ACL reconstruction techniques," Hammond said. "However, surgical technicalities and reproducibility need to be better proven and defined with further research studies to ensure that we are not over-constraining the athlete's knee," he emphasized.

More studies are needed on the addition of LET to ACL surgery as well, Hammond added. "LET as an additional surgical intervention to ACL surgery needs to be further researched, not only as a short-term beneficial procedure, but also as a long-term benefit to our patients' overall knee health to ensure that it truly improves our current ACL methods," he said.

Am J Sports Med. Published online May 4, 2021. Abstract

The study received no outside funding. The researchers and Hammond have disclosed no relevant financial relationships.

Heidi Splete is a medical journalist based in Washington, DC.

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