Researchers explore biomechanical “Rule of Thirds” after second ACL injury

HUNTINGTON, W.Va. – Patient outcomes for those presenting with a second anterior cruciate ligament deficiency or insufficiency and ACL reconstruction do follow a Rule of Thirds concept, according to researchers at the Marshall University Joan C. Edwards School of Medicine in an article in the Journal of Orthopaedics published online June 18, 2022, ahead of print.

The ACL is one of four major ligaments that stabilize the knee and is most commonly injured during sports activities. The Rule of Thirds for ACL-injured patients can be divided into three biomechanical subgroups after injury and prior to reconstruction: 1) those that can function well biomechanically during sports participation without an ACL; 2) those that can function well biomechanically during activities of daily living (ADL) without an intact ACL but cannot return to sports participation; and 3) those that cannot function well biomechanically during ADL of sport without an intact ACL.

After exploring documented incidences of second ACL injuries, researchers found the division of patient function by thirds was also consistent with the Rule of Thirds and likely has a biomechanical basis.

“Our team will use this biomechanical data as we continue to focus our research on the ACL augmentation techniques we have developed at Marshall.  The combination of our enhanced ACL techniques and identification of athletes at risk for further injury will be vital as we look to accelerate return to play after ACL reconstruction,” said Chad D. Lavender, M.D., assistant professor at the Marshall University Joan C. Edwards School of Medicine and orthopaedic surgeon at Marshall Health.

The Cincinnati Group published the original concept of the Rule of Thirds nearly 40 years ago. Subsequently, three decades ago the San Diego Group developed the Surgical Risk Factor (SURF) algorithm, which was designed to prospectively classify the biomechanics of patients who are ACL deficient. The article suggests the Cincinnati classification scheme is descriptive of outcomes and may predict patient function and risk of second ACL injury, though this team has ongoing clinical trials to determine if that’s the case.

“This is a crucial team effort moving forward here at Marshall. We must determine which of these athletes is at potential risk of second ACL injury so that we can target interventions to those individuals to reduce their risk,” said Tim Hewett, Ph.D., professor at the Marshall School of Medicine.  

Authors include Hewett, Lavender and Kate E. Webster, Ph.D., professor and chair of the department of human services and sport at La Trobe University in Australia.

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Date Posted: Wednesday, July 6, 2022