The MOON Group and ACL Surgery: A Decade of Research Redefines What a Cohort Can Achieve

The reshaping of ACL reconstruction — and the road ahead

By Kurt P. Spindler, MD

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Ten years have passed since the Multicenter Orthopaedic Outcomes Network (MOON) Group published its first paper on outcomes following surgical reconstruction for anterior cruciate ligament (ACL) tears. More than 40 papers later, this unprecedented undertaking in orthopaedic outcomes research continues to yield rich clinical insights.

Many of these insights are captured in a major review article in the March 2015 Journal of the American Academy of Orthopaedic Surgeons and sampled in the sidebar below. While these findings are prompting changes to orthopaedic practice, MOON’s most significant impact may well be the new benchmark it has set for conducting multicenter, multisurgeon research in orthopaedics.


MOON: A short history

MOON traces its roots to the Vanderbilt Sports Medicine–Cleveland Clinic Foundation ACL Reconstruction Registry, which was founded in 1993 by me (when I was practicing at Vanderbilt Orthopaedic Institute) and two Cleveland Clinic colleagues: Richard Parker, MD, and Jack Andrish, MD.

This effort evolved into the creation of MOON in 2002 to enroll and longitudinally follow a cohort of patients undergoing surgical reconstruction for ACL tears. Its purpose: to collect and analyze data and establish predictive models for patient-specific outcomes.

The MOON Group has since expanded from Cleveland Clinic and Vanderbilt Orthopaedic Institute to a total of seven institutions — the others are the Hospital for Special Surgery, The Ohio State University, University of Colorado, University of Iowa and Washington University — with 17 participating surgeons. By accumulating data from more than 3,500 ACL reconstructions to date, MOON has become the largest prospective longitudinal ACL reconstruction cohort in the U.S.

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Much more than a registry

MOON is more than a registry because it captures richer data, at a more granular level, and has a predetermined plan for using these data. Our goal since 2002 has been not just to collect baseline information, as a registry does, but to collect specific details about each patient’s demographics, injury, surgery and treatment — then determine exactly how they factor into each patient’s outcome.

The key to achieving our goal is twofold:

  • Collect sufficient follow-up data. This is something registries don’t typically have resources to pursue. Through follow-up questionnaires and select patient visits, MOON has achieved an outstanding 80 percent follow-up rate at two and six years — with the promise of doing so up to 10 years as well. That tops the 50 and 60 percent rates that the much larger orthopaedic cohorts in Europe have achieved.
  • Perform sophisticated multivariate analyses. We have relied on the expertise of biostatisticians to wade through the data complexities and analyze numerous risk factors.

The key role of patient-reported outcomes

Achieving an 80 percent follow-up rate has been paramount to MOON’s success. While patient follow-up may seem arduous for some specialties, it is somewhat easier for orthopaedics, where effectiveness of treatment is predominantly gauged by pain relief and functional improvement, which can be accurately measured and validated by patients without the need for office visits.

For MOON, patients have reported outcomes using the following instruments:

  • Knee Injury and Osteoarthritis Outcome Score (KOOS)
  • Western Ontario and McMaster Universities (WOMAC) Osteoarthritis Index
  • Marx Activity Rating Scale
  • Medical Outcomes Study 36-Item Short Form (SF-36)
  • International Knee Documentation Committee (IKDC) subjective knee evaluation form

These tools, which orthopaedists have been at the fore of developing over the past decades, have enabled us to follow thousands of patients at low cost.

What’s next for MOON?

Despite the many insights from the more than 40 MOON papers to date, drawing definitive and comprehensive conclusions about what happens following ACL repair requires about a decade and a half of follow-up. So our next four years of data collection will be critical.

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The MOON Group is currently applying for a grant to do 10-year follow-ups so we can further differentiate clinically successful and unsuccessful ACL reconstructions. More data will help us determine how to identify patients who may struggle with articular cartilage, meniscus and other collateral damage — and improve how we care for them.

For example, more than 10 percent of patients report painful osteoarthritis symptoms six years after ACL reconstruction. However, we have noticed potential arthritic changes on radiography much earlier — about 2.5 years after surgery — when the patient reports no pain. Data from 10-year follow-up will help us confirm if radiographs really can predict osteoarthritis onset. Then we can potentially find ways to treat it earlier and modify patients’ outcomes.

Sweeping discoveries like this can only come from a collaborative approach and the study of cohort data. MOON surgeons, scientists, biostatisticians and other contributors are making significant improvements to orthopaedic medicine, providing physicians and patients with the highest-quality evidence for decision-making with the aim of improving ACL reconstruction outcomes.

Dr. Spindler is Vice Chairman of Research for the Orthopaedic & Rheumatologic Institute, Director of Orthopaedic Clinical Outcomes and Academic Director of Cleveland Clinic Sports Health.