How to Predict Recurrent Patellar Instability

A team from Mayo Clinic has advanced our knowledge of how to assess patients at high risk for recurrent instability after an initial patellar dislocation. Their work, “The Recurrent Instability of the Patella (RIP) Score: A Statistically Based Model for Prediction of Long-Term Recurrence Risk After First-Time Dislocation,” was published in the January 4, 2019 edition of Arthroscopy.

Co-author Mario Hevesi, M.D., an orthopedic surgeon at Mayo Clinic in Rochester, Minnesota, explained the new research to  OTW, “Lateral patellar dislocation is relatively common, particularly in the young and active population, and greater than 85% of patients injure their medial patellofemoral ligament, a main patellar restraint, following first-time dislocation.”

“Because of this, approximately 30% of patients go on to recurrent instability and 10% go on to surgery. While the risk factors for repeat instability have been individually described, there is to date no good stratification system for counselling patients and surgeons alike for repeat instability risk.”

“Given the phenomenal opportunities presented by the joint research efforts of Mayo Clinic and the Rochester Epidemiology Project, which encompasses over 500,000 patients in a structured, medical research database, we sought to provide a statistically guided scoring system to inform both our practice and the practice of others.”

The authors described the study methodology as: “Eighty-one patients were identified and followed for a mean of 10.1 years. Thirty-eight patients experienced an episode of recurrent instability and 30 underwent patellar stabilization surgery, including 7 who did so before recurrent dislocation.”

“The most important result,” Dr. Hevesi told OTW, “is that by using age, physeal status, the presence of trochlear dysplasia, and TT-TG/PL ratio, recurrence of patellar dislocation could be readily predicted.”

“While previous studies have presented individual risk factors, the calculation of a multivariate, statistically guided scoring system is important as it allows for better establishment of which risk factors are additive and which factors are individually important but lose further significance when evaluated together with others. The RIP score also highlights the high propensity of young and active patients for repeat dislocation, as demonstrated by the statistically based inclusion of both skeletal maturity and age in the final score.”

“Furthermore, it is important that the results and predictive data presented for the RIP score are based on a mean of over 10 years of follow-up. Previous work from our group has demonstrated that recurrent dislocation occurs at a mean of over 3 years following index instability, necessitating long-term follow-up for accurate prognostication.”

“The RIP score provides clinicians with a readily employable, in-clinic tool which provides statistically based information for counseling patients and assisting surgical decision making. By employing the RIP score, surgeons can classify patients who sustain a first-time lateral patellar dislocation into low-, intermediate-, and high-risk categories for recurrent dislocation using easily obtainable demographic factors and standard imaging following index patellar dislocation.”