The Recurrent Instability of the Patella (RIP) Score: A Statistically Based Model for Prediction of Long-Term Recurrence Risk After First-Time Dislocation

Mario Hevesi, Mark J. Heidenreich, Christopher L. Camp, Timothy Hewett, Michael J. Stuart, Diane L. Dahm, Aaron Krych

Research output: Contribution to journalArticle

7 Scopus citations


Purpose: To describe the clinical history of a series of primary, lateral patellar dislocations and determine long-term predictors of recurrent instability while accounting for patients undergoing early operative management. Methods: A large geographic database of more than 500,000 patients was used to identify patients who sustained a first-time lateral patellar dislocation between 1990 and 2010. Charts were individually reviewed to document demographics, radiographic measures including tibial tubercle to trochlear groove distance (TT-TG) and patellar length (PL), recurrent episodes of instability, and patellar stabilization surgery. A risk score that accounted for early surgical management was calculated using Fine and Gray competing risk regression, and its ability to stratify patients was examined using cumulative incidence curves. Results: Eighty-one patients (mean age 19.9 ± 9.4 years, 38 male, 43 female) were identified and followed for a mean of 10.1 years (range 4.1-20.2). Thirty-eight patients (46.9%) experienced an episode of recurrent instability and 30 (37.0%) underwent patellar stabilization surgery, including 7 who did so before recurrent dislocation. A multivariate, statistically derived scoring system, the Recurrent Instability of the Patella Score (RIP Score), that employed age, skeletal maturity, trochlear dysplasia, and TT-TG/PL ratio to predict recurrent instability while accounting for patients managed surgically, was generated. The resulting RIP score stratified patients into low-, intermediate-, and high-risk categories, with 0.0%, 30.6%, and 79.2% 10-year recurrent instability rates, respectively (P =.000004), and an area under the curve of 0.875 (P =.00002). Conclusions: Patients who sustain a first-time, lateral patellar dislocation can be readily classified into low-, intermediate-, and high-risk categories employing the RIP Score based on age, skeletal maturity, trochlear dysplasia, and TT-TG/PL ratio. This long-term risk stratification holds significant potential clinical utility for determination of patients who are at high risk for recurrent instability after primary patellar dislocation. Level of Evidence: Level III, retrospective comparative study.

Original languageEnglish (US)
JournalArthroscopy - Journal of Arthroscopic and Related Surgery
StateAccepted/In press - Jan 1 2019


ASJC Scopus subject areas

  • Orthopedics and Sports Medicine

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