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Scoring system may predict high-risk patients for recurrent instability after patellar dislocation
The recurrent instability of the patella score can be used to stratify patients who sustain a first-time, lateral patellar dislocation into low-risk, intermediate-risk and high-risk categories for recurrence based on the age, skeletal maturity, trochlear dysplasia and tibial tubercle to trochlear groove/patellar length ratio, according to study results.
“The take-home message of our study is that patients sustaining first-time lateral patellar dislocations, a common presentation in a sports/knee practice, can be readily classified for repeat dislocation risk using the [recurrent instability of the patella score ] RIP score,” Mario Hevesi, MD, and Aaron J. Krych, MD, told Healio.com/Orthopedics. “The score is easily calculable in clinic on the order of seconds and is based upon age, skeletal maturity, trochlear dysplasia and [tibial tubercle to trochlear groove/ patellar length] TT-TG/PL ratio. Employing the RIP score therefore allows for a statistically informed approach to recurrent patellar dislocation management with prognostication that can inform patient-surgeon discussions and decision-making.”
Using a geographic database, Hevesi, Krych and colleagues identified 81 patients who sustained a first-time lateral patellar dislocation between 1990 and 2010. Patients were followed for a mean of 10.1 years. Investigators reviewed charts to record demographics and radiographic measures to note tibial tubercle to trochlear groove (TT-TG) distance, patellar length, recurrent episodes of instability and patellar stabilization surgery.
Results showed 38 patients experienced recurrent instability. There were 30 patients who underwent patellar stabilization surgery, of which seven patients underwent surgery before recurrent dislocation. Investigators generated the RIP score, which used age, skeletal maturity, trochlear dysplasia and TT-TG/patellar length ratio to predict recurrent instability and also accounted for surgically managed patients. The RIP score categorized patients into low-risk, intermediate-risk and high-risk groups with recurrent instability rates of 0%, 30.6% and 79.2%, respectively, at 10 years. The area under the curve was 0.875.– by Monica Jaramillo
Disclosure: The researchers report no relevant financial disclosures.
Perspective
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Patellar dislocation is among the most common injuries sustained by adolescents and young adults. Each dislocation event carries significant risk to the articular cartilage. The recurrent instability of the patella score presented by Hevesi and colleagues aims to establish a new model for the prediction of recurrent dislocation. This model differs from earlier published reports by incorporating patients who underwent early operative intervention, as well as including a minimum 4-year follow-up period. The longitudinal follow-up adds significant value as previous studies have shown that the average re-dislocation may happen after greater than 3 years from the initial dislocation event.
This study has shown significant correlation between risk factors and recurrent dislocation using well-established risk factors, including younger age (<25), open physes, trochlear dysplasia, as well as newer measurements to correlate coronal and axial alignment using the TT-TG/PL ratio. Patients with an increasing number of risk factors were easily stratified into low, medium and high risk allowing surgeons to educate patients and parents at a time of life when downtime from surgical recovery can have significant impact on the adolescent’s school, sport and social life and must be undertaken with significant discretion while attempting to limit significant re-injury to the knee.
While retrospective in nature, this study establishes a useful tool for further study into prediction of recurrent dislocation and, if the results hold up, may provide significant data to the surgeon and parent for future decision-making in treatment of patellofemoral instability.
Division of sports medicine
New York
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