Poster 296: Incidence and Risk Factors for Contralateral Patellofemoral Instability

OBJECTIVES: BACKGROUND: Patellofemoral joint instability is common in young athletes and often requires surgical intervention. Incidence and risk factors for ipsilateral instability recurrence have been more discussed in the literature than contralateral instability events. PURPOSE: To evaluate the incidence and risk factors for contralateral patellofemoral instability in patients who have undergone patellar stabilization surgery. METHODS: This retrospective study included 543 patients who had undergone medial patellofemoral ligament reconstruction and/or Fulkerson osteotomy as surgical management for lateral patellofemoral instability. The medical records of these patients were examined to evaluate the non-surgical knee. Available imaging of each affected knee was examined to evaluate for patella alta, skeletal maturity, trochlear dysplasia, tibial tubercle to trochlear groove (TT-TG) distance, and tibial tubercle to posterior collateral ligament (TT-PCL) distance. Demographic factors such as BMI, age, and sex were also examined. A second arm was done excluding patients with previous history of bilateral instability, assessing risk factors using the same methods. This yielded information about incidence and risk factors of “new onset” contralateral instability post-stabilization surgery. RESULTS: Of the 543 patients examined, 205 (37.8%) had evidence of contralateral instability. Patella alta (OR, 2.4), skeletal immaturity (OR, 2.67), and younger age (p<0.0001) were associated with increased risk of bilateral instability. Sex, BMI, TT-TG distance, and TT-PCL distance, and trochlear dysplasia were not associated with increased risk of bilateral instability. In the second study, 63 out of 401 (15.71%) of patients had evidence of new onset contralateral instability post-surgery. Skeletal immaturity (OR, 3.65) was found to be associated with increased risk of instability. CONCLUSIONS: The incidence of bilateral patellofemoral instability was found to be 37.8%. Lower age, skeletal immaturity, and patella alta were found to be associated with increased risk of bilateral instability. Incidence of new-onset contralateral instability was found to be 15.71% and was only associated with skeletal immaturity.