Risk Factors for Recurrence of Patellar Instability in Children and Adolescents

Background: Acute patellar dislocation is the most common traumatic injury about the knee in pediatric and adolescent patients. This study describes factors associated with ipsilateral recurrent patellar instability in these patients after a first-time patellar dislocation.

Methods: A single institution retrospective review of all children and adolescents who experienced a first-time lateral patellar dislocation between 2007-2016 with minimum 1-year follow-up. Information related to demographics, initial injury, treatment, and outcomes were recorded. Radiographic parameters were assessed on radiographs and MRI.

Results: A total of 122 knees in 110 patients met the inclusion criteria. 66% were female, and average age was 14.3± 2.8 years. Average follow-up was 2.6±1.6 years. Of the 122 knees, 111 (91%) were initially treated non-operatively and 11 (9%) were treated operatively. Of the non-operatively treated knees, 68 (61.3%) had a recurrence and 32 (47%) then underwent surgery.

Skeletally immature knees had a 72% recurrence rate compared with a 51% recurrence rate in skeletally mature knees (P=0.025). Skeletal immaturity (HR=1.811, 95% CI=1.10-2.98, P=0.020), family history of patellar instability (HR=3.101, 95% CI=1.12-8.59, P=0.029), history of patellar instability of the contralateral knee (HR=1.652, 95% CI=1.02-2.67, P=0.041), trochlear depth

On multivariate analysis, trochlear depth

Conclusion: Younger age, skeletal immaturity, positive family history or contralateral patellar instability, increased patellar height and reduced trochlear depth were all significant risk factors for recurrence in patients with first-time patellar dislocations. This information will help to counsel patients and their families after first-time patellar dislocation about prognosis, treatments and outcomes.