O2099: Risk Factor Evaluation for Loose Body and Chondral Injury Following First-Time Patellar Dislocation

Background: Traumatic intra-articular loose body formation following lateral patellar dislocation (LPD) remains one of the few consensus indications for surgical intervention for first-time dislocators. However, the rate of loose body formation in this setting is variable in the literature and risk factors for occurrence have not been clearly defined. The purpose of this study is to identify demographic and anatomic risk factors for loose body and chondral injury within a consecutive series of patients following first-time LPD.

Methods: A retrospective review was performed of a consecutive series of patients ≤18 years old treated at a single tertiary care hospital from 2017-2021 after first-time LPD. All subjects underwent magnetic resonance imaging (MRI) after injury (standard of care at our institution). Patients who sustained multiple prior dislocations, had delayed imaging (>3 months after injury), had subluxation without dislocation, or those with syndromic, congenital or neuromuscular etiologies of injury were excluded. Patient demographics, injury characteristics, and patellofemoral imaging measures were recorded. Patients with and without loose body or chondral injury on MRI were compared using descriptive and bivariate statistics. A multivariate logistic regression using established PFI risk factors was performed.

Results: We identified 273 patients (59% female) meeting study criteria with a mean age of 14.15±2.09 years including 49 patients (17.9%) with loose body and 144 (52.7%) with chondral injury. Patients presented for initial orthopaedic provider evaluation and underwent MRI 6.0±5.8 days and 25.7±99.2 days after injury, respectively (Table 1). A more anatomically normal patellar height (mean CDI 1.19 vs. 1.28, p< 0.001) and reduction method (p < 0.001) were associated with a higher rate of loose body formation. Chondral injury was more likely to occur in patients with closed physes/more developed skeletal maturity. Conditional logistic regression identified that each 0.01 increase in CDI decreased the odds of loose body by 3% (p < 0.05).

Conclusion: The rate of clinically significant chondral injury and loose body following patellar dislocation was lower in this consecutive pediatric cohort than in the existing literature. Skeletal maturity appears associated with an increased risk of chondral injury. Anatomically normal CDI ratio and spontaneous reductions are associated with greater likelihood of loose body after first time LPD. These findings serve to enhance risk-counseling with pediatric patients sustaining a first-time LPD and provide guidance for judicious use of advancement imaging in resource limited areas.