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Risk Factor Evaluation for Loose Body Following First-Time Patellar Dislocation in Pediatric Patients
David M Kell1, Kevin J Orellana1, Sarah Wetzel1
1Department of Orthopaedics, The Children's Hospital of Philadelphia, Philadelphia, PA, USA.
Background:
The reported rate of osteochondral loose body (OCLB) formation following lateral patellar dislocation (LPD) and risk factors for occurrence vary widely in the literature. 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 identifying a consecutive series of pediatric patients (≤18 years old) treated at a single tertiary care hospital from 2011 to 2021 after first-time LPD with postinjury magnetic resonance imaging (MRI). Patients with recurrent dislocations; delayed imaging (>3 months after injury); 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. Descriptive and bivariate statistics were applied. A multivariable logistic regression was performed to identify independent risk factors for OCLB after first-time LPD.
Results:
Study criteria identified 360 patients (n = 209, 59% female) with a total of 376 knees/cases analyzed, including 67 cases (17.8%) with loose body. In 88.1% of cases, the donor site of the loose body was identifiable with 56.7% (n = 38) originating from the patella, 31.3% (n = 21) originating from the femur, and 11.9% (n = 8) originating from an unknown donor site. Of the OCLBs with an identifiable donor site, 96.6% (n = 57) were full-thickness chondral injuries. A relatively decreased patellar height (mean Caton-Deschamps Index [CDI]: 1.19 for OCLB cases vs 1.28 for non-OCLB cases, P < .001), spontaneous reduction method (P < .001), and older age (P = .03) were associated with a higher rate of loose body formation. A multivariable logistic regression identified that a 1-standard-deviation (SD) increase (0.18) in CDI led to a 33.1% decrease in the risk of loose body formation (odds ratio = 0.669, P = .011).
Conclusions:
Each additional year of age was associated with a 30% increase in the odds of a loose body, and each 0.18 (1 SD) decrease in CDI with a 33% increase in odds for an OCLB after first-time dislocation. These findings serve to enhance risk-counseling for patients with patellar instability and provide guidance for expedited imaging in certain patients where findings may immediately impact clinical care.
Key Concepts:
(1)Osteochondral loose bodies were present in 17.8% of pediatric first-time lateral patellar dislocations.(2)Osteochondral loose bodies originated from the patella in 56.7% of cases.(3)A relatively decreased patellar height, spontaneous reduction method, and older age were associated with a higher rate of loose body formation.
Level Of Evidence:
III, Retrospective Cohort Study.