Abstract
Background:
Osteochondritis dissecans (OCD) of the knee is a disorder of the subchondral bone and overlying cartilage that commonly affects children and adolescents. If not properly managed, OCD can lead to mechanical symptoms, pain, and early-onset osteoarthritis. Early management of these lesions is essential for optimizing outcomes. Magnetic resonance imaging (MRI) is the preferred modality for assessing lesion severity, morphology, and stability. An MRI feature called the omen sign has been proposed as a potential indicator of disease severity, however, its clinical utility is not well understood. It appears as a hypointense band perpendicular to the articular surface of an OCD lesion. The primary objective of this study was to evaluate the prognostic value of the omen sign in predicting failure of non-operative treatment. Failure was defined as conversion to surgery from non-surgical treatment at baseline.
Hypothesis:
We hypothesized that the omen sign would be associated with failure of non-operative treatment.
Methods:
This retrospective cohort study included 133 patients (aged 5–17) with 147 knees analyzed with confirmed OCD lesions enrolled from a single tertiary pediatric orthopedic center between 2015 and 2025. Presence or absence of the omen sign on baseline MRI was recorded, along with detailed clinical, demographic, and radiographic data. Patient-reported outcome measures, pain scores, and treatment course were analyzed. The primary outcome was conversion to surgery from non-operative baseline treatment. Statistical analyses included chi-square tests, Mann-Whitney U tests, and multivariable logistic regression.
Results:
The omen sign was present in 39 knees (26.5%) and absent in 108 (73.5%). Patients with the omen sign demonstrated significantly higher rates of surgical conversion compared to those without (20.5% vs. 5.6%, p = 0.011). These patients also had significantly larger lesion dimensions for coronal (p = 0.010) and sagittal (p = 0.021) width and coronal (p = 0.011) and sagittal (p = 0.002) depth. After adjusting for age, sex, BMI, and lesion size, the omen sign was not independently predictive of surgery (OR 1.851, p = 0.370). Instead, sagittal lesion width (OR 1.393, p = 0.005) and another MRI finding named the oreo cookie sign (OR 8.227, p = 0.018) were the strongest independent predictors.
Conclusion:
While the omen sign was associated with increased rates of surgical intervention, it was not an independent predictor after adjusting for key covariates. MRI features such as sagittal lesion width and the oreo cookie sign may be more reliable indicators of poor prognosis in pediatric OCD.
