Epidemiology, clinical correlates, and management of focal periphyseal oedema (FOPE) in adolescent knees: retrospective analysis of one thousand, two hundred and one knees

BACKGROUND: Focal periphyseal edema (FOPE) is a characteristic magnetic resonance imaging (MRI) finding in adolescent knee joints with open physes. Although described as a benign and likely self-limiting condition, large population-based studies are scarce. The aim of this study was to retrospectively analyse the incidence and the epidemiological background of this MRI finding, and to correlate FOPE lesions with clinical symptoms and treatment. METHODS: This retrospective case-control study included a total of 1201 knee MRI scans from 897 patients, performed between 2007-2016 at our institution in patients aged ten to 16 years. MRIs were screened for the presence of FOPE and other pathologies. FOPE severity was categorised as mild, moderate and severe, based on lesion size and MRI appearance. Patients' medical records were screened for symptoms, trauma history and treatment. RESULTS: Out of the 1201 MRI scans, 97 FOPE lesions (10.8%) in 93 patients (10.4%) were identified. FOPE was significantly more frequent in girls than in boys (p = 0.007). FOPE was the main MRI finding in 53.6% of patients. Mild FOPE was most common (53.6%). Severe FOPE occurred only when FOPE was the main pathology (p = 0.005). Most FOPE patients (74.2%) were treated conservatively. CONCLUSION: FOPE lesions are a common MRI finding in adolescents presenting with knee pain. They tend to be more severe when occurring as the sole finding and have a significantly higher incidence in females. In this large clinical cohort, FOPE was mainly managed conservatively, supporting its interpretation as a benign, self-limiting differential diagnosis of adolescent knee pain.