Focal Periphyseal Edema (FOPE): A Newly Reported Cause of Knee Pain in Adolescent Athletes

OBJECTIVES: To elucidate the clinical and radiologic features of focal periphyseal edema (FOPE) of the knee, a newly reported cause of knee pain in adolescent athletes, which as been described primarily in only the radiologic literature to date. METHODS: Medical records were reviewed of all patients <19 years old diagnosed with knee FOPE by magnetic resonance imaging (MRI) at a tertiary care pediatric referral center. Clinical history and physical exam findings were recorded to assess whether “symptomatic FOPE” was the cause of the patient’s presenting complaints (i.e. no other identifiable etiology for knee pain) or whether the MRI finding was possibly “incidental FOPE” (i.e. other etiologies of knee pain were evident). Radiologic features, including location, size, and concentration and concomitant pathology were analyzed. RESULTS: 56 patients (mean age, 13.9, range 9-16 years, 96% self-reported athletes) with 60 affected knees were included. Females were more common than males (59% vs. 41%, p=0.159). FOPE cases were followed for a mean of 6.1 months (sd,6.8). The primary sport was a repetitive, high-impact sport in 47 patients (90%), most common of which was soccer (27%), basketball (25%), and competitive running/cross-country/track (17%). On MRI, there were 86 distinct knee FOPE zones in patients, the vast majority of whom were undergoing at least early physeal closure. More instances (n=52,60%) were identified in the distal femur than the proximal tibia (n=34,39%) and proximal fibula (n=1,1%). The mean transverse diameter was 10.4 mm (sd,5.6). Ten (17%) knees were clearly classified into “symptomatic FOPE,” and 50 (83%) knees were classified into “incidental FOPE.” Of the concomitant diagnoses reported clinically and/or radiologically, as detailed in Table 1, the majority were overuse-type conditions, such as patellar tendonitis, osteochondritis dissecans, or medial plica syndrome. Patients with symptomatic FOPE lesions (15.3 mm, sd 8.9) had significantly larger lesions than those with incidental FOPE lesions (9.5 mm, sd 4.3)(p=.021). All patients with symptomatic FOPE underwent spontaneous resolution with only physical therapy/conservative measures. CONCLUSION: In this series of 56 patients with knee FOPE, the majority of cases arose in athletes approaching skeletal maturity, participating in high impact sports, and in conjunction with other knee overuse injuries. Caregivers of adolescent athletes must be aware of this newly described condition with unique, characteristic findings on MRI. For patients with atraumatic knee pain of unclear etiology who are approaching skeletal maturity, FOPE should be considered and may be treated with conservative measures and reassurance of spontaneous resolution with rest and continued growth.