Presentation
Pain of the lateral aspect of the left knee with fever, reduced range of motion and elevated inflammatory markers.
Patient Data
Narrowing of the proximal tibiofibular joint space with thickening and enhancement of the joint capsule, bone marrow edema of the lateral aspect of the tibial plateau and the fibular head, edematous infiltration of the adjacent muscles (tibialis anterior, extensor digitorum longus, fibularis longus, popliteus and gastrocnemius lateral head). Small intramuscular abscess formations are noted within the popliteal muscle well-demonstrated on post-contrast axial T1 fat sat sequence.
Normal appearance of the menisci, cruciate and collateral ligaments.
Case Discussion
The clinical presentation and the MRI features are most consistent with septic arthritis of the proximal tibiofibular joint with small abscess formations of the popliteal muscle.