An unusual cause of febrile knee pain in children: Septic arthritis of the proximal tibiofibular joint (a case report).

Introduction And Importance: Septic arthritis (SA), an infection affecting joints, is primarily attributed to bacteria, viruses, or fungi, with the hip, knee, and ankle being common sites of involvement. However, SA of the proximal tibiofibular joint is exceptionally rare. We report a highly uncommon case of lateral knee pain with fever in an 11-year-old boy caused by SA of the proximal tibiofibular joint.

Case Presentation: The case involves an 11-year-old male admitted with atraumatic knee pain, fever, and limping. Physical examinations revealed no pain or tenderness of the knee joint, but a painful swelling near the proximal tibiofibular region. The patient had a temperature of 38.6 °C and a petechiae-like rash. Initial bloodwork showed an inflammatory syndrome, and blood cultures were negative. Imaging, including X-rays, ultrasound, and MRI, revealed a fusiform collection near the fibula and a 40*10 mm mass. Surgery, performed through a posterolateral approach, identified purulence in the tibiofibular joint. Bacteriological samples confirmed methicillin-sensitive Staphylococcus aureus, with histopathological results confirming non-specific septic synovial involvement. The patient received a six-week course of dual empirical antibiotics and showed afebrile status postoperatively. At the two-year follow-up, the patient walked independently with no restrictions in joint mobility.

Clinical Discussion: SA of the tibiofibular joint is rare but should be considered in febrile knee pain, especially if lateralized.

Conclusions: A favorable outcome require a prompt diagnosis and treatment, involving surgical debridement, appropriate antibiotics, and postoperative immobilization.