Popliteal Fossa Infection, Septic Arthritis of the Knee, Pyomyositis, and Deep Vein Thrombosis Risk in Children.

BACKGROUND: Our aim is to investigate the association between soft tissue infection in the popliteal fossa and hamstring muscles to determine the risk of DVT formation in children with infections in the knee and posterior thigh. METHODS: This prospective cohort study (the Peterborough Paediatric Musculoskeletal Infection Study) has gathered data for 181 children aged 0 to 15 years with infection of their limbs or spine. Those with MRI evidence for infection of the popliteal fossa of the knee were identified, as well as those with thrombosis in the venous system. RESULTS: Popliteal fossa infection was present in 15 children (8% of the 181 in the entire study). Most were associated with septic arthritis of the knee (80%), but some were due to pyomyositis of the hamstrings or calf (20%). Venous thrombosis was noted in 1.1% of the entire 181 study group, but 13% of those with popliteal fossa infection, a 12-fold difference (Fisher exact test statistic 0.0064, P <0.01). One of those with a DVT died from pulmonary embolism a few hours after their MRI scan had been performed. CONCLUSION: Thirteen percent of children with popliteal fossa infection had an associated DVT, so it may be an independent risk factor for thrombosis. To minimize the risk of DVT and its serious complications, we recommend that children presenting to the Emergency Department with pain in the knee, thigh or calf and raised inflammatory markers (CRP/ESR) suspicious for musculoskeletal infection should have their popliteal fossa examined, and if tender, an urgent Doppler ultrasound should be organised. On MRI, attention should be paid to the popliteal fossa on axial STIR images, and if oedema is present around the popliteal vessels, then prophylactic dose anticoagulation should be started, while those with a dilated popliteal vein on MRI should receive treatment dose anticoagulation. LEVEL OF EVIDENCE: Level II. A lesser quality prospective study with patients enrolled at different points in their disease.