Corynebacterium septic arthritis of the knee presenting as a ruptured septic popliteal cyst

A rare case of a septic knee arthritis presenting as an infected ruptured popliteal cyst is described. Infection of a popliteal cyst is an uncommon complication of septic arthritis and presentation can mimic that of an acute deep vein thrombosis, leading to delay in diagnosis and treatment. Of interest, the typical hallmarks of infection and haematological markers of inflammation were all unremarkable in the current case. This case was of additional interest in that there have been no reports in the literature of Corynebacterium spp. being isolated from an infected popliteal cyst. Invasive infections caused by Corynebacterium spp. seem to have a predilection for patients who are immunocompromised. It is especially important in this subset of patients that delays in diagnosis are avoided by including it in the differential of an immunocompromised patient presenting with unilateral lower-extremity pain and swelling.