Ruptured septic popliteal cyst associated with psoriatic arthritis.

Popliteal cyst (Baker’s cyst) was first described by Adams in 1840, popularized by Baker in 1877, and was theorized as an enlarged gastrocnemiussemimembranosus bursa that communicated with the knee and trapped synovial fluid.1 Numerous bursa are located in the popliteal space between the knee ligaments, hamstring tendons, gastrocnemius muscle, and collateral ligaments. The two proposed etiologies of Baker’s cyst include an abnormal herniation of synovial fluid through the posterior knee capsule into the popliteal space or fluid escape from the knee through a normal communication with a bursa located in the popliteal space. This bursa has been reported as the gastrocnemius bursa (located behind the medial head of the gastrocnemius) or semimembranosus bursa (between the semimembranosus and medial head of the gastrocnemius).2 A valvular mechanism allows fluid to pass into the cyst but not escape.3 Intra-articular pathology (meniscal disease, degenerative joint disease, rheumatoid arthritis, patellofemoral arthrosis, or any chronic synovitis) is commonly associated with Baker’s cyst.3,4 Popliteal cyst dissection has been infrequently reported throughout the literature, mostly in cases of rheumatoid arthritis, juvenile rheumatoid arthritis, gonococcal arthritis, and Reiter’s syndrome. Clinically, they mimic deep venous thrombophlebitis.5,6 Popliteal cyst infections also have been reported; however, they are a rare complication of septic arthritis. This article presents a patient with psoriatic arthritis who underwent dissection of a ruptured septic popliteal cyst.