A Baker's Cyst With Distal Extramuscular Extension: A Case Report.

A 49-year-old man presented with repeated episodes of posterior knee effusions 11 months following right knee medial meniscus debridement. He was referred to Physical Medicine & Rehabilitation (PM&R) by his orthopaedic surgeon for further non-operative management. He had previously undergone ipsilateral vein stripping procedures with vascular surgery five months following his meniscal procedure. Magnetic resonance imaging (MRI) of the knee with contrast along with a subsequent ultrasound evaluation with no evident power Doppler flow confirmed the presence of a right posterior-medial gastrocnemius fluid collection extending extramuscularly into the proximal one-third of the medial head of the gastrocnemius muscle. These imaging findings combined with the yellow-clear aspirate consistent with synovial fluid confirmed the presence of a Baker's cyst with unusually distal extramuscular extension and subcutaneous location just superficial to the medial head of the gastrocnemius muscle. Successful implementation of platelet-rich plasma (PRP) and doxycycline tissue sclerosis emphasized the key role that nonoperative modalities have in treating Baker's cysts. The patient continues to respond appropriately with resolution of his symptoms noted three weeks after his initial sclerotherapy session and an additional treatment performed with half the initial dose of doxycycline. This case demonstrates the successful treatment of a Baker's cyst with an unusually distal location.