Baker's Cyst
- A Baker's cyst is a fluid-filled distension of the gastroc-semimembranosis bursa which has a one-way valvular communication with the knee joint. A high concentration of hyaluronic acid and mucopolysaccharides gives the fluid its gelatinous viscus properties. There is usually some underlying joint condition present, typically degenerative joint disease (degenerate meniscal tear, osteoarthritis).
- Many Baker's cysts are asymptomatic and found incidentally on MRI. Others only cause mild popliteal discomfort and tightness. Some may cause more severe pain and stiffness. The size of cysts and the severity of associated symptoms can fluctuate. Cysts can rupture causing intense calf pain and swelling which settles over a few days with rest +/- compression and ice.
- The diagnosis of a fluid-filled Baker's cyst can be confirmed with transillumination using a pen torch. Where there is doubt over the nature of a popliteal swelling, ultrasound will differentiate a fluid-filled Bakers cyst form a more solid neoplastic lesion (e.g. soft tissue sarcoma).
- Most Baker's cysts do not require any specific treatment. Many have generalised pain or joint line pain from early arthritis or secondary effects of a degenerate meniscal tear which should settle with medical management or intra-articular injection.
- For the occasional Baker's cyst which gives significant localised popliteal knee pain and stiffness, limits range of movement or does not settle with a trial of conservative management (3 to 6 months is reasonable), referral to MSK physio may be indicated.
- Surgical excision is not indicated as risks of complications and rates of recurrence are too high, therefore referrals for consideration of surgical management will not be accepted.