15/10/2023
Bakercyste😉👍🏻
Baker’s Cyst 🦵 💡
ETIOLOGY
👉 A Baker´s Cyst, also known as a popliteal or parameniscal cyst, is a fluid-filled sac that forms in the posterior aspect of the knee, typically located between the semimembranosus and medial head of the gastrocnemius.
👉 The eponym “Baker’s cyst” honors British surgeon William Morant Baker’s, who wrote a description of 8 cases of popliteal cysts that he had seen. https://pubmed.ncbi.nlm.nih.gov/8119018/
👉 Baker's cysts are encountered most frequently in adults with a history of trauma (e.g., cartilage or meniscus tears, injury to the knee), in association with degenerative/co-existing knee joint disease (e.g., osteoarthritis, rheumatoid arthritis, infectious arthritis, pigmented villonodular synovitis, meniscal tears), or asymptomatically as an incidental finding. https://pubmed.ncbi.nlm.nih.gov/28007292/
PATHOPHYSIOLOGY
👉 A valvular opening of the posterior capsule, high up on the medial side and deep to the medial head of the gastrocnemius, is present in up to 40% to 54% of healthy adult knees, based on cadaveric studies. https://pubmed.ncbi.nlm.nih.gov/7436561/, https://pubmed.ncbi.nlm.nih.gov/4751777/
👉 Radiopaque dye has been injected into popliteal cysts, confirming that fluid flow is from the knee joint into the cyst, while reverse flow was not possible. https://pubmed.ncbi.nlm.nih.gov/4751777/
👉 It is thought that this 1-way valvular opening allows fluid to pass into the gastrocnemius-semimembranosus bursa. https://pubmed.ncbi.nlm.nih.gov/26137182/
👉 As an effusion is often present with intra-articular pathology, it is possible that the Baker’s cyst may provide a protective effect on the knee by decreasing the hydraulic pressure within the knee through the 1-way valve. https://pubmed.ncbi.nlm.nih.gov/4916772/
👉 This argument is strengthened by the finding that the volume of the popliteal cysts is associated with the size of the knee effusions. https://pubmed.ncbi.nlm.nih.gov/11409127/, https://pubmed.ncbi.nlm.nih.gov/10873212/
👉 This valvular opening allows flow during knee flexion, but it is compressed closed during knee extension due to tension in the semimembranosus and the medial head of gastrocnemius. https://pubmed.ncbi.nlm.nih.gov/7436561/
CLINICAL DIAGNOSIS
👉 A Baker's Cyst typically is diagnosed by having the patient stand and extend the knee full; this is when the mass should be most prominent and firm. When the knee is flexed to 45 degrees, the mass often either softens or fully disappears (this finding is commonly known as “Foucher sign” and is due to cyst compression between the medial head of the gastrocnemius and semimembranosus as they approximate each other and the joint capsule during knee extension, https://pubmed.ncbi.nlm.nih.gov/3579388/)
👉 It is useful for differentiating a Baker’s cyst from other popliteal masses, such as popliteal artery aneurysms, ganglia, adventitial cysts, and tumors, for which the palpation of the mass is unaffected by the knee position. https://pubmed.ncbi.nlm.nih.gov/3579388/
TREATMENT
👉 Treatment is not usually necessary for a Baker's Cyst unless the patient is symptomatic. https://pubmed.ncbi.nlm.nih.gov/30230249/, https://pubmed.ncbi.nlm.nih.gov/27468670/, https://pubmed.ncbi.nlm.nih.gov/27134018/
👉 Incidental findings in the asymptomatic patient are managed with observation and reassurance alone.
👉 The initial treatment for symptomatic popliteal cysts should be nonoperative for at least 6 weeks, unless vascular or neural compression is present and directed towards treatment of the underlying intra-articular lesions. During this time, rehabilitation focusing on maintenance of knee flexibility should be emphasized to avoid stiffness that can develop from pain occurring at terminal flexion and extension.
👉 Intra-articular corticosteroid injections have been found to decrease the size and symptoms of the cysts, and their use can be considered during conservative management. https://pubmed.ncbi.nlm.nih.gov/16547992/
👉 If the pain fails to resolve with this conservative approach, usually under 2 months, then surgical treatment may be considered directed to the intra-articular cause of the joint fluid production and not at the popliteal cyst unless it is unduly large and highly symptomatic. Surgical excision of the Baker’s cyst without treatment of any intra-articular lesions has been reported; however, the results have been disappointing because of the high rate of recurrence. https://pubmed.ncbi.nlm.nih.gov/5536022/, https://pubmed.ncbi.nlm.nih.gov/525326/