Dr. Ebraheim’s animated educational video describes Baker’s cyst of the back of the knee.
A baker’s cyst is sometimes called a “popliteal cyst”. A baker’s cyst is a benign swelling found behind the knee. The baker’s cyst lies posterior to the medial femoral condyle. Te cyst is connected to the knee joint through a valvular opening. Knee effusion or swelling from intra-articular pathology allows the fluid to go through the valve to the cysts in one direction (usually behind the knee). Sometimes the patient complains about swelling behind the knee and that alerts the clinician to the possibility of having a problem inside the knee itself.
The cyst is located between the semimembranosus and the medial gastrocnemius muscles. The cyst is usually located at or below the joint line.
The patient usually has swelling behind the knee with pain, fullness and tenderness. The presence of knee effusion, which is excessive fluid inside the knee, will create fluid pressure that allows unidirectional passage of the fluid from the knee joint, through the valve and into the cyst.
A baker’s cyst is easier to see when the knee is fully extended.
Diagnosis is usually confirmed by MRI that will show the associated intra-articular pathology.
Ultrasound is helpful. Ultrasound is important, especially if the cyst is found to be outside of its typical normal position.
The two most common:
•Meniscal tear, especially the medial meniscus.
Tears of the posterior horn of the meniscus that extend to the capsule, may cause a defect or one-way valve to develop between the knee joint and the bursa that lies between the gastrocnemius and semimembranosus muscles.
If the cyst is present in an atypical location, consider a tumor as a part of the differential diagnosis.
Baker’s cyst is a fluid-filled cyst and not a solid tumor. The cyst should transilluminate.
Treatment of painful large cysts:
•Aspiration of the cyst: blind aspiration or ultrasound guidance.
•Excision of the cyst: recurrence of baker’s cysts is common if the intra-articular pathology continues. The best treatment is arthroscopy and debridement of the intra-articular pathology. Recurrence of the cyst is common following its removal, therefore, the main treatment of baker’s cysts should be directed towards treating the intra-articular pathology (usually meniscal tear or arthritis).
The cyst may burst, causing calf pain and swelling. Rule out deep vein thrombosis (DVT) or thrombophlebitis.
Popliteal cysts in children
•Common soft tissue mass at the back of the knee.
•Occurs more in boys
•Not a tumor
•The cyst may not be intra-articular and may not have a connection to the knee joint.
•Usually not associated with a meniscal tear.
•Surgery is rarely indicated.
•The cysts is usually treated by observation. Spontaneous resolution of the cysts can occur in 10-20 months.
•In difficult cases, aspiration of the cyst may be indicated.
•The cyst may respond to aspiration and steroid injection. Because it is not connected to the knee joint.
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