What is a Baker’s Cyst?

 In Lower Limb

Bakers Cyst

What’s this pain at the back of my knee?

A Baker’s or popliteal cyst is a common source of posterior knee pain. It is a synovial fluid mass that is located within the popliteal fossa (the area at the back of your knee) (1).

A Baker’s or popliteal cyst is a common source of posterior knee pain. #performbetter @pogophysio Click To Tweet

What is it?

A baker’s cyst is often an enlargement of the bursa located beneath the gastrocnemius and the semimembranosus (hamstring) muscle. The bursa when functioning normally helps aid the movement of the semimembranosus and gastrocnemius as the ankle and knee bend and straighten. Part 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 (2, 4). This connection works as a one way valve, allowing fluid to pass into the gastrocnemius-semimembranosus bursa and forming what is known as a Baker’s cyst.

Diagnosis

A Baker’s cyst commonly presents with pain behind the knee and a often observable swollen area which is tender to touch. Commonly end of range flexion (bent knee) is painful such as with squatting or kneeling. Other symptoms may  include posterior or posteromedial fullness, aches and or and stiffness. Additionally often it is uncomfortable in end of range extension (or hyperextension) of the knee.

A Baker’s cyst commonly presents with pain behind the knee. #performbetter @pogophysio Click To Tweet

In adults a Baker’s Cyst is commonly associated with intra-articular knee pathology. Baker’s cysts are generally secondary to other pathology and will generally present chronic in nature. Therefore examination will most commonly reveal co-existing knee meniscal or chondral pathology (1). Testing of the meniscus and palpation of the knee joint line will likely be provocative. Acute Baker’s cyst can occur with repeated forced extension, for example performing kettlebell swings and thrusting your knees into extension.

It is important to differentiate from other cause of posterior knee pain including biceps femoris tendinopathy, popliteus tendinopathy, knee joint effusion (from intra-articular pathology), gastrocnemius tendinopathy or referred pain from the lumbar spine or patellofemoral joint. A thorough history and examination can differentiate between sources of posterior knee pain.

Confirmation of diagnosis can be made through imaging, which may include plain radiographs, arthrography, ultrasound, and MRI. Plain radiographs are not able to detect popliteal cysts, however are useful in evaluating co-existing pathology commonly found in association with popliteal cysts, such as osteoarthritis, inflammatory arthritis, and loose bodies. The cyst itself can be detected via US however this can not identify co-existing pathology that may be the underlying cause, therefore MRI is gold standard for confirming diagnosis (1).

Treatment

Initial treatment is aimed at management of any underlying cause such as a meniscal tear. Management of baker’s cysts is conservative (nonoperative for at least 6 weeks), unless vascular or neural compression is present (3). During this time, rehabilitation is focused on maintenance of knee flexibility to avoid stiffness that can develop from pain occurring at end range flexion and extension. A progressive rehabilitation program will also be tailored to underlying pathology and aimed at restoring full range of movement strength and control. Activity modification to address contributing factors and exercises to rehabilitate underlying pathology.

Aspiration in combination with Intra-articular corticosteroid injections have been found to decrease the size and symptoms of the cysts (1).  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 (3).

Lewis Craig (APAM)
POGO Physiotherapist
Masters of Physiotherapy

Lewis-craig physiotherapist Gold Coast

References:

  1. Brukner and Khan 2009, Brukner and Khan’s Clinical Sports Medicine.
  2. Frush, T. J., & Noyes, F. R. (2015). Baker’s cyst: diagnostic and surgical considerations. Sports health, 7(4), 359-365.
  3. Zhou, X. N., Li, B., Wang, J. S., & Bai, L. H. (2016). Surgical treatment of popliteal cyst: a systematic review and meta-analysis. Journal of orthopaedic surgery and research, 11(1), 22.
  4. Rauschning W. Anatomy and function of the communication between the knee joint and popliteal bursae. Ann Rheum Dis. 1980;39:354-358.

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