A swelling in the space behind the knee (popliteal space) that is composed of a membrane-lined sac filled with synovial fluid that has escaped from the joint. Also known as synovial cyst of the popliteal space. Complications include Deep Vein Thrombosis, Compartment Syndrome etc.
EPIDEMIOLOGY AND CAUSES
One study found that around 25% of patients with knee pain had a Baker’s cyst which was diagnosed by ultrasound.
There are two age incidence peaks between 4 to 7 years and 35 to 70 years.
There is no predilection for race or sex.
The most common conditions associated with Baker’s cyst are Osteoarthritis, Rheumatoid Arthritis, Juvenile Rheumatoid Arthritis.
It’s common with all forms of arthritis. A Baker’s cyst can also result from a sports related injury or blow to the knee. Gout is another common cause.
CLINICAL FEATURES AND PATHOPHYSIOLOGY
The pathogenesis of Baker’s cyst is explained by the presence of a connection between the knee joint and a bursa between the gastrocnemius muscle and the semitendinosus tendon, allowing the flow of fluid. There is a valve effect between the cyst and the joint, due to the action of the semitendinosus and gastrocnemius muscles.
During flexion the “valve” opens and during extension the “valve” closes due to the tension of these muscles. Moreover, the intra-articular pressure of the knee interferes in the formation and in the filling of the popliteal cysts.
The three factors
(a) presence of communication between joint and bursa
(b) valve effect
(c) variation of intra-articular pressure in the knee
corresponds to the pathophysiology of the formation of Baker’s cyst.
Baker’s cyst may be asymptomatic and causes no pain . In advanced and severe cases it shows symptoms such as
Swelling behind the knee
Stiffness and inability to fully flex the knee
If the cyst breaks open, pain may increase significantly along with swelling of the calf.
Rupture of a Baker’s cyst may also cause bruising below the medial malleolus of the ankle (Crescent sign).
PHYSICAL EXAMINATION AND DIAGNOSIS
Apart from clinical observation physical examination reveals that if the cyst is large enough there can be palpable posteromedial fulness or tenderness. A palpable cyst is often firm in full knee extenstion and soft in knee flexion. This finding is known as “foucher sign” and is due to cyst compression.
During the examination testing of knee flexion can be useful. Patients with large cysts may develop loss of knee flexion because the cysts mechanically block flexion.
Ultrasonography allows us to define the size and location of the Baker’s cyst. Ultrasound is able to detect Baker’s cysts near 100%, but lacks to differentiatie from other conditions, such as meniscal cysts or myxoid tumors.
The gold standard for diagnosis of Baker’s cysts and differentiating them from other conditions remains MRI (magnetic resonance imaging) . It allows assessment of the entire spectrum of related disorders. Conditions such as meniscal cysts are more easily differentiated from Baker’s cysts with MRI than ultrasound.
An ice massage (cryotherapy) of 15 minutes every 4-7 hours will reduce the inflammation. The treatment is based on the principles of R.I.C.E (rest, ice, compression, and elevation) followed by some muscle-conditioning exercises.
Rehabilitation program can improve the control of the knee joint by range of motion exercises. It will increase the motion of the joint as well as increase flexibility. Physiotherapist prescribes mobility, a hamstring stretching program and a concurrent quadriceps strengthening program. This will result in less pain at about 6-8 weeks.
Click below for detailed exercise regime
Self treatment for Baker’s Cyst
KT Taping for Baker’s Cyst