Abstract
Baker’s cyst is the result of an abnormal accumulation of synovial fluid in the medial aspect of the popliteal fossa. Often, a tear of the medial meniscus or tendinitis of the medial hamstring is responsible for the development of Baker’s cyst. Patients suffering from rheumatoid arthritis are especially susceptible to the development of Baker’s cysts.
Patients with Baker’s cysts complain of a feeling of fullness behind the knee. They may notice a lump behind the knee that becomes more apparent when they flex the knee. The cyst may continue to enlarge and dissect inferiorly into the calf. Patients suffering from rheumatoid arthritis are susceptible to this phenomenon, and the pain associated with dissection into the calf may be confused with thrombophlebitis, thus leading to inappropriate treatment with anticoagulants. Occasionally, Baker’s cyst spontaneously ruptures, usually after frequent squatting. In this case, rubor and calor may be evident in the calf, again mimicking thrombophlebitis; however, Homans’ sign is negative, and no cords are palpable.
Keywords
Baker’s cyst, knee pain, thrombophlebitis, tendinitis, Homan’s sign, diagnostic sonography, ultrasound guided injection, magnetic resonance imaging
ICD-10 CODE M70.20
The Clinical Syndrome
When bursae become inflamed, they may overproduce synovial fluid, which can become trapped in a saclike cyst. Because of a one-way valve effect, this cyst gradually expands. Baker’s cyst is the result of an abnormal accumulation of synovial fluid in the medial aspect of the popliteal fossa. Often, a tear of the medial meniscus or tendinitis of the medial hamstring is responsible for the development of Baker’s cyst. Patients suffering from rheumatoid arthritis are especially susceptible to the development of Baker’s cysts.
Signs and Symptoms
Patients with Baker’s cysts complain of a feeling of fullness behind the knee ( Fig. 117.1 ). They may notice a lump behind the knee that becomes more apparent when they flex the knee. The cyst may continue to enlarge and dissect inferiorly into the calf ( Fig. 117.2 ). Patients suffering from rheumatoid arthritis are susceptible to this phenomenon, and the pain associated with dissection into the calf may be confused with thrombophlebitis, thus leading to inappropriate treatment with anticoagulants. Occasionally, Baker’s cyst spontaneously ruptures, usually after frequent squatting. In this case, rubor and calor may be evident in the calf, again mimicking thrombophlebitis; however, Homans’ sign is negative, and no cords are palpable ( Fig. 117.3 ).
On physical examination, patients with Baker’s cysts have a cystic swelling in the medial aspect of the popliteal fossa that may be quite large. Activity that includes squatting or walking makes the pain worse, whereas rest and heat provide some relief. The pain is constant and is characterized as aching; it may interfere with sleep.
Testing
Plain radiographs, magnetic resonance imaging (MRI), and ultrasound imaging of the knee are indicated for all patients who present with Baker’s cyst ( Figs. 117.4 and 117.5 ). MRI and ultrasound imaging can also detect internal derangement, an occult mass, or a tumor. Based on the patient’s clinical presentation, additional testing may be warranted, including a complete blood count, erythrocyte sedimentation rate, and antinuclear antibody testing.
