Editors: Frassica, Frank J.; Sponseller, Paul D.; Wilckens, John H.
Title: 5-Minute Orthopaedic Consult, 2nd Edition
Copyright ©2007 Lippincott Williams & Wilkins
> Table of Contents > Popliteal Cyst in the Adult
Popliteal Cyst in the Adult
Carl Wierks MD
Bill Hobbs MD
BasicsDescription
-
Popliteal cyst in an adult is a distended
cyst in the posterior fossa of the knee that often is connected
directly to the joint space. -
Synonym: Baker cyst
Epidemiology
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Bimodal distribution: 1 subset in children, 1 in adults >55 years old:
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In adults, cysts usually are the result of intra-articular abnormalities.
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In children, the cyst is the primary disorder.
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Males and females are affected equally.
Risk Factors
Intra-articular knee disease (meniscus tear or arthritis)
Genetics
No known Mendelian pattern
Etiology
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Herniation of the synovial membrane
through a weak point of the medial posterior capsule between 2
expansions of the semimembranosus tendon -
Formation of a 1-way valve between the joint and the bursa
Associated Conditions
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Rheumatoid arthritis (1)
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Osteoarthritis
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Chronic ACL tear
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Medial or lateral meniscal tears
DiagnosisSigns and Symptoms
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Mass or fullness in the popliteal fossa of the knee
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Knee effusion
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Symptoms of ruptured cyst are warmth, tenderness, and erythema of the calf, or isolated calf swelling, mimicking DVT.
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Large cysts can produce posterior tibial nerve compression neuropathy.
History
Acute or chronic history of pain and/or mass behind knee
Physical Exam
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Fullness and tenderness posteriorly in the popliteal fossa
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Calf tenderness and swelling in the case of ruptured cyst
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Presence of other potential causes of knee swelling, such as meniscal injury (joint line tenderness) or chronic ligamentous tear
Tests
Lab
Rheumatoid factor
Imaging
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Standing flexed posteroanterior and lateral radiographs
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MRI to evaluate the size of the cyst, differentiate it from a soft-tissue tumor, and identify intra-articular abnormalities
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Duplex ultrasound is the most
cost-effective imaging study for diagnosis and can help rule out DVT as
the cause of a ruptured cyst (2).
Pathological Findings
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Swelling in the popliteal fossa bursae, usually secondary to intra-articular disease
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Herniation of the synovial membrane through a weakened area in the posterior joint capsule
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Differentiating from DVT:
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Important because anticoagulation in the presence of a ruptured cyst could lead to hematoma or compartment syndrome
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Physical examination can be unreliable.
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MRA provides the best resolution, but duplex ultrasound is the best test because of its availability and low cost.
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Differential Diagnosis
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Semimembranosus bursa
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Ruptured cyst
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Soft-tissue tumor
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Lipoma in the popliteal fossa
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Synovial cell sarcoma
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Pseudoaneurysm (usually pulsatile)
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Primary bone malignancy (e.g., parosteal osteosarcoma)
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DVT
P.335
TreatmentGeneral Measures
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Symptomatic: Needle aspiration with or without steroid injection:
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Observation with symptomatic care is acceptable if pain is tolerable.
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Address intra-articular pathology (e.g., arthroscopic meniscectomy for meniscus tear)
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Asymptomatic cyst requires no treatment.
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>90% of popliteal cysts have
associated intra-articular abnormalities; these must be addressed to
prevent recurrence of the cyst (3). -
Cysts often resolve spontaneously after treatment of the intra-articular abnormality.
Activity
The patient may continue all activities, limited only by pain.
Special Therapy
Physical Therapy
-
General knee and core strengthening program
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Postoperative therapy as dictated by the surgical procedure; early ROM and weightbearing usually allowed
Medication
Resolution of symptoms in most cysts with nonoperative care and reassurance
First Line
Analgesics and NSAIDs are treatment mainstays.
Second Line
Narcotic analgesics rarely needed
Surgery
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Arthroscopic evaluation and treatment of any intra-articular abnormalities are indicated.
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A cyst that persists after treatment of
the joint disorder can be removed via a posteromedial incision, but it
has a high rate of recurrence unless intra-articular abnormalities are
addressed.
Follow-upPrognosis
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Most cysts resolve once the intra-articular disorder is treated.
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Untreated cysts may increase in size, but they often reach a stable, constant size.
Complications
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Recurrence
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Rupture, causing a painful, swollen calf and lower extremity (simulating DVT)
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Popliteal artery or vein occlusion, posterior tibial nerve entrapment, and compartment syndrome are rare.
Patient Monitoring
Patients are followed at 4–6-week intervals after surgery until ROM and function return.
References
1. Wilson
PD, Eyre-Brook AL, Francis JD. A clinical and anatomical study of the
semimembranosus bursa in relation to popliteal cyst. J Bone Joint Surg 1938;20:963–984.
PD, Eyre-Brook AL, Francis JD. A clinical and anatomical study of the
semimembranosus bursa in relation to popliteal cyst. J Bone Joint Surg 1938;20:963–984.
2. Volteas
SK, Labropoulos N, Leon M, et al. Incidence of ruptured Baker’s cyst
among patients with symptoms of deep vein thrombosis. Br J Surg 1997;84:342.
SK, Labropoulos N, Leon M, et al. Incidence of ruptured Baker’s cyst
among patients with symptoms of deep vein thrombosis. Br J Surg 1997;84:342.
3. Hughston JC, Baker CL, Mello W. Popliteal cyst: a surgical approach. Orthopedics 1991;14:147–150.
Additional Reading
Childress HM. Popliteal cysts associated with undiagnosed posterior lesions of the medial meniscus. J Bone Joint Surg 1954;36A:1233–1237.
Gristina AG, Wilson PD. Popliteal cysts in adults and children: a review of 90 cases. Arch Surg 1964;88:357–363.
Sansone
V, de Ponti A, Paluello GM, et al. Popliteal cysts and associated
disorders of the knee. Critical review with MR imaging. Int Orthop 1995;19: 275–279.
V, de Ponti A, Paluello GM, et al. Popliteal cysts and associated
disorders of the knee. Critical review with MR imaging. Int Orthop 1995;19: 275–279.
MiscellaneousCodes
ICD9-CM
727.51 Popliteal cyst
Patient Teaching
Reassure the patient that the cyst is benign and will not damage the knee.
FAQ
Q: How can a popliteal cyst be differentiated from a soft-tissue tumor such as a synovial cell sarcoma?
A:
Popliteal cysts usually are asymptomatic with incidental findings on
MRI evaluation for knee conditions. If the lesion is getting larger and
is painful, particularly at night, synovial cell sarcoma should be
considered as a diagnosis. MRI and needle aspiration are required to
make the diagnosis.
Popliteal cysts usually are asymptomatic with incidental findings on
MRI evaluation for knee conditions. If the lesion is getting larger and
is painful, particularly at night, synovial cell sarcoma should be
considered as a diagnosis. MRI and needle aspiration are required to
make the diagnosis.
Q: How does a ruptured popliteal cyst present?
A: Patients complain of acute pain and swelling in the calf. Symptoms mimic DVT, which must be ruled out with duplex sonography.