Popliteal cysts were first describedover a century and a half ago. De-spite our increasing knowledge oftheir etiology, pathology, and clini-cal course, they remain something ofa clinical enigma.

Historical Background

A popliteal cyst was first described byAdams in 1840 as an “enlarged bursathat is normally situated beneath theinner head of the gastrocnemius andcommunicates with the joint by aspecies of valvular opening.”1 In1856, Foucher described a recurrentcyst and noted that it became firmwith full knee extension and soft withknee flexion. This pattern is nowknown as “Foucher’s sign.”2

In 1877, Baker further delineatedthe entity as being caused by trappingof fluid in a bursa related to the semi-

membranosus tendon, which causesthe bursa to distend. He asserted thatthe cyst communicates with the jointsynovium and that fluid then leaksinto the bursa but cannot flow in thereverse direction. He also describedthe occurrence of a ruptured bursathat simulated venous thrombosis.After his description, Baker’s namebecame associated with the clinicalentity of a popliteal cyst.1

In the early part of the 20th century,a number of other important observa-tions were made. The most notablewas made by Wilson in 1938,1 whonoted in anatomic dissections that thebursa under the medial head of thegastrocnemius and the bursa underthe semimembranosus often connect.He concluded that most poplitealcysts result from distention of this gas-trocnemius-semimembranosus bursa.

In 1973, Taylor and Rana3 re-ported that postmortem dissections

of 50 knees showed a valvular com-munication between the medial gas-trocnemius bursa and the joint. In1977, Lindgren et al4 demonstratedthat with age there is an increasingfrequency of communication withthe joint, attributable primarily tothinning of the posterior joint cap-sule and progressive degradation ofthe capsule.

Although popliteal cysts may oc-cur on the lateral side of the knee,they typically arise from the bursaassociated with the popliteus ten-don. Therefore, the term “Baker’scyst” is more appropriately used todescribe only those cysts that occuron the posteromedial aspect of theknee between the medial head ofthe gastrocnemius and the semi-membranosus tendon. There is his-torically a high association ofintra-articular lesions with poplitealcysts. All of Baker’s cases were as-sociated with either tuberculosis ofthe knee or a Charcot joint.1 Rheu-matoid arthritis, osteoarthritis,

Vol 4, No 3, May/June 1996 129

Popliteal Cysts: Historical Background and Current Knowledge

Walton W. Curl, MD

Dr. Curl is Associate Professor, Department ofOrthopaedic Surgery, Bowman Gray School ofMedicine, Winston-Salem, NC.

Reprint requests: Dr. Curl, Bowman GraySchool of Medicine, Orthopaedic Surgery andRehabilitation, Medical Center Boulevard, Win-ston-Salem, NC 27157-1070.

Copyright 1996 by the American Academy of Or-thopaedic Surgeons.

Abstract

Popliteal cysts were first described in 1840 by Adams, but it is from Baker’swriting in 1877 that we derive the commonly used eponymic term “Baker’s cyst.”Associated intra-articular lesions are very common with popliteal cysts. Ultra-sonography, arthrography, and magnetic resonance imaging have all proved use-ful in distinguishing popliteal cysts from other cysts and from soft-tissue tumorsabout the knee, as well as in identifying coexisting intra-articular lesions. Cystsin pediatric patients are generally self-limited and should be treated conserva-tively. In the adult population, treatment is primarily nonsurgical. Arthroscopicevaluation is indicated if an intra-articular lesion is causing mechanical symp-toms or if there is no response to appropriate conservative treatment, such as useof nonsteroidal anti-inflammatory drugs and compression sleeves. Surgical exci-sion is reserved for cases in which this approach has been unsuccessful.

J Am Acad Orthop Surg 1996;4:129-133

meniscal tears, and conditions thatcan cause synovitis have been re-ported to be associated with the for-mation of popliteal cysts.

Pathology

The pathologic findings in a poplitealcyst are quite similar to those foundin a ganglion cyst. Popliteal cysts aregenerally lined with flattened,mesothelium-like cells surroundedby fibroblasts and lymphocytes.Hyaline and fibrocartilage elementsmay be found in parts of the wall.The fluid is generally viscous, withcopious amounts of fibrin.

Burleson categorized cysts intothree main types.5 Type 1 cysts are fi-brous, have a wall measuring only 1to 2 mm thick, and are lined with flat-tened, mesothelium-like cells. Type 2cysts have less well-defined, thickerwalls that blend with the surround-ing connective tissue. There is gener-ally more lobulation within the cyst,and the cells are more cuboid than intype 1 cysts. Type 3 cysts have wallsthat are as much as 8 mm thick andthat have more lymphocytes, plasmacells, and histiocytes than the walls oftype 1 and type 2 cysts. This inflam-matory response is more pronouncedin patients with rheumatoid arthritis.

Clinical Presentation

A popliteal cyst typically presents asa mass in the posteromedial aspect ofthe knee. In pediatric patients,masses are usually asymptomaticand are often brought to the physi-cian’s attention by a parent con-cerned about a bulge in the region ofthe posterior popliteal fossa. In olderpatients, attention is often drawn tothe mass because of an achy sensationin the posterior portion of the kneeduring exercise and a fullness notedin the knee on flexion and extension.These symptoms can be isolated but

are more commonly combined withsymptoms related to underlyingpathologic conditions, such as degen-erative joint disease, patellofemoralarthrosis, meniscal disease, or tornanterior cruciate ligament.6 Symp-toms often include pain along the me-dial joint line and a sensation ofgiving way, especially when walkingfor long periods of time or when go-ing up or down stairs.

Rupture of a popliteal cyst can oc-cur suddenly, causing severe pain be-hind the knee and considerableswelling in the calf region. This com-bination has been called “pseu-dothrombophlebitis syndrome,”because the signs and symptoms areoften indistinguishable from those ofthrombophlebitis, even presentingwith a positive Homan’s sign and ten-derness over the posterior aspect ofthe calf.7 A ruptured cyst can some-times be differentiated from throm-bophlebitis clinically. In patients withthrombophlebitis, there may be ahard, palpable cord corresponding tothe thrombosed vein, which is notpresent with a ruptured popliteal cyst.

Because a chronic dissection orleakage of a popliteal cyst can form asymmetrical, cylindrical swelling inthe posterior region of the calf,which can extend all the way to theankle, confusion with deep veinthrombosis is common. The defini-tive diagnosis of deep vein thrombo-sis requires confirmation withvenous Doppler sonography orvenography.

Malignant lesions of the poplitealfossa are rare. However, there arereports in the literature of fibrosar-coma, synovial sarcoma, or malig-nant fibrous histiocytoma beingmistaken for a popliteal cyst.8

Diagnosis

Because popliteal cysts can be mim-icked by other conditions, carefulclinical evaluation is essential. Plain

radiographs are frequently normal,although soft-tissue swelling cansometimes be detected. Arthrogra-phy often demonstrates a communi-cation between the joint and thepopliteal cyst and has been used tocorrectly identify popliteal cysts in10% to 41% of patients.8 False-posi-tive diagnoses may occur if the bursais distended by the arthrographicdye. Arthrographic studies havealso confirmed that the incidence ofthese cysts increases with age.

Ultrasonography has long beenused as a noninvasive technique forevaluation of popliteal cysts, withreliability comparable to that ofarthrography and magnetic reso-nance (MR) imaging.9-11 Althoughultrasonography has been super-seded in frequency of use (but notnecessarily in usefulness and accu-racy) by MR imaging, it continues tohave a role in diagnosis. The ultra-sound study can be useful in distin-guishing cystic lesions from solidmasses in the posterior fossa of theknee.12

Since the introduction of MRimaging, the reported incidences oftrue popliteal cysts have been muchlower than previously estimated. Ina recent study, Fielding et al6 re-viewed 1,127 MR imaging examina-tions and found that the prevalenceof popliteal cysts was 5% overall andthat it increased with age. They alsofound that 82% of popliteal cystswere associated with a meniscal tear,most commonly a tear of the poste-rior portion of the medial meniscus;only 38% of the tears involved thelateral meniscus. An anterior cruci-ate ligament tear was present in 13%of the subjects. A low prevalence ofpopliteal cysts was found in the pe-diatric age group; however, thestudy was retrospective and in-cluded only five patients youngerthan 10 years of age.

Magnetic resonance imaging hasenhanced our ability to distinguishpopliteal cysts from solid lesions and

130 Journal of the American Academy of Orthopaedic Surgeons

Popliteal Cysts

tumors in the popliteal region. Al-though generally more expensive thanother radiologic techniques, it is cer-tainly being used increasingly for as-sessing cystic lesions about the knee.Because of the high content of free wa-ter, the MR imaging features of apopliteal cyst are low signal intensityon T1-weighted images and high sig-nal intensity on T2-weighted images(Fig. 1). There are often septa withinpopliteal cysts. Hemorrhage, loosebodies, and debris may also be found.13

A popliteal cyst can usually beeasily differentiated from a cyst ofeither the lateral or the medialmeniscus. Meniscal cysts typicallydemonstrate a communicating tearin the periphery of the meniscus,and the cyst is usually more medialor more lateral than a true poplitealcyst, which occurs between the me-dial head of the gastrocnemius andthe semimembranosus tendon.14

Treatment

In the adult population, popliteal cystsare often associated with intra-articu-lar lesions.15 Ultrasonography,arthrography, and MR imaging haveall proved useful in diagnosis. Aspira-

tion of the cyst may also be performedfor both diagnostic purposes and treat-ment. Some authors1 advocate inject-ing corticosteroids into a popliteal cyst.In my experience, however, neithercyst aspiration nor corticosteroid injec-tion is more than a temporizing mea-sure; the cyst generally recurs unlessthe intra-articular disorder associatedwith it is addressed. If no intra-articu-lar lesion is present, the cyst can betreated symptomatically and followedconservatively.

Arthroscopic evaluation is indi-cated if an intra-articular lesion iscausing mechanical symptoms and isnot responding to nonsurgical treat-ment, such as nonsteroidal anti-in-flammatory drugs, use of compressionsleeves, and physical therapy, or ifpain or persistent swelling interfereswith function. Treatment of the intra-articular disorder often leads to reso-lution of the cyst as well. Jayson et al16

reported reliable results with anteriorsynovectomy in patients withrheumatoid arthritis.

If the popliteal cyst does not re-spond to conservative measures orarthroscopic intervention, an openexcision may be necessary. A stalkleading from the cyst down to thejoint can often be located and su-

tured over or cauterized, afterwhich the cyst can be removed.The recurrence rate can be quitehigh, however, particularly whenthe articular lesion remains uncor-rected. In the 1979 series ofRauschning and Lindgren,17 a re-current cyst was found in 63% ofthe 40 patients. The authors attrib-uted this primarily to the difficultyof obtaining tight closure of thecapsule, which allowed fluid toleak and re-form the cyst. In a laterseries, Rauschning18 modified histechnique to include arthroscopicevaluation and treatment of intra-articular lesions and use of a pos-teromedial approach for exposure.He emphasized closure of the com-munication and performed a par-tial gastrocnemius-pedicle graft toreinforce the capsular repair. Therewere no recurrences and no post-operative complications in thissmall series of eight patients.

Hughston et al19 described a sim-ilar surgical approach (Fig. 2) intheir series of 30 patients, only 2 ofwhom had recurrences. A postero-medial approach is made through amedial hockey-stick incision withthe knee flexed at a 90-degree angle.The capsular incision begins be-tween the medial epicondyle andthe adductor tubercle and is ex-tended distally along the posterioredge of the tibial collateral ligament,anterior to the popliteal oblique lig-ament. The posterior oblique liga-ment is then retracted posteriorly.The cyst is usually found betweenthe semimembranosus tendon andthe medial head of the gastrocne-mius. The capsular origin of the cystis identified, and the cyst is dis-sected free of its surrounding adhe-sions and excised. The rent in thecapsule is repaired with nonab-sorbable sutures. The capsule canbe reinforced with a pedicle flapfrom the medial head of the gastroc-nemius as Rauschning described,18

if the surgeon so chooses. The

Vol 4, No 3, May/June 1996 131

Walton W. Curl, MD

Fig. 1 A, Axial T2-weighted MR image of the knee demonstrates a posteromedial cyst (C)between the medial head of the gastrocnemius (G) and the semimembranosus tendon (S).B, Sagittal T2-weighted MR image depicts a large posterior popliteal cyst (C).

A B

wound is then closed, and the kneeis immobilized for 48 hours, withweight-bearing as tolerated.

In the pediatric age group, poplitealcysts are generally benign and self-lim-ited. They are rarely associated withintra-articular lesions and are oftenasymptomatic. If the diagnosis is indoubt, ultrasonography or MR imag-ing can be used to pinpoint the diag-nosis and rule out soft-tissue tumors inthe region. As previously pointed out,ultrasonography is generally consid-ered very reliable and is less expensive

than MR imaging. Most pediatric cystsresolve spontaneously, and surgery isnot indicated.20

Summary

Popliteal cysts commonly occur be-tween the gastrocnemius muscleand the semimembranosus tendon.They are generally associated withintra-articular lesions, such as os-teoarthritis or a degenerative menis-cal tear. They are also very commonin association with rheumatoid

arthritis. Magnetic resonance imag-ing can easily distinguish a poplitealcyst from another mass about theknee, such as a meniscal cyst, gan-glion, or soft-tissue tumor. Conser-vative management is the treatmentof choice. Arthroscopy is indicatedfor intra-articular symptoms. If acyst is resistant to conservative treat-ment or arthroscopy, excision maybe necessary. In the pediatric agegroup, popliteal cysts are generallyself-limited and should be treatedconservatively.

132 Journal of the American Academy of Orthopaedic Surgeons

Popliteal Cysts

Semimembranosus

Medialmeniscus

Posterioroblique

A

B C

Medial head ofgastrocnemiusA

C

DPopliteal cyst

Tibial collateral ligament

SemimembranosusB

Fig. 2 A, Medial hockey-stick incision and underlyinganatomic structures in rightknee. B, Area exposed by in-cision. Skin and subcuta-neous tissues have beenremoved to demonstrate re-lationship of popliteal cyst toanterior medial retinacularincision (A–B) and posteriorcapsular incision (C–D). Pos-terior oblique ligament canbe retracted posteriorly forinspection of medial menis-cus and intra-articular aspectof posterior capsule. C,Opening and retraction ofcyst demonstrates adherenceto surrounding tissues. Cystcan then be isolated and ex-cised in its entirety.

Tibialcollateralligament Medial head of

gastrocnemius

Quadriceps

Medial epicondyle

Adductor tubercle

Adductor

Sartorius

Gracilis

Semitendinosus

Oblique popliteal ligament

Gastrocnemius

Semimembranosus

Hockey-stick incision

Posteriorobliqueligament

Retinaculum

Vol 4, No 3, May/June 1996 133

Walton W. Curl, MD

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4. Lindgren PG, Willén R: Gastrocnemio-semimembranosus bursa and its rela-tion to the knee joint: I. Anatomy andhistology. Acta Radiol [Diagn] (Stockh)1977;18:497-512.

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