Baker's Cyst: Diagnostic and Surgical Considerations

Abstract

Context: Popliteal synovial cysts, also known as Baker's cysts, are commonly found in association with intra-articular knee disorders, such as osteoarthritis and meniscus tears. Histologically, the cyst walls resemble synovial tissue with fibrosis evident, and there may be chronic nonspecific inflammation present. Osteocartilaginous loose bodies may also be found within the cyst, even if they are not seen in the knee joint. Baker's cysts can be a source of posterior knee pain that persists despite surgical treatment of the intra-articular lesion, and they are routinely discovered on magnetic resonance imaging scans of the symptomatic knee. Symptoms related to a popliteal cyst origin are infrequent and may be related to size.

Evidence acquisition: A PubMed search was conducted with keywords related to the history, diagnosis, and treatment of Baker's cysts-namely, Baker's cyst, popliteal cyst, diagnosis, treatment, formation of popliteal cyst, surgical indications, and complications. Bibliographies from these references were also reviewed to identify related and pertinent literature.

Study design: Clinical review.

Level of evidence: Level 4.

Results: Baker's cysts are commonly found associated with intra-articular knee disorders. Proper diagnosis, examination, and treatment are paramount in alleviating the pain and discomfort associated with Baker's cysts.

Conclusion: A capsular opening to the semimembranosus-medial head gastrocnemius bursa is a commonly found normal anatomic variant. It is thought that this can lead to the formation of a popliteal cyst in the presence of chronic knee effusions as a result of intra-articular pathology. Management of symptomatic popliteal cysts is conservative. The intra-articular pathology should be first addressed by arthroscopy. If surgical excision later becomes necessary, a limited posteromedial approach is often employed. Other treatments, such as arthroscopic debridement and closure of the valvular mechanism, are not well studied and cannot yet be recommended.

Keywords: Baker’s cysts; intra-articular knee disorders; popliteal synovial cysts.

Figure 1.

Ultrasound images demonstrating anechoic regions within the popliteal fossa representing a popliteal cyst (arrows). (A) Long axis and (B) short axis of the same multiloculated cyst. Note the medial head gastrocnemius tendon between the loculations on image A.

Figure 2.

T2-weighted axial and sagittal images of a popliteal cyst. Note the relationship of the medial head gastrocnemius and semitendinosus tendons to the popliteal cyst on the axial image.

Figure 3.

The limited posteromedial approach may be used for excising small popliteal cysts. This interval is bound by the capsule anteriorly, semimembranosus posteroinferior, and medial head of the gastrocnemius posterosuperior. The extended posteromedial approach is used for excising larger and/or multiloculated popliteal cysts. The dissection proceeds along the posterior border of the sartorial fascia; therefore, the saphenous nerve and its branches should be preserved during superficial dissection. After the sartorial fascia is incised, the pes tendons are retracted anteriorly. Semimembranosus is retracted posteriorly to identify the cyst, although it may occasionally need to be retracted anteriorly to expose multiloculated portions of the cyst.

Figure 4.

Extended posteromedial approach. The tip of the suction device is within the cavity of the popliteal cyst. The wall of the cyst is being grasped with the forceps while the cyst is being dissected free from surrounding soft tissues. (A) Tendon of medial head of the gastrocnemius. (B) Pes anserine tendon group.

Figure 5.

Gastrocnemius tendon used as a patch when sutured over the orifice in the posteromedial capsule after excision of a popliteal cyst. Arrow, tendon.

Figure 6.

View of the posteromedial compartment during arthroscopic popliteal cyst valvular debridement and closure. An arthroscopic shaver is used to debride the valvular opening through a posteromedial portal. The valve is closed by placing sutures via an arthroscopic curved cannulated suture shuttle (Linvatec, Largo, Florida) through the capsule and medial head gastrocnemius tendon.

Figure 7.

Arthroscopic debridement of popliteal cyst. The top image shows the valve orifice viewed through the notch from an anterolateral portal. The middle image was taken with a 30° arthroscope while visualizing into the cyst from an anterolateral portal through the notch. Note the debris in the cyst. The lower image shows the cyst after debridement with a motorized shaver through a posteromedial accessory portal.