Popliteal Cyst Excision Using Open Posterior Approach After Arthroscopic Partial Medial Meniscectomy

Abstract

Popliteal cysts are known to be associated with intra-articular pathology, which must be addressed to prevent cyst recurrence. Indications for popliteal cyst excision include cases in which the popliteal cyst does not respond to conservative treatment or arthroscopic intervention or cases in which an underlying cause cannot be found. Several techniques have been described to excise these cysts. Traditionally, open techniques have been associated with cyst recurrence. More recently, arthroscopic cystectomy has been described. However, the risk of recurrence persists because arthroscopy may not afford complete surgical excision. This technical note presents an open posterior technique for popliteal cyst excision that allows for better visualization and complete removal of the cyst while minimizing the risk of neurovascular complications and soft-tissue damage. It is a safe, effective, and straightforward method to achieve symptomatic relief for refractory popliteal cysts.

Popliteal cysts, also known as Baker cysts, are fluid-filled structures with a synovial lining typically located between the medial head of the gastrocnemius muscle and semimembranosus tendon. Although some popliteal cysts maintain a unidirectional valve communication with the joint cavity, preventing shifting of fluid from the cyst back into the knee joint, others communicate freely.¹ They can occur due to intra-articular pathology, including meniscal and anterior cruciate ligament tears, chondral lesions, and synovitis.² The underlying or associated intra-articular pathology must be addressed to prevent recurrence of the cyst.

Surgical removal of popliteal cysts is indicated in rare cases when the cyst remains symptomatic despite treatment of intra-articular pathology or if no underlying cause is found. Historically, open surgical excision has been performed through a posterior approach or posteromedial approach.^1,3 Arthroscopic closure of the valve without removal of the cyst has shown poor results.^4-6 Arthroscopic valve closure with cyst excision has been described through a posteromedial cyst portal with good preliminary results.^7,8 However, there is still no surgical standard of care for patients with refractory cysts, and concern for recurrence persists.

This technical note presents an open posterior technique for popliteal cyst excision that allows for complete removal of the cyst while minimizing the risk of neurovascular complications and soft-tissue damage. It is a safe, effective, and simple method to achieve symptomatic relief for refractory popliteal cysts.

Surgical Technique

This technique is indicated for cases in which the intra-articular pathology associated with popliteal cysts has been corrected and patients continue to have symptoms from the popliteal cyst without an associated intra-articular lesion. Popliteal cyst excision is always preceded by knee arthroscopy to evaluate for recurrent intra-articular pathology. Popliteal cyst excision is not recommended as a first-line treatment for symptomatic knees. Most cases of popliteal cysts respond to correction of the underlying pathology. If pain persists without an associated cause, popliteal cyst excision through the open posterior approach is indicated.

We describe an open posterior approach for excision of a recurrent popliteal cyst in a patient with a tear of the posterior horn of the medial meniscus. The patient is a 58-year-old active woman presenting with refractory right knee pain, posterior swelling, and tightness. She had undergone previous knee arthroscopy and partial medial meniscectomy with no symptomatic relief. Magnetic resonance imaging shows a large ellipsoid popliteal cyst, measuring 6 cm × 4 cm × 3 cm, in communication with the posteromedial joint cavity (Fig 1).

Fig 1.

Magnetic resonance image of popliteal cyst including (A) sagittal view and (B) axial view showing communication with posteromedial joint cavity.

After induction of general anesthesia, the patient is placed in a leg holder, prepared, and draped. A diagnostic knee arthroscopy is performed, in this case showing a complex horizontal tear of the posterior horn of the medial meniscus with mild patellofemoral chondromalacia. Before the surgeon proceeds to popliteal cyst excision, the potential underlying etiology is addressed and a partial meniscectomy is performed.

Next, the patient is turned from the supine to prone position. At this juncture, the patient is again prepared and draped. In addition, the operative limb is exsanguinated and the tourniquet inflated. The anatomic landmarks are palpated and outlined with a marking pen, including the posterior crease representing the joint line, the popliteal neurovascular bundle, and the popliteal cyst (Fig 2A). A curvilinear incision measuring 4 cm, centered over the popliteal cyst, is taken down to the subcutaneous tissue with careful dissection. Care must be taken not to cross the midline laterally because this could put the neurovascular bundle at risk for injury. Important structures include the popliteal artery, popliteal vein, and tibial nerve. By use of Metzenbaum scissors and blunt dissection, the retinaculum or posterior fascia is identified. An incision is made in line with the skin incision, and the borders of the retinaculum are tagged with sutures for later closure (Fig 2B).

Fig 2.

(A) The curvilinear incision (MI) should be centered over the popliteal cyst, between the medial hamstring tendons and medial head of the gastrocnemius muscle, and overlying the posterior joint line (JL). The popliteal neurovascular bundle (PNB) should be outlined and care taken not to cross the midline laterally so as to avoid risk of injury to these structures. (B) After exposure of the posterior retinaculum, an incision is made in line with the skin incision and the borders of the retinaculum are tagged with sutures for later closure.

The cyst is typically found directly underlying the fascia, between the medial head of the gastrocnemius and the medial hamstring tendons. Blunt dissection shows the cystic wall. An effort is made to remove the cyst without violating the cystic wall. However, decompression or partial decompression may be necessary to maximize visibility and enable extraction of larger cysts through the open incision. Incision of the cyst extrudes viscous yellow-tinted liquid content. In our patient the partial decompression was performed with opening of the retinaculum because the cyst wall abutted the fascia (Video 1, minute 1:51). When the location of the cyst is in doubt, aspiration with a syringe can confirm its location and help differentiate it from surrounding structures, including the medial head of the gastrocnemius and the medial hamstring tendons.

The decompressed or intact cyst is then clamped with an Alice clamp. The surgeon begins excision with blunt dissection of the proximolateral border of the cyst while protecting the popliteal neurovascular bundle. Visualization of the proximolateral aspect of the cyst is paramount as dissection proceeds to the safe zone located distally and medially. Alternating blunt and sharp dissection, the surgeon elevates the cyst off the medial head of the gastrocnemius, medial hamstring tendons, and posteromedial joint capsule, exposing the valve or stalk (Fig 3A). Once again, care is taken to avoid close proximity to the popliteal neurovascular bundle laterally and the saphenous neurovascular bundle medially. Finally, the surgeon completely removes the cyst while keeping the posterior joint capsule intact. The cystic tissue should be sent for pathologic examination.

Fig 3.

(A) After decompression of the cyst, alternating blunt and sharp dissection proceeds from lateral to medial, exposing the stalk. (B) After excision of the cyst and stalk from the posterior joint capsule, surgical exposure is achieved with an Army-Navy retractor holding the medial head of the gastrocnemius muscle (MG) superiorly and an Army-Navy retractor holding the medial hamstring tendons (MHT) inferiorly. The tonsil clamp indicates where the stalk (S) was excised from the posterior capsule.

The surgeon examines the popliteal fossa for any residual popliteal cyst tissue, paying close attention to the stalk or valve. To accomplish this, adequate surgical exposure is necessary. The medial head of the gastrocnemius can be retracted medially with an Army-Navy retractor, and the medial hamstring tendons can be closely inspected for residual cystic tissue before being retracted laterally with an Army-Navy retractor to expose the posterior joint capsule (Fig 3B). The option is available to roughen the remnant stalk with a rasp to promote healing and seal the posterior capsule. Once excision of the cyst is complete, the wound is copiously irrigated. The retinaculum is closed with a No. 0 Vicryl suture (Ethicon, Somerville, NJ) in a taut fashion. After another round of irrigation, subcutaneous tissue and superficial skin are closed in a tension-free manner. The key steps of the procedure are outlined in Table 1.

Table 1.

Key Steps of Open Posterior Popliteal Cyst Excision

Intra-articular pathology should be addressed arthroscopically before proceeding to popliteal cyst excision (Video 1, minute 0:43).

The incision should be centered over the popliteal cyst lateral to the hamstrings and medial to the gastrocnemius muscle (Video 1, minute 1:17).

Cautious incision of the retinaculum and minimal dissection should reveal the popliteal cyst wall (Video 1, minute 1:42).

Care must be taken not to deviate laterally past the midline.

Excision of the cyst proceeds lateral to medial and proximal to distal (Video 1, minute 2:32).

The valve communication should be adequately excised if identified (Video 1, minute 3:20).

The retinaculum is closed tautly with a No. 0 Vicryl suture (Video 1, minute 3:27).

The postoperative protocol includes 1 week of full knee extension in a knee immobilizer to protect the wound from maceration or dehiscence, followed by a physiotherapy protocol in accordance with the intra-articular pathology treated. After 1 week of knee immobilization, postoperative recovery mirrors rehabilitation after standard knee arthroscopy.

Discussion

The precise etiology of popliteal cysts remains unknown. However, it has been established that cysts can be associated with intra-articular pathology that must be addressed to prevent cyst recurrence.^1,2,4 Targeting the valve or stalk has proven to be insufficient.^4-6 A thorough excision of the cyst in its entirety appears to be the most effective treatment for recurrent or idiopathic popliteal cysts.

Rauschning and Lindgren¹ pioneered the posterior approach in the 1970s. They reviewed 41 patients who underwent popliteal cyst excision with this technique with a mean follow-up of 4 years. A high rate of recurrence was found in patients with concomitant intra-articular pathology including advanced osteoarthritis, meniscal tears, and anterior cruciate ligament ruptures. The authors' explanation for recurrence included unaddressed underlying intra-articular pathology, unsatisfactory exposure of the valve or stalk, and inadequate closure of the posterior capsule.

The posteromedial approach described by Hughston et al.³ is thought to provide better visualization of the communication valve. They also found a high rate of posterior horn medial meniscus tears associated with popliteal cysts. They reported good results, with only a small fraction of patients requiring subsequent surgery. However, the approach calls for a long hockey-stick incision with substantial exposure. Since the advent of knee arthroscopy, the incision required has been reduced in size. Despite the miniaturization of the incision, the technique requires extensive dissection.

More recent studies have described arthroscopic cystectomy.^7,8 These techniques target the valve communication and proceed with decompression of the popliteal cyst with an arthroscopic shaver. Ko and Ahn⁸ showed good early follow-up results in their series of 14 patients, with few complications including 1 recurrence. In addition, 2 cases showed inadequate cystectomy because of technical error characterized by difficulty finding the capsule wall. Limitations of their study included a relatively short follow-up and loss of a significant number of patients to follow-up.

Several techniques for popliteal cyst excision have been described. Traditionally, open techniques have been associated with high rates of recurrence because of inadequate excision or management of underlying intra-articular pathology. In addition, care must be taken with open techniques to avoid neurovascular structures. More recently, arthroscopic techniques have shown good short-term results but also display a risk of recurrence.^7,8 An open technique with a relatively smaller incision allows for improved exposure and visualization over arthroscopic approaches and achieves complete cyst excision while minimizing damage to the soft tissues. Postoperative recovery is nearly identical to standard knee arthroscopy. Our institutional case series shows promising results, with symptomatic relief and minimal cyst recurrence. Further outcome studies for this approach are needed. Popliteal cyst excision by an open posterior approach is a safe, effective, and straightforward treatment option for patients with recalcitrant or idiopathic popliteal cysts.

Supplementary Data

Video 1

Key steps of open posterior popliteal cyst excision (please refer to Table 1).