Cystic Lesions About the Knee Treatment & Management

Updated: Dec 29, 2018
  • Author: David M Gonzalez, MD, FACS; Chief Editor: Thomas M DeBerardino, MD  more...
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Treatment

Medical Therapy

Medical treatment of some cysts may be effective. Bursal cysts due to acute trauma sometimes respond to nonsteroidal anti-inflammatory medication, rest, immobilization, and compression. Cysts that form secondary to gouty arthritis respond to an antigout treatment program. Cysts caused by rheumatoid arthritis and osteoarthritis can respond to medical treatment regimens. Infected cysts respond to antibiotics after being surgically drained.

The MRI findings in one retrospective study confirmed that popliteal cysts in pediatric populations can be expected to resolve without treatment. In the study, cysts confined to either the gastrocnemio-semimembranosus bursa or the subgastrocnemius bursa, according to the MRI findings, were classified as type I; cysts that occupied both bursae were classified as type II. All type II cysts converted to type I, and all cysts that disappeared completely were originally type I. [23]

Hautmann et al reported on low-dose radiotherapy as treatment for Baker (popliteal) cysts in 20 knees of patients with osteoarthritis. Cysts decreased in volume by more than 25% after 6 to 12 weeks in 75% of their patients and after 9 to 12 months in 79% of their patients. [24]

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Surgical Therapy

Surgical therapy by excision of the mass is the mainstay of treatment for most symptomatic cysts that are not bursal in nature and that have not responded to nonsurgical treatment. [25, 26] (Note: Treatment should be directed at the cause of the enlarged cyst, such as adventitial bursal cysts caused by an osteochondroma or an enlarged Baker cyst that requires addressing intra-articular causes through arthroscopic surgical procedures.) Other cysts, such as meniscal cysts, extraneural cysts, and ganglion cysts, can respond to surgical excision.

In a study of meniscal tears and associated parameniscal cysts, partial meniscectomy alone, without meniscal cyst decompression, was found to provide excellent short-term and medium-term outcomes. Patients with medial cysts greater than 1.0 cm, with horizontal cleavage tears, or without simultaneous chondroplasty scored higher in the short-term and medium-term. [27]

 

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Preoperative Details

Perform a thorough preoperative workup as described above (see Workup) to confirm that the mass is cystic in nature and is not a solid tumor that may be benign or even malignant.

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Intraoperative Details

Intraoperative details are dependent on the location of the cyst being treated. A prepatellar-infected bursitis is approached through a midline incision. Then, the contents of the bursa are evacuated, and all loculations are lysed. After thorough irrigation and debridement, the wound is packed open and allowed to drain. Appropriate antibiotics are begun, and the wound is readdressed in 2 to 3 days.

A popliteal or Baker cyst can be approached in a number of different ways. One way is to place the patient supine with the knee slightly flexed on the operating table. A lazy-S skin incision is made in the popliteal fossa. The cyst can usually be seen beneath the deep fascia and presents itself between the medial head of the gastrocnemius and the semimembranosus. The cyst is dissected by means of sharp and blunt dissection until its communication with a capsule is seen. The base is excised, and the defect is usually closed.

A study by Yang et al in 76 patients with popliteal cysts reported significantly better outcomes with arthroscopic internal drainage of the cysts, compared with open excision after arthroscopic treatment or open excision. Length of incision (1.6 ± 0.1 cm), incision healing rate (100%), postoperative visual analog score (VAS) for pain (2.7 ± 1.2), hospitalization time (7.8 ± 2.8 days), and Lysholm score at the final follow-up visit (85.8 ± 5.2) all were superior and the recurrence rate was significantly lower with either arthroscopic approach than with open excision only. [28]

Brazier et al provide a step-by-step description of arthroscopic treatment of popliteal cysts. These authors use an arthroscopic approach through a posteromedial portal to decompress the popliteal cyst and take down the posterior transverse synovial infold, a valve-type structure that permits one-way flow of synovial fluid into the cyst. Their operative approach is guided by preoperative knee MRI, which determines the exact location of the cyst. [29]  

Other cysts related to bursitis, such as medial gastrocnemius bursitis and semimembranosus bursitis, are treated in a similar fashion. Depending on the exact location, other approaches can be used, such as the medial hockey-stick incision with the knee flexed at 90°. Basic knowledge of the surgical approaches to the anterior, medial, lateral, and posterior aspects of the knee can serve the surgeon well in approaching any cyst about the knee. [30]

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Postoperative Details

Postoperative rehabilitation is similar after excisions of all knee cysts. After surgery, the patient is placed in a knee immobilizer for comfort. Isometric exercises are begun on day 1, as are straight-leg raises. Weight bearing in the knee immobilizer as tolerated is allowed. Knee range-of-motion exercises are begun in the first few days after surgery as soon as the wound is stable and postoperative inflammation begins to subside.

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Complications

Postoperative complications from knee-cyst excision include infection, nerve or blood vessel damage from the operative dissection, hematoma formation, and recurrence of the cyst. If the inciting cause of the cyst is not addressed, the pain may remain after excision despite removal of the cyst. Meniscal cysts may recur after simple excision of the cyst because the meniscal tear was not addressed.

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Outcome and Prognosis

The treatment objective is to relieve pain and to improve functionality of the extremity by addressing the knee cyst. The best results are obtained if the cyst is properly evaluated, diagnosed, and treated. However, even in the best of hands, recurrence is possible. Baker cysts are notorious for developing synovial fistulae and for becoming infected.

Treating the underlying cause of the knee cyst is key, and appropriate arthroscopic treatment of meniscal tears, articular cartilage injuries, and cruciate ligament tears can also favorably affect results.

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Future and Controversies

The etiology of some knee cysts (eg, meniscal cysts, cruciate ganglion cysts) remains controversial. As further reports and histologic studies continue, the origins of such cysts will become clearer.

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