You are in: eMedicine Specialties > Orthopedic Surgery > KNEE Cystic Lesions About the KneeArticle Last Updated: Mar 30, 2007AUTHOR AND EDITOR INFORMATIONSection 1 of 12
  Author: David M Gonzalez, MD, Clinical Associate Professor, Department of Orthopedic Surgery, University of Texas Health Science Center at San Antonio David M Gonzalez is a member of the following medical societies: American Academy of Orthopaedic Surgeons, American Orthopaedic Society for Sports Medicine, Arthroscopy Association of North America, Texas Medical Association, Texas Orthopaedic Association, and Western Orthopaedic Association Editors: Robert D Bronstein, MD, Associate Professor, Department of Orthopedic Surgery, University of Rochester School of Medicine; Francisco Talavera, PharmD, PhD, Senior Pharmacy Editor, eMedicine; Thomas M DeBerardino, MD, Director, John A Feagin, Jr Sports Medicine Fellowship at West Point, Clinical Instructor in Surgery, Orthopedic Surgery Service, Keller Army Community Hospital at West Point; Dinesh Patel, MD, FACS, Associate Clinical Professor of Orthopedic Surgery, Harvard Medical School; Chief of Arthroscopic Surgery, Department of Orthopedic Surgery, Massachusetts General Hospital; Carlos J Lavernia, MD, FAAOS, Adjunct Clinical Professor, Department of Orthopedic Surgery, University of Miami School of Medicine; Medical Director, Orthopedic Institute at Mercy Hospital Author and Editor Disclosure Synonyms and related keywords: benign soft tissue cysts about the knee, knee cysts, meniscal cysts, popliteal cysts, bursae, bursitis, housemaid's knee, carpet layer's knee, fluid cyst, semisolid cyst, ganglion cysts, intraneural cysts, popliteal artery cysts, rheumatoid arthritis, osteoarthritis, blood-filled bursae, pus-filled bursae, myxoid intraneural cysts INTRODUCTIONSection 2 of 12
  Cysts can occur in many shapes and forms around the knee. A cyst is defined as a closed cavity, or sac, that is lined with epithelium. It can contain liquid or semisolid material, can be normal or abnormal, and can occur in soft tissue or in bone. Benign or malignant masses must be distinguished from cystic lesions. This article discusses benign cysts that occur in the soft tissue around the knee or outside bone and that are filled with fluid or semisolid material. The understanding of various knee cysts is highly dependent on a thorough knowledge of the anatomy of the knee, which is a highly mobile structure. Bursae, sacs or saclike structures that are located at places where friction develops between the soft tissues and around the bony prominences, line many of the ligaments, tendons, and bony prominences around the knee. They can be lined with synovium and respond much the way synovium does to insults and pathologic conditions. Bursae can fill with fluid, and this accounts for the large majority of cysts seen around the knee. According to Gray's Anatomy of the Human Body (1974), there are at least 13 bursae around the knee. Four are present anteriorly; the largest is between the patella and skin. Four are present laterally and posterolaterally. Five are present medially and posteromedially. The bursa between the medial head of the gastrocnemius and the knee capsule, as well as the bursa between the lateral gastrocnemius head and the capsule, often communicate with the knee joint. Although normally quiescent, any of these bursae can become inflamed, fill with fluid, and present as a cystic mass. Two types of bursae are described, those normally present and those whose tissue is adventitious in nature. The adventitious type occurs as a result of chronic irritation over abnormal bony prominences such as an osteochondroma or bunion. This type of bursa lacks an epithelial lining; however, it can become filled with blood from repetitive trauma and it can also become infected. Other soft tissue cysts that occur around the knee are entities such as ganglion cysts; intraneural cysts; popliteal artery cysts and other vascular masses; and a wide assortment of secondary cysts, such as those caused by rheumatoid arthritis and osteoarthritis and those resulting from the blood- and pus-filled bursae. For excellent patient education resources, visit eMedicine's Sports Injury Center and Hand, Wrist, Elbow, and Shoulder Center. Also, see eMedicine's patient education articles Bursitis and Ganglion Cyst. History of the ProcedureDetermination of the treatment plan is dependent on each individual patient and the patient's diagnosis. Nonoperative treatment, including limitation of activity and aspiration of the cyst (with or without injection of corticosteroids), is usually the treatment of choice. Surgical treatment should not be the first option chosen and is not required in most instances. However, once nonoperative treatment is exhausted, the surgical treatment of choice for most cystic masses is excision. Excision of the cyst requires a thorough knowledge of the relationships of the ligaments, tendons, and bone structures of the knee. Surgical excision of these cysts has probably been around since anatomic dissections were first begun. The surgical approach to excision is based on the location and origin of the cyst. Adhering to the basic principles of skin incisions and proper dissection of the tissues can greatly aid in achieving a good result. In the case of meniscal cysts, the treatment approach may differ. Nonoperative measures do not accomplish much more than the temporary relief of symptoms. Symptomatic meniscal cysts are usually treated by addressing the cause and performing an arthroscopic partial meniscectomy. Rarely does the presence of a meniscal cyst require the direct excision of this mass. ProblemThe problems related to cysts around the knee are largely proportional to the size and location of the cyst. One of the most common knee cysts is the popliteal cyst, otherwise known as a Baker cyst; its symptoms can include pain. This type of cyst most often develops in the bursa beneath the medial head of the gastrocnemius and from the semimembranosus bursa. Because the development of popliteal cysts is correlated to intra-articular pathology, they usually point to a problem of 1 or both menisci, a complete or partial cruciate ligament tear, a chondral injury, or a combination of any of these. Large popliteal cysts can rupture and become quite painful; it is important to rule out deep vein thrombosis in these instances. Meniscal cysts, as previously noted, are problematic because of the pain that is often associated with a palpable, firm mass. FrequencySansone et al (1995) reported a 4.7% prevalence rate of popliteal cysts in a series of 1001 adult patients. Their most common associated lesions were meniscal lesions (83%), most frequently involving the posterior horn of the medial meniscus. The authors also found that 43% of the meniscal lesions were associated with articular cartilage damage and that 32% were associated with anterior cruciate ligament tears. However, in children, popliteal cysts usually do not communicate with the knee joint; in rare cases, the cysts are associated with intra-articular pathology. In most cases, the cysts are self-limited; they rarely require surgical excision. Meniscal cysts are less common. The prevalence rate is 1.5-4%. The literature has conflicting reports regarding the most common location of meniscal cysts. According to Campbell et al (2001), in a series of 2572 knee magnetic resonance images (MRIs), meniscal cysts of the medial meniscus were noted to be nearly 2 times more common than cysts of the lateral meniscus. However, in an earlier study by Ryu and Ting (1993), medial and lateral meniscal cysts occurred with equal frequency in a small series of 18 patients. One of the most common bursa affected by chronic trauma is the prepatellar bursa. The resulting condition is also known as housemaid's knee or carpet layer's knee and occurs as a result of the repetitive trauma from kneeling. The prepatellar bursa can become filled with a hematoma and develop a thick capsule, thereby making it feel firm. Other less common bursae that become inflamed are the medial collateral ligament bursa, lateral collateral ligament bursa, infrapatellar bursa, medial gastrocnemius bursa, and the semimembranosus bursa. Multiple reports have described less common benign cysts about the knee. These include ganglion cysts that occur in various areas (eg, cruciate ligaments)and synovium cyst enlargements at the proximal tibiofibular joint. The latter cysts can potentially cause neurologic compromise of the peroneal nerve. Cystic adventitial disease of the popliteal artery has also been reported. Patients with these cysts present with intermittent claudication because the cysts compress the popliteal artery. Reports also describe cases of myxoid intraneural cysts of the common peroneal nerve that are associated with pain around the knee and leg and that require surgical excision. The importance of always considering the possibility that any cyst around the knee can become infected is demonstrated by a rare case report of a popliteal cyst infected with Neisseria gonorrhoeae (Weiner and Fan, 1983). EtiologyCysts about the knee have multiple etiologies, including irritated and inflamed bursae, meniscal cysts caused by intra-articular pathology, and special categories, such as a Baker cyst or popliteal cyst, ganglia (both intra-articular and extra-articular), vascular masses, and extraneural cysts. It is important to realize that other processes can mimic cysts on MRI. Benign and malignant tumors must be ruled out during the workup of any cyst about the knee; other entities to consider are abscesses and vascular masses, such as popliteal vein varices and popliteal artery aneurysms. PathophysiologyThe pathophysiology of benign knee cysts is dependent on the specific etiology. Although at times controversial, the underlying causes of most cysts are similar; a benign cyst results whenever a saclike structure is formed secondary to a mechanical or biochemical irritant. A sac that already is present, such as an epithelial-lined bursa, is subject to the same irritants. These potential spaces then become filled with a fluid or with degenerative myxoid products. Over time, the cyst becomes mucoid and semisolid if resorption of the fluid is slow and if the fluid has a high protein content. ClinicalHistory The workup of all cysts about the knee should start with a thorough history and physical examination. The history should include the following:
Physical Physical examination should include the following:
Presentation The clinical presentation of the more common cysts about the knee is that of a nonpainful or minimally painful soft mass. The location depends on which extra-articular structure is involved. Popliteal cysts usually present as a nonpainful posterior popliteal mass. They may or may not present with intra-articular knee symptoms as well. When pain is present, it is most often due to the intra-articular process that is responsible for the popliteal cyst. Children usually present with a nonpainful mass that is noticed by an adult. Swollen and inflamed bursae can be painful at presentation. Prepatellar bursitis can occur following repetitive trauma of recurrent kneeling, is often occupation-related, and can degenerate and become infected in the acute setting. A pes anserinus bursa, an infrapatellar bursa, and a collateral ligament bursa can also appear as painful, swollen masses in their respective areas. Meniscal cysts most often manifest as pain that is aggravated by activity. These are sometimes palpable, most often on the lateral side, along the anterolateral aspect of the knee joint. Meniscal cysts are more difficult to palpate on the medial side of the knee because they tend to dissect in the tissue planes. Other less common benign cysts about the knee, such as intraneural cysts of the common peroneal nerve, present with pain and sensory changes in the anterior tibial nerve along the anterior aspect of the leg and dorsum of the foot. The muscles of the anterior compartment of the leg can also be involved, manifesting clinically as a footdrop. Patients with cystic adventitial disease of the popliteal artery have been reported to present with intermittent claudication. INDICATIONSSection 3 of 12
Surgical indications for the excision of cysts about the knee depend on the origin and cause of the cyst. Treatment of bursal cysts is nonoperative and aimed at the etiology, whether it is mechanical, biochemical, or immunologic. An adventitial bursa can occur over any prominence (eg, osteochondroma, large osteophyte, surgically placed hardware). Removing the prominence treats the bursitis. Bursal cysts that become inflamed because of a systemic reason are treated by addressing the systemic cause for the swelling and inflammation. Local measures to control swelling also can be used, such as rest, heat, compression, elevation, and immobilization. Indications for surgical treatment of a meniscal cyst are pain that interferes with activity and a palpable mass along the lateral or medial joint line. The diagnosis can be confirmed with an MRI, although an MRI is not necessary with the presence of every knee cyst. Popliteal cysts are usually not surgically excised. Surgical treatment is aimed at the inciting cause of the cyst. This treatment typically involves an arthroscopic surgical procedure of the knee to look for an intra-articular process. MRI can be helpful in guiding and developing a treatment plan. Surgical treatment is usually indicated for other types of cysts that are more rare, such as intraneural cysts, popliteal artery cystic adventitial disease, arterial aneurysms, and symptomatic ganglia. RELEVANT ANATOMYSection 4 of 12
Knowledge of the bursae, tendon sheaths, fascial planes, tendons, ligaments, muscle, articular capsules, major nerves, arteries, veins, and the bony prominences around the knee is critical to the proper surgical and nonsurgical treatment of knee cysts. The most relevant of these structures is the location of the various bursae and tendon sheaths. Considering that the knee is a very mobile structure, it is logical to think that there are numerous bursae to allow for the smooth gliding of tendons, muscles, bone, and skin over each other. The most significant bursa are in these regions: (1) the anterior knee: the prepatellar, suprapatellar, and deep infrapatellar bursae; (2) the medial and posteromedial knee: the pes anserine, medial gastrocnemius, semimembranosus, and medial collateral ligament bursae; and (3) the lateral and posterolateral knee: the inferior bursa of the biceps femoris, as well as the bursae of the lateral gastrocnemius, the iliotibial tract, the lateral collateral ligament, and the popliteal tendon. CONTRAINDICATIONSSection 5 of 12
There are no contraindications to the excision of knee cysts; however, a complete diagnostic workup must be performed prior to excision. Thorough knowledge of the behavior and etiology of the cyst should be understood. Consider popliteal cysts in the adult; they usually resolve after addressing their cause, such as meniscal pathology (eg, arthroscopic resection of a meniscal tear). Surgical excision of a popliteal cyst is rarely performed. WORKUPSection 6 of 12
Lab Studies
Imaging Studies
Other Tests
Histologic FindingsThe cysts are lined with an epithelium. Bursal sacs are lined with a membrane similar to synovium. A Baker cyst is the most common synovial cyst. Adventitial cysts do not have a true epithelial lining or synovial lining and usually have thickened walls. Many meniscal cysts have been shown to have a clear communication with the joint and appear to be lined with synovium. TREATMENTSection 7 of 12
Medical therapyMedical 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. Surgical therapySurgical 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. (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. Preoperative detailsPerform 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. Intraoperative detailsIntraoperative 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. 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. Postoperative detailsPostoperative 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. COMPLICATIONSSection 8 of 12
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. OUTCOME AND PROGNOSISSection 9 of 12
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. FUTURE AND CONTROVERSIESSection 10 of 12
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. MULTIMEDIASection 11 of 12
REFERENCESSection 12 of 12
Cystic Lesions About the Knee excerpt Article Last Updated: Mar 30, 2007 | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
