DEFINITION

Synovial tissue is found lining the joint capsules and tendon sheaths of the body.

Synovitis is characterized by inflammation of the synovial membrane and can be found in a number of pathologic conditions as well as a normal response to injury.

Clinically, synovitis results in painful, swollen, stiff joints. Continued joint inflammation may result in articular cartilage damage and osteopenia.

After medical management has been exhausted, surgery is often indicated if the patient experiences continued pain, swelling, and mechanical symptoms.

A number of conditions are associated with synovitis of the knee, including inflammatory arthritides (rheumatoid arthritis, lupus erythematosus, psoriatic arthritis), degenerative processes (osteoarthritis), proliferative disorders (pigmented villonodular synovitis [PVNS], synovial chondromatosis), crystalline arthropathies (gout, pseudogout), conditions which result in hemarthrosis (trauma, hemophilia A and B, von Willebrand disease, chronic anticoagulation therapy), lead synovitis, hemangiomas, intra-articular

adhesions, fat pad fibrosis, hemophilic synovitis, and fibrotic ligamentum mucosum to name a few.4,5,6,9,10,14,20,21

 

ANATOMY

 

Synovial tissue is the specialized mesenchymal lining of joints. It is composed of a thin layer of synoviocytes above a fibrovascular zone (vascular tissue, fat, connective tissue).

 

Grossly, it appears as smooth and transparent; however, in the setting of inflammation, it becomes thickened, red, and markedly more villous.

 

The primary function of synovial tissue is to provide fluid for joint lubrication and nutrient oxygen and proteins.

 

Histologic hallmarks of chronic synovitis include hyperplasia of the intimal lining, lymphocyte infiltration, and blood vessel proliferation. In the setting of recurrent hemarthroses, variable amounts of hemosiderin may be evident on microscopic examination.

 

Patients with chronic synovitis can have localized or diffuse disease depending on their underlying condition. When localized, imaging studies such as magnetic resonance imaging (MRI) can help direct arthroscopy. With diffuse disease, it is vital to visualize all aspects of the knee during surgical synovectomy to ensure complete eradication of the offending tissue.

 

PATHOGENESIS

 

The pathogenesis of synovitis is variable depending on the underlying etiology (eg, inflammatory arthritis vs. recurrent hemarthrosis vs. proliferative disorders such as PVNS).

 

In chronic synovitis, the synovial lining undergoes hyperplasia, angiogenesis, and increased cellularity (inflammatory cells such as lymphocytes and macrophages).

 

Rheumatoid arthritis is an example of an inflammatory arthritis, which causes chronic synovitis. It presents with the insidious onset of morning stiffness and polyarthralgias. The synovitis that ensues is thought to be an acute autoantibodymediated inflammatory process.

 

PVNS is a proliferative disorder characterized by nodules and villi in the synovium of joints and tendon sheaths. Typically, PVNS is a monoarticular disease with a predilection for the knee.

 

Hemophilia is an X-linked deficiency of clotting factors (hemophilia A, factor VIII; hemophilia B, factor IX), leading to bleeding of varying severity. This condition often results in recurrent hemarthrosis, particularly in the knee, which leads to chronic progressive synovial hyperplasia, pain, and joint destruction.

 

NATURAL HISTORY

 

Repeated bouts of acute synovitis or chronically inflamed synovium can lead to chronic pain, limited range of motion, and ultimately joint degeneration and arthrosis.

 

PATIENT HISTORY AND PHYSICAL FINDINGS

 

A full personal and family history of rheumatologic and hematologic disorders should be elicited, including involvement of other joints and previous episodes of joint pain and swelling.

 

The patient may have a history of recurrent swelling, pain, warmth, stiffness, and mechanical symptoms (FIG 1).

 

Patients should be evaluated for the stigmata of psoriasis (silver plaques), lupus (malar rash), and rheumatoid arthritis (rheumatoid nodules).

 

 

 

In rheumatoid arthritis, the cervical spine is commonly involved and must be evaluated before surgical intervention. Also, the disease is often not limited to the musculoskeletal

 

system: Patients can also have vasculitis, subcutaneous nodules, and pericarditis.

 

P.360

 

 

 

FIG 1 • Patient with a long history of chronic synovitis in his right knee.

 

 

PVNS can cause mechanical symptoms such as locking, similar to a meniscal tear. A palpable mass may be present.

 

 

Intermittent symptoms are more common with localized PVNS; diffuse PVNS often presents with a more chronic course.

 

During the physical examination, the surgeon should look for effusion, tenderness, warmth, mass, and synovial thickening.

 

 

 

 

 

 

Range of motion: Loss of flexion or extension may indicate arthrofibrosis. Lachman test: assesses competence of anterior cruciate ligament Posterior drawer test: assesses competence of posterior cruciate ligament Varus stress test: assesses competence of lateral collateral ligament Valgus stress test: assesses competence of medial collateral ligament

 

Dial test: assesses competence of posterolateral corner and posterior cruciate ligament

 

Malalignment and ligamentous insufficiencies are noted and will likely preclude arthroscopic synovectomy, given their association with joint destruction.

 

Joint aspiration can be therapeutic and diagnostic.

 

Synovial fluid analysis should include documentation of fluid color (ie, brownish in PVNS, indicating recurrent bleeding), testing for rheumatoid factor, complement levels, cell count, Gram stain, culture, and crystal analysis

 

IMAGING AND OTHER DIAGNOSTIC STUDIES

 

Radiographs are important to document the extent of joint destruction and may point toward the etiology of the synovitis.

 

 

The surgeon should look for the characteristic rheumatologic signs of periarticular erosions and osteopenia. Radiologic signs of PVNS and gout include cystic, sclerotic, or erosive changes.

 

 

Linear calcifications within articular cartilage and menisci are found in pseudogout. Synovial chondromatosis is often visible on plain films.

 

 

Advanced degenerative disease is associated with a poorer prognosis after arthroscopy.17 MRI is helpful to assess the scope of joint involvement before surgery (FIG 2).

 

Nodular PVNS can be readily seen as low signal on both T1 and T2 images.

 

 

 

 

FIG 2 • T2-weighted MRI reveals large effusion in patient's knee, subsequently diagnosed by arthroscopic synovectomy as rheumatoid arthritis.

 

DIFFERENTIAL DIAGNOSIS

 

 

Synovial disorders Infection

 

Degenerative joint arthrosis

 

NONOPERATIVE MANAGEMENT

 

Once the etiology of the synovitis is determined, first-line conservative treatment includes medical management of the underlying disease.

 

 

Oral anti-inflammatory medications may be used as well as intra-articular corticosteroid injections. Gentle physical therapy can aid in maintenance of range of motion.

 

If the underlying cause is determined to be infection, there is often no trial of nonoperative management.

SURGICAL MANAGEMENT

 

Both arthroscopic and open synovectomies have been described; however, arthroscopic synovectomy allows the identification and management of synovial lesions that may be missed with open procedures. Additionally,

arthroscopic synovectomy allows for reevaluation after the index procedure with relatively low morbidity.11,18

 

Arthroscopic synovectomy can be the definitive treatment for the many of the aforementioned synovial disorders.

 

For more chronic or recurring conditions such as rheumatoid arthritis or hemophilic synovitis, this surgery can reduce the severity of pain and dysfunction commonly associated with these pathologies. It can reduce the

number of recurrences and may slow the progression of joint arthrosis.11

 

Preoperative Planning

 

Preoperative flexion and extension cervical spine radiographs are necessary to rule out instability in rheumatoid patients.

 

Appropriate medical clearance is necessary to keep perioperative complications to a minimum.

 

General anesthesia rather than local anesthesia is recommended because the procedure can be lengthy. An epidural may also be used when medically indicated and may aid in postoperative pain relief. A Foley catheter may be used in anticipation of prolonged anesthesia, although this is rarely indicated.

 

Equipment

 

 

4.5-mm 30-degree arthroscope

 

 

4.5-mm 70-degree arthroscope (available if visualization is not adequate with 30-degree scope) Small suction shaver

 

 

Arthroscopic electrocautery Arthroscopic basket

 

Examination under anesthesia should be performed prior to the procedure. Care should be taken to document the presence of effusion, range of motion, ligamentous stability, and patellar mobility and tracking. Using a goniometer for exact measurements is helpful for following the postoperative rehabilitation process. Examination of the contralateral knee should always be performed for comparison.

 

 

 

Positioning

P.361

 

The patient is placed supine and brought to the edge of the bed to ensure that the leg may be easily hung over the side (the medial malleoli should be at the edge of the bed).

 

 

An arthroscopic leg holder should not be used as it may prohibit the use of the superomedial and superolateral portals.

 

Alternatively, an arthroscopic lateral post may be placed midthigh on the side of the operative bed.

 

A well-padded thigh tourniquet is placed high on the operative leg.

 

The contralateral leg is placed in a well-padded leg holder, flexing the hip and knee, with the hip in slight abduction. Compressive wrapping or sequential compression stockings should be used on the contralateral leg owing to the length of the procedure (FIG 3).

 

The foot of the bed is dropped, allowing the operative leg to hang free. The bed should be reflexed to produce

slight hip flexion, decreasing the chance of femoral nerve palsy that may be associated with excessive hip extension and leg traction.

 

 

 

FIG 3 • Patient positioning for arthroscopic synovectomy.

 

 

A suction canister trap should be set up for biopsy collection.

 

A grounding pad should be placed for use of an electrocautery device.

 

Approach

 

Portals are marked on the skin; five or six are generally needed for a complete synovectomy (FIG 4).

 

 

 

FIG 4 • Arthroscopic portals marked on the right knee.

 

TECHNIQUES

• Diagnostic Arthroscopy

The operative limb is exsanguinated and the tourniquet is inflated to 250 to 300 mm Hg (TECH FIG 1A).

The procedure begins with placement of an outflow cannula in the superomedial portal as this is rarely used as a viewing portal (TECH FIG 1B).

 

 

 

 

TECH FIG 1 • A. The limb is exsanguinated with an Esmarch bandage. B. Arthroscopic view reveals the outflow in the superomedial portal. C. The superolateral portal is established. D. Arthroscopic view shows establishment of the superolateral working portal under direct visualization.

 

 

Next, an inferolateral portal is created and the arthroscope is placed into the suprapatellar pouch with the knee in extension. Next, a superolateral working portal is established under direct visualization (TECH FIG 1C,D).

 

P.362

• Synovectomy

Suprapatellar Pouch, Medial and Lateral Gutter, and Intercondylar Notch

 

With the arthroscope in the inferolateral portal, the shaver is placed in the superolateral portal. The synovium is resected from the suprapatellar pouch and the lateral gutter (TECH FIG 2A,B).

 

The shaver is moved to the inferomedial portal. The synovium is excised from the medial gutter and the medial aspect of the suprapatellar pouch (TECH FIG 2C,D).

 

 

 

TECH FIG 2 • A. The shaver is placed into the superolateral working portal. B. Arthroscopic view showing partial resection of the lateral gutter synovium. C. The shaver is moved to the inferomedial portal. D. Arthroscopic resection of medial synovium.

 

 

 

TECH FIG 3 • A. The arthroscope is moved to the superolateral portal, and the shaver is placed in the inferolateral portal. B. Arthroscopic view of the resection in the retropatellar space and lateral gutter. C. The arthroscope is moved to the inferomedial portal, and the shaver is placed in the inferolateral portal. D. Arthroscopic view of inferomedial gutter synovial resection.

Retropatellar Pouch, Inferolateral and Inferomedial Gutters

 

The arthroscope is moved to the superolateral portal and the shaver is placed in the inferolateral portal. This enables synovial resection from the inferolateral gutter and the retropatellar space (TECH FIG 3A,B).

 

The shaver is placed in the inferomedial portal to complete the synovectomy of the retropatellar space and the inferomedial gutter (TECH FIG 3C,D).

 

P.363

 

 

 

TECH FIG 4 • A. The arthroscope is returned to the inferolateral portal, and the shaver is in the inferomedial portal. B. Arthroscopic photograph shows the resection of synovectomy in the notch. C. Arthroscopic photo shows complete resection of synovium in the notch. The anterior cruciate ligament is now apparent.

Intercondylar Notch

 

The arthroscope is returned to the inferolateral portal and the shaver is maintained in the inferomedial portal (TECH FIG 4A,B).

 

Resection of synovium in the intercondylar notch and around the cruciate ligaments is carefully performed (TECH FIG 4C).

 

This establishes adequate working space within the notch to allow visualization of the posterior compartments of the knee.

 

Care must be taken to distinguish synovium from ligament.

 

The ligamentum mucosum, if present, can be excised to aid in visualization

Posteromedial Compartment

 

For access to the posteromedial compartment, a blunt-tipped trocar is placed in its arthroscopic sheath and inserted through the inferolateral portal.

 

Alternatively, a switching stick can be placed through the inferolateral portal under direct visualization with the arthroscope placed in the inferomedial portal.

 

 

 

TECH FIG 5 • A. Arthroscopic photograph showing establishment of the posteromedial portal. B. Arthroscope is placed through the notch into the posteromedial compartment with shaver placed into the posteromedial portal. C. Synovial resection in the posteromedial compartment.

 

 

The medial femoral condyle is palpated with the tip and the trocar is pushed posteriorly in the interval between the medial femoral condyle and the posterior cruciate ligament. The surgeon should raise their hand to accommodate the posterior slope of the tibia.

 

The trocar should push into the posteromedial compartment without significant force.

 

If this proves difficult to accomplish, a central transpatellar tendon portal may allow easier access to the posterior compartment.

 

The trocar is removed and the arthroscope is inserted. From this position, the posterior aspect of the medial femoral condyle and the posterior horn of the medial meniscus can be visualized.

 

While looking medially, a posteromedial working portal is developed under direct visualization.

 

A spinal needle is inserted anterior to the medial head of the gastrocnemius to avoid the neurovascular structures (TECH FIG 5A).

 

Once in the appropriate position, a small, longitudinal incision is made through the skin.

 

 

P.364

 

Using a hemostat, the soft tissue is spread until the capsule is reached.

 

Using a blunt-tipped trocar and arthroscopic cannula, the hemostat is replaced to establish a working portal.

 

The surgeon inserts the shaver after removing the trocar and proceeds with resection of the synovium in the posteromedial compartment (TECH FIG 5B,C).

Posterolateral Compartment

 

With a blunt trocar in the arthroscopic cannula, the trocar is placed in the inferomedial portal.

 

The lateral femoral condyle is palpated with the trocar and pushed along the notch between the condyle and the anterior cruciate ligament (TECH FIG 6A).

 

This can also be done with a switching stick, as described in the previous section.

 

Again, the surgeon should raise his or her hand to accommodate the posterior slope of the tibial plateau.

 

The trocar should give way, indicating passage into the posterolateral compartment. It is important not to push through any great resistance to avoid penetrating the capsule and damaging the neurovascular structures.

 

The arthroscope is placed into the cannula. The posterior aspect of the lateral femoral condyle as well as the posterior horn of the lateral meniscus should be seen.

 

A posterolateral portal is made by inserting a spinal needle into the compartment under direct visualization (TECH FIG 6B,C).

 

The needle should be inserted posterior to the fibular collateral ligament and anterior to the lateral head of the gastrocnemius.

 

 

 

TECH FIG 6 • A. A switching stick is placed into the posterolateral compartment under direct visualization. B. The posterolateral portal is made using needle localization. C. Arthroscopic photograph reveals needle localization for the establishment of the posterolateral portal. D. The shaver is placed in the posterolateral portal. E. Arthroscopic photograph showing the resection of synovium in the posterolateral compartment. F. Suction canister filter traps synovial biopsy specimen.

 

 

The soft spot anterior to the biceps femoris muscle and posterior to the iliotibial tract will ensure protection of the peroneal nerve.

 

When making the posterolateral and posteromedial portals, the surgeon should make sure that the instruments can be directed in the coronal plane behind the corresponding femoral condyle.

 

In a manner similar to the posteromedial portal, the skin is incised with a scalpel and the surgeon dissects to and then through the posterior capsule with a hemostat under direct visualization.

 

Maintaining the same angle, the surgeon replaces the hemostat with a blunt trocar in an operative cannula.

 

The surgeon inserts the shaver and proceeds with débridement of the posterolateral compartment (TECH FIG 6D,E).

 

Hypertrophied synovium on the posterior capsule and posterior septum should be resected.

 

The suction must be monitored carefully because the posterior capsule may be penetrated, placing the neurovascular structures at risk.

 

After completion of the synovectomy, the tourniquet is released and hemostasis is achieved with electrocautery. The tourniquet must be released prior to removing the scope and closing the portals to ensure adequate hemostasis.

 

 

The entire suction canister should be sent for pathology and microbiology testing (TECH FIG 6F). A suction drain is typically used for 24 hours postoperatively to minimize hemarthrosis.

 

Light compressive dressing and cryotherapy are used to minimize swelling and encourage early joint motion.

 

 

P.365

 

Hemostasis ▪ At the end of the procedure, hemostasis must be obtained. Failure to do so may

result in hemarthrosis and a suboptimal outcome.

Portal

placement

• The surgeon must be prepared to view the knee from multiple portals.

• Portals must be placed under direct visualization to protect neurovascular structures.

• Cannulas should be used when possible to ensure atraumatic entry and exit of instruments, avoiding soft tissue injury.

Technique

• The surgeon must approach the arthroscopic synovectomy with a well-defined

stepwise approach to excise the pathologic tissue in its entirety.

Biopsy

• Enough tissue must be obtained for pathologic evaluation and diagnosis.

Therapy

• Regaining and maintaining full knee range of motion and quadriceps function is

  critical.

• Obtaining preoperative quadriceps circumference measurements can be helpful in tracking postoperative rehabilitation

PEARLS AND PITFALLS

 

 

POSTOPERATIVE CARE

 

The patient should be made weight bearing as tolerated immediately postoperatively.

 

Continuous passive motion should be considered in cases of complete synovectomy, advancing as tolerated over 1 to 3 days, although there is no definitive evidence to promote its use.

 

Physical therapy is initiated after removal of the suction drain with an emphasis on range of motion and closed-chain exercises.

 

OUTCOMES

When comparing arthroscopic synovectomy to open synovectomy, the arthroscopic technique is associated with lower morbidity and more rapid return of function and lower rates of recurrence in rheumatoid, hemophilia, and other inflammatory arthritides.11,15,18 In addition, synovectomy can be more

complete with accurate visualization of the posterior compartments.21

However, recurrence rates and radiographic progression of disease in the knee and elbow for treatment of rheumatoid arthritis with arthroscopic synovectomy has been shown to exceed those of open treatment,

with the progression to total joint arthroplasty similar in the open versus arthroscopic groups.2

One study of 96 rheumatoid arthritic knees found significant decreases in pain and synovitis at an average of 4 years after arthroscopic synovectomy.13

Radiation synovectomy combined with either open or arthroscopic synovectomy for recurrent synovitis is

 

 

emerging as a viable option in treatment, although long-term and high-level evidence is lacking.1,16,21 Along with the use of rheumatoid medications, arthroscopic synovectomy can reduce inflammation and help preserve range of motion.5

 

Success rates in the relief of pain and swelling have been as high as 80% in the treatment of rheumatoid arthritis.15

 

Arthroscopic synovectomy has been used successfully in the treatment of PVNS.

 

In the past, open synovectomies led to stiffness and pain after the procedure. In a series of 18 patients with diffuse PVNS, one-third of the patients had a recurrence after open synovectomy, and in most

patients, the knee was manipulated in an attempt to decrease stiffness.8

 

Recurrence rates with arthroscopic synovectomy of localized PVNS have been as low as 0% to 11%, with improved range of motion. However, in diffuse variety, the recurrence rate exceeds 50%.7,14

 

A combined arthroscopic and open synovectomy for diffuse PVNS has shown improvement in recurrence rates, decreasing recurrence from 62% and 64% with open or arthroscopic treatment alone to 9% with a

combined open/arthroscopic approach.3

 

Localized PVNS has responded best to arthroscopic treatment.

 

Multiple series have reported no recurrences at follow-up after excision of the lesion.12,14,21

 

The procedure allows improved visualization of lesions and facilitates the discovery of small, localized forms of PVNS.

 

Hemophilic synovitis, also associated with aggressive joint destruction, has responded well symptomatically to arthroscopic synovectomy.

 

Unlike most forms of synovitis, this usually requires a short period of hospitalization because of the underlying systemic disorder.

 

 

The procedure has been effective in reducing recurrent hemarthrosis and maintaining range of motion. However, joint deterioration continues to occur, although probably at a slower rate.20

 

The biggest predictor of long-term functional outcomes is preexisting degenerative changes within the

joint.19

 

COMPLICATIONS

Recurrent hemarthrosis, often requiring repeat aspirations or surgical irrigation and débridement

This can be minimized with attention to detail during the synovectomy to ensure resection of all visible synovium.

Loss of range of motion

Joint stiffness and flexion contracture can be challenging to treat. Dynamic bracing can be used.

Rare complications include infection, either superficial or intra-articular; neurovascular injury; rapid onset of joint arthrosis; or cruciate ligament damage.

A well-documented pre- and postoperative neurovascular exam should be recorded.

 

 

 

P.366

REFERENCES

1. Akmese R, Yildiz KI, Isik C, et al. Combined arthroscopic synovectomy and radiosynoviorthesis in the

   treatment of chronic non-specific synovitis of the knee. Arch Orthop Trauma Surg 2013;133(11):1567-1573.

    

    

2. Chalmers PN, Sherman SL, Raphael BS, et al. Rheumatoid synovectomy: does the surgical approach matter? Clin Orthop Relat Res 2011;469(7):2062-2071.

    

    

3. Colman MW, Ye J, Weiss KR, et al. Does combined open and arthroscopic synovectomy for diffuse PVNS of the knee improve recurrence rates? Clin Orthop Relat Res 2013;471(3):883-890.

    

    

4. Comin JA, Rodriguez-Merchan EC. Arthroscopic synovectomy in the management of painful localized post-traumatic synovitis of the knee joint. Arthroscopy 1997;13:606-608.

    

    

5. Fiacco U, Cozzi L, Rigon C, et al. Arthroscopic synovectomy in rheumatoid and psoriatic knee joint synovitis: long-term outcome. Br J Rheumatol 1996;35:463-470.

    

    

6. Gilbert MS, Radomisli TE. Therapeutic options in the management of hemophilic synovitis. Clin Orthop Relat Res 1997;343:88-92.

    

    

7. Jain JK, Vidyasagar JV, Sagar R, et al. Arthroscopic synovectomy in pigmented villonodular synovitis of the knee: clinical series and outcome. 2013;37(12):2363-2369.

    

    

8. Johansson JE, Ajjoub S, Coughlin LP, et al. Pigmented villonodular synovitis of joints. Clin Orthop Relat Res 1982;163:159-166.

    

    

9. Klein W, Jensen KU. Arthroscopic synovectomy of the knee joint: indication, technique and follow-up results. Arthroscopy 1988;4:63-71.

    

    

10. Lee BI, Yoo JE, Lee SH, et al. Localized pigmented villonodular synovitis of the knee: arthroscopic treatment. Arthroscopy 1998;14:764-768.

     

     

11. Matsui N, Taneda Y, Ohta H, et al. Arthroscopic versus open synovectomy in the rheumatoid knee. Int Orthop 1989;13:17-20.

     

     

12. Moskovich R, Parisien JS. Localized pigmented villonodular synovitis of the knee. Clin Orthop Relat Res 1991;271:218-224.

     

     

13. Ogilvie-Harris DJ, Basinski A. Arthroscopic synovectomy of the knee for rheumatoid arthritis. Arthroscopy 1991;7:91.

     

     

14. Oglivie-Harris DJ, McLean J, Zarnett ME. Pigmented villonodular synovitis of the knee. J Bone Joint Surg Am 1992;74A:119-123.

     

     

15. Ogilvie-Harris DJ, Weisleder L. Arthroscopic synovectomy of the knee: is it helpful? Arthroscopy 1995;11:91-95.

     

     

16. Oztemur Z, Bulut O, Korkmaz M, et al. Surgical synovectomy combined with yttrium 90 in patients with recurrent joint synovitis. Rheumatol Int 2013;33(5):1321-1326.

     

     

17. Roch-Bras F, Daures JP, Legouffe MC, et al. Treatment of chronic knee synovitis with arthroscopic synovectomy: long-term results. Rheumatology 2002;29:1171-1175.

     

     

18. Shibata T, Shiraoka K, Takubo N. Comparison between arthroscopic and open synovectomy for the knee in rheumatoid arthritis. Arch Orthop Trauma Surg 1986;105:257-262.

     

     

19. Verma N, Valentino LA, Chawla A. Arthroscopic synovectomy in haemophilia: indications, technique and results. Haemophilia 2007;13 (suppl 3):38-44.

     

     

20. Wiedel JD. Arthroscopic synovectomy of the knee in hemophilia: 10 to 15 year follow-up. Clin Orthop Relat Res 1996;328:46-53.

     

     

21. Zvijac JE, Lau AC, Hechtman KS, et al. Arthroscopic treatment of pigmented villonodular synovitis of the knee. Arthroscopy 1999;15: 613-617.