Anne E. Colton, Charles Bush-Joseph, and Jeffrey S. Earhart
DEFINITION
Synovitis is inflammation of the synovial membrane. The synovial lining undergoes hyperplasia, most prominent in rheumatoid arthritis. A mononuclear infiltration often makes up the sublining. Redundant synovial folds and villae may be present.
Synovitis secondary to inflammatory conditions can lead to painful, swollen, and stiff knees.
After medical management has been exhausted, surgery is indicated if the patient experiences continued pain, swelling, and mechanical symptoms.
Conditions associated with knee synovitis include rheumatoid arthritis, pigmented villonodular synovitis (PVNS), synovial osteochondromatosis, psoriatic arthritis, osteoarthritis, lupus arthrosis, gout, synovial hemangiomas, plicae, intra-articular adhesions, fat pad fibrosis, posttraumatic synovitis, hemophilic synovitis, and fibrotic ligamentum muscosum.1–3,5,6,9,14,15
ANATOMY
Synovial tissue is a specialized mesenchymal lining of joints.
Normal synovium supplies nutrients for the articular cartilage and produces lubricants that bathe the joint surfaces to allow smooth gliding. It is a specialized mesenchymal tissue.
Histologic hallmarks of chronic synovitis include hyperplasia of the intimal lining, lymphocyte infiltration, and blood vessel proliferation.
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.
PATHOGENESIS
In chronic synovitis, the synovial lining undergoes hyperplasia, angiogenesis, and increased cellularity (inflammatory cells such as lymphocytes and macrophages).
Rheumatoid arthritis is one of many immunoinflammatory diseases. It presents as an insidious onset of morning stiffness with multiple joint involvement. The synovitis that ensues is likely an acute autoantibody-mediated inflammatory response.
PVNS is a proliferation of nodules and villi in the synovium of joints. Typically it is monoarticular, most commonly affecting the knee.
Hemophilia is an X-linked deficiency of clotting factors, leading to bleeding of varying severity.
The knee is the most common site of hemarthrosis. The repeated hemarthroses can lead to a chronic, progressive synovial hyperplasia.
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 episodes of knee or other joint swelling in the past.
The patient may have a history of recurrent swelling, pain, warmth, stiffness, and mechanical symptoms (FIG 1).
Patients may have the stigmata of psoriasis or lupus.
PVNS can cause mechanical symptoms such as locking, not unlike a meniscal tear. A palpable mass may be present.
Intermittent symptoms are more common with localized PVNS; diffuse PVNS has more of a chronic presentation.
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.
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
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.
FIG 1 • Patient with a long history of chronic synovitis in his right knee.
Synovial fluid analysis should include documentation of fluid color (ie, brownish in PVNS, indicating recurrent bleeding), testing for rheumatoid factor, complement levels,
FIG 2 • T2-weighted MRI reveals large effusion in patient's knee, subsequently diagnosed by arthroscopic synovectomy as rheumatoid arthritis.
IMAGING AND OTHER DIAGNOSTIC STUDIES
Radiographs are important to document the extent of joint destruction.
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 lesions.
Synovial chondromatosis is often visible.
Advanced degenerative disease is associated with a poorer prognosis after arthroscopy.12
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.
DIFFERENTIAL DIAGNOSIS
Synovial disorders
Infection
Degenerative joint arthrosis
NONOPERATIVE MANAGEMENT
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.
SURGICAL MANAGEMENT
Arthroscopic synovectomy allows the identification and management of synovial lesions that may be missed with open procedures and also allows re-evaluation after the index procedure with a low morbidity.7,13
Arthroscopic synovectomy can provide definitive treatment for the many 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.7
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.
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
The examination under anesthesia should document the presence of effusion, range of motion, ligamentous stability, and patellar mobility and tracking. Examination of the contralateral knee should always be performed for comparison.
Positioning
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.
An arthroscopic leg holder is not used because it may prohibit the use of the superomedial and superolateral portals.
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 is also flexed 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.
An arthroscopic lateral post may be placed midthigh on the side of the operative bed.
A suction canister trap should be set up for biopsy collection.
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 is begun with outflow in the superomedial portal because this is rarely used as a viewing portal (TECH FIG 1B).
An incision is made in the inferolateral portal. The arthroscope is placed into the suprapatellar pouch with the knee in extension. A superolateral working portal is established (TECH FIG 1C,D).
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.
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.
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).
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.
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.
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.
Posteromedial Compartment
For access to the posteromedial compartment, a blunttipped 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.
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, raising the hand to accommodate the posterior slope of the tibia.
The trocar should push into the posteromedial compartment without too much force.
If this proves difficult to accomplish, a central patellar 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.
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).
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.
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 hand is raised 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.
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 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.
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.
POSTOPERATIVE CARE
The patient is weight bearing as tolerated.
Continuous passive motion is advised in cases of complete synovectomy, advancing as tolerated over 1 to 3 days.
Physical therapy is initiated after removal of the suction drain. Closed-chain exercises are emphasized.
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.7,10,13 In addition, synovectomy can be more complete with accurate visualization of the posterior compartments.15
One study of 96 rheumatoid arthritic knees found significant decreases in pain and synovitis at an average of 4 years after arthroscopic synovectomy.11
Along with the use of rheumatoid medications, arthroscopic synovectomy can reduce inflammation and help preserve range of motion.2
Success rates in the relief of pain and swelling have been as high as 80% in the treatment of rheumatoid arthritis.10
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.4
Recurrence rates with arthroscopic synovectomy of PVNS have been as low as 11%, with improved range of motion.9
Localized PVNS has responded best to arthroscopic treatment.
Multiple series have reported no recurrences at follow-up after excision of the lesion.8,9,15
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.14
COMPLICATIONS
Recurrent hemarthrosis, often requiring repeat aspirations or surgical irrigation and débridement
Loss of range of motio.
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.
REFERENCES
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