INTRODUCTION — Synovectomy refers to the destruction or surgical removal of the membrane (synovium) that lines a joint. As the largest articulation and the one most frequently affected by chronic inflammation, the knee is the joint most often selected for synovectomy. Open surgical, chemical, radiation, and arthroscopic synovectomies are all options for removing potentially damaging synovium from the knee.
There are various disorders that are indications for synovectomy. Among them are chronic inflammatory arthritides (eg, rheumatoid arthritis, psoriatic arthritis, Lyme arthritis), benign neoplastic disorders (eg, osteochondromatosis, tenosynovial giant cell tumor [formerly pigmented villonodular synovitis]), and recurrent hemarthrosis (eg, hemophilia). (See appropriate topics.)
Surgical debridement of synovial tissue, either open or arthroscopic, is also indicated for the treatment of some joint infections. (See "Septic arthritis in adults".)
The role of synovial biopsy and synovectomy in the diagnosis and management of inflammatory arthritis of the knee is reviewed here.
Synovial biospy and diagnosis — In chronic inflammatory arthritis of the knee, microbiologic and histopathologic examination of synovium may be useful in diagnostic and prognostic studies. Arthroscopically guided synovial biopsy is an attractive alternative to closed needle biopsy techniques. However, with the emergence of ultrasound-guided needle biopsy, the role for arthroscopic biopsy may be diminished .
Arthroscopic synovial biopsy appears to have a role in challenging diagnostic cases [2,3]. In one study, the use of arthroscopic synovial biopsy as a diagnostic tool had a sensitivity of 85 percent with a specificity of 100 percent for giving a conclusive diagnosis when clinical diagnosis was equivocal .
Synovial biopsy and joint examination — Arthroscopic synovial biopsy, as well as articular and synovial examination, may also provide useful prognostic information concerning disease progression among patients with inflammatory arthritis. Establishing the stage in the progression of changes from effusion and synovial proliferation with hyperemia through pannus formation with cartilaginous erosions to bony erosions allows some prediction of the efficacy of treatments, such as arthroscopic debridement or synovectomy, and of the likelihood of the need for eventual joint replacement. As an example, one study of 26 knees in patients with rheumatoid arthritis (five knees), juvenile idiopathic arthritis (18 knees), or psoriatic arthritis (three knees) used arthroscopy and clinical examination to assess the efficacy of open synovectomy in the knee . Arthroscopy included synovial biopsy for immunohistologic evaluation. The absence or low incidence of immunoglobulin A (IgA)-positive plasma cells in biopsies of knee synovium, as well as the amount of fibrin in the superficial layer 12 months after the synovectomy, suggested a less aggressive disease process and predicted a more reliable outcome after synovectomy. However, preoperative biopsies and those done six months after synovectomy were not predictive.
Open synovectomy — The beneficial role of open synovectomy of the knee has been clearly demonstrated for inflammatory arthritis, hemophilic synovitis, tenosynovial giant cell tumor (formerly pigmented villonodular synovitis), and synovial chondromatosis [5-9]. By ablating the synovial joint lining, this operative technique reduces inflammation, thereby reducing pain, swelling, and loss of joint motion. Synovectomy should be considered when medical management for a minimum of six months fails to control synovitis and pain. However, open synovectomy of the knee may result in significant morbidity; it is also associated with prolonged hospitalization and rehabilitation and may cause significant blood loss.
The long-term results of multiple studies of open synovectomy indicate that the procedure, although effective in temporarily relieving pain, is primarily palliative [4-6,8]:
●One report evaluated the efficacy of synovectomy in 78 knees among 55 patients with rheumatoid arthritis followed for a minimum of 10 years after surgery . Seventy-five of the knees had moderate or severe pain preoperatively. Surgery resulted in significant pain relief, as only 24 of the 75 knees continued to have moderate or severe pain . Symptom relief was more reliable in patients who underwent surgery prior to the development of significant radiographic evidence of degenerative change. However, surgery failed to halt disease progression; no significant difference in joint space narrowing was observed between the two knees of patients in whom surgery was performed on only one knee.
●The failure to delay the deterioration of secondary degenerative changes leads to knee replacement in many patients within a few years after synovectomy. In one study of 83 cases of knee synovectomy for rheumatoid arthritis, over 50 percent had undergone an osteotomy or total knee replacement at five years after surgery .
●A prospective five-year clinical follow-up study of open synovectomy in chronic inflammatory joint disease employed arthroscopic examination of the joint before, six months after, and 12 months after surgery . Patients were found to have decreased pain and swelling for up to six months after the procedure. The amount of wear on visual examination of the articular cartilage was the best predictor of good outcome, and those with recurrent synovitis at 12 months did worse at five-year follow-up. Patients with absent or low numbers of immunoglobulin A (IgA)-positive plasma cells on histologic examination of the synovium had better clinical scores at five years.
In light of the temporary nature of the procedure and the high cost and complication rate of the open synovectomy technique, additional techniques have been introduced to avoid the open procedure.
Arthroscopic synovectomy — Arthroscopic synovectomy, in the hands of a skilled arthroscopist, produces results comparable to open synovectomy, but with decreased morbidity and with considerably decreased cost. The procedure is associated with a decreased rate of infection, causes little if any loss of motion of the knee as long as early range of motion is encouraged, and can usually be performed in the outpatient setting, unless medical conditions require inpatient observation postoperatively.
Arthroscopic synovectomy is performed under general or spinal anesthesia, and a tourniquet is used. The knee is distended using a pressure irrigation system. The procedure requires considerable patience and a systematic approach to ensure that as much synovium as possible is removed. A specialized suction shaver and use of multiple portals, including posterior portals, facilitate a more complete excision. The posterior portals have significant associated risks of neurovascular damage, particularly to the saphenous vein and nerve. Care must be exercised to ensure that the excision is not too deep since this may promote scarring and subsequent loss of motion.
Because the excision, particularly posteriorly, may be incomplete, an open synovectomy using anterior and posterior incisions is recommended in the treatment of tenosynovial giant cell tumor when there is a significant bulk of abnormal tissue. Otherwise, recurrence will lead to an early resumption of symptoms. (See "Treatment for tenosynovial giant cell tumor and other benign neoplasms affecting soft tissue and bone", section on 'Tenosynovial giant cell tumor'.)
The efficacy of arthroscopic synovectomy was evaluated in one study of 96 patients with a variety of inflammatory arthritic disorders who underwent arthroscopic synovectomy because of at least six months of persistent synovitis and effusion of the knee that did not respond to medical management . Preoperatively, 56 percent had knee pain. At four years after the procedure, only 21 percent had pain, and 24 percent had a synovitis.
This study group was subsequently enlarged to 211 synovectomies and was followed over a period of 2 to 10 years after arthroscopy . The following results were reported:
●The 112 rheumatoid knees responded better (80 percent characterized as good or excellent) than the 32 knees with other inflammatory arthritides, such as psoriatic arthritis or ankylosing spondylitis (60 percent characterized as good or excellent).
●Recurrence occurred in only 2 of 19 cases of tenosynovial giant cell tumor.
●There were no recurrences in 17 patients with synovial chondromatosis.
●The 31 knees with nonspecific or posttraumatic synovitis showed decreased synovitis, but only one-half had reduced pain and improved function.
Arthroscopic synovectomy of the knee in patients with rheumatoid arthritis is, therefore, indicated after failure of an adequate trial of medical management for six months in a patient with persisting synovitis, with little or no degenerative changes on radiographs, and with functional class of I or II according to the American College of Rheumatology criteria . Patients with a greater functional impairment are usually candidates for more extensive surgery.
Arthroscopic or open synovectomy can also play a role in the management of the arthritic complications of hemophilia. One study of synovectomy in 13 knees in 11 patients (eight open and five arthroscopic) showed a reduction in recurrent hemarthroses at an average follow-up of two and eight years for the arthroscopic and open groups, respectively . In most cases, arthroscopic synovectomy increased the range of motion, and open synovectomy reduced or did not affect the range of motion. The roentgenographic progression of disease decreased but did not stop after synovectomy. (See "Treatment of bleeding and perioperative management in hemophilia A and B" and "Overview of hemarthrosis".)
Laser synovial ablation may prove to be a useful modality in this setting. The effectiveness of a holmium:yttrium-aluminum-garnet (holmium:YAG) laser system was assessed in 17 patients with rheumatoid arthritis . Symptomatic improvement was more likely in those with less severe joint space narrowing (Larsen grade I or II). The proper role for this technique requires further study.
Open versus arthroscopic synovectomy — Arthroscopic synovectomy may be associated with a greater risk of disease recurrence and radiologic progression than open synovectomy, although they appear to result in a comparable degree of pain relief. These techniques have not been compared in randomized trials, but they were compared indirectly in a 2011 meta-analysis of 58 studies involving 2589 patients (with mean follow-up of 6.1 years) who underwent open or arthroscopic synovectomy for rheumatoid arthritis . Those undergoing arthroscopic synovectomy in the knees had a statistically significant lower risk of progression to total joint arthroplasty compared with those undergoing open synovectomy (11 versus 19 percent). Radiographic progression was statistically significantly less frequent in the elbow and knees in patients who underwent the arthroscopic procedures (66 versus 28 percent and 75 versus 55 percent, respectively). However, the proportion of patients reporting less pain was similar for the two groups in each of the joints studied (mean of 75 percent). Limitations of the analysis included the performance of the majority of the studies prior to the availability of biologic disease-modifying antirheumatic drugs (DMARDs) and the tendency of the arthroscopic studies to have been performed more recently than many of the open synovectomy studies.
Chemical synovectomy — Chemical synovectomy utilizing intraarticular injection of osmium tetroxide (osmic acid) or alkylating agents has been used to perform a “medical synovectomy” in patients with synovial inflammation due to various disorders, including rheumatoid arthritis, psoriatic arthritis, tenosynovial giant cell tumor, and ankylosing spondylitis . However, concerns about potential mutagenicity of alkylating agents have limited enthusiasm for their use.
The possible value of osmium tetroxide synovectomy was illustrated in an uncontrolled consecutive series of 65 patients with various diseases causing persistent knee inflammation . Aspiration of the symptomatic knee, with removal of as much fluid as possible, was followed by the injection of local anesthetic (10 mL of 1 percent lidocaine). After the local anesthetic had taken effect, 10 mL of an aqueous solution of osmium tetroxide (100 mg/10 mL) was instilled. Then, 20 mg of triamcinolone hexacetonide were injected, and the needle was removed. Knee immobilization and bed rest for 24 hours were employed to reduce the risk of leakage. The following results were noted:
●Responses to the injections were good to excellent in 86 percent of patients when assessed six weeks following the injection. However, recurrence of synovitis occurred gradually, and 80 percent of injected knees were again inflamed three years following the initial injection.
●Adverse effects of osmium tetroxide chemical synovectomy included immediate postinjection pain in 12 percent of injections, skin burns at the site of needle insertion in 3 percent, and early “reactive” effusion that required aspiration.
While chemical synovectomy with osmium tetroxide appears to be a generally safe technique for controlling synovitis of the knee that has not responded to other medical therapy, it is performed at only a few tertiary centers .
Radiation synovectomy — Radiation synovectomy with the use of short-acting dysprosium-165-ferric hydroxide macro aggregates is an effective alternative to open synovectomy. One study, for example, found that 39 of 59 patients with rheumatoid arthritis at two-year follow-up had complete or almost complete relief of pain, a small or no effusion, and improved or no loss of motion .
By contrast, despite initial suggestions of efficacy , radiation synovectomy utilizing another radioisotope (yttrium-90) combined with intraarticular glucocorticoid injection may be no more effective than intraarticular glucocorticoids alone. This was illustrated in a study that randomly assigned the knees of 97 patients with chronic sterile synovitis to yttrium plus glucocorticoid (20 mg of triamcinolone hexacetonide or 40 mg of triamcinolone acetonide) and assessed a composite measure of clinical response . Yttrium plus glucocorticoids did not produce a greater response than intraarticular glucocorticoids alone (48 percent responded in each group), nor were the responses more durable. A subsequent study comparing the use of yttrium-90, phosphorus-32, or rhenium-188 with triamcinolone alone suggested comparable efficacy; however, a longer duration of pain relief was observed in the radiation synovectomy groups as compared with the triamcinolone group .
Limited geographic availability and the experimental nature of this procedure in many locales limit the consideration of radiation synovectomy as a general solution.
Combined arthroscopic and radiation synovectomy — Limited data from one study suggest that combined surgical and radiation synovectomy with yttrium-90 lead to a stable improvement in knee function for up to five years . However, the combination of arthroscopic and radiation synovectomy has not been compared with either strategy alone.
SUMMARY AND RECOMMENDATIONS
●Synovectomy refers to the destruction or surgical removal of the membrane (synovium) that lines a joint. Open surgical, chemical, radiation, and arthroscopic synovectomies are all options for removing potentially damaging synovium. (See 'Introduction' above.)
●The role of synovial biopsy and synovectomy has diminished with the development of clinical and laboratory diagnostics and success of biologic treatments for inflammatory arthritis. (See 'Introduction' above.)
●In chronic inflammatory arthritis of the knee, microbiologic and histopathologic examination of synovium may be useful in diagnostic and prognostic studies. Arthroscopically guided synovial biopsy is an attractive alternative to closed needle biopsy techniques. (See 'Synovial biopsy' above.)
●The benefit of open synovectomy of the knee has been demonstrated for inflammatory arthritis, hemophilic synovitis, tenosynovial giant cell tumor (formerly pigmented villonodular synovitis), and synovial chondromatosis. By ablating the synovial joint lining, signs and symptoms of inflammation are reduced. Synovectomy should be considered when medical management for a minimum of six months fails to control synovitis and pain. However, open synovectomy of the knee may result in significant morbidity, and, although it can be effective in temporarily relieving pain, the procedure is primarily palliative. (See 'Open synovectomy' above.)
●Arthroscopic synovectomy can produce results comparable to open synovectomy, but with decreased morbidity and cost. It can usually be performed in the outpatient setting, unless medical conditions require inpatient observation postoperatively, and it is performed under general or spinal anesthesia. It has shown benefit in patients with rheumatoid arthritis, tenosynovial giant cell tumor, synovial chondromatosis, and hemophilic arthritis and in some patients with nonspecific or posttraumatic synovitis. (See 'Arthroscopic synovectomy' above.)
●Chemical synovectomy and radiation synovectomy may reduce synovial inflammation, but their availability is limited to experimental use in a limited number of tertiary care centers. (See 'Chemical synovectomy' above and 'Radiation synovectomy' above.)
ACKNOWLEDGMENT — The UpToDate editorial staff acknowledges R John Wright, MD, who contributed to an earlier version of this topic review.
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