Pigmented Villonodular Synovitis (PVS) is a chronic proliferative disease of the synovium that occurs in joints, tendon sheaths, and bursae. Both have the same histological features, including iron deposits, abnormal proliferation of fibrous stromal cells, histiocytes and multinucleated giant cells. From September 1997 to July 2006, 11 cases of PVS of the knee were admitted to our department, all of which were treated by arthroscopic surgery and confirmed by pathological examination. They are reported as follows. 1. Clinical data and methods 1.1 General data The 11 cases in this group, 7 males and 4 females. The age ranged from 39 to 66 years old, with an average of 53.1 years old. The duration of the disease ranged from 4 months to 25 years, with an average of 5.5 years. There were 4 cases of left knee and 7 cases of right knee. The preoperative Lysholm score was 53.7±20.0. Preoperatively, 8 cases were initially diagnosed by MRI, and the other 3 cases were preoperatively diagnosed with meniscal injury in 2 cases and osteoarthritis in 1 case. 11 cases were postoperatively confirmed to have combined meniscal injury in 4 cases and osteoarthritis in 4 cases. Clinical manifestations: joint swelling in 9 cases, all with floating patella sign; no swelling in 2 cases. The suprapatellar capsule was spongy in 8 cases, of which 9 cases were accompanied by obvious joint pain. Joint movement was limited in 6 cases, 5º~90º. There was a history of minor trauma in 9 cases. Auxiliary examination: normal body temperature, normal blood sedimentation in 8 cases, the other 3 cases were not checked. Radiographs showed joint swelling in 9 cases, joint degeneration with bony redundancy and mild stenosis in 2 cases. 9 knees were scanned with MRI before surgery, and 8 cases suggested intra-articular effusion with low signal mixed in between. 1.2 Methods Arthroscopy was used: 30º, 70º arthroscope, series of planing knives, arthroscopic special electric knife and Arthrocare 2000 plasma surgery system. Continuous epidural anesthesia was administered in 10 cases in the supine position throughout (the affected knee could be draped over the bedside) and 1 case in the supine position followed by the attached position. Anterolateral, anteromedial, and suprapatellar medial-lateral approaches were preferred. The surgical operation: for diffuse and limited cases, the synovial lesion was gradually removed with a planer, and then the lesion beyond the reach of the planer was supplemented with a microscopic electric knife and the Arthrocare 2000 plasma surgical system and carefully cauterized to stop the bleeding. -Internal and external saphenous fossa. In diffuse nodules, the Arthrocare 2000 plasma system is used to gradually separate the nodule from the synovium and remove it from the joint cavity piece by piece with a medullary forceps. This procedure should not be forced to be performed arthroscopically, and if necessary, an additional auxiliary incision should be made to completely remove the lesion. In the limited type, the lesion is carefully cauterized with a plasma surgical system after complete removal of the lesion by choosing a suitable access. For the lesioned synovial membrane often invades the cruciate ligament and meniscus edge, in order to avoid excessive resection damage to the ligament and meniscus, the lesioned synovial membrane is gradually torn away with a medullary forceps and carefully cauterized with a radiofrequency knife at low energy to be complete. Postoperatively, they were sent for pathological examination. Four cases with combined meniscal injury and osteoarthritis were treated at the same time. 1.3 Postoperative management After surgery, no drainage tube was placed, the joint cavity was injected with 3 ml of bupivacaine (0.75%) + 0.1 mg of epinephrine, and a large cotton pad was wrapped with pressure for 5 days, and quadriceps exercises were started 24 hours after surgery, and weight bearing of the affected limb was allowed from 48 to 72 hours. The arthroscopic incision was removed in 7 days, and the adjuvant incision was removed in 12 days. Patients were kept in the hospital for observation for 5 to 7 days after surgery. 1.4 Postoperative external radiotherapy was performed after wound healing. Postoperative external radiotherapy was performed for diffuse type (6 cases) and diffuse nodal type (2 cases), and the total dose of irradiation was 2000~3000 cGy in 10 times, except for 1 case who only completed 600 cGy because he did not agree to continue radiotherapy, and the other patients were irradiated every other day. External radiotherapy was not done in 3 cases of limited type. 2. Results Arthroscopic manifestations: 9 cases had joint effusion extracted, with the volume of effusion ranging from 5 ml to 80 ml, averaging 31.8 ml, of which 5 cases were dark red (Figure 1) and 4 cases had yellow turbid fluid; 2 cases did not have fluid extracted. Microscopically, we saw diffuse growth of yellowish-brown villi in the joint cavity, with different lengths, which could be distributed anywhere in the joint cavity (Figure 2), even eroding the meniscus and cartilage surface. Two of the diffuse patients showed excessive growth of villi breaking off and becoming villi free in the suprapatellar capsule, while the other two cases showed multiple diffuse yellowish-brown nodules connected to occupy the synovial surface, and some of the nodules had protruded outside the joint capsule at the The other two cases showed multiple diffuse yellow-brown nodules connected to occupy the synovial surface and some of them had protruded outside the joint capsule to form a mass in the soft tissue of the suprapatellar bursa or N fossa, with a diameter of 1-4.5 cm, which was difficult to excise (Figure 3); the three cases of the limited type were isolated nodules, with a diameter of 1-3 cm and a hard, yellow-brown color, mostly on the synovial surface and a few under the synovium and eroding the joint capsule (Figure 4). All cases were pathologically confirmed (Figure 5). Full knee arthroscopic synovectomy of the lesion was performed in 10 cases. In one case, a nodular lesion in the posterior aspect of the joint protruded outside the posterior joint capsule, and after the intra-articular lesion had been treated microscopically, it was then turned in the prone position and re-rolled for posterior open surgical resection. The average operative time was 70 minutes (40 to 150 minutes). Follow-up of 12 to 108 months was obtained in 11 cases, with a mean of 46 months. Lysholm score and MRI were performed for joint function at follow-up. One case of the diffuse type did not complete external radiotherapy after surgery, and a mass returned in situ 3 months later, and the recurrence was confirmed by MRI. The Lysholm joint function score increased from (53.7±20.0) to (87.5±3.8) before surgery. There was a significant difference in the pre- and post-operative scores.