Patients with PVNS demonstrate evidence of an effusion or a hemarthrosis when minor trauma results in a hemorrhage. In the localized type, locking due to the presence of an intra-articular mass is common, and in both the diffuse and localized from, there may be limited joint arc of motion. A palpable mass is not usually appreciated unless there are extra-articular disease manifestations. Most commonly, the extra-articular disease occurs in the popliteal fossa or intercondylar notch (Fig. 35-4). In advanced cases, findings consistent with degenerative arthrosis are evident.

Plain radiographic findings in the early stage of disease are either normal or may show a displaced suprapatellar fat plane due to presence of an effusion. A capsular-based noncalcified soft tissue mass may be present (7). In later stages, periarticular cysts are present and cartilage thinning is seen (4). The findings on magnetic resonance imaging (MRI) are more dramatic and in many cases diagnostic. A soft tissue mass with alternating areas of bright signal and dark signal void on both T1 and T2 sequence represents the fluid (bright on T2) and fat (bright on T1) accumulation as well as hemosiderin deposits within the soft tissue (dark on both T1 and T2), respectively (Fig. 35-5). In the appropriate clinical setting, these findings are nearly diagnostic of PVNS, although rheumatoid arthritis may have a similar appearance (23,31). The nodular form may not always be localized to one location and instead may occur in multiple compartments within the joint. It is essential to precisely
determine the extent of the disease on MRI as this will directly affect the surgical approach to the disease. In doubtful cases, the diagnosis can be established with a biopsy.

The intraoperative gross appearance of disease is characteristic. In the diffuse form, multiple fronds of reddish-brown pigment-stained synovial tissue represent villous projections floating in synovial fluid. In the nodular form, a thickened reddish-brown and yellow stained xanthomatous soft tissue mass with cavitary areas of fluid accumulation is seen and the mass may spread dramatically in the suprapatellar pouch (Fig. 35-6) or intercondylar notch.

Histologically, PVNS is indistinguishable from a giant cell tumor of tendon sheath (nodular tenosynovitis). A proliferation of round synovial-like cells is present with occasional multinucleated osteoclast-type giant cells, xanthomatous cells, and inflammatory cells interspersed throughout the lesion (Fig. 35-7) (5,15).

The controversy regarding open versus arthroscopic synovectomy is difficult to resolve. With either technique, in the diffuse form, the recurrence rate ranges from 8% to 50% (10,25,32). The only factor which is conclusively known to prevent local recurrence is complete and aggressive resection of the affected tissues. The benefits of arthroscopic synovectomy are a quicker rehabilitation and avoidance of arthrotomy and postoperative knee stiffness. The disadvantages are related to performing an intralesional excision or debridement, potential for intra-articular spread of disease converting a localized form to diffuse disease, seeding of portal sites (Fig. 35-8), difficulty accessing posterior and extra-articular locations of disease, and difficulty in removal of markedly thickened
synovial tissue. Advantages of an open synovectomy over the arthroscopic technique are the ability to do a marginal or en bloc excision of the mass, complete a total synovectomy as opposed to a only a debridement, and the expeditious nature of an arthrotomy. Excellent results using cryosurgery in addition to open synovectomy have been reported (20). However, the open procedure can be technically challenging to perform adequately through a popliteal exposure and may result in postoperative adhesions if a normal arc of knee motion is not regained promptly after surgery. No prospective trials directly comparing these techniques have been performed, and they would be considerably difficult to power adequately due to the rarity of the disease.