Pigmented villonodular synovitis (PVNS) is a nonneoplastic proliferative disorder that can affect any synovial-lined structure, including bursae, tendons, and joints. PVNS is most commonly reported in the knee, but also occurs in the hip joint. The process occurs most frequently in the third or fourth decades of life, with no sex predilection,68 and should be considered in the differential diagnosis for all young patients presenting with uncharacteristic clinical and/or radiographic features suggestive of early hip degeneration.69 In the hip, PVNS most commonly presents in a monoarticular distribution, but bilateral hip involvement has been reported.70 The etiology and pathogenesis remain obscure and undefined; the most widely accepted theories attribute this disorder to a chronic inflammatory response or a benign but locally aggressive condition of fibrohistiocytic origin.68,71 At the cellular level, PVNS is characterized by hypervascular proliferative syn-
ovium, which is hemosiderin-laden and contains multinucle-ate giant cells and macrophages. These cellular immune mediators express local inflammatory cytokines, which play an important role in the stimulation of osteoclastic bone resorption, resulting in the destruction of articular cartilage and erosion of periarticular bone which characterizes PVNS.72 These alterations in the basic synovial tissue function ultimately result in symptomatic joint dysfunction and degeneration if not diagnosed and treated.
PVNS has been described in a number of forms, which include localized (focal), diffuse, and extra-articular. The process typically begins in and usually remains confined to the joint capsule.70 The localized or focal form involves a distinct section of the synovium, which is often described as nodular.73 The diffuse form involves the entire synovium,74 and the extra-articular form has been reported in isolation and in conjunction with diffuse intra-articular involvement.70,75 These different forms may explain the variable presentation of the disease, and may also carry different prognoses, recurrence rates, and treatment options. The localized or focal form of PVNS seems to carry a better prognosis and have a lower recurrence.70 This favorable outcome may be related to early diagnosis and treatment. The diffuse form, in contrast, has a poor prognosis, with high recurrence rates and locally aggressive progression.76,71 The diffuse form unfortunately may be more common,74 and may present with or progress to extra-articular extension and end-stage joint destruction. The extra-articular form may be an extension from a defect in the hip capsule, presenting as groin swelling or a soft tissue mass. Cotten et al have reported the extra-articular form in 6 of 58 patients treated with an open technique.70 Extra-articular extension of hip joint PVNS has also been reported as a cause of secondary symptomatic compression neuropathy of the femoral and sciatic nerves.75 There is no published histopathologic differentiation to suggest a difference between the localized and diffuse forms of the process, and the contrast may simply relate to the timing of the initial investigation and diagnosis. Focal or localized PVNS may be the early stages of the process, and diffuse and extra-articular forms may be the result of longstanding, progressive joint involvement that has been undiagnosed.
Patients with PVNS in the hip joint may present initially with a broad spectrum of slowly progressive symptoms including mild discomfort, stiffness, and limitation of motion. The physical examination may be only slightly altered or completely normal in these early stages. When the early stages have been treated expectantly for a long period of time as a muscle strain or early osteoarthritis, extensive hip joint and periarticular bone destruction may be seen upon initial presentation to the orthopedic surgeon. Progression of the disease to a more advanced state results in symptoms of persistent discomfort and mechanical impingement at the extremes of motion. The inconsistent nature of the presentation in the hip often leads to significant delays in diagnosis, and in one survey the mean delay to diagnosis was 4 years.77 A high clinical suspicion is therefore required in the evaluation of this condition, and can be aided by specific findings on plain radiographs, as outlined in Chapter 3. Bony erosions and loss of the joint space on plain radiographs tend to be gradual and occur late in the disease process.68,78 Therefore, MRI should be considered early in young patients with unexplained unremitting hip pain that does not respond to or improve with conservative treat-ment.68,70,78,79 Magnetic resonance imaging usually demonstrates key diagnostic features, which include joint effusion, elevation of the joint capsule, hyperplastic synovium, and low signal intensity resulting from hemosiderin deposition in the synovium.80 Although very supportive, these MRI findings are not diagnostic. The final diagnosis of PVNS is pathologic and requires a tissue biopsy for histopathologic evaluation and confirmation. MRI findings can be very beneficial in mapping the extent and form of the process, and for directing biopsy and early conservative and surgical intervention.
The role of hip arthroscopy can be both diagnostic and therapeutic, and its minimally invasive nature has made its use more appealing than arthrotomy. As in other uncommon synovial disorders, arthroscopic evaluation and treatment of hip PVNS has been extrapolated from the more common treatment of the disease in the knee joint. In the knee joint, numerous orthopedic surgeons have reported favorable short- to mid-term results following synovectomy by open, arthro-scopic, and/or synoviothresis, alone or in combination therapy.73,74,76,81 Most authors agree that treatment is most successful, measured by favorable joint function and lack of recurrence, when PVNS is treated before joint degeneration is visible on radiographs. In some reports, even late or recurrent disease responded favorably to arthroscopic synovec-tomy and resulted in a short-term funtional improvement.77
Another consensus is that, when faced with recurrence, arthroscopy, combined with or converted to an open procedure, could curtail rapid progression. In advanced knee disease, or after multiple recurrences, complete synovectomy and total joint arthroplasty have been indicated, and have not been adversely affected by the previous procedures. Arthroscopic synovectomy is the procedure of choice for the initial treatment of PVNS in the knee joint, and although the results of large series are not reported for the hip joint, the procedure should also positively affect the progression of the process in this location.
In the hip, arthroscopy should be considered early in young adults with hip pain of unknown origin and with radiographic findings to suggest PVNS. The treatment options for hip joint PVNS depend completely on the timing of the diagnosis and the nature of synovial involvement. Early diagnosis is critical so steps can be taken to prevent progression to advanced hip joint degeneration.69 The delay between the onset of symptoms and the histopathologic confirmation of this condition generally accounts for the massive local bone inva-sion.78 Only early diagnosis permits conservative surgical treatment (i.e. total synovectomy). Although the reported results of synovectomy are not stellar, 65% success in a multicenter series after 3-year mean follow-up,77 the alternative treatments in this population are also a potential long-term problem. If the the disease is diagnosed late, destructive lesions may be too extensive, and arthrodesis or total hip arthroplasty may be indicated for pain management and mobility.82
Hip arthroscopy can provide tissue for pathologic identification and also visualization of the focal or diffuse nature of the process, the status of the articular cartilage, and offers the ability to perform a partial synovectomy.3 (Figure 14.10). In the young patient population affected, this minimally invasive technique is more acceptable than formal arthrotomy, and is also more likely to be done at an early stage when the most benefit can be achieved. Earlier diagnosis through arthros-copy and subsequent chemical synoviothesis might reduce the need for more aggressive surgery and improve the progno-sis.78 The information collected during hip arthroscopy can direct an appropriate treatment plan based on visualization of the joint.3 PVNS of the hip has been treated with open and arthroscopic synovectomy, chemical or radionuclear syn-oviothesis, and/or total hip arthroplasty.83 Synovectomy is effective only when articular cartilage is preserved. Localized or focal disease in the hip has been successfully treated with both open and arthroscopic synovectomy. The diffuse form is more difficult to treat with any means, and has a high likelihood of recurrence when a complete synovectomy is not per-formed.71 Complete hip joint synovectomy is difficult if not impossible to do using arthroscopic techniques, but at the time of initial biopsy can be attempted and then followed by chemical or radionuclear synoviothesis. If the diffuse form recurs, a combined arthroscopic and open technique can be used to perform the synovectomy without dislocation of the femoral head.84 Diffuse PVNS, when recurrent, eventually results
in advanced joint degeneration, which is most predictably treated with total hip arthroplasty. Total hip arthroplasty, although of concern in such a young population, appears to be the procedure of choice for either advanced cases of PVNS or those that have failed joint-sparing procedures.83
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