Pseudotumor After Metal-on-Metal Hip Arthroplasty.

Abstract

To the Editor: An 86-year-old woman with a history of Alzheimer's disease, chronic obstructive pulmonary disease, depression, osteoporosis, and right and left total hip replacements (metal-on-metal implants, performed 13 and 11 years ago, respectively) presented with subacute right hip pain. She was functionally independent, living at home with her daughter and mobilizing without gait aids. She presented with 3 weeks of worsening right hip pain without any history of trauma or falls. She was afebrile and had minimal tenderness on palpation, with full range of motion over the hip joint. X-ray of the right hip showed no fractures but periprosthetic sclerosis, and ultrasound showed a chronic complex collection. Two separate aspirates of the collection were sterile. After discussion with the patient's daughter, a conservative approach was adopted, with a trial of empirical oral antibiotic suppression for presumed chronic hip prosthesis infection. Over the next 8 months, her pain worsened and was associated with marked swelling anteriorly and posterior-laterally around the hip joint despite ongoing antibiotics. She now required a frame to walk. Computed tomography (CT) of the pelvis showed bilateral sacral ala and pubic rami fractures. There were circumscribed soft tissue density masses surrounding the right total hip replacement measuring 5 by 3 cm anteriorly and 6 by 5 cm posteriorly that showed rapid enlargement on serial scans. A core biopsy of the masses was performed and yielded negative cultures, with histopathology showing hematoma with no evidence of organization present. Postcontrast magnetic resonance imaging (MRI) showed a heterogenous hyperintense mass without significant enhancement (Figure 1). A diagnosis of pseudotumor secondary to metallosis was made based on the clinical findings with minimal inflammation over the hip joint, the characteristic MRI findings, the negative microbiology, and lack of response to antibiotics. Testing found high serum cobalt levels (22 nmol/L, normal range 2–7 nmol/L) further supporting the diagnosis, but her serum chromium was normal at 15 nmol/L (normal range 2–40 nmol/L). Metal-on-metal (MoM) hip replacements have been commonly used in Australia (21,400 between 1999 and 2010), with advantages of low wear rates and incidence of dislocation, but there are concerns that the release of metal (chromium and cobalt) ions and particles from these implants may have adverse cardiac, neurological, endocrine, and dermatological effects.1 A local inflammatory reaction to this process has also been described and may form pseudotumors or be mistaken for infection, as in this case. These periprosthetic soft tissue lesions have been described as bursae, cysts, inflammatory or granulomatous masses, or adverse reactions to metal debris (metallosis).2 The diagnosis is often confirmed using soft-tissue imaging modalities such as ultrasound or metal artifact reduction sequence MRI.3 Histology and serum or hip aspirate metal ion levels can be helpful. Pseudotumors after hip arthroplasty have been described since 1976. Aggressive granulomatous lesions were found in cemented metal-on-polyethylene total hip arthroplasty,4 but similar pathology related to metal-on-metal bearings has only recently been recognized.4 There is often a latent period of 2 to 15 years after the initial total joint replacement before this foreign-body reaction becomes clinically or radiologically apparent.4 Precise incidence and prevalence is unknown because there are appreciable numbers of asymptomatic or subclinical pseudotumors.5 The pathogenesis is due to osteolysis adjacent to prosthetic material and a cytotoxic and delayed hypersensitivity (Type IV) response to the deposition of cobalt–chrome wear particles in periprosthetic tissues.6 Histologically, a spectrum of changes comprising pure metallosis, aseptic lymphocytic vasculitis associated lesion, and granulomatous inflammation is seen.7 All people with MoM implants have modestly high serum chromium and cobalt concentrations, but symptomatic individuals with serum chromium levels greater than 15 ng/mL and cobalt levels greater than 10 ng/mL are likely to have significant implant deterioration.8 On MRI, the pseudotumor can vary in size (but often >5 cm), can be fluid or solid with minimal or no contrast enhancement, and can extend out from the femoral neck into surrounding tissues.9 Pseudotumors might incidentally be present in individuals with well-functioning hip prostheses, suggesting that the presence of a pseudotumor may not necessarily indicate the need for revision arthroplasty.10 However, concerns about the progression of asymptomatic pseudotumors and the fact that pseudotumor revisions tend to do poorly are potential reasons for early revision.5 In frail elderly adults, particularly with dementia, there are concerns about operative risks, short future lifespan, and a preference for conservative management. Conservative management seems appropriate for the woman describe herein until operative management for palliative reasons cannot be postponed any longer. Conflict of Interest: The editor in chief has reviewed the conflict of interest checklist provided by the authors and has determined that the authors have no financial or any other kind of personal conflicts with this paper. Author Contributions: Lim: literature review, preparation of manuscript. Jeremiah: preparation of manuscript. Altuntas, Sinnappu, O'Sullivan, Lim: editing of manuscript. Sponsor's Role: No sponsor for this case report.