Discussion:

•            Despite the good initial clinical results of the metal-on-metal (MoM) bearings, the MoM can cause clinical problems associated with the metallic debris. The deposition of metallic wear particles in periprosthetic tissues induces a spectrum of changes. One of the issue is development of the solid or cystic masses around the site of arthroplasty. These periprosthetic soft tissue lesions have been referred to variously as aseptic lymphocytic vasculitis-associated lesions (ALVAL), adverse reaction to metal debris and pseudotumors.

•            There is no clear consensus in the literature defining the boundaries of each term. Metallosis is the macroscopic staining of soft tissue. The aseptic lymphocytic vasculitis-associated lesion (ALVAL) is a histologic term and accompany with metallosis, effusion, soft-tissue necrosis or pseudotumor formation. Pseudotumor described a cystic or solid mass with a histology of ALVAL. The term “adverse reaction to metal debris” is an umbrella term including metallosis, ALVAL, and pseudotumors. Despite the heterogeneity of these lesions in the clinical presentations, aggressiveness, and histologic appearance, the use of the umbrella term ‘adverse reactions to metal debris’ has been suggested by some authors.

•            The reported prevalence of the pseudotumor has ranged from 4% to 71%. Although it has been suggested that this finding may correlate with inferior patient outcomes, the long term biologic consequences and the clinical effects of these raised metal ions remain largely unknown. The MRI-based grading systems were proposed to score the severity of adverse reaction of MoM. However, a recent study demonstrated that patient symptoms are not correlated with presence or size of pseudotumor.

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