CORRInsights®: Current Pathologic Scoring Systems for Metal-on-metal THA Revisions are not Reproducible

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Some patients with metal-on-metal (MoM) hip implants, metal-on-polyethylene implants, or other hip arthroplasty constructs develop adverse local tissue reactions (ALTRs). Sometimes those reactions are associated with wear debris particles, macrophages, and osteolysis, but only rare lymphocytes. Other ALTRs contain very few visible particles, but extensive lymphoplasmacytic inflammation and necrosis. Soft-tissue masses and/or effusions may occur, while other times the peri-implant membrane is more linear. Occasionally, these changes are associated with elevated serum metal ion levels. Despite more than a decade of investigations, radiologists, orthopaedic surgeons, pathologists, and biomaterials experts have not yet reached a consensus about the importance of, or even how to describe these reactions. These disagreements are rooted, in part, by a lack of correlation among our disciplines.
Recognizing that tissues around damaged implants show a spectrum of changes, and that any given arthroplasty may show features reflecting more than one mechanism of failure, several groups of researchers have developed grading systems for individual observations [2, 3, 5-7], or combinations of features [1, 4], to semiquantitatively grade the extent to which the morphologic findings in tissue might reflect an adaptive immune response versus infection, mechanical factors, or an innate inflammatory reaction to debris.
In the current study by Smeekes and colleagues, three pathologists tested the reproducibility of two commonly used scoring systems [1, 4], the aseptic lymphocyte vasculitis-associated lesion (ALVAL) score and the modified Oxford ALVAL score. The results provide documentation of what many pathologists have maintained for years: These two scoring systems lack the level of reproducibility that most physicians expect from a routine laboratory test. That does not mean the scoring systems are of no value, but it does illustrate that semiquantitative grading of this type can be difficult and we have room for improvement.
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