TABLE II.
Modified Mirra Classification Used to Assess Tissue Reactions and Wear Particle Load in Periprosthetic Tissue Samples
| Histology | 0 | 1+ | 2+ | 3+ |
|---|---|---|---|---|
| Acute inflammatory cells (neutrophils) | 0 cells/HPFa | 1–5 cells/HPF | 6–49 cells/HPF | 50 or more/HPF |
| Mononuclear histiocytes | 0 cells/HPF | 1–5 cells/HPF | 6–49 cells/HPF | 50 or more/HPF |
| Chronic inflammatory cells (lymphocytes, plasma cells, lymphoid follicles) | 0 cells/HPF | 1–9 cells/HPF | 10–49 cells/HPF | 50 or more/HPF |
| Giant cells (multinucleated histiocytes) | 0 cells/HPF | 1 cell/HPF | 2–4 cells/HPF | 5 or more cells/HPF |
| Metal particles | Normal colored histiocytes (no visible, black metal particles per histiocyte) | Slate blue histiocytes (<10 visible, black metal particles per histiocyte) | Dusty black histiocytes (10 to 100 visible, black Metal particles per histiocyte) | Jet black histiocytes (>100 visible, black metal particles per histiocyte) |
| Necrosis | 0 mm of necrosis/slide | 1–2 mm of necrosis/slide | 3–9 mm of necrosis/slide | >1 cm of necrosis/slide |
a
HPF: high power field (×40).