The modified Mirra classification can be used to describe the pathologic changes seen with a prosthetic joint in a standardized way.
Parameters:
(1) neutrophils (acute inflammatory cells) per high power field (400x)
(2) histiocytes per high power field (400x)
(3) lymphocytes and plasma cells (chronic inflammation) per high power field (400x) OR lymphoid follicles per low power field (100x)
(4) multinucleated giant scells per high power field (400x)
(5) metal particles per histiocyte
(6) globules of polymethylmethacrylate per low power field (100x)
(7) areas of necrobiosis per slide
(8) areas of conventional necrosis per slide
(9) areas of necrotic debris surrounded by histiocytes (tumoral calcinosis-like) per slide
(10) nonviable bone chips per lower power field (100x)
The findings of 5 microscopic fields were averaged.
|
Parameter |
Finding |
Points |
|
neutrophils |
none per hpf |
0 |
|
|
1 to 5 per hpf |
1 |
|
|
6 to 49 per hpf |
2 |
|
|
>= 50 per hpf |
3 |
|
histiocytes |
none per hpf |
0 |
|
|
1 to 5 per hpf |
1 |
|
|
6 to 49 per hpf |
2 |
|
|
>= 50 per hpf |
3 |
|
lymphocytes or plasma cells |
none per hpf |
0 |
|
|
1 to 9 per hpf |
1 |
|
|
10 to 49 per hpf |
2 |
|
|
>= 50 per hpf |
3 |
|
lymphoid follicles |
none per lpf |
0 |
|
|
1 per lpf |
1 |
|
|
2 or 3 per lpf |
2 |
|
|
>=4 per lpf |
3 |
|
multinucleated giant cells |
none per hpf |
0 |
|
|
1 per hpf |
1 |
|
|
2 to 4 per hpf |
2 |
|
|
>= 5 per hpf |
3 |
|
metal particles per histiocyte |
none per histiocytes |
0 |
|
|
1 to 9 (slate blue histiocytes) |
1 |
|
|
10 to 100 (dusty black histiocytes) |
2 |
|
|
> 100 (jet black histiiocytes) |
3 |
|
globules of methlmethracrylate |
none per lpf |
0 |
|
|
1 to 3 per lpf |
1 |
|
|
4 to 6 per lpf |
2 |
|
|
>= 7 per lpf |
3 |
|
necrobiosis |
none per slide |
0 |
|
|
1 to 2 mm per slide |
1 |
|
|
3 to 9 mm per slide |
2 |
|
|
>= 10 mm per slide |
3 |
|
conventional necrosis |
none per slide |
0 |
|
|
1 to 2 mm per slide |
1 |
|
|
3 to 9 mm per slide |
2 |
|
|
>= 10 mm per slide |
3 |
|
tumoral calcinosis-like necrosis (conventional necrosis surrounded by layers of histiocytes) |
none per slide |
0 |
|
|
1 to 2 mm per slide |
1 |
|
|
3 to 9 mm per slide |
2 |
|
|
>= 10 mm per slide |
3 |
|
nonviable bone chips |
none per slide |
0 |
|
|
1 to 5 per slide |
1 |
|
|
6 to 10 per slide |
2 |
|
|
> 10 per slide |
3 |
where:
• Necrobiosis features a collagenous background which can be seen under polarized light.
subscore for chronic inflammation =
= MAX(points for lymphocytes and plasma cells, points for lymphoid follicles)
total score =
= SUM(points for 9 parameters other than chronic inflammation) + (subscore for chronic inflammation)
If there were several slides of the same site, then the total scores were averaged.
Interpretation:
• minimum score: 0
• maximum score: 30
Specialty: Surgery, orthopedic
