Mirel’s scoring system rates 4 criteria from 1 to 3 with maximum possible score of 12 to assess the risk of pathological fracture due to metastases and also serves as a guide for considering prophylactic fixation. The parameters of the criteria can be remembered using the mnemonic MIREL’S.
- M – Morphology of metastases
- I – Intensity of pain
- R – Ratio of lesion size to bone diameter (as seen on plain radiograph)
- E – Eight (cut-off value)
- L – Location of metastases
- ‘S – Looks like 15 (score 8 = 15% risk of pathological fracture)
| Score | Site of lesion | Size of lesion | Nature of lesion | Pain |
|---|---|---|---|---|
| 1 | Upper limb | < 1/3 of cortex | Blastic | Mild |
| 2 | Lower limb | 1/3–2/3 of cortex | Mixed | Moderate |
| 3 | Trochanteric region | > 2/3 of cortex | Lytic | Functional |
He recommended prophylactic fixation with a patient scoring more than 8 or more. With this scoring system, patient with functional pain (severe pain at rest or pain with use of limb) and lytic lesion automatically scores 8 or more. However, it was created before the bisphosphonates were used. With a score of 8, clinical judgement is necessary for decision making.
| Mirels’ score | Clinical recommendation |
|---|---|
| ≤ 7 | Radiotherapy and observation |
| 8 | Use clinical judgment |
| ≥ 9 | Prophylactic fixation |
Risk of pathological fracture according to Mirel’s score:
- <6: 0%
- 8: 15%
- 12: 100%
Harrington (preceded Mirel’s criteria and is not validated) defined an impending fracture as:
- ‘Lytic’ bony lesion
- Involving > ½ the diameter of the bone (>2.5 cm in greatest diameter)
- Associated with persistent pain
- Radiographic progression after radiation.
Example: A lytic metastasis in the proximal diaphysis of right femur which encompasses half of the diameter of bone producing severe limb pain at rest would score: 3 (lytic) + 2 (lower limb) + 2 (1/2 diameter) + 3 (functional pain) = 10. This is an impending fracture according to Harrington’s criteria as well. Fracture is likely to occur without operative intervention and hence, prophylactic fixation with intramedullary nail should be considered in this case.