Clinical calculator
Mirels Calculator
Mirels' Score for Pathological Fracture Risk
Mirels' score estimates the risk of pathological fracture through a long bone metastasis by scoring four variables — site, pain, radiographic appearance and lesion size — from 1 to 3 each, giving a total from 4 to 12, where 9 or more is the conventional threshold for prophylactic fixation.
What the Mirels score means
Mirels scores run from 4 to 12, where a lower score is better. The bands below are conventional reporting categories, not diagnostic cut-offs.
- Low risk — fracture unlikely4–7
Risk of pathological fracture is low. Irradiation and observation are usually appropriate, with prophylactic fixation not indicated on the score alone.
- Borderline — clinical judgement required8–8
A score of exactly 8 sits at the decision boundary. Mirels advised that these lesions be considered individually, weighing life expectancy, the response of the tumour to radiotherapy and the patient’s functional demands.
- High risk — prophylactic fixation indicated9–12
Risk of pathological fracture is high enough that prophylactic internal fixation is generally recommended before irradiation.
Published criteria and reliability
The published cut-offs that define this instrument, and the measured agreement between observers using it. Each is reported with the population it was derived in.
| Type | Value | Subscale | Population | Follow-up | Source |
|---|---|---|---|---|---|
| Criterion | ≥ 9 — prophylactic fixation recommended | — | Long bone metastases, original derivation series | — | Mirels H 1989 |
| Criterion | 8 — borderline, individual clinical judgement | — | Long bone metastases | — | Mirels H 1989 |
| Criterion | ≤ 7 — irradiation and observation | — | Long bone metastases | — | Mirels H 1989 |
| Criterion | Fracture rate approximately 4% at 7, 15% at 8 and 33% at 9 | — | Original derivation series of 78 lesions | — | Mirels H 1989 |
| Criterion | Sensitivity is high but specificity is low, so the score over-predicts fracture | — | Systematic review of Mirels validation studies | — | Jawad MU 2010 |
Criterion is a published cut-off, definition or performance figure belonging to a classification or decision rule — it is not a change score and should not be read as one.
How the score is calculated
Stated in full so the calculation can be independently checked, and reproduced by hand if needed.
Four variables are each scored from 1 to 3. Site: upper limb 1, lower limb 2, peritrochanteric 3. Pain: mild 1, moderate 2, functional 3. Lesion: blastic 1, mixed 2, lytic 3. Size relative to cortical diameter: less than one third 1, one third to two thirds 2, more than two thirds 3. The four scores are added to give a total from 4 to 12. A total of 9 or more indicates a fracture risk high enough to justify prophylactic internal fixation before irradiation; 7 or less indicates a lesion that can be irradiated and observed; 8 is a borderline score requiring individual clinical judgement.
Missing data
All four variables must be scored. There is no substitution rule and a partial total cannot be compared against the published thresholds.
Instrument profile
- Developer
- Hilton Mirels
- Institution
- Groote Schuur Hospital, Cape Town, South Africa
- First published
- 1989
- Items
- 4
- Response format
- Four variables scored 1–3
- Score range
- 4 to 12
- Direction
- Lower score = better
- Completion time
- About 2 minutes
- Age range
- Adults
- Regions
- General Health, Hip
- Conditions
- Metastatic bone disease, Impending pathological fracture, Bone metastasis, Multiple myeloma
- Procedures
- Prophylactic intramedullary nailing, Radiotherapy, Internal fixation
- Observer agreement
- Interobserver agreement is good for site and pain, and only moderate for lesion size and radiographic character
- Validity
- Remains the most widely used and most widely validated scoring system for impending pathological fracture, and is embedded in several national guidelines.
- Reliability
- The score over-predicts fracture, so using the threshold of 9 mechanically results in prophylactic fixation of lesions that would never have fractured. It was derived on plain radiographs before routine CT, and CT-based measures of cortical involvement predict fracture better.
When to use the Mirels
Well suited to
- A long bone metastasis where the question is whether to fix prophylactically or to irradiate and observe.
- Multidisciplinary discussion of metastatic bone disease, where it provides a common language for risk.
Limitations and poor fits
- Spinal metastases, for which the Spinal Instability Neoplastic Score was designed.
- Lesions that have already fractured — the score predicts fracture, it does not grade one.
- As the sole basis for surgery, particularly at a score of 8, and particularly where life expectancy is short.
- Primary bone tumours, which were not in the derivation population.
Mirels compared with other instruments
Instruments measuring a related construct, with the practical difference between them.
| Instrument | Items | Range | What it adds |
|---|---|---|---|
| SINS | 6 | 0–18 | The Spinal Instability Neoplastic Score grades the mechanical stability of a spine affected by tumour by adding six components — location, mechanical pain, lesion quality, alignment, vertebral body collapse and posterolateral involvement — to a total from 0 to 18, where 0 to 6 is stable, 7 to 12 is indeterminate and 13 to 18 is unstable, and any total of 7 or more warrants surgical consultation. |
| CCI | 17 | 0–37 | The Charlson Comorbidity Index is a weighted checklist of 16 comorbid conditions that produces a comorbidity score of 0 to 33, to which up to 4 points are added for age, and which estimates 10-year survival at roughly 98% for a total of 0, 90% for 2, 53% for 4 and 21% for 5. |
Copyright and permitted use
Published openly because it is the question every clinician and researcher asks before using an instrument, and almost nobody answers it.
A published clinical scoring system. The variables and their point values are freely reproducible and no licence is required.
References
- Mirels H. Metastatic disease in long bones: a proposed scoring system for diagnosing impending pathologic fractures. Clinical Orthopaedics and Related Research. 1989.PMID 2684463
- Jawad MU, Scully SP. In brief: classifications in brief: Mirels' classification: metastatic disease in long bones and impending pathologic fracture. Clinical Orthopaedics and Related Research. 2010.PMID 20352387
- Damron TA, Morgan H, Prakash D, Grant W, Aronowitz J, Heiner J. Critical evaluation of Mirels' rating system for impending pathologic fractures. Clinical Orthopaedics and Related Research. 2003.PMID 14600613
Editorial status
This page has not yet been signed off by a named clinical reviewer. The scoring logic is stated in full above so it can be independently verified, and every threshold is traceable to its source. See our editorial methodology.