Metastatic Disease | Mirels Score | Prophylactic Fixation | Workup First
MIRELS STABILITY SCORE
Critical Must-Knows
- Workup First: Never fix a pathological fracture without knowing the primary (unless impending emergency). Biopsy track might spread tumor.
- BLT with a Kosher Pickle: Breast, Lung, Thyroid, Kidney, Prostate (Most common bone mets).
- Renal/Thyroid tumors: Highly vascular & Radio-resistant. Pre-op embolization often needed.
- Survival Estimate: Fixation should outlast the patient's life expectancy (durable construct).
- Fixation Logic: Fixation spans the whole bone (prevent new fractures). Cement augmentation improves stability.
Clinical Pearls
- "Always ask about constitutional symptoms (weight loss, night sweats)
- "Solitary lesion greater than 40y is Mets/Myeloma until proven otherwise
- "Solitary lesion less than 20y is Primary Bone Tumor until proven otherwise
- "Do not nail a primary bone sarcoma (contaminates whole compartment)
Critical Exam Points
The Solitary Lesion
Biopsy Trap: If the primary is unknown, DO NOT perform internal fixation. You must stage and biopsy first. An inappropriate nail can upstage a sarcoma to Stage IV or necessitate amputation.
Vascular Tumors
Renal & Thyroid: These metastases are significantly vascular. Pre-operative embolization is mandatory to prevent exsanguination on the table.
Mirels Score
Know it cold: Site, Pain, Lesion Type, Size. This is the gold standard answer for "When to operate prophylactically".
Whole Bone Fixation
Span the Bone: Disease can progress elsewhere. Use a long IM nail or long plate to protect the entire humerus, not just the lesion.
At a Glance - Management Decision
| Mirels Score | Fracture Status | Primary Known | Treatment |
|---|---|---|---|
| Score less than 7 | None (Impending) | Yes | Radiotherapy |
| Score greater than 9 | Impending | Yes | Prophylactic Nail/Plate |
| Fractured | Complete | Yes | Acute Fixation + Post-op RT |
| Any | Any | NO (Unknown) | Workup first (Biopsy) |
BLT-KPCommon Bone Metastases
| B | Breast Lytic/Blastic mixed |
| L | Lung Lytic |
| T | Thyroid Lytic (Vascular) |
| K | Kidney (Renal) Lytic (Vascular) |
| P | Prostate Blastic |
| B | Breast Lytic/Blastic mixed | K | Kidney (Renal) Lytic (Vascular) |
| L | Lung Lytic | P | Prostate Blastic |
| T | Thyroid Lytic (Vascular) |
Hook:BLT with a Kosher Pickle for lunch.
SPLSMirels Score Components
| S | Site Upper limb score 1, Lower limb score 2, Peritrochanteric score 3 |
| P | Pain Mild, Moderate, Functional |
| L | Lesion Blastic, Mixed, Lytic |
| S | Size Less than 1/3, 1/3-2/3, Greater than 2/3 diameter |
| S | Site Upper limb score 1, Lower limb score 2, Peritrochanteric score 3 | L | Lesion Blastic, Mixed, Lytic |
| P | Pain Mild, Moderate, Functional | S | Size Less than 1/3, 1/3-2/3, Greater than 2/3 diameter |
Hook:Some People Like Statistics.
CRABMultiple Myeloma Features
| C | Calcium elevation Hypercalcemia |
| R | Renal insufficiency High creatinine |
| A | Anemia Normocytic anemia |
| B | Bone lesions Lytic lesions (Raindrop skull) |
| C | Calcium elevation Hypercalcemia | A | Anemia Normocytic anemia |
| R | Renal insufficiency High creatinine | B | Bone lesions Lytic lesions (Raindrop skull) |
Hook:Beware the CRAB in patients over 40 with back pain.
Overview
Pathological fractures of the humerus occur when bone weakened by disease (cystic, metabolic, or neoplastic) fails under physiological loads. In adults over 40, metastatic disease and myeloma are the overwhelming causes. The humerus is the second most common site for long bone metastases (after femur).
Epidemiology
Incidence:
- Bone is the 3rd most common site of metastatic disease.
- Humerus involvement: 20% of bone mets.
- Increasing due to improved cancer survival rates.
Prognosis
Survival (Median):
- Prostate/Breast: Years (24-36 months).
- Renal/Thyroid: Intermediate (12 months).
- Lung: Short (less than 6 months).
- Fixation must be durable enough for expected survival.
Anatomy and Pathophysiology
Pathophysiology of Metastasis
Hematogenous Spread:
- Tumor emboli deposit in vascular marrow (Red marrow).
- Batson's Plexus (low pressure venous system) facilitates spread.
- Cytokines (RANKL/PTHrP) stimulate osteoclasts.
Osteolytic vs Osteoblastic:
- Lytic: Lung, Renal, Thyroid, Breast (mixed), Myeloma. Bone destruction leads to Fracture.
- Blastic: Prostate, Breast (mixed). Bone formation leads to Brittle bone.
Lytic lesions are more prone to fracture and harder to fix.
Classification
Mirels Scoring System
Used to predict fracture risk in impending pathological fractures.
| Variable | Score 1 | Score 2 | Score 3 |
|---|---|---|---|
| Site | Upper Limb | Lower Limb | Peritrochanteric |
| Pain | Mild | Moderate | Functional |
| Lesion | Blastic | Mixed | Lytic |
| Size | Less than 1/3 | 1/3 - 2/3 | Greater than 2/3 |
Score Calculation: Sum of all 4 variables. Minimum 4, Maximum 12.
Mirels Interpretation
| Total Score | Fracture Risk | Recommendation |
|---|---|---|
| Less than or equal to 7 | 0-4% | Radiotherapy / Observation |
| 8 | 15% | Clinical Judgement |
| Greater than or equal to 9 | 33% | Prophylactic Fixation |
Clinical Pearl
Mirels score applies to metastatic disease in long bones. It does NOT apply to primary bone tumors or spinal metastases.
History
Key Questions:
- Known history of cancer?
- Constitutional symptoms: Weight loss, night sweat, fatigue.
- Pain history: Mechanical ( fracture) vs Biological (night pain).
- Functional demand.
Night pain typically indicates active tumor.
Examination
Inspection:
- Soft tissue mass? (Sarcoma concern).
- Previous mastectomy scars?
- Thyroid enlargement?
Neurovascular:
- Radial nerve commonly involved in humeral shaft fractures.
- Check Lymph nodes (Axillary/Supraclavicular).
Examination focuses on finding a primary source.
Investigations
Imaging & Staging
X-ray:
- "Moth-eaten" or "Permeative" appearance.
- Cortical destruction.
- Pathological fracture (transverse, minimal trauma).
CT Scan:
- Chest/Abdomen/Pelvis (Staging).
- Defines bone stick remaining.
Bone Scan / PET:
- Identifies other skeletal metastases.
- Solitary vs Multiple (Prognostic).
Complete staging is mandatory.
Management Algorithm
Treatment Decision Making
Indications:
- Low Mirels score (less than 8).
- Terminally ill (Life expectancy less than 6 weeks).
- Non-displaced fracture in severe comorbidities.
- Radiosensitive tumor (Myeloma/Lymphoma/Small Cell Lung).
Treatment:
- Radiotherapy (RT).
- Functional bracing.
- Bisphosphonates.
Pain relief is the primary goal.
Surgical Technique
Fixation Strategy
Standard for Diaphysis:
- Load sharing device.
- Prophylactic or Acute.
- Reaming: Careful! Can spread tumor or cause fat embolism.
- Locking: Static locking (proximal and distal). Or Cement screw augmentation.
Advantages: Minimally invasive, preserves soft tissue, immediate stability.
Complications
Potential Complications
Tumor Progression
Local Recurrence: If RT is not given post-op, tumor continues to grow and destroys fixation. Hardware failure is inevitable if patient survives long enough.
Bleeding
Intra-operative Hemorrhage: Especially Renal Cell/Thyroid. Embolize pre-op!
Non-union
Radiation Effect: RT inhibits bone healing. Pathological fractures often rely on the hardware for life (union is not guaranteed).
Embolism
Fat/Tumor Embolism: Reaming increases intramedullary pressure. Vent the canal or use unreamed nails in high-risk pulmonary patients.
Postoperative Care
Rehabilitation Protocol
- Sling for comfort.
- Immediate use: Construct should allow weight bearing (as tolerated).
- No restrictions usually (construct must be strictly stable).
- Radiotherapy planning begins (once wound dry).
- Bisphosphonate therapy (Zoledronic acid / Denosumab).
- Surveillance for hardware failure.
- Systemic therapy for underlying disease.
Outcomes
Prognosis
- Pain Relief: Excellent (80-90% improvement) after fixation.
- Function: Restoration of ability to feed/groom.
- Ambulatory: Upper limb fixation allows use of walking aids.
- Hardware Failure: 5-10%, usually due to disease progression or long survival.
Evidence Base
Key Studies
Mirels - Scoring System for Impending Fractures
- Retrospective analysis of 78 irradiated metastatic long-bone lesions (27 fractured, 51 did not)
- Four weighted variables: site, pain, lesion type, size (range 4-12)
- Mean score 7 in non-fracture group vs 10 in fracture group; risk rises progressively above 7
- Lesions scoring 7 or lower safely irradiated; 8 or higher recommended for prophylactic fixation
Capanna & Campanacci - Appendicular Metastasis Treatment
- Comprehensive framework for surgical treatment of appendicular skeletal metastases
- Stratifies fixation by life expectancy and solitary vs multiple disease
- Promotes durable load-bearing constructs (cement augmentation, endoprosthesis) over biological union
- Solitary metastasis from favourable primaries (renal, thyroid) considered for wide resection
Katagiri et al. - Prognostic Scoring
- 350 patients with skeletal metastases; Cox model identified 5 survival factors
- Factors: primary site, poor performance status (ECOG 3-4), visceral/cerebral mets, prior chemotherapy, multiple bone mets
- Score 6 or more: 31% survival at 6 months, 11% at 1 year; score 2 or less: 98% at 6 months, 89% at 1 year
- Guides choice between simple palliative fixation and durable reconstruction
Patchell et al. - Surgery + Radiation vs Radiation
- Randomised trial (n=101) in metastatic spinal cord compression; principle applies to mechanical instability generally
- Surgery plus RT vs RT alone: 84% vs 57% able to walk after treatment (OR 6.2, p=0.001)
- Surgery group retained ambulation far longer (median 122 vs 13 days) and needed fewer steroids/opioids
- Trial stopped early at interim analysis for surgical superiority
Harrington - Criteria for Prophylactic Fixation
- Established the classic indications for prophylactic fixation of lytic metastatic lesions
- Lesion 2.5 cm or larger in size
- Destruction of 50% or more of the cortex
- Persistent local pain with loading despite adequate radiotherapy
Arpornsuksant et al. - Local Progression After IM Nailing
- 122 patients with long-bone metastases (humerus 27%) treated by intramedullary nail
- Cumulative local tumour progression only 4.9% at 12 months; reoperation in 2%
- Renal cell carcinoma (OR 5.1) and older age were the only factors linked to progression
- No survival difference between those with and without local progression
Viva Scenarios
Use these scenarios to practise clinical reasoning and management decisions
"You are called to ED for a 60-year-old male with a solitary lytic lesion of the humerus and a fracture. He has no history of cancer. What is your plan?"
"Describe the Mirels Score and how you use it."
"How do you manage a pathological humerus fracture from Renal Cell Carcinoma?"
MCQ Practice
Self-Assessment Questions
Q1: Mirels Score
Q: Which factor is weighted most heavily (highest score) in the Mirels scoring system for "Site"?
- A) Humerus
- B) Radius
- C) Femoral Shaft
- D) Peritrochanteric region
- E) Tibia
A: D - The Peritrochanteric region is assigned a score of 3 due to the high biomechanical loads and consequences of failure. Upper limb is 1, Lower limb (shaft) is 2.
Q2: Primary Source
Q: What is the most common source of bone metastasis in women?
- A) Lung
- B) Thyroid
- C) Breast
- D) Kidney
- E) Cervix
A: C - Breast cancer is the most common source of bone metastases in women (about 70%). Prostate is most common in men.
Q3: Vascularity
Q: Which primary tumor gives rise to highly vascular bone metastases requiring pre-operative embolization?
- A) Breast
- B) Prostate
- C) Renal Cell Carcinoma
- D) Lung
- E) Melanoma
A: C - Renal Cell and Thyroid carcinomas are classically highly vascular. Pre-operative embolization is recommended to control bleeding.
Q4: Prophylaxis Threshold
Q: A Mirels score of 10 indicates:
- A) Low risk of fracture (less than 4%)
- B) Moderate risk, Observation indicated
- C) High risk, Prophylactic fixation indicated
- D) Imminent death
- E) Need for amputation
A: C - A score of 9 or greater indicates a high risk of fracture (greater than 33%) and is the threshold for recommending prophylactic fixation.
Q5: Contraindication
Q: Internal fixation of a pathological fracture is potentially contraindicated if:
- A) The patient has multiple metastases
- B) The primary tumor is unknown (solitary lesion)
- C) The Mirels score is 12
- D) The fracture is displaced
- E) The patient is on bisphosphonate therapy
A: B - If the primary is unknown and the lesion is solitary, internal fixation (nailing) is contraindicated until a primary bone sarcoma is ruled out via biopsy/staging, to avoid compartment contamination.
Differential Diagnosis
A destructive humeral lesion in an adult is metastasis or myeloma until proven otherwise, but the differential changes dramatically with age and imaging. Distinguishing these before any fixation is the single most important decision.
Differential Diagnosis of a Destructive Humeral Lesion
| Diagnosis | Typical Age | Imaging Clue | Key Discriminator |
|---|---|---|---|
| Metastasis | Over 40 | Multiple lytic/mixed lesions, moth-eaten | Known primary or constitutional symptoms |
| Multiple myeloma | Over 50 | Punched-out lytic lesions, cold on bone scan | Positive SPEP/free light chains, CRAB features |
| Primary bone sarcoma | Under 30 (or any age) | Aggressive periosteal reaction, soft-tissue mass | Solitary aggressive lesion, no primary on staging |
| Lymphoma of bone | Any | Permeative lesion, large soft-tissue component | Tissue diagnosis; often radiosensitive |
| Benign lesion (UBC, enchondroma, fibrous dysplasia) | Under 30 | Well-defined, non-aggressive margin | No cortical breach, no soft-tissue mass |
Clinical Pearl
The decisive distinction is metastasis/myeloma (fix it) versus primary bone sarcoma (do NOT touch it without an oncology MDT). When the primary is unknown, treat every solitary lesion as a potential sarcoma until staging and biopsy say otherwise.
Controversies & Areas of Uncertainty
Mirels Threshold
Mirels has high sensitivity but low specificity, so a score of 9 or more over-predicts fracture and may lead to over-treatment. A score of 8 remains a clinical-judgement grey zone where functional demand and prognosis drive the decision.
Nail vs Plate-and-Cement
No randomised data favours intramedullary nailing over locked plating with cement augmentation for the humeral shaft. Nail protects the whole bone; plate allows debulking and direct lesion control. Choice is lesion-location and surgeon dependent.
Reaming and Embolism
Whether to ream remains debated. Reaming improves nail fit but raises intramedullary pressure and theoretical tumour/fat embolism risk; many advocate venting or unreamed nails in patients with poor pulmonary reserve.
Solitary Renal/Thyroid Met
For a solitary metastasis from a favourable primary, the balance between palliative fixation and wide resection with endoprosthetic reconstruction is unsettled and should be an oncology MDT decision based on prognosis.
Guidelines, Registries & Global Practice
Global epidemiology: Bone is the third most common site of metastatic disease after lung and liver, and the humerus is the second most common long bone affected after the femur (around 20% of long-bone metastases). Breast, lung, thyroid, renal and prostate cancers account for the overwhelming majority. Rising cancer survival worldwide is increasing the absolute burden of skeletal metastases.
Society Guidance, Side by Side
| Body | Position on Metastatic Bone Disease |
|---|---|
| AAOS / MSTS (US) | Endorse Mirels and Harrington criteria; durable fixation that spans the bone, with postoperative radiotherapy to the whole implant |
| BOA / BOOS (UK) | British Orthopaedic Oncology Society guidance: discuss all suspected bone tumours with a specialist centre before fixation; biopsy unknown primaries first |
| NICE (UK) | Metastatic spinal cord compression pathway emphasises urgent imaging and surgery for instability (mirrors Patchell principle) |
| AO Foundation | Load-sharing intramedullary fixation or cement-augmented plating; whole-bone protection |
| EFORT / EMSOS (Europe) | Multidisciplinary tumour board, prognosis-adapted reconstruction (simple fixation vs endoprosthesis) |
Registry and survival data: National sarcoma and bone-tumour registries (e.g. EMSOS in Europe) and arthroplasty registries (NJR, AOANJRR) track endoprosthetic survival for proximal humeral replacement. Implant survival is generally limited by patient survival rather than mechanical failure in this palliative population.
High- vs limited-resource practice variation:
- Well-resourced settings: Routine pre-operative embolisation for renal/thyroid metastases, ready access to modular endoprostheses, denosumab/zoledronic acid, and same-admission radiotherapy planning.
- Limited-resource settings: Reliance on conventional nails and bone cement; embolisation and endoprostheses may be unavailable, shifting practice toward plate-and-cement constructs and external bracing; antiresorptive therapy access is variable.
A universal principle across all settings: never fix a destructive bone lesion of unknown origin without staging and, where indicated, biopsy.
Pathological Fractures - Exam Quick Reference
Clinical summary
Key Facts
- •Causes: Breast, Lung, Thyroid, Kidney, Prostate
- •Threshold: Mirels score greater than 9
- •Trap: Solitary lesion (Unknown primary) = STOP
- •Vascular: Renal/Thyroid (Embolize)
- •Fixation: Durable (Nail or Cemented Plate)
- •Survival: Fixation must last longer than the patient
Mirels Score (SPLS)
- •Site (Upper/Lower/Troch)
- •Pain (Mild/Mod/Func)
- •Lesion (Blastic/Mixed/Lytic)
- •Size (less than 1/3, 1/3-2/3, greater than 2/3)
Surgical Steps
- •Positioning (Beach chair/Supine)
- •Approach (Deltopectoral/Split)
- •Biopsy (If needed, frozen section)
- •Reaming (Gentle/Unreamed if pulmonary risk)
- •Nail Insertion (Span whole bone)
- •Cement Augmentation (If proximal/distal voids)
- •Closure (Layered)
Common Pitfalls
- •Nailing a primary sarcoma
- •Missing hypercalcemia
- •Underestimating bleeding in Renal mets
- •Inadequate fixation length (Must span bone)
- •Ignoring radial nerve in percutaneous nailing
Examiner Favorites
- •Calculate Mirels for this X-ray...
- •Workup of solitary lesion
- •Role of radiotherapy vs surgery
- •Mechanism of bisphosphonates
- •What to do if fixation fails?