Atypical Femoral Fracture
CIM Case: Atypical Femoral Fracture
Clinical Scenario
Patient: 72-year-old woman Presentation: Fall from standing while walking, sudden right thigh pain and inability to weight-bear Relevant history: Postmenopausal osteoporosis on alendronate for 8 years, left thigh aching for past 4 months (intermittent, worse with walking), rheumatoid arthritis on low-dose prednisolone, previous vertebral compression fractures (T11, L1), vitamin D deficiency (treated) Examination findings:
- BMI 22, thin habitus
- Right leg shortened and externally rotated
- Tenderness at mid-thigh level
- Unable to perform straight leg raise
- Neurovascularly intact distally
- Left thigh: tenderness over lateral mid-femur on palpation
- No wounds or bruising
- Kyphotic thoracic spine
Investigations Provided
Laboratory Results
| Test | Result | Normal Range | Interpretation |
|---|---|---|---|
| Hb | 118 g/L | 115-155 g/L | Normal |
| WCC | 7.2 ×10⁹/L | 4-11 ×10⁹/L | Normal |
| Platelets | 245 ×10⁹/L | 150-400 ×10⁹/L | Normal |
| CRP | 8 mg/L | <5 mg/L | Mildly elevated |
| Calcium | 2.35 mmol/L | 2.2-2.6 mmol/L | Normal |
| Phosphate | 1.1 mmol/L | 0.8-1.5 mmol/L | Normal |
| ALP | 95 U/L | 30-120 U/L | Normal |
| Vitamin D | 65 nmol/L | >50 nmol/L | Adequate (supplemented) |
| PTH | 4.5 pmol/L | 1.5-6.5 pmol/L | Normal |
| Creatinine | 82 μmol/L | 45-90 μmol/L | Normal |
| eGFR | 68 mL/min | >60 | Mildly reduced |
Imaging
Image 1: AP and Lateral Radiographs of Right Femur
Radiological features:
- Transverse fracture through lateral cortex of femoral diaphysis
- Located distal to lesser trochanter, proximal to supracondylar flare
- Non-comminuted (simple fracture pattern)
- Short oblique component
- Focal lateral cortical thickening ("beaking") at fracture site
- Medial spike (characteristic morphology)
- Generalised cortical thickening of diaphysis
- No periosteal reaction beyond immediate fracture site
Image 2: Full-Length Bilateral Femur X-rays
Findings:
- Right: Complete atypical femoral fracture as described
- Left: Lateral cortical thickening ("dreaded black line") at mid-diaphysis
- Localised periosteal reaction over lateral cortex
- Incomplete stress fracture (lateral cortex only)
- No complete fracture
Questions & Model Answers
What is the diagnosis and what criteria define it?
What is the association with bisphosphonates and what is the mechanism?
Describe your initial management of this patient.
Describe your operative technique for this fracture.
How do you manage the contralateral incomplete fracture?
What are the expected outcomes and long-term considerations?
Key Teaching Points
Pattern Recognition
This pattern suggests Atypical Femoral Fracture:
- Postmenopausal woman on long-term bisphosphonate (>5 years)
- Minimal trauma mechanism (standing fall)
- Subtrochanteric or diaphyseal location
- Transverse/short oblique pattern (NOT spiral)
- Lateral cortical beaking on X-ray
- Prodromal thigh pain (may have had for weeks/months)
Distinguishing from Typical Osteoporotic Fracture:
| Feature | Atypical | Typical |
|---|---|---|
| Location | Subtrochanteric/diaphyseal | Femoral neck, intertrochanteric |
| Pattern | Transverse, non-comminuted | Variable, often comminuted |
| Lateral cortex | Beaking, thickening | Normal |
| Prodromal pain | Common (weeks-months) | Rare |
| Healing | Delayed | Usually uneventful |
Critical Management Points
- Full-length bilateral X-rays - 30-40% have contralateral involvement
- Stop bisphosphonate - but continue calcium and vitamin D
- Long cephalomedullary nail - never short nails
- Expect delayed union - warn patient, consider teriparatide
- Prophylactic fixation - for symptomatic incomplete fractures
- MDT involvement - orthopaedics, endocrinology, fracture liaison
Common Examiner Follow-ups
Q: "What is the 'dreaded black line'?"
The dreaded black line refers to the radiolucent line visible on the lateral cortex of the femur in incomplete atypical femoral fractures. It represents the stress fracture propagating through cortical bone. Its presence indicates high risk of progression to complete fracture and is an indication for prophylactic nailing if symptomatic.
Q: "Should all patients on bisphosphonates have a drug holiday?"
Drug holiday considerations:
- After 5 years of oral bisphosphonate (or 3 years IV)
- For patients at moderate fracture risk
- Continue in high-risk patients (previous fragility fracture, very low BMD)
- Monitor during holiday with DEXA and bone turnover markers
- Resume if fracture risk increases
Current guidelines (ASBMR 2016, NICE 2017):
- Individualise based on fracture risk
- Benefits of treatment generally outweigh risks of atypical fracture
- Reassess after 3-5 years of treatment
Q: "What is the role of teriparatide?"
Teriparatide (recombinant PTH 1-34):
- Anabolic agent - stimulates bone formation
- May promote healing of atypical fractures
- Duration: 24 months maximum (lifetime)
- Contraindicated if prior radiation, Paget's, hypercalcaemia
- Expensive, requires daily injection
- Consider for incomplete fractures or delayed union
Evidence: Case series suggest improved healing, but no RCTs specifically for atypical fractures.
Q: "How do you counsel a patient who presents with prodromal thigh pain on long-term bisphosphonate?"
Counselling approach:
- Explain concern for stress reaction/incomplete fracture
- Order full-length bilateral femur X-rays
- If positive: discuss prophylactic fixation vs observation
- If negative: consider MRI if high clinical suspicion
- Stop bisphosphonate
- Modify activity (avoid high-impact exercise)
- Ensure adequate calcium, vitamin D
- Follow up in 4-6 weeks with repeat imaging
Related Topics
- Osteoporosis Management
- Bisphosphonate Therapy
- Subtrochanteric Fractures
- Femoral Shaft Fractures
- Intramedullary Nailing Techniques
- Pathological Fractures