Atypical femoral fracture
Definition
- Insufficiency fracture of femoral shaft or subtrochanteric region
- Strongly associated with long-term Bisphosphonates or other potent antiresorptive therapy
- Diagnostic criteria are according to the ASBMR task force
Major Criteria (radiographic; typically ≥4 of 5)
- Location: Femur subtrochanteric or diaphyseal (shaft) region
- Pattern: Transverse or short oblique fracture
- Trauma: Occurs with minimal or no trauma
- Fracture morphology: Simple (no/minimal comminution)
- Complete fractures often have a medial spike
Minor Criteria (supportive)
- Cortical thickening/beaking (especially lateral cortex)
- Periosteal reaction of the lateral cortex
- Prior prolonged aching pain (prodrome)
- Bilateral involvement or delayed healing
- Drug history: bisphosphonates or other antiresorptives, chronic steroids, PPIs
Clinical Points
- Dull thigh/groin pain may precede fracture (prodrome)
- Commonly delayed union or non-union
- Review and usually stop bisphosphonate (or other antiresorptive) therapy if AFF is diagnosed
- Early surgical fixation even for incomplete fractures (usually prophylactic for contralateral site)
Differential diagnosis
| Differential | Typical Location | Clinical Context | Fracture Pattern | Key Distinguishing Features |
|---|---|---|---|---|
| Osteoporotic Fracture | Femoral neck, intertrochanteric | Elderly, fall/low trauma | Comminuted, spiral/oblique | Not diaphyseal/subtrochanteric; comminuted |
| Femoral shaft stress fracture | Shaft (often medial/compressive cortex) | Athletes, overuse | Incomplete, variable | Medial cortex; No long term history of antiresorptive |
| Pathological fracture | Any location | Primary bone tumour, metastasis, infection | Any (often destructive without clear fracture line) | Lytic/blastic lesion, mass, abnormal marrow |
| Traumatic Fracture | Any femoral region | High-energy trauma | Comminuted, segmental | Clear history of significant trauma |
| Other Metabolic Bone Disease | Variable | Osteomalacia, Paget disease, HPT | Variable | Lab/radiology findings of metabolic disease |
Checklist
- Look for lateral cortical beaking/thickening (may precede fracture)
- Incomplete (“crack”/stress reaction) or complete fractures
- Simple, non-comminuted fracture
- Always check both femurs
Caution
- Don’t overcall AFF: Reserve this diagnosis for cases meeting the major criteria, typically in the setting of long-term bisphosphonate or other antiresorptive therapy.
- Don’t miss a tumour: If radiological pattern or clinical course is atypical, investigate for underlying lesion.
