Atypical femoral fracture

Definition

Atypical femoral fractures are rare stress fractures that occur in the subtrochanteric or diaphyseal region of the femur, most often on the lateral cortex.

They are associated with minimal or no trauma and often linked to long-term bisphosphonate use or other bone metabolism disorders.

Source: American Society for Bone and Mineral Research (ASBMR) Criteria

ASBMR Diagnostic Criteria (Major & Minor)

To diagnose AFF, 4 out of 5 major features should be present.

Major Features

  1. Minimal or no trauma (e.g., fall from standing height or less)
  2. Fracture originates at the lateral cortex; may be transverse or short oblique
  3. Complete fracture involves both cortices, may have medial spike
    • Incomplete fracture involves only the lateral cortex
  4. Non- or minimally comminuted fracture
  5. Localized periosteal or endosteal thickening (“beaking” or “flaring”) of the lateral cortex

Minor Features

(Not required for diagnosis but often associated)

  • Bilateral fractures and symptoms
  • Delayed healing
  • Comorbidities or medication use

History & Risk Factors

  1. Comorbidities
    • Collagen diseases (e.g., Rheumatoid arthritis)
    • Chronic obstructive pulmonary disease (COPD)
  2. Nutritional Deficiency
    • Low calcium or Vitamin D levels
  3. Medications
    • Bisphosphonates (long-term use)
    • PPIs
    • Glucocorticoids

Investigations

  1. X-ray:
    • Shows focal cortical thickening at the lateral cortex
    • Transverse fracture pattern
  2. MRI / Bone Scan:
    • Detects stress reaction or incomplete fractures
  3. DEXA Scan:
    • Evaluate bone mineral density
  4. Biochemical Work-up:
    • Serum calcium, phosphate, Vitamin D, PTH, and bone turnover markers

Pathophysiology

  1. Reduced bone turnover (due to bisphosphonate suppression of osteoclast activity)
  2. Low bone geometry adaptation (increased tensile stress at lateral cortex)
  3. Other contributing factors:
    • Mechanical stress
    • Drugs
    • Comorbidities

Clinical Features

Type Pain Fracture Type Progression
Complete Pain present Transverse Non-comminuted
Incomplete Pain may be present Lateral cortex only May progress to complete fracture

Symptoms

  • Dull aching pain in thigh or groin
  • Often bilateral
  • May precede fracture by weeks to months

Management

Non-Operative (Incomplete Fracture without pain)

  • Discontinue bisphosphonate therapy
  • Start Calcium and Vitamin D supplementation
  • Teriparatide (Parathyroid hormone analog) for bone remodeling
  • Protected weight-bearing or rest

Operative Management

  • Intramedullary (IM) nailing: preferred for complete or painful incomplete fractures
    • Provides full-length protection of femur
  • Complications:
    • Hardware failure
    • Delayed or non-union
  • Plating: reserved for cases with very narrow femoral canal or poor bone stock

Approach

Clinical Scenarios

Finding Pain Management
No fracture (stress reaction) Present Rest, vitamin D, stop bisphosphonate
Incomplete fracture Painful Prophylactic IM nailing
Complete fracture Painful IM nail fixation

Oh et al. (Japan):

Summary Points

  • AFF = Atypical, low-energy, lateral cortical stress fracture
  • Common in long-term bisphosphonate users
  • ASBMR: 4 of 5 major criteria required for diagnosis
  • Management: Stop bisphosphonate, supplement Ca + Vit D, consider IM nail
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