A 65-year-old on long-term bisphosphonate therapy (alendronate for 8 years) presents with sudden onset thigh pain after minimal trauma. X-ray shows a complete subtrochanteric femoral fracture with a horizontal fracture line and lateral cortical beaking. Which fracture type is this, and what is the mechanism?
- A Pathological fracture due to metastatic bone disease — bisphosphonates increase cancer risk
- B Standard subtrochanteric stress fracture from high-impact activity
- C Atypical femoral fracture (AFF) caused by suppression of bone remodeling leading to microdamage accumulation and stress fracture ✓
- D Bisphosphonate-induced osteonecrosis of the femur shaft
Explanation
Atypical femoral fractures (AFF) are a recognized complication of long-term bisphosphonate use (>3-5 years). Bisphosphonates suppress osteoclast-mediated bone remodeling; without turnover, microdamage accumulates in cortical bone, especially in the lateral (tension) cortex of the subtrochanteric region. Characteristics of AFF: subtrochanteric or femoral shaft location, transverse/oblique fracture line <30°, lateral cortical beaking/flaring, medial spike, minimal/no comminution, bilateral involvement in 25-50%. Prodromal thigh/groin pain is common. Management includes IM nailing. Bisphosphonates should be discontinued ('drug holiday') in established AFF.
Reference: Maheshwari Essential Orthopaedics, 6th ed.
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