A 52-year-old woman on long-term bisphosphonate therapy presents with a low-energy subtrochanteric femur fracture. X-ray shows cortical thickening of the lateral femoral cortex with a simple transverse or oblique fracture line. The most accurate diagnosis is:

• A Pathological fracture from metastatic disease
• B Stress fracture from repetitive loading in an osteopenic femur
• C Paget's disease–related bowing fracture
• D Atypical femoral fracture (AFF) due to bisphosphonate-associated over-suppression of bone turnover ✓

Explanation

Atypical femoral fractures are a recognized adverse effect of prolonged bisphosphonate use, caused by suppression of bone remodeling leading to accumulation of micro-damage. The radiological hallmark is lateral cortical thickening ('beaking') with a transverse or short oblique fracture line in the subtrochanteric or diaphyseal femur. Metastatic lesions show lytic or mixed lesions without cortical thickening. Stress fractures lack cortical beaking. Paget's typically shows cortical thickening with bowing but different radiological pattern.

Reference: Maheshwari Essential Orthopaedics, 6th ed.

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Written and medically reviewed by the StethoPrep medical team.