A patient on long-term bisphosphonate therapy (8 years for osteoporosis) develops sudden bilateral thigh pain after minimal exertion. Radiographs show bilateral focal lateral cortical thickening (beaking) of the subtrochanteric femoral shaft. The diagnosis is:

• A Atypical subtrochanteric femoral fracture (atypical femur fracture — AFF) related to bisphosphonate use ✓
• B Paget's disease of bone causing bowing fractures
• C Metastatic deposits from an occult primary
• D Stress fractures from osteomalacia due to bisphosphonate-induced vitamin D impairment

Explanation

Atypical femur fractures (AFF) are a rare but serious complication of long-term bisphosphonate use (typically > 3–5 years). They are transverse (not spiral) fractures at the subtrochanteric or femoral shaft region, preceded by prodromal bilateral thigh or groin pain, and show characteristic lateral cortical thickening (beaking or flaring) on radiograph. The mechanism involves over-suppression of bone remodelling, preventing repair of accumulated microfractures. Management includes stopping bisphosphonates, teriparatide consideration, and prophylactic IMN for prodromal cases.

Reference: Maheshwari Essential Orthopaedics, 6th ed.

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Written and medically reviewed by the StethoPrep medical team.