Looser's zones (pseudofractures) seen on X-ray in osteomalacia are pathologically caused by:
- A Periosteal thickening over stress fractures
- B Osteoclastic resorption lacunae at tendon insertions
- C Microfractures at nutrient artery entry points with accumulation of unmineralised osteoid ✓
- D Subperiosteal resorption by excess parathyroid hormone
Correct answer: C. Microfractures at nutrient artery entry points with accumulation of unmineralised osteoid
Explanation
Looser's zones (Milkman's fractures) are radiolucent bands perpendicular to the cortex, typically bilateral and symmetrical, seen at nutrient artery entry points. Histologically, they represent accumulation of unmineralised osteoid filling microstress fractures — the unmineralised osteoid cannot mineralise due to deficient calcium/phosphate substrate. They are found at the medial femoral neck, pubic rami, ribs, scapular axillary border, and proximal ulna. They are pathognomonic of osteomalacia/rickets and distinguish it from osteoporosis (normal bone matrix, reduced quantity).
Reference: Maheshwari Essential Orthopaedics, 6th ed.
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