A 4-year-old boy from a resource-limited setting presents with widening of wrists and ankles, cupping and fraying of the metaphyses on X-ray, and a 'rachitic rosary' on chest examination. Serum calcium is low-normal, phosphate is low, and alkaline phosphatase is markedly elevated. Which pathological process is the primary defect?
- A Excessive osteoclastic resorption of trabecular bone
- B Excessive deposition of unmineralized osteoid in mature bone
- C Failure of mineralization of cartilage and osteoid at the growth plate ✓
- D Fibrovascular replacement of normal marrow
Correct answer: C. Failure of mineralization of cartilage and osteoid at the growth plate
Explanation
Rickets is a childhood disorder of failed mineralization of the growth plate (epiphyseal cartilage), leading to widened, cupped, frayed metaphyses. Osteomalacia is the adult counterpart involving unmineralized osteoid in mature bone. Excessive osteoclastic resorption describes Paget's lytic phase. Fibrovascular marrow replacement is seen in osteonecrosis or Camurati-Engelmann disease.
Reference: Robbins and Cotran Pathologic Basis of Disease, 10th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.