A bone biopsy from a patient with Paget's disease shows large, irregularly shaped osteoclasts with many nuclei (up to 100) and a chaotic 'mosaic' pattern of cement lines on histology. The cement lines in normal lamellar bone are composed primarily of:
- A Osteopontin-rich calcified matrix marking the reversal line between bone resorption and deposition ✓
- B Mineralised collagen type I fibres running circumferentially
- C Non-mineralised osteoid awaiting mineralisation
- D Fibronectin bridges connecting adjacent osteons
Correct answer: A. Osteopontin-rich calcified matrix marking the reversal line between bone resorption and deposition
Explanation
Cement (reversal) lines are hypermineralised boundaries between adjacent osteons or between zones of bone resorption and new bone deposition. They are rich in non-collagenous matrix proteins, particularly osteopontin and osteonectin, with relatively little collagen. In Paget's disease the disorganised remodelling cycles produce a jigsaw 'mosaic' pattern of cement lines that is pathognomonic. In normal lamellar bone, these lines delineate the outer limit of each osteon and act as stress-absorption boundaries.
Reference: BD Chaurasia's Human Anatomy, 8th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.