In a bone biopsy taken from a patient with Paget's disease, the histological hallmark is disorganized bone with irregular cement lines creating a 'mosaic' or 'jigsaw puzzle' pattern. This pattern indicates repeated cycles of which two processes?

• A Endochondral and intramembranous ossification occurring simultaneously
• B Periosteal apposition and haversian remodeling in alternating phases
• C Marrow fibrosis and woven bone formation
• D Osteoclastic resorption followed by disorganized osteoblastic bone formation at the same site ✓

Explanation

In Paget's disease, the primary histological abnormality is markedly increased and disorganized bone turnover. Giant osteoclasts (with up to 100 nuclei) rapidly resorb bone, followed immediately by equally rapid but disorganized osteoblastic bone formation that lays down woven (rather than lamellar) bone. Each cycle of resorption and formation leaves an irregular cement line (basophilic reversal line). Repeated cycles at overlapping sites produce the characteristic 'mosaic' pattern — irregular fragments of lamellar bone separated by numerous cement lines, resembling a jigsaw puzzle. This woven bone is structurally weak, prone to fracture, and enlarges, accounting for the bowing deformities.

Reference: BD Chaurasia's Human Anatomy, 8th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.