A fracture treated with rigid internal fixation using compression plating unites without any visible callus on serial radiographs. Which process best explains this pattern of union?

• A Endochondral ossification through a fibrocartilaginous callus
• B Chondrocyte proliferation followed by calcified cartilage formation
• C Intramembranous ossification within an abundant haematoma
• D Direct osteonal remodelling across the fracture by cutting cones ✓

Explanation

Rigid compression fixation eliminates interfragmentary motion and strain, so secondary callus does not form. Healing occurs by primary or direct cortical union, where cutting cones of osteoclasts tunnel across the fracture line followed by osteoblastic new lamellar bone deposition in Haversian systems. The distractor describing endochondral ossification is the hallmark of secondary healing, which requires some micromotion and occurs with casts, nails and bridge plates.

Reference: Robbins and Cotran Pathologic Basis of Disease, 10th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

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