Which of the following features is characteristic of primary (direct) cortical bone healing rather than secondary (callus) healing?

• A Formation of abundant external periosteal callus visible on radiograph
• B Direct haversian remodelling by osteoclastic cutting cones crossing the fracture gap ✓
• C Healing through endochondral ossification of a cartilaginous template
• D Requires controlled micromotion at the fracture site

Explanation

Primary bone healing occurs when the fracture is anatomically reduced and fixed with absolute stability, eliminating interfragmentary motion. Osteoclastic cutting cones tunnel directly across the fracture, followed by angiogenesis and osteoblastic deposition of new haversian systems, with no visible callus. External callus formation, cartilage formation, and endochondral ossification are hallmarks of secondary healing, which requires some interfragmentary micromotion and occurs under relative stability such as a nail or bridge plate.

Reference: AO Principles of Fracture Management, 3rd ed.

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Written and medically reviewed by the StethoPrep medical team.