A femoral shaft fracture is fixed with a compression plate applied with lag screws across the fracture, achieving rigid interfragmentary compression. Serial radiographs show union with virtually no external callus. This pattern of healing occurs because:

• A Periosteal blood supply is destroyed by the plate, so callus cannot form
• B The plate shields the fracture from mechanical stimuli, so healing proceeds through fibrous tissue instead of callus
• C Strain at the fracture site is so low that bone forms directly by osteonal (Haversian) remodelling without a cartilage stage ✓
• D Compression plating accelerates the cartilaginous callus phase so that it is radiographically invisible

Explanation

Rigid fixation reduces interfragmentary strain below the tolerance of fibrocartilage, so primary (direct) bone healing occurs: cutting cones cross the fracture directly and remodel by Haversian osteons, with no haematoma, soft callus or woven bone stage. Option B describes stress shielding, which causes osteopenia beneath the plate, not altered healing mode. The periosteal contribution is reduced by stripping but that is not why callus is absent.

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

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Written and medically reviewed by the StethoPrep medical team.