What is the typical sequence of bone healing, and how does smoking affect it?

• A. Inflammation only
• B. Soft tissue healing precedes fracture healing
• C. Inflammation → soft callus → hard callus → remodeling; smoking impairs healing and increases nonunion risk
• D. Immediate vascularization without callus formation

Answer: (C)

Bone healing happens in stages: first an inflammatory phase with hematoma and inflammatory cells, then soft callus formation that bridges the fracture with fibrous and cartilaginous tissue, followed by hard callus formation as woven bone is laid down, and finally remodeling where the woven bone is replaced by mature lamellar bone. Smoking disrupts this process mainly by reducing blood flow and oxygen delivery to the healing site—nicotine causes vasoconstriction and carbon monoxide lowers oxygen carrying capacity. This slows the inflammatory response resolution, impairs callus formation and mineralization, and delays remodeling, increasing the risk of delayed union or nonunion. That’s why the sequence described, along with the note that smoking impairs healing and raises nonunion risk, is the best answer.