A medical student asks the surgical registrar to explain why a sutured, clean surgical incision regains strength over weeks rather than days. Which account of the phases of wound healing and wound strength is correct?
- AWounds regain full pre-injury tensile strength within one week of suturing
- BEpithelialisation is the final event of healing, occurring after about a year
- CCollagen I is laid down first in proliferation and later replaced by collagen III in remodelling
- DMacrophages have no role beyond the first hour
- EHealing proceeds through haemostasis, inflammation, proliferation (collagen III) and remodelling (replaced by collagen I), reaching 70 to 80% strength at most
Show answer and explanation
Correct answer: E
Primary-intention healing runs through four overlapping phases. Haemostasis: platelet plug and fibrin, with platelet granules releasing the growth factors (PDGF, TGF-beta) that recruit what follows. Inflammation (days 0 to 3): neutrophils debride bacteria and dead tissue, then macrophages take over as the conductors of the wound — phagocytosing debris and secreting the cytokines that summon fibroblasts; a wound deprived of macrophages barely heals. Proliferation (about day 3 to week 3): fibroblasts synthesise collagen — initially type III — while angiogenesis builds granulation tissue and the epithelium seals the surface within about 48 hours in an apposed incision. Remodelling (three weeks to more than a year): type III collagen is degraded and replaced by cross-linked type I along stress lines, and myofibroblasts contract the wound. The strength curve is the practical takeaway: roughly 10% of normal at one week, 20% at three weeks, 50 to 60% by three months, plateauing at about 70 to 80% — never full strength, which is why fascia is closed with long-lasting sutures and why heavy straining is restricted for weeks after laparotomy.
Why the others are wrong: A — one-week strength is around 10%; early suture removal relies on apposition, not strength. B — epithelial cover is an early proliferative event, complete in days in a closed wound. C — the sequence is III first, remodelled to I. D — macrophages dominate healing from day 2 onward.
Key point: Haemostasis → inflammation → proliferation (collagen III, granulation, epithelial seal) → remodelling (collagen I, contraction): strength is ~20% at three weeks and never exceeds ~80% of original — the reason fascial closures use durable sutures and convalescence restricts strain.