Step 1 topics → General Pathology → Abnormal Wound Healing (Keloid, Hypertrophic Scar, Dehiscence, Contracture)

Abnormal Wound Healing (Keloid, Hypertrophic Scar, Dehiscence, Contracture)

USMLE Step 1 trap: Conflates keloids with hypertrophic scars, missing the key distinction of boundary extension and recurrence. Hypertrophic scars remain confined to the original wound boundaries and may regress, whereas keloids extend beyond wound margins, do not regress, and have a higher recurrence rate after excision.

Abnormal wound healing is a high-yield area within general pathology that trips up students who memorize terms without understanding the underlying mechanisms. The key entities — keloids, hypertrophic scars, wound dehiscence, and contractures — each arise from specific failures or exaggerations of normal healing phases, and USMLE Step 1 will test whether you can distinguish them in clinical vignettes, not just define them. You need to know not only what each entity is, but when it occurs, who gets it, and what cellular or molecular process is driving it.

The exam approaches this topic from multiple angles. Expect differential-diagnosis questions asking you to distinguish keloid from hypertrophic scar based on clinical features described in a stem. Expect application questions where you're given a postoperative patient and asked to identify the risk window for dehiscence. Contractures show up most often as clinical correlates — a burn patient with restricted joint movement, for example — where you need to know that myofibroblasts are the cellular culprit. USMLE Step 1 loves to use these scenarios to probe whether you understand mechanism, not just vocabulary.

The trickiest part is separating keloids from hypertrophic scars — most students treat them as the same thing with different sizes, which is wrong. They also tend to misplace dehiscence risk to the first day or two post-op, when the actual danger window is days 5–10. Contractures are often a knowledge gap entirely because the connection to myofibroblast activity isn't always emphasized in lecture. Build your understanding around mechanisms and timing, and these questions become straightforward.

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Common misconceptions

Common mistake
Wrong: Keloids and hypertrophic scars are the same entity differing only in size.
Right: Hypertrophic scars remain confined to the original wound boundaries and may regress, whereas keloids extend beyond wound margins, do not regress, and have a higher recurrence rate after excision.
Keloids and hypertrophic scars are not simply different sizes of the same process. The defining distinction is anatomical boundary: hypertrophic scars stay within the original wound margins and often regress spontaneously over time, while keloids actively grow beyond the wound edges and do not regress on their own. Clinically this matters because keloids also have a much higher recurrence rate after surgical excision — which is why excision alone is often insufficient and adjunct therapy is needed.
Common mistake
Wrong: Wound dehiscence is most likely to occur in the first 1–2 days after surgery.
Right: Wound dehiscence most commonly occurs around postoperative day 5–10, when the inflammatory phase has subsided but collagen remodeling has not yet provided adequate tensile strength.
Dehiscence is not an immediate postoperative event — the first day or two post-op, the wound is held together by sutures and the fibrin clot, so mechanical failure at that point would reflect a technical problem, not a healing failure. The real danger window is postoperative days 5–10, after the acute inflammatory phase has wound down but before collagen cross-linking has built up enough tensile strength. This is exactly when the wound is most vulnerable to mechanical stress, and it's why early ambulation, coughing, or poor nutrition can precipitate dehiscence in that window.
Common mistake
Gap: Missing that contractures are caused by pathologic myofibroblast-driven contraction, classically after burn injuries
Contractures result from excessive myofibroblast activity during healing of large wounds or burns, leading to permanent shortening of tissue that can restrict joint movement.
Contractures are not just 'tight scars' — they result from pathologic overactivation of myofibroblasts, which are specialized cells that have acquired smooth muscle-like contractile properties during the healing process. In large wounds or burns, these myofibroblasts contract and deposit collagen in a way that permanently shortens the tissue, restricting range of motion at nearby joints. The classic teaching scenario is a burn patient who develops a flexion contracture across a joint — this is the direct consequence of unregulated myofibroblast-driven wound contraction.
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What the exam tests

  1. Given a clinical description of a scar, determine whether it is a keloid or a hypertrophic scar based on whether it extends beyond the original wound margins and whether it has any tendency to spontaneously regress.
  2. Identify the postoperative time window (days 5–10) when wound dehiscence is most likely to occur, and explain why that window is dangerous in terms of collagen remodeling and tensile strength.
  3. Recognize that contractures — especially after burn injuries — result from excessive myofibroblast contraction during healing, and understand how this can permanently restrict joint mobility.

Can you avoid these mistakes?

A 28-year-old Black woman has a raised, firm scar on her earlobe that extends 2 cm beyond the original piercing site. She reports it has been growing for the past year despite no new trauma. What distinguishes this lesion from a hypertrophic scar, and what would you expect if it were surgically excised?
A patient undergoes an abdominal laparotomy. On which postoperative day is wound dehiscence most likely to occur, and what is the underlying reason related to the biology of wound healing at that time?
A child sustains a full-thickness burn over the anterior aspect of the elbow. Six months later, he cannot fully extend the arm. What cell type is primarily responsible for this complication, and what is the mechanism?
You are shown two patients: one with a scar that faded over 18 months and remained within the incision line, and another whose scar expanded beyond the wound edges and is unchanged 3 years later. Which is the keloid, and what underlying difference in healing biology explains the behavior of each?

Related topics

Phases of Wound Healing Reversible vs Irreversible Cell Injury Types of Necrosis Apoptosis (Intrinsic and Extrinsic Pathways) Cell Adaptations (Atrophy, Hypertrophy, Hyperplasia, Metaplasia, Dysplasia)

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