A 28-year-old man is brought to the emergency department after a motor vehicle accident. On examination, he has multiple injuries on his left arm. One area shows a scraped, raw appearance with oozing of blood and tissue fluid, while another area shows a blue-purple discoloration of intact skin with swelling. Which single feature best distinguishes an abrasion from a contusion?

Explanation

## Distinguishing Abrasion from Contusion ### Key Anatomical Difference **Key Point:** The critical discriminator between abrasion and contusion is the **integrity of the skin surface**. An abrasion involves loss of epidermis ± dermis, whereas a contusion has **intact skin** with damage only to underlying tissues. ### Comparative Table | Feature | Abrasion | Contusion | |---------|----------|----------| | **Skin surface** | Abraded, raw, denuded | Intact | | **Bleeding** | Oozing (capillary) | Usually no external bleeding | | **Appearance** | Scraped, granular | Blue-purple discoloration | | **Depth** | Epidermis ± dermis | Subcutaneous tissues, muscle | | **Healing** | Leaves scar (if deep) | Resolves without scarring | | **Mechanism** | Friction/rubbing force | Blunt impact without breaking skin | ### Why This Matters Clinically **Clinical Pearl:** In forensic examination, abrasions are considered **incised wounds** (loss of continuity), while contusions are **closed injuries**. This distinction affects wound management, infection risk, and scar formation. **High-Yield:** The presence of **abraded, raw tissue** (loss of epidermis) is pathognomonic for abrasion. A contusion, no matter how severe the swelling and discoloration, will always have an intact skin surface. ### Memory Aid **Mnemonic: ABRASION = Abraded Broken skin** - **A**braded surface (epidermis lost) - **B**leeding (capillary ooze) - **R**aw appearance - **A**cute inflammation - **S**car formation (if deep) - **I**ntegrity lost - **O**pen wound - **N**eeds dressing **Mnemonic: CONTUSION = Closed blunt injury** - **C**losed skin (intact) - **O**ver blunt trauma - **N**o skin break - **T**issue damage (deep) - **U**nder intact surface - **S**welling and discoloration - **I**nternal bleeding - **O**pen to complications (if severe) - **N**o scar (usually) [cite:Reddy Forensic Medicine 33e Ch 8]