**Question:** Crepitus will be seen in the tissues surrounding an
infection by:

**Core Concept:** Crepitus is a palpable sound or grating sensation produced by the presence of gas within tissues due to gas-forming infections.

**Why the Correct Answer is Right:**
The correct answer is D. **Subcutaneous emphysema** is the condition where gas accumulates in the subcutaneous tissues due to a gas-forming infection, such as gas gangrene or gas-producing abscess. This gas is usually produced by the action of anaerobic bacteria like Clostridium perfringens. The gas accumulates between the skin and the underlying muscles, leading to the characteristic crepitus when palpated.

**Why Each Wrong Option is Incorrect:**
A. **Inflammation (erythema)** is a common finding in acute infections but does not produce crepitus. Inflammation is a result of histamine release, vasodilation, and increased vascular permeability.
B. **Gangrene** is a severe complication of deep tissue infections, not a cause of crepitus. In gangrene, there is tissue necrosis without gas production.
C. **Subcutaneous emphysema** is the correct answer but is mentioned earlier for completeness.
D. **Subcutaneous emphysema** is caused by gas-forming infections and leads to crepitus upon palpation.

**Clinical Pearl:** Crepitus is a critical sign to look for when examining a suspected gas-forming infection. It is essential to differentiate it from other causes of crepitus, such as subcutaneous emphysema or fibrosis.

**Correct Answer:** C. Subcutaneous emphysema

**Why Subcutaneous emphysema causes crepitus:**
Subcutaneous emphysema occurs when gas-forming organisms, such as Clostridium perfringens, produce gas within the subcutaneous tissues. The gas accumulates between the skin and the underlying muscles, causing the crepitus when palpated. The correct answer is D. Subcutaneous emphysema, which is mentioned earlier for completeness.