**Question:** Pressure sores usually occur when external pressure exceeds capillary occlusive pressure over

A. bones
B. joints
C. tendons
D. arteries

**Core Concept:**

The development of pressure sores, also known as pressure ulcers or bedsores, is a consequence of prolonged pressure over bony prominences or areas with reduced blood flow, leading to tissue ischemia and necrosis. Capillary occlusive pressure is the pressure at which blood flow is completely blocked in the capillaries, and it depends on factors like blood vessel diameter, flow velocity, and blood viscosity.

**Why the Correct Answer is Right:**

Correct answer D, arteries, is the correct choice because pressure sores primarily occur when external pressure exceeds the capillary occlusive pressure over areas with rich blood supply, ensuring adequate oxygen and nutrient delivery to the tissues. Arteries are the primary blood vessels responsible for supplying oxygen and nutrients to the tissues, while the other options are not directly related to the capillary occlusive pressure:

- Bones (option A) are not the primary concern as they do not directly affect the capillary occlusive pressure. Although bones may cause local tissue compression, the primary concern is the capillary pressure.
- Joints (option B) might be involved in pressure sores due to their limited mobility and immobility, but they are not directly responsible for the capillary occlusive pressure.
- Tendons (option C) are not directly related to capillary occlusive pressure as they are fibrous bands of tissue connecting muscles to bones and do not directly affect blood flow or pressure.

**Why Each Wrong Option is Incorrect:**

- Bones: Although bones can cause local tissue compression, the primary concern is the capillary occlusive pressure.
- Joints: Joints can be involved in pressure sores due to their limited mobility and immobility, but they are not directly responsible for capillary occlusive pressure.
- Tendons: Tendons are not directly related to capillary occlusive pressure as they are fibrous bands of tissue connecting muscles to bones and do not directly affect blood flow or pressure.

**Clinical Pearl:**

Clinically, it is essential to assess patients at risk for pressure ulcers, particularly those with limited mobility or prolonged immobility, and those with compromised skin integrity or underlying tissue conditions like diabetes. Early recognition and intervention can prevent progression of pressure sores and promote wound healing.