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

A. bony prominences
B. muscles
C. subcutaneous tissue
D. blood vessels

**Core Concept:** The development of pressure ulcers, also known as pressure sores or decubitus ulcers, is primarily dependent on the prolonged compression of skin and underlying tissues against a hard surface, which reduces or prevents adequate blood supply to the affected area. This can lead to tissue ischemia and subsequent tissue damage.

**Why the Correct Answer is Right:** Pressure ulcers primarily develop due to external pressure exerted on bony prominences (e.g., elbows, knees, heels, and the sacrum), which are areas with a lack of subcutaneous tissue and fat to distribute pressure evenly. When external pressure exceeds capillary occlusive pressure over these areas, it results in impaired blood flow and tissue ischemia. This leads to tissue damage, which manifests as pressure ulcers.

**Why Each Wrong Option is Incorrect:**

A. Muscles are not the primary site for pressure ulcers to occur. While muscles can be affected indirectly due to compression, the primary focus should be on bony prominences.

B. Muscles are not the primary site for pressure ulcers to occur as they have ample amounts of subcutaneous tissue to distribute pressure.

C. Subcutaneous tissue is present over bony prominences and is essential to cushion the underlying bones from external pressure. However, the primary focus should be on the bony prominences themselves.

D. Blood vessels are not the site where pressure ulcers form. Although reduced blood flow due to pressure over blood vessels can exacerbate the condition, the primary focus should be on the bony prominences and the lack of protective subcutaneous tissue over them.

**Clinical Pearl:** Prolonged pressure over bony prominences without proper cushioning can lead to tissue ischemia and subsequent tissue damage, resulting in pressure ulcers. Early identification and management of pressure ulcers are crucial in preventing complications and improving patient outcomes.