In sickle cell disease, vaso-occlusive crises most commonly affect which anatomical site?

Explanation

## Most Common Site of Vaso-Occlusive Crisis in SCD **Key Point:** The femoral head and humeral head (long bones) are the most common sites of vaso-occlusive infarction in sickle cell disease, causing acute bone pain crisis and chronic osteonecrosis. ### Why Bones Are Most Commonly Affected 1. **High metabolic demand** — bone marrow has high oxygen consumption 2. **Slow blood flow** — metaphyseal vessels have sluggish circulation, promoting sickling 3. **Acidic microenvironment** — favors polymerization of HbS 4. **Frequent sickling** — repeated infarction → chronic osteonecrosis ### Sites of Vaso-Occlusion in SCD: Frequency Ranking | Site | Frequency | Clinical Presentation | Consequence | |------|-----------|----------------------|-------------| | **Femoral & humeral heads** | Most common | Acute bone pain, swelling | Osteonecrosis, arthropathy | | **Spleen** | Common (early childhood) | Left upper quadrant pain | Autoinfarction, functional asplenia | | **Kidneys** | Common | Hematuria, papillary necrosis | Chronic kidney disease | | **Meninges/brain** | Less common | Stroke symptoms | Acute ischemic stroke | | **Lungs** | Common (ACS) | Chest pain, infiltrate | Pulmonary infarction | | **Liver** | Uncommon | Right upper quadrant pain | Hepatic infarction | **High-Yield:** Osteonecrosis (avascular necrosis) of the femoral head is a major cause of morbidity in adult SCD patients, often requiring hip replacement. **Clinical Pearl:** The **hand-foot syndrome** (dactylitis) is the earliest manifestation of vaso-occlusion in infants with SCD, typically presenting between 6 months and 2 years of age, affecting the small bones of hands and feet. **Mnemonic — Sites of Infarction in SCD: "BONES"** - **B**ones (femoral, humeral heads) — most common - **O**rgan (spleen, kidney, liver) - **N**eurologic (brain, stroke) - **E**ndothelial (lungs, ACS) - **S**ystemic (multi-organ involvement) **Warning:** Do not confuse acute bone pain crisis (vaso-occlusive) with osteomyelitis in SCD; both can present similarly, but SCD patients are at risk for both conditions—culture and imaging are essential.