CAMRT Radiography Practice Exam

Which carpal bone is most susceptible to avascular necrosis?

1. Lunate

2. Trapezium

3. Scaphoid

4. Capitate

The correct answer is: Scaphoid

The scaphoid bone is the most susceptible to avascular necrosis primarily due to its unique blood supply. The blood flow to the scaphoid is mainly retrograde, meaning it enters from the distal portion of the bone and travels towards the proximal end. When a fracture occurs, particularly if it is at the waist of the scaphoid, the blood supply to the proximal part can be compromised, leading to avascular necrosis. This condition occurs when the bone tissue dies due to a lack of blood flow, which is particularly critical for the scaphoid given its limited vascular supply compared to other carpal bones. In contrast, other carpal bones such as the lunate, trapezium, and capitate have a more robust blood supply, making them less prone to avascular necrosis. The lunate can suffer from conditions like Kienböck's disease, but its susceptibility is not as high as that of the scaphoid. The trapezium and capitate also have direct blood supply that is generally less at risk of avascular issues, reinforcing the scaphoid's unique vulnerability in this regard.