College of Massage Therapists of British Columbia (CMTBC) Practice Exam

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Which carpal bone is most vulnerable to osteonecrosis?

Lunate
Scaphoid
Capitate
Trapezium

The correct answer is: Scaphoid

The scaphoid bone is particularly vulnerable to osteonecrosis due to its unique blood supply. The scaphoid is located towards the base of the thumb and features a distal and proximal segment. The blood supply primarily comes from branches of the radial artery, a significant portion of which enters the bone distally. When a fracture occurs in the scaphoid, especially around the waist of the bone, it can disrupt the blood flow to the proximal fragment. This can lead to avascular necrosis, as the proximal segment may not receive adequate blood supply. The risk of osteonecrosis is a significant concern in scaphoid fractures, making it the carpal bone most commonly associated with this condition. In contrast, the lunate, capitate, and trapezium bones do not exhibit the same level of vulnerability to osteonecrosis that the scaphoid does, largely due to their anatomical positioning and blood supply. While they can sustain injuries and other conditions, they have more reliable vascularization compared to the scaphoid, which reinforces the latter's increased susceptibility to avascular necrosis.