A 21-year-old man presents to the clinic for follow-up of a scaphoid waist fracture sustained three weeks ago. He was initially placed in a thumb spica splint. He is concerned about the long-term healing of the bone. The physician explains to him that the scaphoid is particularly vulnerable to healing complications due to its unique vascular anatomy. The majority of the blood supply to the scaphoid enters at the distal tubercle and the waist, traveling in a retrograde fashion to reach the more proximal portions.
Based on this anatomical characteristic, a fracture at which of the following locations carries the highest risk for developing avascular necrosis?
The correct answer is:
C) Proximal pole
The scaphoid bone receives its blood supply primarily from the radial artery. Approximately 80% of the blood supply enters the scaphoid through the dorsal ridge (near the waist) and the distal tubercle. This blood then flows in a retrograde direction from the distal and middle portions of the bone toward the proximal pole. Because of this end-artery supply with no significant collateral circulation from the proximal side, a fracture across the waist or proximal pole can sever the blood vessels, leaving the proximal fragment entirely ischemic. This leads to a high incidence of avascular necrosis (AVN) and non-union in proximal pole fractures compared to distal ones.
Answer choice A: Distal pole, is incorrect. The distal pole is closer to the entry points of the arterial supply, meaning it maintains excellent perfusion even if a fracture occurs elsewhere.
Answer choice B: Distal tubercle, is incorrect. This is one of the primary entry points for the scaphoid's blood supply. Fractures here have an excellent prognosis for healing.
Answer choice D: Scaphoid waist, is incorrect. While waist fractures are common and do carry a risk of AVN (about 10-15%), the risk is significantly lower than that of the proximal pole, which is further downstream from the retrograde flow.
Answer choice E: Scaphotrapezial joint, is incorrect. This refers to a joint space, not a location on the scaphoid bone itself. While arthritis can occur here, it is not a fracture site associated with avascular necrosis of the scaphoid.
Key Learning Point
The scaphoid bone has a retrograde blood supply provided by branches of the radial artery that enter distally. Consequently, he proximal pole is the most proximal portion of the bone but the last to receive blood, making it the area at highest risk for avascular necrosis following a fracture.
