The RA carried as much or more flow than the UA in 83.4% of our patients. Clinical experience tells us that hand perfusion is uncommonly impaired, despite the use of the RA for arterial lines, blood gases, ligation in trauma, arterial conduits, free flaps, and hemodialysis access.25- 35 Even if the RA thromboses from RA manipulation, numerous authors have suggested that it may recanalize.15,29,70 What, then, is the clinical significance of this high percentage of RA dominance or equivalence? Studying wrist anatomy yields some possible answers (Figure 1).37 The hand is supplied by the RA, UA, and 2 interosseous arteries. The RA trifurcates at the wrist. Anteriorly, the RA bifurcates into superficial and deep branches that supply the superficial and deep palmar arches, which anastomose to the UA. Posteriorly, the RA sends off a dorsal carpal branch, which forms the dorsal carpal arch. The anterior and posterior interosseous arteries, like the peroneal artery in the lower extremity, give off branches to the RA and UA in the wrist. If the RA is obliterated at the deep branch, it may have no effect because of collateral perfusion by 1 or both of the other RA branches. Obliterating the RA more proximally at the trifurcation, on the other hand, may have a profound effect if the UA or interosseous arteries or both are insufficient. Even if the UA or interosseous arteries are impaired, loss of RA flow may precipitate remodeling of the remaining vessels and avert ischemia. Alternatively, any 1 of the 3 RA branches may recanalize, or the RA connection to the interosseous arteries may help supply the hand. Still, it would be prudent to rule out the use of the RA in "obvious" cases in which the RA is strongly dominant and collateral perfusion is minimal or nonexistent, which this study suggests occurs more commonly than previously believed.