Wrist position affects loading of the dorsal scaphoid: possible effect on extrinsic scaphoid blood flow.

Cadaver studies using radial artery injection techniques were used to study the vascular supply along the dorsal ridge of the scaphoid. These revealed an intraarticular membrane between the wrist capsule and the dorsal ridge of the scaphoid through which arteriolar vessels (25-100 microm internal diameter) passed. Biomechanical tests revealed that the extensor carpi radialis brevis may apply significant pressure to the dorsal ridge of the scaphoid when the wrist is flexed. The highest pressures occurred with the wrist flexed at 60 degrees or 90 degrees and in slight (15 degrees ) ulnar deviation. The authors suggest that these vascular and biomechanical factors may contribute to the aetiology for idiopathic osteonecrosis of the scaphoid.