Three-dimensional motion between the fragments of an experimental scaphoid
waist fracture was measured during dynamic forearm pronation and supination
in a short-arm thumb spica cast with and without applied tendon loads. Met
al markers placed in each fragment were tracked using high-speed biplane ra
diographic image sequences and stereophotogrammetric analysis. Peak displac
ements (from the intact state) exceeded 1 mm in all specimens, with the lar
gest movements occurring in the radial direction during pronation (mean: 2:
1 mm unloaded, 2.5 mm loaded). Total range of displacement motion between f
ragments exceeded 3 mm (mean ulnar/radial direction: 3.4 mm unloaded, 4.1 m
m loaded). Dorsal/palmar and proximal/distal displacements were minimal exc
ept at the extremes of forearm pronation/supination. Rotations between frag
ments were small (within +/-6 degrees) and varied considerably across speci
mens. No significant differences were found between loaded and unloaded tri
als. Thus, in the absence of long-arm thumb spica casting to limit forearm
rotation, significant motion between the fragments of a scaphoid waist frac
ture is likely. (J Hand Surg 1999;24A: 984-991. Copyright (C) 1999 by the A
merican Society for Surgery of the Hand.)