The effect of pronation and supination on the minimally displaced scaphoid fracture.

The amount of rotation that occurs at the scaphoid waist fracture site with pronation and supination of the forearm is studied in 10 upper extremities from cadavers. Two colinear metal markers were placed in the osteotomized scaphoid and a below-the-elbow cast was applied. Spiral volumetric computed tomography scanning of the scaphoid was done with multiplanar reformation to evaluate displacement of the metal markers. Four of the 10 specimens also were studied without any immobilization. The total magnitude of motion from pronation to supination averaged 0.2 mm in the specimens with a below-the-elbow thumb spica cast, and 2.4 mm in specimens without immobilization. The current study showed no significant rotation at the minimally displaced scaphoid waist fracture site during pronation and supination in a below-the-elbow cast. Furthermore, there is unacceptable rotation at the fracture site in the absence of a cast. Based on this study, a below-the-elbow thumb spica cast seems adequate for fracture immobilization; however, clinical correlation is needed.