INTRODUCTION: Healing rates exceeding 95% are reported for acute scaphoid fractures with early recognition and proper immobilization. Below-elbow immobilization may increase the risk of potential displacement through shear forces transmitted by the radioscaphocapitate (RSC) ligament. The role of the RSC ligament on the amount of rotation that occurs at the scaphoid waist fracture site is studied. METHODS: In ten fresh-frozen cadaveric upper extremities, the amount of rotation of an osteotomized scaphoid was arthroscopically evaluated in neutral, pronated, and supinated positions, before and after arthroscopic RSC ligament sectioning. Testing was also done after application of a weight to both the flexor and extensor tendons. RESULTS: With the RSC ligament intact and the wrist pronated without immobilization, rotation was <1mm in 25%, 1-2mm in 62.5%, and >2mm in 12.5%. After sectioning the RSC ligament, the pronated wrist without immobilization rotated <1mm in 75% and 1-2mm in 25%. No rotation at the fracture site was seen with supination. No rotation at the fracture site was seen when the wrist was immobilized. There was no difference between loaded and unloaded trials. DISCUSSION AND CONCLUSION: Pronation of the forearm without wrist immobilization, with resultant radiocarpal rotation, caused the greatest rotational force across the scaphoid fracture in this study. With the wrist immobilized, as in a short arm cast, the fracture appeared stable. Sectioning of the RSC ligament resulted in a reduced amount of rotation at the scaphoid waist fracture, thus the RSC ligament may be a deforming force in these injuries.