Analysis of instability patterns in acute scaphoid fractures by 4-dimensional computed tomographic imaging - A prospective cohort pilot study protocol.

INTRODUCTION: A scaphoid fracture is the most common carpal fracture. When healing of the fracture fails (nonunion), a specific pattern of osteoarthrosis occurs, resulting in pain, restricted wrist motion and disability. Scaphoid fracture classification systems recognize fragment displacement as an important cause of nonunion. The fracture is considered unstable if the fragments are displaced. However, whether and how displaced bone fragments move with respect to one another has not yet been investigated in vivo. With a four-dimensional (4D) computed tomographic (CT) imaging technique we aim to analyze the interfragmentary motion patterns of displaced and non-displaced scaphoid fragments. Furthermore, the correlation between fragment motion and the development of a scaphoid nonunion is investigated. We hypothesize that fragment displacement is not correlated to fragment instability; and concurrent nonunion is related to fragment instability and not to interfragmentary displacement. METHODS: In a prospective single-center cohort pilot study, patients with a one-sided acute scaphoid fracture and no history of trauma to the contralateral wrist are illegible for inclusion. Twelve patients with a non-displaced scaphoid fracture and 12 patients with a displaced scaphoid fracture are evaluated. Both wrists are scanned with 4D-CT imaging during active flexion-extension and radio-ulnar deviation motion. The contralateral wrist serves as kinematic reference. Relative displacement of the distal scaphoid fragment with respect to the proximal scaphoid fragment, is described by translations and rotations (the kinematic parameters), as a function of the position of the capitate. Non-displaced scaphoid fractures are treated conservatively, displaced scaphoid fractures receive intraoperative screw fixation. Follow-up with CT scans is conducted until consolidation at 1½, 3 and 6 months. This trial is registered in the Dutch Toetsingonline trial registration system, number: NL60680.018.17. ETHICS: This study is approved by the Medical Ethics Committee of the Academic Medical Center, Amsterdam.