The Biomechanical Stability of a Single Headless Compression Screw Construct to Fix Scaphoid Waist Fractures

Scaphoid fracture fixation using a single headless compression screw (HCS) may permit unacceptable rotation at the fracture site. This study aimed to assess the biomechanical stability of a single HCS construct to fix scaphoid waist fractures. (1) Does a single HCS provide rotational stability? (2) What degree of rotation is found at the central axis of a scaphoid without fixation? In eight fresh frozen cadavers, two parallel K-wires were placed in the scaphoid to mark rotation and an osteotomy was created at the scaphoid waist. To determine whether rotation was present between the proximal and distal poles, radiographs of the wrist at terminal range of motion (ROM) were reviewed for relative change in wire position. The fracture was then reduced, and an HCS was then advanced across the fracture; rotation was again evaluated. Rotation was quantified in the group without fixation using a sensor that measured angular rotation. Before screw fixation, interfragmentary rotation was found to average 22.5° during flexion/extension, 19.0° during pronation/supination, and 34.0° during radial/ulnar deviation around the central axis. The radiographs after osteotomy demonstrated rotation in all specimens. After fixation with an HCS, radiographs demonstrated relative rotation of the two halves of the scaphoid in all ROMs for all specimens, except flexion for one specimen. Internal angular tension was observed within the scaphoid, and rotation of 20° to 30° was noted around the central axis during simulated ROM mimicking nonsurgical treatment. A single HCS failed to prevent fragment-relative rotation at the fracture site.