Ideal Starting Point and Trajectory of a Screw for the Dorsal Approach to Scaphoid Fractures.

Abstract

To determine the screw starting point and trajectory for the dorsal approach to scaphoid fractures that provides a combination of length and compression at the fracture site. Computed tomography scans were obtained of 10 scaphoid fractures for 3 common fracture types. A computerized model was generated for each scaphoid. Screw starting point, length, and angle to the fracture plane were analyzed for starting points and trajectories within a safe zone that protected against cortical penetration. A novel analysis was developed to assess a combination of screw length and angle to fracture plane, termed "effective compression length" (ECL). ECL assessed the screw working distance perpendicular to the fracture. Results were analyzed to determine optimal screw starting point and trajectory. For proximal pole fractures, a screw perpendicular to the fracture was 9.7 mm from the longitudinal axis starting point (LASP). The screw with the largest ECL was 6.8 mm from the LASP, crossing the fracture at a 67° obliquity. For waist fractures, a perpendicular screw was 7.8 mm from the LASP. The screw with the largest ECL was 6.0 mm away, crossing the fracture at 74°. For distal oblique fractures, a perpendicular screw was 10.2 mm from the LASP. The screw with the largest ECL was 6.4 mm away, crossing the fracture at 70°. A screw with the classic starting point and trajectory crossed the fracture at obliquities of 48°, 51°, and 45° for proximal, waist, and distal fractures, respectively. Scaphoid screws placed with the classic starting point and trajectory cross the fracture at an obliquity. By altering the screw starting point and trajectory, screws with adequate length will be more perpendicular to the fracture plane. Screw starting point and trajectory for scaphoid fractures may be altered based on fracture type to obtain a long screw that is closer to perpendicular to the fracture.