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Ideal Starting Point and Trajectory of Screw for Dorsal Approach to Scaphoid Fractures
Asher Kupperman, MD; Ryan Breighner, PhD; Eliana Saltzman, BA; Darryl B Sneag, MD; Scott W Wolfe, MD; Steve Lee, MD
Hospital for Special Surgery, New York, NY
Introduction: Scaphoid fractures are treated using compression screws placed along the longitudinal axis. Scaphoid fractures, however, are rarely perpendicular to this axis. Studies have found there is less fracture site motion, higher stability, and shorter time to union for fractures treated with perpendicular rather than longitudinal screw placement. The purpose of our study was to determine the best screw path that combined increased length and perpendicularity to the fracture.
Methods: Under IRB approval, existing CT scans were searched for ten scaphoid fracture cases of three different fracture types. The fracture plane was identified using multiplanar reconstruction and a 3D mesh of the scaphoid was generated. 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 the interaction of screw length and obliquity to fracture plane, termed “effective compressive length” (ECL). ECL quantifies the screw’s working length that is perpendicular to the fracture. Results were analyzed to determine the optimal screw path and starting point.
Results: For proximal pole fractures, a screw perpendicular to the fracture was 9.7 mm from the longitudinal axis starting point (LASP), while the screw with the largest ECL was 6.8 mm from the LASP, crossing the fracture at an obliquity of 67 degrees. For waist fractures, a perpendicular screw was 7.8 mm from the LASP, while the screw with the largest ECL was 6.0 mm away from the LASP and crossed the fracture at 74 degrees. For distal oblique fractures, a perpendicular screw was 10.2 mm from the LASP, while the screw with the largest ECL was 6.4 mm away from the LASP, crossing the fracture at 70 degrees. A screw with the classic starting point and trajectory crossed the fracture at obliquities of 48, 51, and 45 degrees for proximal pole, waist, and distal oblique fractures, respectively. Screws perpendicular to the fracture plane averaged 18.6 mm. Screws that provided the largest ECL averaged 21.8 mm. The longest possible screw averaged 24.0 mm.
Conclusion: Scaphoid screws installed with with the classic longitudinal placement intersect the fracture plane obliquely. Screw path can be altered based on the patient’s specific fracture to obtain a screw path which is both sufficiently long and sufficiently perpendicular to the fracture plane.
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