Single versus double screw fixation for the treatment of scaphoid waist fractures: Finite element analysis and preliminary clinical results in scaphoid nonunion

Objectives: This study aims to compare the single versus double screw fixation of scaphoid waist fractures using finite clement analysis, and to present the preliminary clinical results of double screw fixation in a consecutive series of patients with scaphoid nonunion. Patients and methods: A transverse scaphoid waist fracture. (Herbert type H2) model was fixed with either single. or double cannulated compression screws. Displacement and rotation of the fragments were performed using three-dimensional finite element analysis in three different wrist positions. A retrospective review was performed on 13 male patients (mean age 31.6 +/- 12.8 years; range, 17 to 64 years) who underwent double screw fixation for an established scaphoid nonunion in our clinic between January 2015 and December 2017. Assessment of union was established with serial plain radiographs in eight patients and with wrist computed tomography in five patients. Clinical evaluation was performed using the Mayo wrist score and visual analog scale (VAS). Results: In all wrist positions. the displacement of the fracture gap in double screw fixation in all planes (x, y, and z) was less than in single screw fixation. Similarly, rotation of the fracture fragments around the longitudinal axis of the scaphoid was lower in double screw fixation. Complete union was obtained in all patients. The mean time to union was 5 +/- 0.75 months (range, 4 to 6 months). The mean VAS was 0.8 +/- 0.9 (range, 0 to 3). Mayo wrist score was 91 +/- 6.9 (range, 80 to 100) at the final follow-up. Conclusion: Double-screw fixation technique may be a solution to reduce the rate of scaphoid nonunion in unstable type B2 scaphoid fractures or nonunion.