Scaphoid screw fixation perpendicular to the fracture plane: Comparing volar and dorsal approaches

Introduction: To percutaneously fixate a midwaist scaphoid fracture, both volar and dorsal approaches are considered valid options although they may have different screw insertion angles relative to the scaphoid fracture plane influencing fixation stability. In this virtual simulation study, we investigated the accessibility of placing a screw perpendicular to the fracture plane in transverse and horizontal oblique scaphoid midwaist fracture models and compared standard volar and dorsal approaches. Material and methods: Computed tomography scans of 38 healthy wrists were used to obtain virtual 3-dimensional wrist models in flexion and extension. In case the trapezium in volar approach or the distal radius in dorsal approach obstructed the screw axis perpendicular to the fracture plane, an alternative non-obstructed screw axis was chosen as close as possible to the perpendicular axis. The deviation angle between the best possible non-obstructed screw placement and true perpendicular screw placement was quantified. Results: For transverse fractures, the average deviation angle (± standard deviation) was 8° (± 5°) in volar approach and 0° (± 0°) in dorsal approach. For horizontal oblique fractures, these angles were 40° (± 6°) and 14° (± 8°), respectively. Discussion: In our simulations, compared to the volar approach, the dorsal approach provided the most precise screw placement perpendicular to the fracture plane, with the largest differences for horizontal oblique fractures. When taken in addition to screw purchase, thread engagement and protrusion risk, information about screw orientation may help surgeons in deciding between percutaneous approaches in scaphoid surgery on which there is currently no consensus. Level of evidence: N/A.