Deviations in positioning variable pitch screws- scaphoid waist fractures.

Area of Science:

• Orthopedic surgery
• Biomechanical engineering
• Bone fracture repair

Background:

• Headless cannulated variable pitch compression screws are the standard surgical treatment for unstable scaphoid fractures.
• Optimal screw placement is essential for maintaining wrist stability and preventing complications.

Purpose of the Study:

• To evaluate the biomechanical impact of varying screw insertion angles on the stability and stiffness of scaphoid fracture fixation.
• To determine the optimal screw placement for maximizing fixation strength in scaphoid fractures.

Main Methods:

• A controlled laboratory study utilizing artificial bone models of the scaphoid.
• Biomechanical testing involving shearing tests with axial force applied to a 45° flexed scaphoid model.
• Assessment of screw positions at the central axis, 10°, and 20° deviations.

Main Results:

• The central screw placement demonstrated the highest stiffness and failure force.
• A 10° deviation resulted in a slight decrease in stiffness and failure force.
• A 20° deviation led to a significant reduction in both stiffness (29.3N/mm) and failure force (50.3N).

Conclusions:

• Deviations from the central insertion axis of compression screws negatively impact fixation stability and strength in scaphoid fractures.
• Maintaining central placement is critical for achieving optimal biomechanical performance and successful treatment outcomes.
• These findings underscore the importance of precise surgical technique in scaphoid fracture fixation.