Improving socket design to prevent difficult removal of locking screws

Area of Science:

• Biomaterials Engineering
• Orthopedic Surgery
• Mechanical Engineering

Background:

• Titanium screws are increasingly used in medical implants.
• Driver slippage and cold welding issues with titanium screws, especially hex sockets, lead to difficult removal and surgical complications.
• Improved screw socket design is needed to prevent these problems.

Purpose of the Study:

• To evaluate and compare the performance of various screw socket designs.
• To identify optimal designs that prevent driver slippage and facilitate screw removal.
• To address complications associated with titanium screw fixation.

Main Methods:

• Manufactured titanium screws with small (hex, Torx, cruciate) and large (hex, Torx, Octatorx, Torx+ I-III) sockets.
• Conducted torsional tests on screw heads and drivers at 1mm and 2mm insertion depths.
• Recorded maximum torque and failure patterns for ten specimens of each design.

Main Results:

• Hex sockets exhibited slippage and reduced torque, particularly at 1mm depth.
• Large sockets generally provided higher torque than small sockets.
• Octatorx and Torx plus designs demonstrated superior torque and resistance to slippage compared to hex sockets.

Conclusions:

• Hex socket design is prone to slippage and torque reduction, especially with insufficient driver engagement.
• Larger socket designs and advanced geometries (Octatorx, Torx plus) significantly enhance torque and prevent slippage.
• Optimized screw socket designs can effectively mitigate issues of slippage and difficult removal in titanium screws.