3D printed locking osteosynthesis screw threads have comparable strength to machined or hand-tapped screw threads

Area of Science:

• Orthopedic surgery
• Biomaterials engineering
• Additive manufacturing

Background:

• Additive manufacturing (3D printing) is gaining traction for personalized orthopedic implants.
• 3D printed components, such as locking osteosynthesis plates, necessitate post-printing screw thread formation.

Purpose of the Study:

• To compare the mechanical strength of 3D printed screw threads against traditionally machined and hand-tapped threads.
• To evaluate the effect of different post-processing methods and build orientations on the performance of 3D printed threads.

Main Methods:

• 115 additively manufactured specimens with tapered screw holes were tested.
• Threads were created using machining, hand-tapping, or 3D printing with varying build orientations (0°, 20°, 45°, 90°).
• 3D printed threads were tested as-printed or post-processed with a tap using water or cutting oil lubrication.

Main Results:

• 3D printed threads post-processed with oil at a 90° build orientation exhibited pushout forces comparable to machined and hand-tapped threads.
• Threads that were as-printed or post-processed with water showed significantly lower pushout forces.
• Machined threads (median: 6757 N) and hand-tapped threads (median: 7805 N) showed high pushout forces, with oil-lubricated 3D printed threads reaching a median of 6377 N.

Conclusions:

• 3D printed screw threads for locking osteosynthesis plates can achieve mechanical strength comparable to conventional methods when properly post-processed.
• Post-processing with cutting oil is crucial for optimizing the performance of 3D printed threads.
• This research validates the potential of additive manufacturing for producing functional screw threads in orthopedic implants.