Fixation strength of four headless compression screws.

Area of Science:

• Orthopedic surgery
• Biomedical engineering
• Materials science

Background:

• Headless screws are increasingly used for scaphoid fractures to enable early patient mobilization.
• Optimizing biomechanical fixation is crucial for implants supporting early functional recovery.

Purpose of the Study:

• To evaluate and compare the biomechanical fixation strength of four different headless compression screws.
• To assess implant performance under distracting and bending forces in a simulated scaphoid fracture model.

Main Methods:

• Four headless screws (Acutrak Standard, Acutrak Mini, Synthes 3.0, Herbert-Whipple) were tested in a polyurethane foam scaphoid fracture model.
• Implants were subjected to pull-apart and four-point bending forces until failure.
• Pull-apart tests were conducted across three simulated bone densities (osteoporotic, osteopenic, normal).

Main Results:

• Acutrak Standard screws exhibited the highest pull-apart strength, followed by Synthes 3.0, Acutrak Mini, and Herbert-Whipple.
• Fully threaded Acutrak screws failed at proximal threads, while shanked Synthes and Herbert-Whipple screws failed at distal threads.
• Acutrak screws also demonstrated superior resistance to bending forces.

Conclusions:

• The fully threaded, conical design of Acutrak screws provides superior biomechanical fixation compared to shanked designs (Synthes, Herbert-Whipple).
• Simulated bone density significantly influences pull-apart fixation strength, with higher densities requiring greater force.
• These findings support the use of Acutrak screws for enhanced stability in scaphoid fracture fixation, facilitating early mobilization.