Mechanical Performance of Metallic Bone Screws Evaluated Using Bone Models

Area of Science:

• Biomaterials Science
• Orthopedic Biomechanics
• Materials Engineering

Background:

• Orthopedic implants, including screws and bolts, are crucial for bone fracture fixation.
• Understanding the mechanical properties of these devices and their interaction with bone is essential for improving surgical outcomes.
• Bone models are vital for standardized mechanical testing of orthopedic devices.

Purpose of the Study:

• To evaluate the mechanical performance of cortical bone screws, cancellous bone screws, and locking bolts.
• To determine the relationship between screw design parameters (core diameter, surface area) and mechanical properties.
• To assess the influence of bone model density on screw fixation strength.

Main Methods:

• Conducted torsional breaking, durability, screw driving torque, and screw pullout tests on various screw types and bone models.
• Utilized polyurethane foam bone models with varying densities to simulate bone mechanical properties.
• Analyzed torque-rotational angle curves to estimate proof and rupture torques.

Main Results:

• Screw proof/rupture torques and durability limits increased with core diameter.
• Bone model strength (compressive, tensile, shear) increased with density.
• Maximum driving torque correlated positively with screw core diameter and effective surface area.
• Maximum pullout load increased linearly with screw engagement (rotations) and bone model strength.

Conclusions:

• Screw core diameter and effective surface area are key factors influencing mechanical performance.
• Bone density significantly affects screw fixation strength.
• Screws exhibiting low driving torque and high pullout load are desirable for excellent fixation and warrant further development.