Bone screws are a widely used in orthopaedic surgery for fracture fixation. Many times bone screws are used in combination with bone plates, but they can also be used to hold together larger bone fragments in comminuted fractures. Bone screws can be made of many different materials, most common are stainless steel and titanium, however progress is being made on the development of bioactive resorbable screws. There are a variety of tests used to characterize the torsional properties of bone screws. Beyond simply testing the breaking torque and torsional rigidity of screws, it's necessary to characterize the force and torque required to drive a bone screw and the self-tapping performance of self-tapping bone screws. Tests that load bone screws to failure often utilize collet style grips to apply uniform loads without and prevent slipping without damaging the specimen. Driving and self-tapping tests generally use a medium, providing similar properties to natural bone tissue, such as the rigid polyurethane foam specified in ASTM F1839. ASTM and ISO have developed standardized test methods for testing the torsional properties of bone screws. These test methods are primarily intended to measure the uniformity of products and to compare the mechanical properties of different type bone screws and bone screw materials. ASTM F543 contains four test methods for torsional properties of metallic bone screws, driving torque of medical bone screws, axial pullout strength of medical bone screws, and self-tapping performance of medical bone screws. ISO 6475 contains a single test for the breaking torque and angle of rotation at failure for metal bone screws. TestResources offers test machines for testing the torsional properties of bone screws. Note that on the latest published standard of ASTM F543 changed equipment requirements. An Axial-torsion test machine is now necessary to conduct all tests.
Applicable Testing Standards
- ISO 6475 Bone Screw Torsion Test Methods | Equipment
- ASTM F117 Torque Medical Bone Screws Test Machine
- ASTM F543 Medical Bone Screw Torsion Test Equipment
- ASTM F1839 Rigid Polyurethane Foam - Orthopedic Devices
Recommended Test Machine
Force ratings up to 5 kN (1,125 lbf) and torque ratings up to 20 Nm (177 lbf∙in)
Can apply axial and torsional loads simultaneously
Performs both static and slow-speed dynamic testing
All electric and oil-free operation
Torques up to 500 Nm (4,500 lbf∙in)
Speeds from 2 RPM to 120 RPM
Adjustable test space
Convenient tabletop design
Force ratings up to 2.5 kN (580 lbf) and torque ratings up to 20 Nm (177 lbf∙in)
Can apply axial and torsional loads simultaneously
Axial frequencies up to 15 Hz and torsional frequencies up to 30 Hz
All electric and oil-free operation
Force ratings up to 50 kN (11,250 lbf) and torque ratings up to 180 Nm (1,600 lbf∙in)
Can apply axial and torsional loads simultaneously
Performs both static and dynamic tests
All electric and oil-free operation
Recommended Testing Accessories
Allows for testing in temperature-controlled water or saline solution
PID controlled temperature up to 45°C (113°F)
Size is optimized per application
Accompanied by a broad set of accessories that are designed for biomedical baths
