ASTM F543 Axial and Torsion Testing of Bone Screws

Bone screws are used in surgical procedures for securing implants, osteosynthesis devices or fracture fixation plates to the skeletal system. In normal clinical use, a surgeon applies combined axial and torsional forces to the bone screw as they are implanted within the body. Manufacturers and scientists test bone screws to determine various mechanical properties to evaluate new materials and designs.

• ASTM F543-07 Test A1: “Test Method for Determining the Torsional Properties of Metallic Bone Screws” requires the screw to be sufficiently clamped and a rotational velocity between 1 and 5 rpm to be applied until specimen failure and to measure the torque profile and the rotational angle.
• ASTM F534-07 Test A2: “Test Method for Driving Torque of Medical Bone Screws” measures the torque required to insert and remove the screw with a constant rotational velocity between 1 and 5 rpm while maintaining an axial load of no more than 10 N in compression.
• ASTM F543-07 Test A3: “Test Method for Determining the Axial Pull-out Strength of Medical Bone Screws” measures the force required to axially remove the screw that has been fully inserted in the test block using the method from Test A2. The pull-out fixture then applies a tensile load at a constant rate of 5 mm/min until the failure of the bone screw or removal from the test block.
• ASTM F543-07 Test A4:“Test Method for Determining the Self-Tapping Performance of Self-Tapping Medical Bone Screws” specifies the procedure to evaluate the axial loading required to engage a self-tapping bone screw into a standard laboratory material. Although considered a simple clinical procedure, reproduction of this in vitro results in a relatively complex motion due to the interaction between the rotation and linear axes of a test machine. The test requires a continuous rotational velocity of up to 30 rpm, while the axial load is incremented during the insertion at a rate of 2 N/s. The objective of the test is to record the torque profile as the bone screw is inserted into the material and then removed.

The ElectroPuls™ E10000 Linear-Torsion machine or ElectroPuls E3000 Linear-Torsion test instrument are all-electric dynamic test system that provides a unique linear and torsion actuator system that is capable of synchronized linear and multi-rotation testing and is the ideal platform for performing the full range of tests prescribed by the standard. The combined actuator package is mounted in the upper crosshead of the machine, leaving the base clear for mounting of the biaxial Dynacell™ load cell and the fixtures to hold the material and bone screw.

We control the test system by using WaveMatrix™ Dynamic Test Software. This provides the ability to easily set-up the multi-axial tests as a series of steps and displays the required information as a test proceeds. Special fixtures are used to clamp the material to the biaxial load cell and a drill chuck used for the drive bits.

We recommend that you review the standard to fully understand its requirements.