ASTM F543 Annex A2 is used to measure the torque required to drive a bone screw into a test block made of a rigid unicellular polyurethane foam. The results obtained from this test bear no direct correlation to the torque required to insert a bone screw in human or animal bone. This method is used as a quality control check for maintaining product uniformity.
The basic test procedure for determining the insertion and removal torque is as follows:
Clamp the test block with a pre-drilled pilot hole into the machine.
Drive the bone screw into the test block at a rate between 1 and 5 rpm. The insertion torque will be the maximum torque measured within the first four revolutions of the bone screw.
Reverse direction and record the maximum removal torque during the four revolutions required to remove the bone screw.
Note: A 1.14 kg (2.5 lb) or less axial force should be applied to maintain engagement between the screw head and drive bit.
The embedded video demonstrates the ADMET E81 Torsion Tester recording the insertion and removal torque of a bone screw according to ASTM F543-A2. The test apparatus is a 20Nm capacity vertical torsion tester equipped with ADMET’s MTESTQuattro® PC based Torsion Testing Software.