Volume 9, Issue 3 (March 2012)
ASTM F2624-07—Evaluating an Alternate Fixture for Testing Extra Discal Motion Preserving Implants
ASTM F2624-07 prescribes applying flexion/extension, lateral bending, and axial rotation moments to test and evaluate extra discal motion preserving implants (EDMPI). The standard provides a suggested laterally oriented construct (LOC) for conducting flexion/extension (FE) testing. The suggested construct does not have a fixed center of rotation (COR). An alternate set of fixtures to conduct FE testing using a vertically oriented construct (VOC) with a fixed COR is presented. Testing was conducted to quantify the loads applied to an EDMPI using both types of fixtures, quantify shear loading applied to the actuator, determine whether results are frequency dependent, and evaluate whether the fixtures can differentiate between EDMPI using a measure of displacement amplitude. A miniature load cell was mounted to both fixtures to quantify load applied to an EDMPI during testing at several different applied loads or torques and at two testing frequencies (2 Hz and 5 Hz). Lateral actuator shear was measured using a dial indicator. The load cell was replaced with cylindrical test specimens made of stainless steel, titanium, polyether ether ketone, or a polyethylene cable slipped inside a polyurethane tube, and the testing repeated. Results indicated that both fixtures generated similar tensile/compressive loads at an EDMPI. The LOC fixture generated more actuator shear than the VOC. Using a VOC fixture rather than the LOC suggested in ASTM F2624-07 in FE testing may be a reasonable alternative for certain types of devices.