Significance and Use
5.1 Total Facet Prosthesis Components—The total facet replacement may comprise a variety of shapes and configurations. Its forms may include, but are not limited to: ball-and-socket articulating joints, joints having a free-floating or semi-constrained third body, metallic load-bearing surfaces, and spring and dampening mechanisms. Additionally, it may have a unilateral or bilateral design.
5.2 Spinal Testing Apparatus:
5.2.1 Test Chambers—In case of a multispecimen machine, each chamber shall be isolated to prevent cross-contamination of the test specimens. The chamber shall be made entirely of corrosion-resistant materials, such as acrylic plastic or stainless steel, and shall be removable from the machine for thorough cleaning between tests.
5.2.2 Component Clamping/Fixturing—Since the purpose of the test is to characterize the wear and kinematic function of the total facet prosthesis, the method for mounting components in the test chamber shall not compromise the accuracy of assessment of the weight loss or stiffness variation during the test. For example, prostheses having complicated superior and inferior surfaces for contacting bone (for example, sintered beads, hydroxylapatite (HA) coating, plasma spray) may be specially manufactured to modify that surface in a manner that does not affect the wear simulation.
5.2.3 The device should be securely (rigidly) attached at its bone-implant interface to the mating test fixtures.
5.2.4 The motion of the superior test fixture (more posterior fixture in Figs. 1 and 2) relative to the inferior testing fixture shall be constrained in three-dimensional space except for the components in the direction of specified test motions/loads.
FIG. 1 Diagrams of Possible Test Apparatus for Allowing Simultaneous Lateral Bending and Axial Rotation Motions with Anterior-Posterior Directed Facet Loading
NOTE 1: This setup would require two rotational actuators and one translational actuator.
FIG. 2 Diagrams of Possible Test Apparatus for Allowing Simultaneous Flexion-Extension and Lateral Bending Motions with Anterior-Posterior Directed Facet Loading
NOTE 1: This setup would require two rotational actuators and one translational actuator.
5.2.5 Load and Motion:
5.2.5.1 Facet loads (fx) are initially applied in the direction of the positive X-axis.
5.2.5.2 Flexion load and motion are positive moment and rotation about the Y-axis.
5.2.5.3 Extension load and motion are negative moment and rotation about the Y-axis.
5.2.5.4 Lateral bend load and motion are positive and negative moments and rotations about the X-axis.
5.2.5.5 Axial rotation load and motion are positive and negative moments and rotations about the Z-axis.
5.2.6 Frequency—Test frequency shall be determined and justified by the user of this practice, and shall not exceed 2 Hz without adequate justification ensuring that the applied motion (load) profiles remain within specified tolerances and that the total facet prosthesis’s wear and functional characteristics are not significantly affected. See X1.6.
5.2.7 Cycle Counter—One complete motion is the entire range from starting position through the range of motion (or load when in load control) and returning to the starting position (load). Cycles are to be counted using an automated counting device.
Scope
1.1 This practice provides guidance for the functional, kinematic, and wear testing of motion-preserving total facet prostheses for the lumbar spine. These implants are intended to allow motion and lend support to the functional spinal unit(s) through replacement of the natural facets.
1.2 This practice is not intended to address the bone implant interface or the static characteristics of the prosthesis components. Fatigue characteristics are included, but only as a by-product of cyclic wear testing under facet load and thus are not addressed in the typical process of generating a Stress-Life (S-N) characterization.
1.3 Biocompatibility of the materials used in a total facet prosthesis are not addressed in this practice.
1.4 The values stated in SI units are to be regarded as standard. No other units of measurement are included in this standard.
1.4.1 The values stated in SI units are to be regarded as the standard with the exception of angular measurements, which may be reported in either degrees or radians.
1.5 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety, health, and environmental practices and determine the applicability of regulatory limitations prior to use.
1.6 This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
