Standard Guide for Impingement Testing of Total Disc Prostheses

Importancia y uso:

5.1 This guide can be used to develop test parameters for evaluating fatigue and wear behavior of IVD prostheses under impingement loading. It must be recognized, however, that there are likely many possible impingement conditions for a given IVD prosthesis.

5.2 The user should attempt to determine the clinically relevant and geometrically possible impingement conditions and dictated by the design and impingement wear test parameters that may result in wear and fatigue damage for the IVD prosthesis. The user should also attempt to select the device size which will represent a worst case for the impingement conditions and parameters selected.

5.3 The user should reference and utilize existing sources of information to identify the impingement test parameters that produce the clinically relevant impingement wear and damage for their IVD prosthesis. Prior clinical experience with the device design may aid in the development of impingement test parameters through analysis of device retrievals and radiographs. However, prior clinical experience with the IVD being tested should not be considered as a prerequisite for performing impingement testing.

5.4 This guide details a three-step process for assessing device impingement under a selected set of conditions:

5.4.1 The user selects previously identified impingement conditions, one at a time, or clinically observed conditions.

5.4.2 The user selects the worst-case size of device to apply the selected conditions.

5.4.3 Solid modeling and the quasistatic test method should be employed to assess the impingement condition and determine the impingement test parameters—most importantly, the angular displacement limits to be used in the impingement wear test.

5.4.4 The impingement wear test is then conducted using the impingement test parameters.

5.5 This guide serves to evaluate devices with various designs, materials (i.e., metal-on-metal versus polymer-on-polymer), and stiffness in the impingement region using the same axial force and angular displacement control.

5.5.1 In the case where the device has no limit in a given direction or does not allow motion in a given direction, a rationale for excluding that condition should be provided (e.g., intended design or function of the device).

5.6 Impingement occurs over a range between an initial and an ultimate angle rather than at a discrete angle and location because both design (e.g., mobile bearings) and material combinations (e.g., inclusion of polymeric materials) may lead to compliance, deformation, and wear, which in turn may lead to a change in the angular displacement at which contact occurs over the course of the test. A range of angular displacement is therefore prescribed to ensure that the impingement region is fully loaded during each impingement cycle.

5.7 The suggested test parameters in Table 1 have been provided with the objective of minimizing Mode I wear at the bearing surface while providing sufficient motion to fully offload the bearing surface for each cycle. Given that the intended function of the devices is typically to articulate, it may be impossible to fully eliminate Mode 1 wear at the intended bearing interface.

5.8 The point of impingement (POI) is a simplification for the purpose of determining an impingement moment arm and thus calculating the theoretical ultimate moment (M_t). M_t may be useful for comparing device designs.

5.9 The contribution of axial rotation to impingement damage is still under-studied. However, retrieval analysis has provided evidence that it may contribute to impingement damage. Many total disc replacements are unconstrained in axial rotation. Therefore, unlike flexion-extension or lateral bending where a moment versus angular displacement response can be readily developed, axial rotation will have a near-zero moment response. The axial rotation parameters provided in Section 15 are based on the Mode 1 wear test methods and should be assessed and altered if justification (e.g., wear patterns from retrievals, scientific literature, etc.) exists.

Subcomité:

F04.25

Referida por:

F3292-25

Volúmen:

13.02

Número ICS:

11.180.10 (Aids and adaptation for moving)

Palabras clave:

impingement spinal implants; intervertebral disc prosthesis; total disc prostheses; wear assessment;