ISO 18192-1 Implants for Surgery - Wear of Total Intervertebral Disc Prostheses - Part 1: Loading and Displacement Parameters for Wear Testing and Corresponding Environmental Conditions for Testing

The standard “ISO 18192-1 Implants for surgery - Wear of total intervertebral disc prostheses - Part 1: Loading and displacement parameters for wear testing and corresponding environmental conditions for testing” developed by the International Organization for Standardization (ISO) describes a test procedure for relative angular motion between articulating components. This standard also defines the pattern of applied force, test speed and duration, specimen configuration, and the test environment to be used for wear testing of total intervertebral disc prostheses.

This standard covers both lumbar and cervical prostheses. This standard does not apply to partial disc replacements such as nucleus replacements or facet joint replacements. The test method focuses on wear testing. Additional mechanical testing such as fatigue testing may be required.

This standard does not reproduce complex in vivo loads and motions. Wear data obtained with this test method allows comparisons between different implant types but may differ from clinical wear performance. Users may consider running additional wear tests that address specific safety issues of the individual implant design being tested.

For the purposes of this standard, the following terms and definitions apply:

• Axial rotation is angular motion in the transverse plane about the Z axis.
• Flexion/extension is angular movement in the sagittal plane about the Y axis.
• Functional failure is failure that results in the implant failing to withstand load and/or move as originally intended in the implant's design.
• Lateral bending is angular movement in the frontal plane about the X-axis.
• Mechanical failure is the initiation of a defect in the material (e.g. the initiation of a fatigue crack).
• The origin is the center of the coordinate system located at the instantaneous center of rotation in the neutral position of the total disc replacement.
• User-defined failure is any failure criterion determined and controlled by the user, taking into account the specific design of the implant to be tested.
• The X-axis is the positive X-axis directed forward.
• The y-axis is oriented laterally to the left.
• The Z-axis is oriented upward.
• The cycle limit is the number of cycles at which the test terminates if no functional failure has occurred.

When performing the test, the upper and lower components of a test specimen are placed in position in the configuration designed for clinical use. The test apparatus transmits a specified time-varying force between the components together with specified relative angular displacements. If polymers are the subject of investigation, a load-impregnated control specimen is subjected to the same time-varying force to determine the creep of the test specimen or the amount of mass change resulting from fluid transfer. The test is conducted in a controlled environment simulating physiological conditions.

The liquid test medium is serum diluted with deionized water (balance) to a concentration of 20 g plus/minus 2 g protein/l. If desired, the liquid test medium may be filtered through a 2 µm filter. To minimize microbial contamination, the liquid test medium should be stored frozen until required for testing. An antimicrobial reagent (such as sodium azide) may be added. Such reagents may be potentially hazardous. The pH of the liquid test medium should be routinely monitored.

If this is not practical due to the physical properties of the implant system, the lower and upper components should be provided with an articular surface between them, which is held in place by its normal direct support, for example, bone cement or a machined replica of the inner surface of the support. If the component forming the articular surface is fixed to a support, the machined replica should meet the same fixation conditions.

If it is not practical to use normal support or cement fixation due to the physical properties of the implant system, the support system for the lower or upper component should represent the normal design characteristics and conditions of use but allow for non-destructive removal of the component for measurement of wear. The recommended minimum number of specimens for wear testing should be six. If fewer than six specimens are tested, appropriate justification should be provided. The number of specimens tested may be subject to national legal regulations.

At least one additional sample should be used to correct for weight gain by fluid uptake. The load suction control is loaded according to the load profile given for the implant type. The user may decide not to use a suction control when testing materials that do not absorb surrounding fluid, such as metal materials.

Among the numerous tests, measurements, analyses and evaluation studies that our organization has carried out for businesses in various sectors, our organization also provides testing services defined in the standard “ISO 18192-1 Implants for surgery - Wear of total intervertebral disc prostheses - Part 1: Loading and displacement parameters for wear testing and corresponding environmental conditions for testing” with its trained and expert staff and advanced technological equipment.