ISO 18192-3 Implants for Surgery - Wear of Total Intervertebral Disc Prostheses - Part 3: Impact Wear Test and Associated Environmental Conditions for Testing Lumbar Prostheses Under Adverse Kinematic Conditions

The standard “ISO 18192-3 Implants for surgery - Wear of total intervertebral disc prostheses - Part 3: Impact wear test and associated environmental conditions for testing lumbar prostheses under adverse kinematic conditions” developed by the International Organization for Standardization (ISO) describes a test procedure to simulate and evaluate lumbar spinal disc prosthesis wear under adverse impact conditions.

For the purposes of this standard, the terms and definitions given in ISO 18192-1 and the following apply:

• Impaction, the point at which two opposing components collide or restrict motion, is usually indicated by a sharp change in force or moment.
• Range of motion refers to the amount of angular displacement that a total disc replacement prosthesis can undergo from the neutral position of the device around a defined spherical axis to the point where impingement occurs. If an implant impinges at an angle of 15 degrees from the implant neutral position in flexion and 20 degrees from the implant neutral position in extension, the implant range of motion can be defined as plus 15 degrees/minus 20 degrees in flexion/extension.
• The distance between the center of rotation and the point of impact refers to the distance between the point of impact and the nominal center of rotation for flexion, extension or lateral bending movements.
• The axial load during impact is the axial load (in newtons) applied to the device when the device is in impact.
• The point of impact is the point of contact between two opposing components that causes impact.

Based on current clinical evidence, lumbar spine disc prostheses experience compression in extension/flexion, lateral bending, axial rotation, and combinations thereof, with extension being the most commonly reported mode for the lumbar spine. Adverse impact test conditions are determined based on available clinical data, engineering analysis, and other relevant information in the literature. Axial load and time-varying angular displacement are applied to test specimens to simulate repeated contact between design features of the specimens.

In practice, four possible individual impact scenarios have been identified:

• Flexion
• Extension
• Lateral bending
• Combined flexion and lateral bending

Additionally, axial rotation combined with any of the above modes of motion should be considered if necessary to obtain a clinically relevant impact wear signature or worst case impact scenario. A load-impregnated control specimen is subjected to the same time-varying force to determine the amount of mass change due to fluid transfer or creep of the test specimen if polymers are the subject of investigation. Testing occurs in a controlled environment simulating physiological conditions.

When performing the test, liquid test medium consisting of serum diluted with deionized water to a concentration of 20 g plus/minus 2 g protein/l should be prepared in accordance with the ISO 18192-1 standard. If the pH value of the liquid test medium is routinely monitored, an increase in the pH value indicates an increase in microbial activity and the values ​​should be included in the test report.

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 abutment. If the component forming the articular surface is fixed to a support, the machined replica should meet the same fixation conditions.

If it is impractical 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 normal design specifications and conditions of use but allow non-destructive removal of the component for measurement of wear.

For impact wear testing, it is recommended to test six samples.

Among the numerous testing, measurement, analysis and evaluation studies that our organization has provided for businesses in various sectors, our organization also provides testing services defined in the standard “ISO 18192-3 Implants for surgery - Wear of total intervertebral disc prostheses - Part 3: Impact wear test and related environmental conditions for testing lumbar prostheses under adverse kinematic conditions” with its trained and expert staff and advanced technological equipment.