ISO 12189 Implants for Surgery - Mechanical Testing of Implantable Spine Devices - Fatigue Test Method for Spine Implant Assemblies Using the Anterior Support

The standard “ISO 12189 Implants for surgery - Mechanical testing of implantable spinal devices - Fatigue test method for spinal implant assemblies using an anterior support” developed by the International Organization for Standardization (ISO) describes methods for fatigue testing of spinal implant assemblies (for fusion or motion retention) using an anterior support. This standard aims to provide a basis for evaluating the intrinsic static and dynamic strength of spinal implants.

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

• The active length of the longitudinal member refers to the straight line distance between the connection center of the upper anchor and the connection center of the lower anchor.
• The model moment arm is the distance perpendicular to the applied load between the placement point of an anchor and the load application center.
• Failure is the permanent deformation resulting from fracture. Plastic deformation or loosening beyond ultimate displacement that renders the spinal implant assembly ineffective or inadequately resistant to load.
• The anchor insertion point is where the anchor is connected to the segment model.
• The intended spinal location is the anatomical region of the spine intended for application of the spinal implant device. Spinal implant devices are developed for specific spinal locations, such as the anterior cervical spine or the posterior cervical, thoracolumbar, lumbar, and lumbosacral spine.
• Maximum output load refers to the maximum load that can be applied to a spinal implant assembly where all tested structures withstand 5 million cycles without failure.
• A spinal implant assembly is a complete spinal implant configuration intended for surgical use. A spinal implant assembly will include anchors, interconnects, and longitudinal members and may include transverse members.
• The spinal implant construct is the complete spinal implant assembly attached to the appropriate test support.
• The UHMWPE test block is the component of the test apparatus for mounting the spinal implant assembly. A specific UHMWPE test block design is required for each intended spinal location and intended method of application. The figures provided throughout the standard describe the recommended designs for test blocks (lumbar specimens) and the recommended design for cervical specimens. However, alternative designs may be used as long as equivalent performance is demonstrated. Spinal implant assemblies contain different types of anchors. Each type of anchor has an intended method of application to the spine.

The purpose of this international standard is to provide a fatigue testing method that allows testing of spine devices that are not suitable for corpectomy testing. This method is based on the use of modified ultra-high molecular weight polyethylene (UHMWPE) test blocks and springs. This test support consists of test blocks made of UHMWPE representing the vertebrae and standard springs representing the intervertebral disc stiffness. The springs are selected from the standardized panel provided by the ISO 10243 standard. Then, fatigue tests in flexion compression are performed on the spine implant structure to evaluate the spine implant assembly (fatigue testing).

The attachment points may deviate from these dimensions when the design of the spinal implant assembly or the manufacturer's surgical instructions for installation dictate otherwise.

The use of a simulated body fluid, saline (1 g sodium chloride per 000 9 ml of water), may be considered. In this case, the liquid test medium should be introduced (before the fatigue test) in such a way that the contact surfaces of the test spinal implant structure are completely submerged. The temperature of the liquid test medium should be maintained at 37 degrees plus/minus 2 degrees, and measurements should be made during the tests at a location representative of the bulk temperature of the liquid.

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