Testing Spinal Fusion Systems per FDA Guidelines

The linked FDA Guidance Document published in 2004 applies to plate and rod-based fusion spinal systems, as well as vertebral body replacement devices. Each rod and plate-based spinal system is described by one or more system types (e.g., a thoracolumbar anterior plate system and pedicle screw system). The guidance document does not address interbody fusion and non-fusion devices (i.e., cages or disc replacement devices) or other nonfusion spinal devices. The static and dynamic fatigue test requirements are extensive and require servo controlled electrodynamic fatigue test machines, or alternatively, servo hydraulic test machines. Spinal Implant Mechanical Testing Overview The FDA recommends that you perform all testing on spinal assembly system constructs comprised of components in worst case (e.g., most likely to loosen or fail) final design version. The tested components should comprise of the worst case constructs in terms of design, interconnection mechanism, materials, manufacturing-related processing, etc. Testing should involve the worst case construct of the total system, unless you have an adequate rationale for testing only individual components. Cervical Spinal System Testing System Type Recommended Testing Anterior, Cervical System Static and dynamic axial compression bending testing Static torsion testing Posterior Cervical, Nonpedicle System Static and dynamic axial compression bending testing Static and dynamic torsion testing Cervical, Pedicle Systems Static and dynamic axial compression bending testing Static and dynamic torsion testing If the system attaches to the occiput, then dynamic torsion testing is required. A modified version of ASTM F1717 is recommended for testing constructs intended to be connected to the occiput. Non-Cervical Spinal System Testing System Type Recommended Testing Anterior, Noncervical System Static and dynamic axial compression bending testing Static torsion testing Posterior Noncervical, Nonpedicle System Static and dynamic axial compression bending testing Static torsion testing Noncervical, Pedicle Systems Static and dynamic axial compression bending testing Static torsion testing Vertebral Body Replacement Device/System (VBR) Static and dynamic axial compression bending testing Static and dynamic torsion testing Expulsion For the dynamic axial compression bending tests, the FDA recommends that you meet one of the following conditions: asymptotic load level greater than or equal to 3000N (675 lb) at 5,000,000 cycles asymptotic load level greater than or equal to 1500N (340 lb) at 10,000,000 cycles Expulsion testing may not be necessary for a VBR system that incorporates a supplemental fixation system that is physically attached to it (e.g., by a threaded bolt). Static and Fatigue Testing Descriptions Static construct testing should involve six or more samples of the worst case construct. According to the FDA, fatigue construct testing is most commonly performed per ASTM F1717. Use ASTM F1717 to provide a standard comparison to predicate device testing and to declare conformity to that standard. Choose alternative test methods that you show are substantially equivalent to the ASTM standard to address the mechanical loading issues at hand. ASTM F1717 is based on metallic spinal systems and may not be applicable to systems made out of other materials. Additional testing and/or modifications to ASTM F1717 may be required if the new system is manufactured out of a polymer or other materials. The fatigue construct testing should involve six or more samples of the worst case construct to generate an Applied Force vs. Number of Cycles (AF/N) curve that characterizes the asymptotic endurance limit at a runout value of five million cycles compared to an appropriate predicate system. ASTM F1717 recommends a Stress versus Log number of cycles (S/N) curve; however, an AF/N curve is acceptable. Test two or more samples at the lowest load level in order to establish a resulting endurance load limit. Test Report The FDA recommends you provide a complete test report with the following information: identification of the components that comprised the constructs or subconstructs tested the rationale for why those components comprised the worst case constructs or subconstructs the rationale for the loading modes chosen (e.g., axial, bending, torsion) identification of testing configuration and environment and a rationale for why that configuration and environment were chosen Test results a discussion of the results in terms of the expected in vivo and clinical performance of the assembly if there are differences between the subject system and the system actually tested (e.g., tests performed on prototype), an explanation of how or why the results are relevant in supporting a substantial equivalence determination. Note this brief summary of FDA Guidelines does not include extensive and critical information required to meet FDA regulatory requirements. Contact the FDA for their full support. The original source of the information presented above is the FDA and TestResources intent is to facilitate and encourage you to contact them for further information regarding their requirements and expectations regarding all regulatory matters.

Applicable Testing Standards

Recommended Test Machine

800 Series Fatigue Test Machines

Static and fatigue forces up to 50 kN (11,250 lbf)
Frequency ratings up to 75 Hz
Oil-free, all electric actuator for clean test conditions
Lower purchase, operating, and maintenance costs than hydraulic equivalents

830 Series Axial Torsion Test Machine

Force ratings up to 50 kN (11,250 lbf) and torque ratings up to 180 Nm (1,600 lbf∙in)
Can apply axial and torsional loads simultaneously
Performs both static and dynamic tests
All electric and oil-free operation