Spinal Implants and Intervertebral Fusion Devices are tested according to several ASTM standards. ASTM F2267 is intended to provide a basis for the mechanical comparison among past, present and future non-biologic intervertebral body fusion devices. These, sometimes hollow, devices are inserted to promote arthrodesis(fusion) at a given spinal motion segment. Construct are governed by ASTM F1717. The mechanical tests are conducted using simplified loading schemes and do not attempt to mimic the complex loads of the spine. An ADMET eXpert 2600 series Testing System equipped with MTESTQuattro will perform the tests required for this specification. An simple outline of the test procedures is as follows:
Axial Compression Subsidence Test – Metallic Blocks are used to determine stiffness of the device. Polyurethane Blocks are used to determine the likelihood of the part collapsing on itself. Device is secured between 2 blocks.
Stiffness procedure-25mm/min until functional or mechanical failure is obtained.
Subsidence procedure-0.1mm/sec until functional or mechanical failure is obtained.
Both procedures -plot Load vs. Displacement.
Yield Displacement, Stiffness, Yield Load or Moment, Ultimate Displacement, and Ultimate Load or Moment are to be recorded.
Sampling-
- 5 samples,
- polyethylene blocks(1 test) and Metallic blocks(can be reused) used for securing the specimen
- Push rod (38cm from center of spherical surface)
- Inferior sphere holds polyurethane block and is fixed to prevent movement.
- Superior fixture connects to pushrod by minimal friction sphere joint.
Determine Kp by Kp=Ks*Kd/(Kd-Ks)
Kp– Stiffness of Polyurethane Block
Kd-Stiffness of Intervertebral Body Fusion Device
Ks-Stiffness of System
ADMET eXpert 2610 5kN or 10kN – Tension/Compression or Biaxial (shown above) Testing System equipped with MTESTQuattro controller for static tests. System is shown with a multi axis load cell capable of measuring Fx, Fy, Fz and Mz.
