ASTM F1798 Partial constructions for spinal implants

We offer various test methods for the mechanical characterization of partial constructions of spinal implants according to ASTM F1798. A substructure consists of an element for the connection to a vertebral body (hook or screw) and a longitudinally proceeding element (rod or plate), which are connected to one another via a connecting mechanism. Within the scope of the test, loads and moments are applied in three directions (corresponding to a vertebral body): anterior-posterior (x), lateral (y) and longitudinal (z). From the following range, we will select the appropriate test procedures for the partial constructs of your individual spinal implants:

• Static test methods
  1. Anterior-posterior and lateral loading:
  The longitudinally proceeding component is firmly clamped in the test device and a load (max. 25 mm/min) is applied over the connecting element in the x- and y-directions, respectively. The force-displacement curves are recorded and evaluated with regard to the mechanical properties (including stiffness and strength).
  
  2. Connection Stability:
  In this test, the connection stability between the connecting element and the longitudinal element is determined. One side of the longitudinal element is firmly clamped while the other side remains free. A load (max. 25 mm/min) parallel to the longitudinal element is applied to the connecting element via a sleeve until the connecting element is released. A force-displacement curve reveals a significant drop in force, which marks the exceeding of the connection strength.
  
  3. Flexion extension and transversal moment:
  The longitudinal component is firmly clamped in the test device and a load (max. 25 mm/min) is applied in the z-direction. The connecting element serves as a lever arm, so that a moment about the x- or y-axis is generated. The force-displacement curves are recorded and evaluated with regard to the mechanical properties (including stiffness and strength).
  
  4. Axial torsion:
  In this test, the connection stability between the connecting element and the longitudinal element is determined under torsion. One side of the longitudinal element is firmly clamped while the other side remains free. A torque (max. 25 °/min) is applied to the connecting element via a sleeve until the connecting element is released. A moment-angle curve can be used to determine a significant drop in the torque, which marks the exceeding of the connection strength.
  
  
• Dynamic test methods
  Following the static tests, the tests with new test specimens are performed dynamically over 2.5 million cycles. The load should be 75% of the load at which the partial construct has failed statically. If the partial construct fails before reaching the 2.5 million cycles, the load is successively reduced until three test specimens pass through. Following the dynamic tests, the axial joint strength is tested under torsion to determine residual stability. The tests should be carried out under laboratory conditions (air and room temperature), but can also be repeated in Ringer solution at 37 °C, if necessary, in order to simulate the physiological ambient conditions and to consider possible corrosive effects.