Kinematic Stability Evaluation of Spinal Fusion Devices by Synthetic FSU Model

The purpose of the paper is to open discussion for an alternative methodology for stability testing of spinal fusion devices that does not require cadaveric tissue. A simulated single level functional spinal unit (FSU) model was used to evaluate spinal fusion devices as an alternative to using cadaveric human tissue models. Initially, this study was proposed as a feasibility investigation prior to investing in a cadaveric study, but was then developed into an alternative, stand-alone method that eliminates variabilities associated with cadaveric tissue testing for providing comparison testing between spinal devices. The objective of this paper is to present the development of the synthetic FSU model and the apparatus for providing kinematic stability testing on lumbar interbody spinal devices. The synthetic model geometry was based on morphological parameters for the lumbar spine using rigid foam per ASTM F1839. A universal servo-controlled test frame provided the pure moment loading through a system of cables and pulleys for the application of flexion-extension, lateral bending, and axial rotation. Comparable testing was performed using short cyclical, fully reversing runs up to 50 cycles where the last ten cycles were evaluated.