Verification of Pure Moment Testing in a Multi-Degree of Freedom Spine Testing Apparatus

Abstract

Background Pure moment testing is a common method used in cadaveric spine testing. The fundamental basis for the widespread acceptance of applying a pure moment is uniform loading along the column of the spine. To the author’s knowledge, this protocol has not been experimentally verified on a multi-degree-of-freedom testing apparatus. Due to its ubiquitous use in spine biomechanics laboratories, confirmation of this comparative cadaveric test protocol is paramount. Methods Group A specimens (n = 13) were used to test the pure moment protocol, using 3 constructs that changed the number of involved vertebrae, orientation and rigidity of the spine construct. Group B specimens (n = 6) were used to determine if potting orientation, testing order or degradation affected the range of motion (ROM) using 8 constructs. Each group was subjected to 3 cycles of flexion-extension, lateral bending and axial torsion. The data from the third cycle was used to calculate the ROM for each method. Results Group A testing resulted in significant differences in ROM across the 3 constructs for lateral bending and axial torsion ( P < 0.02), and trended towards a difference for flexion-extension ( P = 0.055). Group B testing showed an increase in ROM across 8 constructs ( P < 0.04), but no significant difference due to the orientation change. Conclusion The increased ROM across constructs observed in both groups indicates that the cause is likely due to the testing order or degradation of the specimens, with orientation having no observed effect. The data does not invalidate pure moment testing and its use should persist.