Static and Dynamic Articular Facet Loads

Previous work on biodynamic response to whole-body +G_z (caudocephalad) acceleration gave ample evidence of facet loads in intact cadaveric spines. The computation of facet loads was based on an assumption that the total spine load was proportional to the measured seat pan load. In this study, the aim is to investigate the magnitude of the facet load during static and dynamic loading of an exised spinal segment. The applied loads resulted in a close simulation of those experienced by the intervertebral disc during whole-body impacts. An intervertebral load cell was used as the controlling mechanism in the duplication of the whole-body run in a testing machine. During these tests, both the total spine load and the intervertebral load were measured and thus the facet load was determined without relying on any assumptions.

Results from tests on 5 different cadaveric spinal segments, involving 32 static runs and 62 dynamic runs, show that facet loads exist under both static and dynamic loading and that these joints were capable of carrying upt to 40% of the total spine load.