Fromtheauthors’hypothesisthatthefacetjoints are an integral component of the loading mechanism, an experiment was designed to load isolated facet surfaces to failure. The resulting fracture patterns proved to be comparable with those in clinical cases of severe burst fracture, suggesting that the facets transmit loads of sufficient magnitude to cause damage to the posterior bony complex. ● Analytical and finite-element analyses were then performed to support or refute the experimental results. The information gained from these studies andareviewoftheliteratureonfacetjointloading wasappliedtothedesignofatestingprotocolusing motion segments. ● Theresultsareinsupportoftheauthors’hypothesis that anterior shear in addition to axial compression, is a critical factor in producing the severe canal compromise that characterizes acute burst fractures of the thoracolumbar spine