Two aspects of thoracolumbar injury were studied:​ mechanisms of thoracolumbar fracture, and the biomechanical function of spinal orthoses used in the treatment of thoracolumbar injuries.

A detailed three-dimensional finite element model of the thoracolumbar spine (T11-T12-L1) was developed. Two different types of facet articulations, lumbar-type and thoracic-type, were modeled to test the hypothes is that an abrupt facet orientation transition at T12 can produce stress concentrations leading to fracture. Unexpectedly, under complex loading conditions of axial compression plus extension moment, abrupt facet orientation transition did not produce the highest vertebral body stresses - lumbar-type facets did. The results indicate that in the thoracolumbar region, the superiormost vertebra with lumbar-type superior facets may have a greater risk of injury than the "transition vertebra" above it.

An experimental protocol to study the biomechanical function of "three-point" hyperextension spinal orthoses was developed and carried out on six healthy male subjects. Jewett and CASH hyperextension orthoses were instrumented with custom-made force transducers to determine the amount of moment applied to the trunk by each orthosis during various trunk range of motion and static isometric trunk extension effort tasks. The results indicated that 'three-point' hyperextension orthoses apply extension moments to the trunk upon the initial fitting of the orthosis, and that these orthosis moments increase with attempted trunk flexion and with trunk extension effort. Both orthoses limited spinal deformation rather than hip rotation. The Jewett orthosis developed higher forces than the CASH in response to external loads applied to the trunk. No decrease in trunk muscle EMG activity occurred with orthosis wear in the trunk extension efforts.

Orthosis preload and orthosis stiffness were studied analytically using the finite element method. The detailed T11-T12-L1 finite element model was incorporated into a simpler beam representation of the orthotically stabilized trunk to determine effect of orthosis on spinal stresses, for intact and injured cases. Experimental trends concerning orthosis stiffness were confirmed in the analytical study. Orthosis preload may be detrimental in terms of spinal stresses, depending on the injury.

Finally, the concept of a four-point hyperextension orthosis was developed, and preliminary tests were carried out, demonstrating its feasibility.