COMPARISON OF RESIDUAL STABILITY IN THORACOLUMBAR SPINE FRACTURES USING NEUTRAL ZONE MEASUREMENTS

Because treatment algorithms for spinal injuries depend largely on the clinical assessment of stability after injury, this study both quanti fied and compared the mechanical stability after three different patte rns of injury in the thoracolumbar spine. We created compression fract ures, burst fractures, and flexion-distraction injuries in 26 thoracol umbar specimens from human cadavers in order to compare residual stabi lity as a function of type of injury. Spinal stability was evaluated u sing measurements of the boundaries of the neutral zone, which provide a measure of spinal laxity in various directions of motion. An increa se after injury was indicative of greater spinal laxity and hence redu ced residual stability. Geometric characteristics (or parameters) of t he neutral zone boundaries were used for statistical comparison betwee n the types of injury. Of the three groups, burst fractures retained t he least residual stability and compression fractures, the greatest, T he angular ranges of motion in the neutral zone for burst fractures de monstrated increases (compared with average values for intact specimen s) of 154% in flexion-extension, 134% in lateral bending, and 108% in torsion after injury. The results for flexion-distraction injuries wer e similar to those for burst fractures in flexion-extension (126%) and torsion (62%); however, more residual stability was retained in later al bending than was seen for burst fractures (48%). Compression fractu res retained the most residual stability, with increases in motion of 40% in flexion-extension, 56% in lateral bending, and 3% in torsion. T hese findings may be useful in determining the necessity for surgical stabilization of the spine and selection of the appropriate system of fixation.