Validity of the three-column theory of thoracolumbar fractures. A biomechanic investigation.

STUDY DESIGN This study validated the three-column theory of fractures by correlating the multidirectional instabilities and the vertebral injuries to each of the three columns, using a biomechanic trauma model. OBJECTIVES The objective was to validate the three-column theory as applied to the thoracolumbar fractures. SUMMARY OF BACKGROUND DATA The widely used three-column theory of fractures for classification and evaluation was based on retrospective analysis of radiographs. No biomechanic study, using realistic spinal fractures and multidirectional instability measurements, was available. METHODS Using 16 fresh cadaveric thoracolumbar human spine specimens, two groups of burst fractures were produced by either simple axial compression or flexion-compression, using a high-speed trauma model. Multidirectional flexibility was measured before and after the trauma, thus quantifying the instability of the burst fracture. Computed tomography scans were taken after the fracture, and a newly developed injury scoring scheme quantified the injuries to the anterior, middle, and posterior columns. Statistical correlations were obtained between the flexibility parameters and injuries to each of the three columns. RESULTS In the axial compression group, the middle column injury, compared with the other two columns, showed the highest correlations to eight of the nine flexibility parameters (average R2 = 0.77). In the flexion-compression group, again the middle column injury showed the highest correlations to eight of the nine flexibility parameters (average R2 = 0.85). CONCLUSIONS The results of this study supported the three-column theory of the thoracolumbar fractures and bolstered the concept of the middle column being the primary determinant of mechanical stability of this region of the spine.