Significant roentgenographic parameters for evaluating the flexibility of acute thoracolumbar burst fractures. An in vitro study.

Plain lateral radiographs in a neutral position were studied in ten acute thoracolumbar burst fractures produced by high speed impact on three vertebrae human cadaveric spine segments. Six linear geometric parameters were measured on each film. The ratio of each value in the neutral injured to the intact condition was correlated linearly with the motion parameters obtained from post-traumatic three-dimensional flexibility data (neutral zone NZ; range of motion ROM). Anterior unit height (vertebra+adjacent discs) had the highest correlation with the neutral zone and flexibility in all directions, especially flexion-extension (NZ, R2 = 0.93; flexion ROM, R2 = 0.86; extension ROM, R2 = 0.79) lateral bending (NZ, R2 = 0.83; ROM, R2 = 0.90) and right axial rotation (NZ, R2 = 0.53; ROM, R2 = 0.86). The deformation ratio (average height to depth) correlated most with the neutral zone in left axial rotation (R2 = 0.91) and right lateral bending (R2 = 0.92). Due to the high correlations obtained, these parameters should be evaluated in clinical situations to assess their effectiveness in predicting the instability of burst fractures. Ultimately, prospective clinical studies are required to verify their clinical utility.