FUNCTIONAL-MORPHOLOGY OF THE SPINAL-CANAL AFTER END-PLATE, WEDGE, ANDBURST FRACTURES

Changes in the canal diameter during physiological motions are importa nt considerations in the treatment of patients who have a burst fractu re with the presence of bony fragments, but without neurologic deficit . In this in vitro study, the changes in the soft-canal diameter of th e thoracolumbar region, when intact and after different fractures, was investigated under several different loading conditions. The soft-can al diameter was clearly identified on the lateral radiographs by attac hing a series of steel balls to the posterior longitudinal ligament an d ligamentum flavum in the midsagittal plane. Endplate, wedge, and bur st fractures were produced incrementally in 19 three-vertebrae human c adaveric spine specimens by high-speed impacts. After each injury, a s eries of functional lateral radiographs were taken. The minimal canal diameter (MCD) was obtained by digitizing the images of the steel ball s on radiographs using a custom-designed computer program. In the inta ct specimens, the MCD at the disc level changed significantly in flexi on, extension, and compression, when compared with the MCD in the unlo aded neutral position. However, the changes were small. The MCD after endplate and wedge fractures changed in a similar way. However, after the burst fracture, the MCD at the bone fragment level increased remar kably by a distraction force. It also significantly improved by an ant erior shear force in comparison to the corresponding MCD in the neutra l position. However, this change was smaller than the change due to th e distraction force.