DYNAMIC CANAL ENCROACHMENT DURING THORACOLUMBAR BURST FRACTURES

In the burst fractures seen clinically, often poor correlation exists between the neurological deficit and the canal encroachment measured o n posttrauma radiographic images. The purpose of the present study was to determine whether the dynamic canal encroachment during the trauma is greater than the static canal encroachment posttrauma. We successf ully produced burst fractures in nine of 15 fresh human cadaveric thor acolumbar spine specimens (T11-L1). The specimens were incrementally i mpacted in a high-speed trauma apparatus until fracture occurred. Duri ng the trauma, dynamic canal encroachments were measured using three s pecially designed transducers placed in the canal at the levels of the superior end-plates of the T12 and L1 and the T12/L1 disk. After the trauma, residual static spinal canal encroachments were measured from the radiographs of the specimens that were prepared with 1.6-mm diamet er steel balls lining the canal in the midsagittal plane. We found tha t the average canal diameter was 16.6 +/- 1.3 mm and the static canal encroachment was 18.0% of the canal diameter. The corresponding dynami c canal encroachment was 33.3%. Thus, the dynamic canal encroachment w as 85% more than the static measurement. The clinical significance of this study lies in providing awareness to the clinician that the dynam ic canal encroachment is significantly greater than the static canal e ncroachment seen on posttrauma radiographs or computed tomography scan s. The finding may also explain the clinical observation of poor corre lation between the canal encroachment measured radiographically and th e neurological deficit.