REDUCED TRANSVERSE SPINAL AREA SECONDARY TO BURST FRACTURES - IS THERE A RELATIONSHIP TO NEUROLOGIC INJURY

A retrospective case-control study was undertaken to determine the bes t technique to measure neural canal encroachment at each lumbar level following burst fracture and its relationship to the presence of neuro logic deficit. Only patients with postinjury CT scans demonstrating a disrupted posterior body with a retropulsed bone fragment were include d. Patients were divided into groups based on the level of bony injury (T12-L5) and neurologic status. Neurologic injury was classified as f ollows: normal (N), root (R), or cauda equina/conus/paraplegic/parapar etic (C/P). The mean transverse spinal area (TSA, cm(2)), spinal canal percentage patency (PP), and midsagittal diameter (MSD) were determin ed for each neurologic group and lumbar level. A ''calculated'' TSA, b ased on midsagittal and anterior-posterior diameters, was also derived for each patient. The data were compared level by level and correlate d with the patient's neurologic status. At L1, the critical TSA was 1. 0 cm(2). All patients with TSAs less than this were paraplegic. At bot h T12 and L1, TSAs in the range of 1.0-1.25 cm(2) were observed in bot h normal and neurologically impaired patients. A critically significan t TSA was not established for levels T12, L2, L3, L4, or L5; however, the data indicated that a smaller TSA can be tolerated at successively caudal levels without neurologic deficit. No meaningful correlation b etween root injury and TSA was observed. The data also indicated that measurement of TSA. is a more accurate method for evaluating neural ca nal encroachment than PP or MSD. The ''calculated'' TSA is a simple, o bjective method for obtaining this information without the aid of a co mputer. This study suggests that absolute TSA should be utilized in fu ture studies evaluating decompressive treatment of thoracolumbar patho logy.