M.F. Dvorak, S.P. Kingwell, V.K. Noonan, C.G. Fisher, and O. Keynan reply:
We would like to thank Dr. Rice et al. for their comments regarding our paper, "Relationship of Neural Axis Level of Injury to Motor Recovery and Health-Related Quality of Life in Patients with a Thoracolumbar Spinal Injury." We would like to clarify how the imaging studies of our patients contributed to the variables that we studied.
First of all, the area of maximal compression was determined for all patients from preoperative imaging studies and was not inferred from images acquired after surgery. For some patients, a preoperative MRI was available and, for those patients, that modality was used to determine the spinal vertebral level of maximal spinal canal occlusion. For other patients, this information was determined from a preoperative computerized axial tomography (CT) scan. For a T12-L1 fracture dislocation, for example, our treatment protocol is to perform a CT scan while the patient is still in the emergency department but to urgently take the patient to the operating room for surgical open reduction and stabilization without waiting for an MRI scan to be performed. Although most of our patients underwent preoperative MRI scans, this was not the case for all of them.
The second variable that we analyzed was the neurological level of maximal compression, and this required a determination of the location of the tip of the conus medullaris. This determination was made, for every patient, on the basis of the MRI scan; however, some of the MRIs were performed prior to surgery and, as Dr. Rice et al. have identified, some were performed afterwards. In some cases, due to the level and extent of compression as well as the quality of the initial preoperative MRI, a precise determination of the tip of the conus medullaris could not be made on the basis of the preoperative MRI. In these cases, a postoperative MRI was performed to clarify the location of the termination of the spinal cord. MRI scans performed years after the injury were never used to determine the location of compression; they were only used to identify the location of the conus medullaris.
We agree with the other comments made by Dr. Rice et al. and acknowledge that cross-sectional outcomes may confound our analysis. As far as the variability in treatment is concerned, we acknowledge the variety of treatments in our patients; however, we have maintained consistent principles of management and have always focused on achieving decompression and stabilization of these injuries through either direct or indirect means. We did not believe that our study sample afforded us the power to analyze how the various types of treatment influenced outcomes.