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Relationship of Neural Axis Level of Injury to Motor Recovery and Health-Related Quality of Life in Patients with a Thoracolumbar Spinal Injury
Stephen P. Kingwell, MD, FRCS(C)1; Vanessa K. Noonan, MSc1; Charles G. Fisher, MD, MHSc, FRCS(C)1; Douglas A. Graeb, MD, FRCP(C)2; Ory Keynan, MD3; Hongbin Zhang, MSc1; Marcel F. Dvorak, MD, FRCS(C)1
1 Division of Spine, Department of Orthopaedics, University of British Columbia, Room 6180, Blusson Spinal Cord Centre, 6th Floor, 818 West 10th Avenue, Vancouver, BC V5Z 1M9, Canada. E-mail address for M.F. Dvorak: marcel.dvorak@vch.ca
2 Department of Radiology, Vancouver General Hospital, 899 12th Avenue West, Vancouver, BC V5Z 1M9, Canada
3 Department of Orthopaedics “B,” Tel Aviv Sourasky Medical Center, 6 Weitzman Street, Tel Aviv 64239, Israel
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Disclosure: In support of their research for or preparation of this work, one or more of the authors received, in any one year, outside funding or grants in excess of $10,000 from the Rick Hansen Neurotrauma Fund. Neither they nor a member of their immediate families received payments or other benefits or a commitment or agreement to provide such benefits from a commercial entity.

A commentary by Laurence B. Kempton, MD, and Harry N. Herkowitz, MD, is available at www.jbjs.org/commentary and as supplemental material to the online version of this article.
Investigation performed at the Division of Spine, Department of Orthopaedics, University of British Columbia, Vancouver, British Columbia, Canada

Copyright ©2010 American Society for Journal of Bone and Joint Surgery, Inc.
J Bone Joint Surg Am, 2010 Jul 07;92(7):1591-1599. doi: 10.2106/JBJS.I.00512
A commentary by Harry N. Herkowitz, MD, is available here
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Abstract

Background: 

Outcomes following traumatic conus medullaris and cauda equina injuries are typically predicted on the basis of the vertebral level of injury. This may be misleading as it is based on the assumption that the conus medullaris terminates at L1 despite its variable location. Our primary objective was to determine whether the neural axis level of injury (the spinal cord, conus medullaris, or cauda equina) as determined with magnetic resonance imaging is better than the vertebral level of injury for prediction of motor improvement in patients with a neurological deficit secondary to a thoracolumbar spinal injury.

Methods: 

Patients diagnosed with a motor deficit secondary to a thoracolumbar spinal injury, and who met the inclusion criteria, were contacted. Each patient had a magnetic resonance imaging scan that was reviewed by a spine surgeon and a neuroradiologist to determine the termination of the conus medullaris and the neural axis level of injury. Patient demographic data were collected prospectively at the time of admission. Admission and follow-up neurological assessments were performed by formally trained dedicated spine physiotherapists.

Results: 

Fifty-one patients were evaluated at a median of 6.2 years (range, 2.7 to 12.3 years) postinjury. The final motor scores differed significantly according to whether the patient had a spinal cord injury (mean, 62.8 points; 95% confidence interval, 55.4 to 70.2), conus medullaris injury (mean, 78.6 points; 95% confidence interval, 70.3 to 86.9), or cauda equina injury (mean, 88.8 points; 95% confidence interval, 78.9 to 98.7) (p = 0.0007). A univariate analysis showed the improvement in the motor scores after the cauda equina injuries (mean, 17.1 points; 95% confidence interval, 8.3 to 25.9) to be significantly greater than that after the spinal cord injuries (mean, 7.7 points; 95% confidence interval, 3.1 to 12.3) (p = 0.03). A multivariate analysis showed that an absence of initial sacral sensation had a negative effect on motor recovery by a factor of 13.2 points (95% confidence interval, 4.2 to 22.1). When compared with classifying our patients on the basis of the neural axis level of injury, reclassifying them on the basis of the vertebral level of injury resulted in a misclassification rate of 33%.

Conclusions: 

The motor recovery of patients with a thoracolumbar spinal injury and a neurological deficit is affected by both the neural axis level of injury as well as the initial motor score. The results of this study can help the clinician to determine a prognosis for patients who sustain these common injuries provided that he or she evaluates the precise level of neural axis injury utilizing magnetic resonance imaging.

Level of Evidence: 

Prognostic Level II. See Instructions to Authors for a complete description of levels of evidence.

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    References

    Accreditation Statement
    These activities have been planned and implemented in accordance with the Essential Areas and policies of the Accreditation Council for Continuing Medical Education (ACCME) through the joint sponsorship of the American Academy of Orthopaedic Surgeons and The Journal of Bone and Joint Surgery, Inc. The American Academy of Orthopaedic Surgeons is accredited by the ACCME to provide continuing medical education for physicians.
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    Marcel F. Dvorak, MD, FRCS(C)
    Posted on October 08, 2010
    Dr. Dvorak and colleagues respond to Dr. Rice
    NULL

    We would like to thank Dr Rice for his 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" (2010;92:1591-9). We would like to clarify how the patients’ imaging contributed to the variables that we studied. First of all, the area of maximal compression was determined in all cases from pre-operative imaging studies and not inferred from images taken after surgery. In some cases a pre-operative Magnetic Resonance Imaging Scan (MRI) was available and in those cases it was used to determine the spinal vertebral level of maximal spinal canal occlusion. In other cases, this information was determined from a Computerized Axial Tomography Scans (CT). In the case of a T12-L1 fracture dislocation, for example, our treatment protocol is to perform a CT scan in emergency but to urgently take the patient to the operating room for surgical open reduction and stabilization without waiting for the MRI. Although most of our patients had pre-operative 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, from MRI scans, in every case, of the location of the tip of the conus medullaris. This determination was performed on MRI scans for all patients, however some of the MRI’s were performed prior to surgery and as Dr. Rice has identified, some were performed afterwards. In some cases, due to the level and extent of compression as well as the quality of the initial pre-operative MRI, a precise determination of the tip of the conus medullaris could not be made on the pre-operative MRI. In these cases, a post-operative 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 relied upon to simply identify the location of the conus medullaris. We agree with the other comments made by Dr. Rice 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 which have always focused on achieving decompression and stabilization of these injuries through either direct or indirect means. We did not feel that our study sample afforded us the power to analyze the various types of treatment and their influence on outcomes.

    Alejandro Gomez Rice, MD
    Posted on August 16, 2010
    Methodological Issues
    Hospital Universitario Getafe, Spain

    To the Editor:

    Kingwell and colleagues filled a substantial void in the published literature regarding the role of MRI as predictor of motor improvement in spinal injury in their article, "Relationship of Neural Axis Level of Injury to Motor Recovery and Health-Related Quality of Life in Patients with a Thoracolumbar Spinal Injury" (2010;92:1591-9), but I believe there is lack of uniformity regarding assessment method and management. I would like to highlight some methodological issues:

    In some patients, MRI was done years after surgery in order to identify the area of maximum compression, while in other patients MRI was performed before surgery. I do not believe a postoperative MRI is an acceptable method for evaluating compression, and the authors should be aware of the possibility that MRI artifacts could lead to misdiagnosis as a false compression could be identified (1-2). It is also well known that a spontaneous remodeling of the Spinal Canal occurs with time after the injury (3), therefore an MRI performed years after the injury is not an accurate method to locate the area of maximum compression. Some patients had up to 12 years follow-up. As the authors correctly point out, the time between injury and assessment may have an influence in the clinical outcome although this variable was not identified as a confounding factor. It would seem that this variable and patient aging would affect at least the SF-36 scores (4). Most of the patients included in this study were treated operatively but the treatment interventions lack uniformity. There is no information regarding if the chosen treatment method had any influence in the clinical results or the SF-36 scores. Having preoperative MRI in some patients, we do not even know if the Posterior Ligament Complex status was considered in order to decide the adequacy of the treatment - as some recent literature suggests (5). Clearly, an article that provides an outcome evaluation needs to take these factors into consideration. I believe this lack of uniformity casts substantial doubt on the validity of the results.

    The authors did not receive any outside funding or grants in support of their research for or preparation of this work. Neither they nor a member of their immediate families received payments or other benefits or a commitment or agreement to provide such benefits from a commercial entity.

    References

    1. Kwon DY, Kim BJ, Park KW. MRI artifact mimicking root compression by interbody cage displacement. Am J Phys Med Rehabil. 2008;87:423-4.

    2. Salazar JL, Misra M, Bloom D, Dobben G. MRI artifacts following anterior cervical diskectomy. Surg Neurol. 1997;48:23-9.

    3. Crossman PT, Scott JM. Does `canal clearance´ affect neurological outcome after thoracolumbar burst fractures? J Bone Joint Surg Br. 2001;83:151-2.

    4. Hopman WM, Towheed T, Anastassiades T, Tenenhouse A, Poliquin S, Berger C, Joseph L, Brown JP, Murray TM, Adachi JD, Hanley DA, Papadimitropoulos E. Canadian normative data for the SF-36 health survey. Canadian Multicentre Osteoporosis Study Research Group. CMAJ. 2000;163:265-71.

    5. Vaccaro AR, Lehman RA Jr, Hurlbert RJ, Anderson PA, Harris M, Hedlund R, Harrop J, Dvorak M, Wood K, Fehlings MG, Fisher C, Zeiller SC, Anderson DG, Bono CM, Stock GH, Brown AK, Kuklo T, Oner FC. A new classification of thoracolumbar injuries: the importance of injury morphology, the integrity of the posterior ligamentous complex, and neurologic status. Spine (Phila Pa 1976). 2005;30:2325-33.

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