Because of the compressive nature of most human traumatic spinal cord injuries (SCI), surgical decompression as a means to lessen secondary injury seems sound theoretically. Based on this hypothesis, several pre-clinical and clinical studies were carried out to assess whether surgical intervention can improve the outcome in practice. Despite a few inconsistencies, studies on animal SCI models strongly support the effectiveness of early surgical decompression. However, clinical studies show extensive discrepancy in terms of benefit of the surgical decompression. Among other factors, the timing of decompression is a prominent difference between the two groups of investigations. Unlike human studies, decompression within seconds or minutes is readily performed on animal models. In addition, very diverse timeframes are used to define early and late surgery in a clinical setting. While “early” is most commonly defined as 24 to 72 hours post-injury, evidence of surgery within very earlier hours after injury also exists in the literature, mostly show promising results. For instance, the study by Cengiz et al., which is one of the very few level 2b evidence studies in this area, suggested that surgical decompression earlier than 8 hours can result in a favorable neurological outcome (Cengiz, Kalkan, Bayir, Ilik, & Basefer, 2008). However, cutoff points of less than 12 hours appear rarely in human studies due to infeasibility. Therefore, it is suspected that surgical decompression within few hours or even minutes after injury is potentially beneficial. However, due to the lack of strong clinical evidence it remains unclear whether the effects are so significant to justify the substantial cost and effort required for achieving a sizable reduction in the duration between the spinal cord injury and the surgical decompression.

To shed light on this obscurity, high quality studies including randomized clinical trials with large sample sizes assessing short- and long-term outcomes of surgery within very few hours post-injury are necessary. Meanwhile, we can reflect on the pre-clinical studies to provide insight to the issue.

Pre-clinical studies are greatly heterogenic and vary in methodology. However, the results are interestingly in harmony regardless of animal species and SCI models, outcome measures, and quality. They almost conformably show that the benefits of surgical decompression decrease with time. The meta-analysis of preclinical studies performed by Batchelor et al supported improvement of neurobehavioral outcomes after early decompression in animal SCI models. In another systematic review investigating surgical decompression after traumatic spinal cord injury, Furlan et al. concluded that time is the key determinant of outcome after surgical decompression in animal models and benefits are optimized if the decompression is performed before 6 hours (Furlan, Noonan, Cadotte, & Fehlings, 2011). To have a rough estimation of the trend of the decreased surgical effectiveness over time, it is worthwhile to have an overview of the existing evidence altogether regardless of methodological variations and see the big picture with the time assumed to be the main theme.

As a preliminary exploration, results of 15 pre-clinical studies included in the meta-analysis of Batchelor et al., 2013 were collected and compared in a matrix. There was considerable heterogeneity between the studies due to various study design, incorporating different animal models such as rodents, dogs and sheep, with the timing of decompression ranging from immediate to 10 weeks. Spinal cord injury was produced via different techniques such as weight drop, nylon tie, clip compression, and balloon compression, resulting in different compression pressure. Several outcome measures were utilized, including behavioral assessment measures (Basso, Beattie and Bresnahan (BBB) locomotor rating scales, Tarlov's system, rotarod latency, and screen grasping), as well as measurement of spinal cord blood flow and evoked potentials. Most of the studies performed group comparisons regarding the timing of compression/decompression. The data from the literature did not allow an extensive analysis over time while pressure being constant (Batchelor, 2014). Thus, we could only perform an imprecise estimation of the trend of the outcome over time. For each investigation, we estimated the relative response of each study group to the intervention using a scoring scale attributed based on interpretation of the reported results; with 0 attributed to the minimum i.e. no neurological improvement, 1 for less promising (but still positive) outcome, up to 2 as the most favorable improvement. The overall score for each time point was estimated by averaging the available scores at the corresponding time point. Based upon this scaling method, a scatter plot was produced. The Y-axis represented relative outcome and the X-axis showed timing of decompression. The best fit curve of this scatter plot was estimated to display the approximate trend of response to decompression over time.

According to this estimation, the effectiveness of surgical decompression abruptly dropped in the first very few hours, with a clear cut point of 150 minutes, and then almost steadily paced towards the minimum, i.e., no observed improvement. The message of this rough estimation deserves to pay particular attention. The defined “early” timelines commonly used in the clinical studies by far fall into the steady part of the curve. In this case, a considerable dilution effect is imposed that undermines the positive outcome which would be obtained if the decompression had been performed in the critical early few hours. This can explain the equivocal effects of early decompression reported in the clinical studies.

The most important limitation of our investigation was the lack of quantitative values of normalized effect size for individual experiences, together with the corresponding timing and pressure of decompression. In addition, the disadvantage of seeing the big picture is that details are missed and precision is sacrificed. Methodologically robust studies on this issue are recommended. The results of such studies can promote modifications in the approach towards the acute spinal cord injury, particularly with regard to investing on shortening the time between the injury and the surgical decompression.


Authors:

Vafa Rahimi-Movaghar, M.D., Professor of Neurosurgery, Shariati Hospital, Tehran University of Medical Sciences, Sina Trauma and Surgery Research Center, Tehran University of Medical Sciences, Research Centre for Neural Repair, University of Tehran, Tehran, Iran
Saba Jafarpour, M.D., Research assistant, Sina Trauma and Surgery Research Center, Tehran University of Medical Sciences, Tehran, Iran


References

Batchelor, P. E. (2014, 3/3/2014). [Re: Question and request for information regarding your paper ].
Cengiz, S. L., Kalkan, E., Bayir, A., Ilik, K., & Basefer, A. (2008). Timing of thoracolomber spine stabilization in trauma patients; impact on neurological outcome and clinical course. A real prospective (rct) randomized controlled study. Arch Orthop Trauma Surg, 128(9), 959-966. doi: 10.1007/s00402-007-0518-1
Furlan, J. C., Noonan, V., Cadotte, D. W., & Fehlings, M. G. (2011). Timing of decompressive surgery of spinal cord after traumatic spinal cord injury: an evidence-based examination of pre-clinical and clinical studies. J Neurotrauma, 28(8), 1371-1399. doi: 10.1089/neu.2009.1147