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Charles H. Tator, Robin Hashimoto, Annie Raich, Daniel Norvell, Michael G. Fehlings, James S. Harrop, James Guest, Bizhan Aarabi and Robert G. Grossman

There is a need to enhance the pipeline of discovery and evaluation of neuroprotective pharmacological agents for patients with spinal cord injury (SCI). Although much effort and money has been expended on discovering effective agents for acute and subacute SCI, no agents that produce major benefit have been proven to date. The deficiencies of all aspects of the pipeline, including the basic science input and the clinical testing output, require examination to determine remedial strategies. Where has the neuroprotective/pharmacotherapy preclinical process failed and what needs to be done to achieve success? These are the questions raised in the present review, which has 2 objectives: 1) identification of articles that address issues related to the translational readiness of preclinical SCI pharmacological therapies; and 2) examination of the preclinical studies of 5 selected agents evaluated in animal models of SCI (including blunt force trauma, penetrating trauma, or ischemia). The 5 agents were riluzole, glyburide, magnesium sulfate, nimodipine, and minocycline, and these were selected because of their promise of translational readiness as determined by the North American Clinical Trials Network Consortium.

The authors found that there are major deficiencies in the effort that has been extended to coordinate and conduct preclinical neuroprotection/pharmacotherapy trials in the SCI field. Apart from a few notable exceptions such as the NIH effort to replicate promising strategies, this field has been poorly coordinated. Only a small number of articles have even attempted an overall evaluation of the neuroprotective/pharmacotherapy agents used in preclinical SCI trials. There is no consensus about how to select the agents for translation to humans on the basis of their preclinical performance and according to agreed-upon preclinical performance criteria.

In the absence of such a system and to select the next agent for translation, the Consortium has developed a Treatment Strategy Selection Committee, and this committee selected the most promising 5 agents for potential translation. The results show that the preclinical work on these 5 agents has left numerous gaps in knowledge about their preclinical performance and confirm the need for significant changes in preclinical neuroprotection/pharmacotherapy trials in SCI. A recommendation is made for the development and validation of a preclinical scoring system involving worldwide experts in preclinical and clinical SCI.

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Marc Moisi, Christian Fisahn, Lara Tkachenko, Shiveindra Jeyamohan, Stephen Reintjes, Peter Grunert, Daniel C. Norvell, R. Shane Tubbs, Jeni Page, David W. Newell, Peter Nora, Rod J. Oskouian and Jens Chapman

OBJECTIVE

Posterior atlantoaxial stabilization and fusion using C-1 lateral mass screw fixation has become commonly used in the treatment of instability and for reconstructive indications since its introduction by Goel and Laheri in 1994 and modification by Harms in 2001. Placement of such lateral mass screws can be challenging because of the proximity to the spinal cord, vertebral artery, an extensive venous plexus, and the C-2 nerve root, which overlies the designated starting point on the posterior center of the lateral mass. An alternative posterior access point starting on the posterior arch of C-1 could provide a C-2 nerve root–sparing starting point for screw placement, with the potential benefit of greater directional control and simpler trajectory. The authors present a cadaveric study comparing an alternative strategy (i.e., a C-1 screw with a posterior arch starting point) to the conventional strategy (i.e., using the lower lateral mass entry site), specifically assessing the safety of screw placement to preserve the C-2 nerve root.

METHODS

Five US-trained spine fellows instrumented 17 fresh human cadaveric heads using the Goel/Harms C-1 lateral mass (GHLM) technique on the left and the posterior arch lateral mass (PALM) technique on the right, under fluoroscopic guidance. After screw placement, a CT scan was obtained on each specimen to assess for radiographic screw placement accuracy. Four faculty spine surgeons, blinded to the surgeon who instrumented the cadaver, independently graded the quality of screw placement using a modified Upendra classification.

RESULTS

Of the 17 specimens, the C-2 nerve root was anatomically impinged in 13 (76.5%) of the specimens. The GHLM technique was graded Type 1 or 2, which is considered “acceptable,” in 12 specimens (70.6%), and graded Type 3 or 4 (“unacceptable”) in 5 specimens (29.4%). In contrast, the PALM technique had 17 (100%) of 17 graded Type 1 or 2 (p = 0.015). There were no vertebral artery injuries found in either technique. All screw violations occurred in the medial direction.

CONCLUSIONS

The PALM technique showed statistically fewer medial penetrations than the GHLM technique in this study. The reason for this is not clear, but may stem from a more angulated ”up-and-in” screw direction necessary with a lower starting point.