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Quantitative Gross and CT measurements of Cadaveric Cervical Vertebrae (C3 – C6) as Guidelines for the Lateral mass screw fixation

Santosh K. Sangari, MBBS, Master of Surgery (Anatomy),1 Thomas E. Heinneman, MD,2,3 Mathew S. Conti,2 Paul-Michel F. Dossous, MD,2,4 David J. Dillon, PhD,2 Apostolos J. Tsiouris, MD,5 Se Young Pyo, MD,6,7 Estomih P. Mtui, MD,1 Roger Härtl, MD6

1Program in Anatomy and Body Visualization, Department of Radiology, Weill Cornell Medicine, New York, NY, 2Weill Cornell Medical College, New York, NY, 3Otolaryngology – Head and Neck Surgery, UCLA Health, Los Angeles, CA, 4Department of Orthopedic Surgery, Albany Medical Center Hospital, Albany, NY, 5Department of Radiology, Neuroradiology section, New York-Presbyterian Hospital, Weill Cornell Medicine, New York, NY, 6Brain and Spine Center, NewYork-Presbyterian Hospital, Weill Cornell Medicine, New York, NY, 7Department of Neurosurgery, College of Medicine, Inje University, Busan Paik Hospital, Busan Korea

Abstract

Background

Lateral mass screw fixation is the treatment of choice for posterior cervical stabilization. Long or misdirected screws carry a risk of injury to spinal nerve roots or vertebral artery. This study was aimed to assess the gross anatomic and CT measurements of typical cervical vertebrae for the selection of lateral mass screws.

Methods

Dimensions of the articular pillars were measured on 1) Dry cervical vertebrae with Vernier calipers and 2) Multiplanar reformations of CT scans of the same vertebrae with Viewer software package. The data was statistically evaluated.

Results

The transverse diameter of the articular pillars with Vernier calipers varied from 6.0 to 15.4 mm (mean=10.5 mm ± 1.5) and on CT scans ranged from 8.2 – 16.1 mm (mean=11.6 mm ± 1.4). The antero-posterior diameter, an estimate of the screw length by Roy-Camille technique varied from 3.9 to 12.7 mm (mean=8.6 mm ± 1.6) by Vernier calipers and from 6.4 to 13.3 mm (mean=9.1 ± 1.2) on CT scans. The oblique AP diameter, an estimate of screw length by Magerl method varied from 10.8 to 20.3 mm (mean=14.9 mm ± 1.8) by Vernier calipers and from 11.4 to 19.3 mm (mean=14.5 mm ± 1.7) on CT. The CT measurements for height, transverse and AP diameter of the articular pillars were 0.5 - 1.0 mm larger than dimensions by Vernier calipers. No statistically significant difference was observed between the caliper and CT measurements for the oblique AP diameter.

Conclusion

CT measurements of the articular pillars may slightly overestimate the desired screw length selected by spine surgeons when compared to actual anatomy. Although means of the articular pillars correspond to the screw lengths used, substantial number of observations below 10 mm for Roy-Camille trajectory and below 14 mm for Magerl trajectory requires careful preoperative planning and intra-operative confirmation to avoid long/misdirected lateral mass screws.

keywords: 
Lateral mass screws, articular pillar, typical cervical vertebra, Posterior fixation
Volume 10 Article 43
doi: 
10.14444/3043