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J Neurosurg Spine. 2017 Aug;27(2):150-157. doi: 10.3171/2016.12.SPINE16738. Epub 2017 May 19.

Widening of the safe trajectory range during subaxial cervical pedicle screw placement: advantages of a curved pedicle probe and laterally located starting point without creating a funnel-shaped hole.

Author information

1
Department of Neurological Surgery, Asan Medical Center, University of Ulsan College of Medicine, Seoul; and.
2
Departments of 2 Neurology and.
3
Neurological Surgery, Gangneung Asan Hospital, University of Ulsan College of Medicine, Gangneung, Korea.

Abstract

OBJECTIVE The small diameter of cervical pedicles and a large transverse cervical pedicle angle are challenges that have led spinal surgeons to investigate how they could achieve a wider safety trajectory and reduce the insertion angle during cervical pedicle screw (CPS) placement. In this paper, the authors detail the advantages of using a curved pedicle probe and a laterally located entry point for overcoming these challenges. METHODS From March 2012 to May 2016, the authors performed posterior cervical fusions using CPSs on 119 consecutive patients. The lateral mass screw conversion and the CPS breach rate were analyzed. Using preoperative CT, it was determined that θlat is similar to the anatomical pedicle angle, and θmed is the minimally acceptable medial angle. The actual insertion medial angle (θins) was determined by postoperative CT. To identify how much of the medial angle on θins could be reduced from the anatomical pedicle angle (θlat), and how much closer to θmed, (θinsmed) / (θlatmed) was calculated. To verify shifting of the entry point and widening of the trajectory, the mean df/Df (i.e., shifted facet point/planned facet point) values were analyzed. RESULTS The total number of planed CPSs was 759, the conversion rate was 4.61% (35/759), and the accuracy rate was 95.9% (694/724). The authors could calculate that θins could be expected near the 90%, 80%, 80%, 80%, and 110% value of θlat on C-3, C-4, C-5, C-6, and C-7 levels, respectively, with the (θinsmed) / (θlatmed) equation. The mean df/Df values were 0.64, 0.62, 0.63, 0.63, and 1.24 on the C3-7 levels, respectively. CONCLUSIONS Through the use of a curved pedicle probe and a laterally located starting point, the planned and laterally located entry point medial shift was made during CPS placement. The entry point shift yielded a wider, safe trajectory and reduced the burden of making a large medial angle, similar to an anatomical cervical pedicle lateral angle, for safe CPS placement without creating a funnel-shaped hole.

KEYWORDS:

CPS = cervical pedicle screw; Df = horizontal distance of the superior articular process; Dlat = a single line on the pedicle level to connect the planned entry point to the axial middle point of the pedicle; Dmed = a line on the pedicle level to connect a medial entry point (i.e., a half-facet point) to the axial middle point of the pedicle; VA = vertebral artery; cervical pedicle screw; curved probe; df = distance between the most medial facet point and the same sagittal facet point with the entry point of the CPS actually inserted; entry point; funnel-shaped hole; medial angle; pedicle probe; safe trajectory; starting point; surgical technique; θins = actual insertion angle of the pedicle screw measured on postoperative CT; θlat = angle between a vertical line and a line to connect the planned entry point and the axial middle point of the pedicle; θmed = angle between a vertical line and a line to connect a new medial entry point and the axial middle point of the pedicle

PMID:
28524752
DOI:
10.3171/2016.12.SPINE16738
[Indexed for MEDLINE]

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