Optimal anatomical angle and distance for drilling in cervical oblique corpectomy: A surgical anatomical study

Abstract

Background: One of the difficulties of oblique corpectomy, less discussed in the literature, is the problem of how to achieve an optimum corpectomy. Therefore, this anatomico-radiological study was conducted to shed light on the use of the microscope at an appropriate angle and optimum drill distances in clinical cases undergoing cervical oblique corpectomy surgery.

Materials and methods: We examined the average distance of the diagonal line extending from the medial aspect of the ipsilateral vertebral foramen to the contralateral pedicle in cervical computed tomography -angiography axial scans in four cervical vertebrae, C3, C4, C5, and C6. We also measured the average angle between this diagonal trajectory and the horizontal line, making a total of 712 measurements in 89 patients.

Results: We found that horizontal drilling with an average length of 23-26 mm at an acute angle of about 22° -23° is optimal for adequate decompression of the spinal cord in the oblique corpectomy approach. Depending on the patient and the level of the vertebra, the distance and the angle of the horizontal drilling may range from 18 mm to 31 mm and from 15° to 33°, respectively.

Conclusions: For an optimum cervical oblique corpectomy that provides adequate spinal cord decompression and maintains spinal stability, it is necessary to operate under a surgical microscope positioned at an acute angle and to know the horizontal drilling distance.

Keywords: Anatomy; cervical oblique corpectomy; cervical vertebrae; multilevel corpectomy; neck anatomy; surgical anatomy; vertebral anatomy.

Figure 1

Surgical anatomical route of oblique corpectomy is shown on a cadaver specimen. The carotid artery, sympathetic trunk, vagal nerve, and VA are in a close proximity.[13] Written permission for reproduction was obtained from Elsevier. Sup. Cerv. Gang - superior cervical ganglion, CCA - common carotid artery, Int. Jug: internal jugular, CN - Cranial nerve, VA - vertebral artery

Figure 2

Oblique corpectomy consists of two steps in the form of vertical and horizontal drilling of vertebral bodies to obtain an oblique, convex shape, which preserves the vertebral body bone to the greatest possible extent. Vertebral drilling is first performed vertically until the cancellous bone is completely drilled. Then, drilling is continued diagonally until the contralateral pedicle is reached. (Sketch by the corresponding author)

Figure 3

Ideally, oblique corpectomy should provide adequate spinal cord decompression while requiring minimal bone resection that will not impair spinal stability. The geometry of vertical and horizontal (oblique) bone drilling is important at this point. An optimum drilling example is shown in (a). Two examples of undesirable oblique corpectomy are shown in (b) (insufficient decompression) and (c) (excessive bone resection). Modifications in vertical drilling width and horizontal (oblique) drilling angle could theoretically be the cause of obviously different final appearances in the examples given. (Sketch by the corresponding author)

Figure 4

Measurement methods of F-P distance and p angle. (a) Axial CT-angiography scan shows F point, P point and measured line of the distance between them, (b) Axial CT-angiography scan shows the measurement of P angle between F-P line arm and a horizontal arm running through P point. CT - Computed tomography, F - Foraminal, P - Pedicular

Figure 5

The boxplot diagram displays the distribution of the distance values for four vertebral levels in a standardized way. The mean F-P distance at the C3, C4, C5, and C6 levels were 23.0 ± 1.7 mm (range = 18–27 mm), 24.0 ± 1.7 mm (range = 20–28 mm), 25.2 ± 2 mm (range = 20–31 mm), and 25.8 ± 1.9 mm (range = 22–31 mm), respectively. F - Foraminal; P - Pedicular

Figure 6

The boxplot diagram displays the distribution of the p angle values for four vertebral levels. The mean angle p at the C3, C4, C5, and C6 levels were 21.9° ± 3.1° (range = 15°–30°), 22.0° ± 3.1° (range = 15°–32°), 23.3° ± 3.3° (range = 15°–33°), and 23.2° ± 3.1° (range = 18°–33°), respectively