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Year : 2021  |  Volume : 69  |  Issue : 5  |  Page : 1142--1143

Time to Think Beyond Spine Fixation for Cervical Spine: Aligning the Whole Spine

P Sarat Chandra 
 Department of Neurosurgery, AIIMS, New Delhi, India

Correspondence Address:
Prof. P Sarat Chandra
Unit 1, Department of Neurosurgery, AIIMS, New Delhi - 110 029

How to cite this article:
Chandra P S. Time to Think Beyond Spine Fixation for Cervical Spine: Aligning the Whole Spine.Neurol India 2021;69:1142-1143

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Chandra P S. Time to Think Beyond Spine Fixation for Cervical Spine: Aligning the Whole Spine. Neurol India [serial online] 2021 [cited 2022 Jan 18 ];69:1142-1143
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The cervical spine is a highly complex and mobile segment. It is a highly mobile segment being of significant advantage for bipedal human beings. However, it also becomes susceptible to early degeneration and complications. This is reinforced by the fact that it has to support a cranium with almost 5 kgs of weight. In recent years, the cervical spine's role has been recognized in aligning the rest of the spine and maintaining the pelvic tilt, especially to maintain horizontal gaze. In the past, the issues related to spinal malalignment and Health-related quality of life (HRQOL) parameters mainly were associated with the thoracolumbar and pelvic spine.

The cervical spine has the dual role of maintaining the head over the body and maintaining the horizontal gaze. The centre of mass of the head in the sagittal plane lies directly over the occipital condyle, about 1 cm anterior to the external auditory canal.[1] Any deviation from this leads to an increase in loads and may aggravate degenerative changes. Interestingly, the cervical spine is divided into three primary columns. This was first proposed by Louis[2] and later validated by Pal and Sherk.[3] The anterior column consists of vertebral bodies and discs, whereas the posterior column consists of facet joints. This is in contrast to Denis's classification of the thoracolumbar spine. In the cervical spine, the weight of the head passes through the occipital condyle, then to the lateral masses of C1, and then to the C1-C2 joint. It then passes through the C3 anterior column via the C2-3 disc (1/3rd of the weight) and the posterior column through the C2-3 facets (2/3rds of the weight).[3] The natural curvature of the cervical spine maintains a lordotic shape due to the wedge-shaped cervical vertebrae and the need to compensate the kyphotic thoracic spine.[4] Deviations from this curvature lead to pain and disability due to the development of prolonged instability. The three primary methods to assess cervical lordosis include Cobb angle, Jackson physiological stress lines, and Harrison posterior tangent method.[5],[6] It is said that the Cobb angle is the easiest to perform; Cobb C1-7 overestimates the lordosis, whereas the C2-7 underestimates the lordosis. Harrison's method is slightly tricky but is most reliable. Translation of the cervical spine in the sagittal plane is measured by assessing the sagittal vertical axis (SVA). It may be measured by dropping plumblines from C2 to C7 and measuring the distance between them. It is clinically relevant as larger C-2 SVA correlates with poorer HRQOL.[7] The chin brow to vertical angle (CBVA) is the assessment of horizontal gaze. The measurement is helpful for the management of severe, rigid, cervical kyphotic deformities as loss of horizontal gaze has a profound impact on activities of daily living and quality of life. The CBVA is defined as the angle subtended between a line drawn from the patient's chin to brow and a vertical line. Surgical correction of the CBVA requires extension of the cervical spine.[8]

The normal cervical alignment is difficult to calculate as a wide range of normal alignments have been described.[9],[10] In asymptomatic normal volunteers, a large proportion of cervical lordosis is localized to C1-2, and this is progressively reduced to lower cervical levels. This is similar to lumbar lordosis, where the maximum lordosis is at the L5-S1 level. This may be explained by the fact that the center of gravity of the head sits almost directly over the centers of C-1 and C-2 vertebral bodies. The mean total cervical lordosis is around 40 deg, whereas the occiput-C1 segment is kyphotic. Only about 6 deg of lordosis occurs at the lower cervical vertebrae (C5-7). The loss of sub-axial lordosis has been reported in occiput-C2 fusions where excessive hyper-lordosis is created at the occiput-C2 level. This type of unfavorable reciprocal change is also observed in lumbar and thoracic osteotomy and reported by Lafage et al.[11] It has been shown that there is no difference between asymptomatic men and women in total cervical lordosis, whereas there is a positive correlation between cervical lordosis and increasing age. The average odontoid–C7 plumb line distance ranges from 15 to 17 mm ± 11.2 mm. Thus, it is now becoming evident that cervical spine fixations do significantly affect the whole spinal alignment.

For craniovertebral junction anomalies, Chandra et al. introduced the concepts of sagittal inclination, coronal inclination, and craniocervical tilt.[12],[13],[14] The spinal regions (the pelvis and the lumbar, thoracic, and cervical regions) are not independent of one another, and multiple significant correlations have been found among them. Blondel et al. (unpublished data, 2012) investigated all spinal parameters in an asymptomatic volunteer population with a mean age of 45 years (range 20–77 years). Following an extensive analysis, the authors found that pelvic incidence correlates with lumbar lordosis, lumbar lordosis correlates with thoracic kyphosis, and thoracic kyphosis correlates with cervical lordosis. Thus, an increase in pelvic incidence correlates with an increase in lumbar lordosis, which correlates with an increase in thoracic kyphosis, which correlates with an increase in cervical lordosis.[15] Similarly, Chandra et al.[16] demonstrated that following the technique of DCER (distraction, compression, extension, and reduction) for correcting basilar invagination and atlantoaxial dislocation, there was a significant decrease in the hyper-lordosis after the surgery. Mean preoperative lordosis was 24.89 ± 18.51°, and postoperative was 15.38 ± 12.66°, (P value < 0.0001). There was a significant correlation of increasing grade of pseudo-joints with increasing degree of lordosis (correlation-0.435, P < 0.0001). The study published in this issue included a total of 102 patients with cervical compressive myelopathy. They were divided into two groups, Group A, who underwent cervical laminectomy with lateral mass fixation only, whereas Group B underwent C7-T1 trans-facet fixation also. At 2 years' follow-up of 53 patients, it was found that patients in the latter group had a better upper limb motor function (3.77 ± 1.14 vs. 4.44 ± 0.50; P = 0.021) and total MJOS (modified Japanese orthopedic association) score (13.85 ± 3.49 vs. 15.37 ± 1.86; P < 0.052). Following this study, the authors have suggested that following cervical laminectomy and posterior fixation, with the inclusion of the C7-T1 junction, it may serve better to preserve the curvature and improve motor functions.[17]

It is now evident that the whole spine operates as a single dynamic unit in this day and age. Any stabilizations performed in one particular segment will have a significant impact on the rest of the spine. While this was well established for the thoracolumbar spine, it is becoming more evident for the cervical spine as well. Thus, for any kind of short or long segment fixations, it is essential to measure the pre-operative cervical and whole spine alignments. Surgeries should be planned carefully in such a manner that these alignments are respected and preserved after surgery.

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