Evaluating Cervical Alignment

The cervical spine is notable for its intricate complexity and holds the greatest range of motion in the entire spine while also offering robust support and stability for the head. However, the balance increases as people age, manifesting in degenerative changes affecting both the discs and the facet joints. These changes alter cervical spine alignment and can lead to pain.

Cervical spondylotic myelopathy is a degenerative condition of the cervical spine. The prevalent hypothesis attributes such myelopathy to the onset of disc and facet joint degeneration that cause disc bulging and bone spurs that thus impinge on the spinal cord and nerve roots. However, some recent studies suggest that cervical sagittal alignment can cause cervical myelopathy. Evaniew et al performed a prospective study on 250 patients who presented with cervical myelopathy.[1] The authors found that an increased cervical sagittal vertical axis (cSVA) measured from C2-7 and T1 slope were associated with inferior health-related quality of life at presentation among patients with CSM, but no significant associations were observed following surgical treatment. At 12 months after surgery, there were no significant associations between alignment parameters, changes in alignment, or shifts in health-related quality of life, function, or symptoms. This observation is echoed in additional research, such as the retrospective study by Lin et al, which reinforced the correlation between increased disability and alterations in cervical alignment parameters on 90 patients who had surgery for cervical spondylotic myelopathy.[2] The authors noted that the disability of the neck increased with increasing C2-C7 SVA and T1S-CL and decreasing cervical lordosis before surgical reconstruction.

Further research delves into the impact of cervical sagittal alignment on postoperative outcomes following cervical spine surgery. Hyun et al performed a retrospective study on 38 patients who underwent posterior cervical decompression and fusion for cervical myelopathy.[3] The authors found that disability of the neck increased with cervical sagittal malalignment after cervical spine surgery and that a greater T1S-CL mismatch was associated with a greater degree of cervical malalignment. Specifically, a mismatch greater than 26.1° corresponded to positive cervical sagittal malalignment, defined as C2-C7 SVA greater than 50 mm.

The evaluation of sagittal alignment of the cervical spine is determined by measuring the cervical sagittal vertical axis (SVA), which is determined by measuring the distance between either the C2 or C7 plumb line, and using a vertical line drawn from the posterior superior corner of the sacrum. The cervical SVA (C2 SVA) has also be described as measuring the distance between a plumb line dropped from the center of C2 and the posterior superior aspect of C7 (C2–C7 SVA) (Figure 1A). Other measurements that can be evaluated include cervical lordosis (CL), T1 slope (T1S), neck tilt (NT) and thoracic inlet angle (TIA). Cervical lordosis can be determined by drawing a line perpendicular to the inferior endplate of C2 and a perpendicular line to the inferior endplate of C7. The angle formed by these perpendicular lines forms what is referred to as cervical lordosis (Figure 1B). The T1 slope can be determined by drawing a horizontal line and another line along the superior end plate of T1 (Figure 1C). Neck tilt can be determined using the angle formed by a vertical line drawn from the tip of the sternum and the center of the upper end plate of the sternum with another line drawn from the center of the T1 upper end plate (Figure 1D).

In conclusion, the intricate anatomy of the cervical spine with advances in age increases its susceptibility to degenerative changes. The alteration in spine alignment underscores the need for accurate measurements to optimize surgical outcomes and enhance patient quality of life. Knowing these measurements are additional tools that spine surgeons can use to evaluate cervical alignment and improve a surgeon’s ability to diagnose cervical malalignment and thus improve outcomes.

References

1. Evaniew N, Charest-Morin R, Jacobs WB, et al; Canadian Spine Outcomes and Research Network (CSORN). Cervical sagittal alignment in patients with cervical spondylotic myelopathy: an observational study from the Canadian Spine Outcomes and Research Network. Spine (Phila Pa 1976). 2022;47(5):E177-E186.

2. Lin T, Chen P, Wang Z, Chen G, Liu W. Does cervical sagittal balance affect the preoperative Neck Disability Index in patients With cervical myelopathy? Clin Spine Surg. 2020;33(1):E21-E25.

3. Hyun SJ, Kim KJ, Jahng TA, Kim HJ. Relationship between T1 slope and cervical alignment following multilevel posterior cervical fusion surgery: impact of T1 slope minus cervical lordosis. Spine (Phila Pa 1976). 2016;41(7):E396-E402.

Author: Yu-Po Lee, MD

From UCI Health in Orange County, California.