Cervical Alignment and its Impact on Spinal Health
The main functions of the cervical spine are to maintain the position of the head in relation to the body and to control the level of horizontal gaze. The sagittal plane’s center of mass
Cervical Alignment and its Impact on Spinal Health
The main functions of the cervical spine are to maintain the position of the head in relation to the body and to control the level of horizontal gaze. The sagittal plane’s center of mass of the head is located directly above the occipital condyle, approximately one centimeter anterior and superior to the external auditory canal.
Any deviations from the typical alignment of the head’s mass will cause an increase in cantilever loads, leading to a rise in the amount of energy muscles need to expend. To describe the stability of the cervical spine, literature has divided its bone structure into three primary columns, one anterior and two posterior:
- The vertebral bodies and discs make up the anterior column, while the two posterior columns are made up of the facet joints that articulate with each other.
- The middle column is composed of the posterior half of the vertebral body, the posterior annulus fibrosis, and the posterior longitudinal ligament.
- The ligamentous complex and the posterior arch make up the posterior column.
The head’s weight is supported by the condyle. This weight is then passed to a joint called C1-2 and divided into two parts – anterior column (including a disc between C2 and C3) and posterior column (including joints between C2 and C3).
Most of the weight is carried by the posterior column, which takes up about 64%, while the anterior column carries around 36%. The lumbar spine has been found to bear more weight in the front part (67% to 82%), and less weight in the back part (18% to 33%).
The cervical spine naturally has a curved shape called lordosis, which is created by the wedge-shaped cervical vertebrae and helps to balance out the curve in the thoracic spine called kyphosis. Kyphosis is a natural curve that allows the lungs to expand properly, but it can increase with age.
At the bottom of the lordotic curve, it meets the rigid kyphotic curve in the upper back, which is called the CTJ. Changes in the natural curvature, such as a loss of lordosis or the development of cervical kyphosis, are linked to pain and difficulty moving.
On the left, a normal cervical lordosis is shown with a small distance of 1.5 cm between the C-2 and C-7 plumb lines. On the right, cervical sagittal malalignment is shown with a large distance of more than 4 cm between the C-2 and C-7 plumb lines.
Cervical Lordosis Assessment Methods
There are three main ways to measure cervical lordosis:
- Cobb angle method: It involves drawing two parallel lines – one along the bottom of the second vertebra (C-2) and one from the front of the first vertebra (C-1) to the back of the spinous process – as well as another line parallel to the bottom of the seventh vertebra (C-7). Then, perpendicular lines are drawn from each of the first two lines, and the angle where they meet is the angle of the cervical curvature.
- Jackson physiological stress line method: Two lines are drawn parallel to the posterior surface of the C-7 and C-2 vertebrae. The angle between these two lines is then measured.
- Harrison posterior tangent method: Lines are drawn parallel to the posterior surfaces of each cervical vertebra from C-2 to C-7, and the segmental angles are added together to obtain the overall curvature angle of the neck.
Literature has proposed that the Cobb angle measured from C1 to C7 can give a higher value for cervical lordosis, while the Cobb angle from C2 to C7 may give a lower value.
The Harrison method may provide a more accurate measurement, but it is not widely used due to its complexity. Nevertheless, the Cobb method is still commonly used in clinical settings due to its simplicity and reliability in measuring cervical lordosis.
Determining Cervical Lordosis using three different methods:
- Cobb Angle Method
- Jackson Physiological Stress Line Method
- Harrison Posterior Tangent Method
There are various ways to measure the sagittal plane translation of the cervical spine, and one of them is through the use of cervical SVA (Sagittal Vertical Axis). The distance between the C-2 and C-7 plumb lines can be used to measure sagittal alignment globally.
This is done by measuring the C-2 SVA and C-7 SVA, which measure the distance between the posterior superior corner of the sacrum and the C-2 and C-7 plumb lines, respectively. Another way to measure cervical SVA is to use a regional approach, which involves measuring the distance between the posterosuperior aspect of C-7 and a plumb line dropped from the centroid of C-2 or the dens.
A new method to evaluate global sagittal alignment is the gravity line, which is measured from the center of gravity of the head and proposed as an alternative to the C-7 plumb line.
Using a plumb line from the center of gravity of the head, instead of C-2, can also be applied to assess regional cervical SVA. The center of gravity of the head 