1) Description of Measurement

Cervical sagittal vertical axis (SVA) quantifies the anterior–posterior global alignment of the cervical spine by measuring the horizontal offset between a cranial reference point and a caudal cervical landmark. It reflects the forward or backward translation of the head over the cervical spine and is a key parameter in the evaluation of cervical sagittal balance, deformity, and postoperative outcomes.

Increased cervical SVA correlates with neck pain, disability, impaired horizontal gaze, and poor health-related quality of life.

2) Instructions to Measure

• Obtain a true mid-sagittal CT reconstruction showing the skull base through C7.

• Identify the center of the C2 vertebral body.

• From this point, drop a vertical plumb line parallel to the vertical axis of the image.

• Identify the posterior–superior corner of the C7 vertebral body.

• Measure the horizontal distance (mm) between the C2 plumb line and the posterior–superior corner of C7.

• Record this value as the C2–C7 SVA.

3) Normal vs. Pathologic Ranges

• Normal sagittal alignment: ≤ 20 mm

• Mild anterior malalignment: 21 - 40 mm

• Severe sagittal imbalance: > 40 mm

Key points:

• Increasing SVA correlates with worse Neck Disability Index (NDI) scores.

• Postoperative correction toward normal values is associated with improved functional outcomes.

4) Important References

Tang JA, Scheer JK, Smith JS, et al; ISSG. The impact of standing regional cervical sagittal alignment on outcomes in posterior cervical fusion surgery. Neurosurgery. 2015 Mar;76 Suppl 1:S14-21; discussion S21. doi: 10.1227/01.neu.0000462074.66077.2b.

Ames CP, Blondel B, Scheer JK, et al. Cervical radiographical alignment: comprehensive assessment techniques and potential importance in cervical myelopathy. Spine (Phila Pa 1976). 2013 Oct 15;38(22 Suppl 1):S149-60. doi: 10.1097/BRS.0b013e3182a7f449.

Fujiwara H, Oda T, Makino T, et al. Impact of Cervical Sagittal Alignment on Axial Neck Pain and Health-related Quality of Life After Cervical Laminoplasty in Patients With Cervical Spondylotic Myelopathy or Ossification of the Posterior Longitudinal Ligament: A Prospective Comparative Study. Clin Spine Surg. 2018 May;31(4):E245-E251. doi: 10.1097/BSD.0000000000000619.

5) Other info....

Although traditionally measured on standing lateral radiographs, cervical SVA can be reliably estimated on upright CT or neutral-position CT reconstructions.

Should be interpreted alongside:

• C2–C7 lordosis

• T1 slope

• Chin–brow vertical angle (CBVA)

Excessive cervical SVA often represents compensatory mechanisms for thoracolumbar deformity.

When SVA is markedly abnormal, full-spine imaging is recommended to evaluate global sagittal balance.