Strain of the vertebral artery during passive neck movements and spinal manipulation of the cervical spine: An observational study

Background

Neck pain is a common condition, and a frequent treatment is chiropractic cervical spinal manipulation therapy (cSMT). However, cervical spinal manipulations have been associated with excessive cervical artery elongations, allegedly causing arterial dissection leading to stroke.

Purpose

The primary purpose of this study was to quantify the total vertebral artery elongations during cSMT, and secondarily, quantify the vertebral artery elongations during the pre-manipulative orientation of the head and neck and the subsequent elongations during the actual thrust.

Methods

Vertebral artery strains were measured at the cervical levels C0–C1, C1–C2, and C2–C3 using piezoelectric crystals that were sutured to the wall of the left and right vertebral artery in three cadavers. Vertebral artery strains were measured continuously for a full set of passive range of motion testing and for the chiropractic spinal manipulation.

Findings

For the range of motion testing, the greatest average vertebral artery strains at the C0–C1 level were 6.9% for ipsilateral flexion-rotation, at the C1–C2 level 4.3% for contralateral rotation, and at the C2–C3 level 3.7% for contralateral flexion-rotation. For the chiropractic spinal manipulation, the average maximal strains at the C0–C1, C1–C2 and C2–C3 levels were 1.3%, 0.1%, and 1.0%, respectively. The maximal average vertebral artery strains in the pre-manipulative phase were 0.5% and the corresponding maximal vertebral artery strains during the manipulative thrust was 1.1%.

Interpretation

Passive range of motion testing produced strains in the vertebral artery were 5.3 times (C0–C1), 7.2 times (C1–C2), and 3.7 times (C2–C3) greater than the corresponding strains during chiropractic spinal manipulation, suggesting that strains in the vertebral artery during chiropractic spinal manipulation were much smaller than the strains that can occur during normal everyday movements of the head and neck. Furthermore, vertebral artery strains in the pre-manipulative phase did not contribute to the peak strains on the contralateral vertebral artery and helped reduce strains on the ipsilateral side.