Normal Spine Alignment
For examinations, one should know the normal range of degrees of:
- Thoracic kyphosis
- Lumbar lordosis
- Sagittal alignment
- Important blood vessels
The normal range of degrees of thoracic kyphosis is 20° to 50°. The mean in normal adults is 35°. The normal range of degrees of lumbar lordosis is 40° to 80°. The mean in normal adults is approximately 60°.
The spine is usually straight in the sagittal plane between T10 and L2. The majority of lumbar lordosis occurs between L4 and S1.
The alignment of the spine is important in normal upright posture. There is a normal degree of lordosis in the cervical and lumbar spines and a moderate degree of kyphosis in the thoracic spine. The head, spine, and pelvis are connected and balanced. If the spine is out of balance, then a deformity can develop causing fatigue of the paraspinal muscles.
The normal sagittal alignment in an upright patient is as follows:
- Plumb line
The sagittal plumb line falls from the odontoid process through the C7-T1 intervertebral disk and then anterior to the thoracic spine. The plumb line then crosses the spine at the T12-L1 intervertebral disk, and then travels posterior to the spine. The plumb line crosses at the posterior corner of the S1 vertebra.1
The endplates and pedicles of the L3 vertebra are normally parallel to the ground.
The vertebral artery arises from the subclavian artery (the first and largest branch) on the right side of the body and the aortic arch on the left side. The vertebral artery enters the lateral mass foramen of the sixth cervical vertebra before ascending to the brain.
The major blood supply to the cervical spinal cord comes from the anterior spinal artery, which arises from the deep cervical artery. This vessel most commonly accompanies the left C6 spinal nerve.
One must be careful not to damage the vertebral artery when exposing the posterior and superior aspect of the C1 vertebra. It is especially important when using a Cobb elevator or an electrocautery not to dissect too far from the midline.
The vertebral artery lies close to the midline. On the superior aspect, the groove for the vertebral artery lies 8 mm to 12 mm from the midline. On the posterior aspect of the vertebral body, the vertebral artery lies 12 mm to 23 mm from the midline.
The blood supply of the lower spinal cord can be interrupted if the segmental vessels are interrupted. The major blood supply is from the artery of Adamkiewicz. This vessel is often on the left side and it accompanies the ventral root of the T9, T10, or T11 spinal nerve.
- Marco RAW, An HS. Anatomy of the spine. In: Orthopaedic Knowledge Update: Spine 2. Rosemont, Ill: American Academy of Orthopaedic Surgeons; 2002:7-9.