Sagittal Balance of the Spine

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The C7 plumb line. The spine is sagittaly balanced when the plumb line from C7 touches the posterior edge of S1. Spinal imbalance is positive when the line falls in front of this point, and negative if it falls behind this point.

Sagittal balance forms part of the plain radiographic assessment of spinal deformity including kyphotic or lordotic deformities and scoliosis.

Usage

There are numerous ways of assessing this, using various bony landmarks and angles to evaluate whether or not a normal distribution of weight and stresses is present through the axial skeleton, some incorporating the position of the head, while others focussing on the pelvis, have been described 1,2:

• C7 plumb line
• sagittal vertical axis
• chin-brow vertical angle
• kyphosis tilt angle
• pelvic incidence
• pelvic tilt
• sacral slope
• spinopelvic angle
• spinosacral angle

Whilst many methods exist to assess sagittal balance, an abnormal plumb line (in either direction) is predictive of higher rates of micromotion and dysfunction after solid fixation ref as well as adjacent level disease 4.

Measurement

C7 plumb line

One of the simplest and most widely used methods is performed on lateral standing full-length films and requires a vertical line (plumb line) drawn from the middle of the body of the C7 vertebral body. This line should pass through the superior endplate of S1, or more precisely within 2 cm (some use 1.7 cm) of the posterosuperior corner of the S1 vertebral body 1,2.

The position of this line is can be positive, neutral or negative:

• positive balance: the plumb line passes more than 2 cm in front of the posterosuperior corner of the S1 vertebral body
• neutral balance: the plumb line passes within 2 cm of the posterosuperior corner of the S1 vertebral body
• negative balance: the plumb line passes more than 2 cm behind the posterosuperior corner of the S1 vertebral body

Clinical Implications

A positive sagittal balance in the lumbar spine is associated with low back pain. (see discussion on page Idiopathic Scoliosis). However a positive balance in the cervical spine is of less importance than commonly thought (so called "head forward posture" or "loss of lordosis"). There is an increased risk of posterior disc herniation only, but there is no correlation with future clinical symptoms over 10 years.

See Also

• See Huec et al for a free open access article on this topic, from an orthopaedic surgery perspective.
• Coronal Balance of the Spine

References

Part or all of this article or section is derived from Sagittal balance by Dr Henry Knipe and Assoc Prof Frank Gaillard et al., used under CC BY-NC-SA 3.0

Literature Review

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