What is the role of radiography in the workup of kyphosis?

Updated: May 04, 2020
  • Author: R Carter Cassidy, MD; Chief Editor: Jeffrey A Goldstein, MD  more...
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Radiographs are crucial both for diagnosing kyphosis and for planning treatment.

The most useful radiographs are upright posteroanterior (PA) and lateral images of the entire spine. These views enable the reviewer to assess the sagittal balance of the entire spine and to determine whether a scoliosis is present. (See the image below.)

Preoperative lateral radiograph of patient with 85 Preoperative lateral radiograph of patient with 85° thoracic deformity secondary to Scheuermann kyphosis.

Significant improvement in our understanding of the sagittal radiographic profile has allowed improved quantification and description of deformities and better identification of treatment targets. Measurements are made on radiographs by using the standard Cobb technique for scoliosis, which has been adapted to the measurement of kyphosis. Thoracic kyphosis is measured from T1 to T12, though the upper thoracic vertebral endplates are often difficult to see. All radiographs should be evaluated for pelvic parameters; the critical role the position of the pelvis plays in overall spinal balance and patient satisfaction is well understood. 

Normal measurements for the thoracic spine vary widely, but the accepted definition of normal, according to the Scoliosis Research Society (SRS), is 20-40°. A plumb line dropped from C7 should pass through or just anterior to S1 on a lateral full-length image. This technique helps in assessing and quantifying the patient's overall sagittal alignment.

In 2005, Glassman et al published data demonstrating that symptom severity in patients with a significant sagittal imbalance correlated in a linear fashion to the deformity. [25]

Schwab et al identified the following threshold parameters for severe disability, [27] defined as Oswestry Disability Index (ODI) greater than 40:

  • Pelvic tilt greater than 22°
  • Spinal vertical axis (SVA) greater than 47 mm
  • Mismatch between pelvic incidence (PI) and lumbar lordosis (LL), or PI-LL, of 11° or more

These measurements are felt to be solid goals of surgical treatment, as well as useful aids in procedural planning.

Another attempt to measure the sagittal balance is the T1-spinopelvic inclination (T1-SPI), which is another measure of global spinal balance with reference to the position of the pelvis. A study demonstrated that at higher levels of pelvic tilt, patients had much worse function, as measured by poorer scores on the ODI, the Short Form (SF)-12, and the SRS-22 scale. [28] The T1-SPI was found to be better correlated with these health-related quality-of-life (HRQOL) measures than the SVA was.

This measure was refined further by adding the value to the pelvic tilt. The resulting measure, the T1-pelvic angle (TPA), also correlates with HRQOL parameters. Furthermore, bceause it is an angular measurement, it does not change depending on whether the patient is sitting or standing, and it does not require calibration of the film. [29]

Radiographs obtained with the patient in a supine lateral hyperextension position over a bolster can be used to determine the flexibility of the curve. This information is useful in surgical planning. A flexible curve is best corrected with posterior-only fusion, whereas a stiff curve may necessitate an anterior-only or combined anterior-posterior procedure. A curve that corrects to 50° or less on hyperextension can be treated with posterior-only fusion. [17, 30]  Postural kyphosis rarely exceeds 60°, and it should correct to normal with hyperextension.

Another system of global spine evaluation, the GAP (Global Alignment and Proportion) score, was developed and correlated with mechanical complications after surgery. This score uses pelvic version, lumbar lordosis, the relative lordosis in the L4-S1 vs L1-S1 segment, PI, and patient age. When postoperative radiographs were evaluated with this system, mechanical complications were found to be much more common with a higher GAP score. [31]  This again highlights the importance of achieving global balance after operation for sagittal plane deformity.

Evaluation of the L5-kyphosis apex line (L5-KAL) has been described as a potential means of indicating the thoracic curve change in patients with Scheuermann disease or postural kyphosis. In a cross-sectional study by Bezalel et al, significant positive associations were observed between the L5-KAL and thoracic kyphosis, lumbar lordosis, the C7 line, and self-perceived body image. [32]

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