From the Guidelines
To determine kyphosis angle, the Cobb method is the most commonly used technique, as it provides a reliable measurement of the degree of kyphosis. This method involves identifying the most tilted vertebrae at the upper and lower ends of the kyphotic curve on a lateral spine X-ray, drawing lines parallel to the endplates of these vertebrae, and then drawing perpendicular lines from these. The angle formed by the intersection of these perpendicular lines is the kyphosis angle, with normal thoracic kyphosis typically ranging from 20-45 degrees 1. For measuring maximum kyphosis (Kmax), this represents the largest kyphosis angle measured within the curve, which is particularly important in conditions like Scheuermann's disease or post-traumatic kyphosis. Some key points to consider when measuring kyphosis angle include:
- Using standing lateral radiographs to account for gravitational effects
- Considering dynamic imaging to assess flexibility of the curve
- Regular monitoring of these angles in growing children with spinal deformities These measurements are crucial in evaluating spinal alignment, monitoring progression of spinal deformities, and making treatment decisions regarding bracing or surgical intervention, such as spinal osteotomy in patients with severe kyphosis, as recommended by the American College of Rheumatology/Spondylitis Association of America/Spondyloarthritis Research and Treatment Network 1.
From the Research
Methods for Measuring Kyphosis Angle
- The Cobb angle is a widely used method for measuring kyphosis, which can be measured manually or by digitization from supine lateral spine radiographs 2.
- The Debrunner kyphometer is a clinical standing measure that has been compared to the Cobb angle, showing reasonable agreement between the two methods 2.
- Other methods for measuring kyphosis include the use of an inclinometer, which has been shown to be a valid measure of thoracic kyphosis 3.
- Photogrammetry is another technique that has been investigated for measuring thoracic kyphosis, showing excellent test-retest reliability and strong correlation with radiographic Cobb angle 4.
Comparison of Measurement Methods
- A study comparing the Cobb technique with an alternative Cobb method and a computer-assisted curve assessment technique found strong associations between curvature and angle data derived from the three methods 5.
- Another study found that the traditional Cobb method tended to overestimate kyphosis in the presence of vertebral body end-plate deformation 5.
- The use of an inclinometer has been shown to produce angles that are comparable to the modified Cobb angle obtained from radiographs 3.
- Photogrammetry has been shown to have excellent test-retest reliability and strong correlation with radiographic Cobb angle, supporting its application in clinical practice 4.
Factors Affecting Measurement Accuracy
- Vertebral body and disc shape can influence kyphosis measurements, with the degree of kyphosis being strongly reflective of the extent of deformity of the vertebral bodies 5.
- Age has been identified as a confounder in the measurement of thoracic kyphosis using an inclinometer 3.
- The clarity of radiographs can also affect measurement accuracy, although this was not found to be significant in one study 6.