Rasterstereographic analysis of the thoracic sagittal curvature: A reliability study

Limitations associated with radiological evaluation of spinal curvature have resulted in the increased application of noninvasive optical imaging systems to define various shape parameters of the spine. There is little information describing the reliability of the measurement of the thoracic spine upright posture using these imaging systems. The objective of this study was to examine the reliability of thoracic kyphosis measurement from noninvasive back surface analysis. Repeated imaging of back shape was performed in 10 volunteers of widely different ages (range 19–64 years), and in a back phantom, utilizing the Jenoptik Formetric video rasterstereography imaging system. Coefficients of variation (CV) for five repeated measurements of the subjects ranged from 2.4% to 3.0% for the kyphosis parameters measured. The reproducible nature of derived angles was further reflected by low standard deviation values (1.2° to 2.0°). Inter-trial CV values for repeated imaging of the back phantom ranged from 0.4% to 1.3%. High intraclass correlation coefficients were noted for all the measurements (0.98 to 0.99). Consistent results were demonstrated across the varying age cohorts. The reliability of rasterstereographic evaluation of thoracic kyphosis is largely influenced by the variability in subject posture, with minimal errors arising from internal system inaccuracies. These results confirm the utility of rasterstereographic back shape imaging in the detection of relatively small curve changes and hence its potential clinical role in monitoring kyphosis progression.