Reliability and validity of non-radiological measures of thoracic kyphosis in chronic obstructive pulmonary disease

Background/Aims: Thoracic kyphosis in people with chronic obstructive pulmonary disease can be measured from digital photogrammetry or three-dimensional motion capture. This study aimed to determine the reliability, validity and agreement for non-radiological measures of thoracic kyphosis in chronic obstructive pulmonary disease. Methods: A total of 19 participants with chronic obstructive pulmonary disease were included. Cobb angles from chest radiographs and spinous process landmarks using photogrammetry and three-dimensional motion capture were evaluated. Findings: The mean kyphosis (± standard deviation) was 48.8 ± 10.9 degrees by radiograph; 49.6 ± 12.9 degrees by three-dimensional motion capture and 52.2 ± 11.1 degrees by photogrammetry. Radiographic Cobb angle and photogrammetry measurements demonstrated excellent intra- and inter-rater reliability. Correlation between non-radiological kyphosis measurements and chest radiographs was strong (Pearson's r 2 >0.75 for both). Limits of agreement between radiographs and 3D motion capture were –9 degrees to 7 degrees, and –12 to 8 degrees between radiographs and photogrammetry. Conclusions: Non-radiological measures of thoracic kyphosis are reliable and valid in chronic obstructive pulmonary disease.