Implications for the use of postural analysis as a clinical diagnostic tool: Reliability of quantifying upright standing spinal postures from photographic images

Objectives: A repeated measures design was used to test the reliability of standing spine postures within subjects using a biologically relevant measure determined by digitization of images and to compare the results to a previously tested vertical reference method. Methods: Twenty subjects attended 3 sessions consisting of 5 trials each. Photographs of the sagittal and posterior views of normal upright standing were taken. Landmarks were digitized and cervical, thoracic, and lumbar spinal angles were calculated using the algebraic dot product. Intraclass correlation coefficients were used to evaluate intrasubject reliability across sessions. Results: According to the intraclass correlation coefficients, posture had good to excellent reliability in the sagittal view and provided a more stable measure of spinal angles than the posterior view. Mean repositioning errors were less than 6 degrees and 2 degrees in the sagittal and posterior views, respectively. Conclusions: Although the repeatability of posture was improved in the sagittal view, when a biologic measure was used instead of an external vertical reference to calculate spinal angles, individual subject posture was still variable. This brings into question the effectiveness and validity of using surface skin markers to track postural changes due to clinical interventions. If the postural analysis approach is to be used to detect changes due to clinical treatment, such changes must be larger than the baseline repositioning errors seen in healthy subjects.