The reliability of spinal motion palpation determination of the location of the stiffest spinal site is influenced by confidence ratings: a secondary analysis of three studies

BACKGROUND: This is a secondary analysis of three previous studies on the cervical, thoracic, and lumbar spines. It uses continuous analysis of the stiffest spinal site rather than more typical level-by-level analysis to assess interexaminer reliability, and the impacts of examiner confidence and spinal region. The primary goal was secondary analysis of the combined data; secondary goal was de novo analysis of combined data emphasizing absolute indices of examiner agreement; and tertiary goal was analysis of actual vs. simulated data to determine to what degree the information provided by motion palpation impacted interexaminer reliability. METHODS: This study emphasized Median Absolute Examiner Differences and Bland-Altman Limits of Agreement to calculate examiner differences, which are immune to subject homogeneity, and de-emphasized intraclass correlation, which is not. It calculated Median Absolute Deviation to determine data dispersion. The study analyzed the entire n = 113 combined dataset, as well as subgroups stratified by examiner confidence and spinal region. Simulations were run using a random number generator to provide chance data for examiners' findings of the stiffest spinal site, the analysis of which was compared with that of the actual data. RESULTS: Median Absolute Examiner Differences for the combined dataset were 0.7 of one vertebral level, suggesting examiners usually agreed on the stiffest spinal site or the motion segment including it. When both examiners were confident in their findings (53.4%), the median examiner difference decreased to 0.6 levels, increasing to 1.0 levels when one lacked confidence and to 1.8 levels when both lacked confidence. Reliability was greater in the cervical and lumbar spines (each 0.6 vertebral levels examiner differences) than in the thoracic spine (1.1 levels examiner differences). The actual information provided by motion palpation compared to simulated data improved interexaminer reliability by a factor ranging from 1.8 times to 4.7 times, depending on the regional subset analyzed. CONCLUSIONS: Examiner decisions regarding the location of the stiffest spinal site were deemed adequately reliable, especially when the examiners were confident. Researchers and clinicians alike might best design their study protocols and practice methods using the stiffest segment protocol as an alternative to level-by-level spinal analysis.