Reference intervals of spinal mobility measures in normal individuals: the mobility study

Objectives To establish reference intervals (RIs) for spinal mobility measures as recommended for patients with axial spondyloarthritis, and to determine the effect of age, height and gender on spinal mobility, in normal individuals. Methods A cross-sectional study (MOBILITY) was conducted among normal individuals aged 20-69years. Recruitment was stratified by gender, age (10-year categories) and height (10cm categories). Eleven spinal mobility measures were assessed. Age specific RIs and percentiles were derived for each measure. Results 393 volunteers were included. All spinal mobility measures decreased with increasing age. Therefore, age specific RIs were developed. The 95% RIs (2.5th and 97.5th percentiles), as well as the 5th, 10th, 25th, 50th, 75th and 90th percentiles for each spinal mobility measure and different ages are presented. Mobility percentile curves were also plotted for each of the measures. For instance, the 95% RI for lateral spinal flexion was 16.2-28.0cm for a 25-year-old subject, 13.2-25.0cm for a 45-year-old subject and 10.1-21.9cm for a 65-year-old subject. After adjustment for age, there was no need for gender specific RIs, while RIs of some measures are height-adjusted. Conclusions Age specific RIs and percentiles were derived for each of the spinal mobility measures for normal individuals. These may guide clinicians when assessing the mobility of patients with axial spondyloarthritis. The RIs may serve as cut-off levels for normal' versus abnormal', whereas the mobility percentile curves may be used to assess the level of mobility of patients with axial spondyloarthritis.