Background Spinal mobility is frequently assessed in the follow-up of patients with axial SpA, which is also in accordance with the recommendations by the Assessment of Spondyloarthritis international Society (ASAS). However, the interpretation of spinal mobility measures has been hampered by the absence of reference values.
Objectives To establish reference intervals (RIs) for spinal mobility measures.
Methods A cross-sectional study (“MOBILITY-study”) was conducted among healthy volunteers aged 20-69 years old. Recruitment was stratified by gender, age (10-year categories) and height (10cm categories). Participants were Caucasian volunteering to be measured in either the Netherlands or Portugal. Exclusion criteria were factors potentially influencing spinal mobility (eg. back surgery, low back pain). Several spinal mobility measures were assessed: lateral spinal flexion (LSF, cm), cervical rotation (degrees), intermalleolar distance (cm), chest expansion (cm), 10cm- and 15cm-Schober’s test. The Bath Ankylosing Spondylitis Mobility Index (BASMI) was computed. Age-specific equations for percentiles of spinal mobility measures were derived by maximum likelihood. Each parameter of normal or exponential-normal density was modeled as a fractional polynomial function of age. The estimated 95% RI (2.5th and 97.5th percentiles), as well as the 5th, 10th, 25th and 50th percentiles, are presented. RIs can be computed for any age, but examples were chosen for the ages of 25, 35 and 45, for comparison purposes with mobility measurements of patients with axial SpA.
Results 393 volunteers were included (only the category of 60-69 year-old women with height >1.80m was incomplete, due to difficulties in recruitment). RIs were derived and are presented in the Table. Percentiles graphs were also plotted for each of the measurements, with the best-fitting equation. The lower border of the RI for both Schober’s 10cm and 15cm test lies below the “cutoff” of 5cm frequently used in clinical practice. No individual had a BASMI<0.15, being the median value of 1.3 for a patient of 25 years old and increasing with age.
Conclusions Age-specific RIs and percentiles were derived for each of the spinal mobility measures for normal individuals. These RIs may guide clinicians when assessing the mobility of patients with axial SpA, and may serve as cut-off levels for ‘normal’ vs. ‘abnormal’.
Disclosure of Interest None Declared