Background/Purpose: Spinal mobility is one of the core outcomes recommended by the Assessment of Spondyloarthritis international Society (ASAS) for following patients with axial SpA. It is currently unknown how these spinal mobility measures perform in healthy subjects and to what extent they are influenced by age, gender and height. We aimed to assess the effect of age, gender and height on spinal mobility measures among healthy individuals.

Methods: A cross-sectional study (“MOBILITY-study”) was conducted in healthy volunteers aged 20-69 years old. Recruitment was stratified by gender, age (10-year categories) and height (10cm categories). Participants were Caucasians volunteering to be measured in the Netherlands and Portugal. Exclusion criteria were factors potentially influencing spinal mobility (such as previous back surgery, known spinal osteoarthritis or low back pain). The following measures were assessed: tragus-to-wall distance (TTW, cm), occiput-to-wall distance (OTW, cm), lateral spinal flexion (LSF, cm), cervical rotation (CR, degrees), intermalleolar distance (IMD, cm), chest expansion (CE, cm) and Schober’s test. The Bath Ankylosing Spondylitis Mobility Index (BASMI) was computed. The effects of age, gender, height and weight were investigated using linear regression analyses (univariable followed by multivariable, forward selection procedure), adjusting for potential confounders and taking relevant interactions into account.

Results: 393 volunteers were included. A significant decrease in all spinal mobility measures was found by increasing age, and age was included in all multivariable models (some of the models are presented in the table). E.g. an increase of 10 years was associated with a decrease of 1.5cm in LSF or a decrease of 3.4cm in IMD. Height was associated with the following spinal mobility measures: TTW, LSF, CE, IMD and BASMI, with a higher height being associated with better mobility. E.g. every increase in height of 10cm resulted in an increase of 4.2cm in IMD, an increase of 0.3cm in LSF and an increase of 1.1cm in CE.  Gender was associated with CE and CR, with women having a worse mobility. Weight was positively associated with TTW, OTW and Schober’s test: An increase of 10kg resulted in an increase of 0.3cm in TTW, 0.2cm in OTW and 0.2cm in Schober’s test. There was a significant interaction between the effects of age and gender on BASMI: in women, age was the only factor with a significant effect on BASMI (β 0.03, 95%CI 0.03; 0.04). In men, age (β 0.03, 95%CI 0.02; 0.04), and weight (β -0.01, 95%CI -0.01; -0.00) significantly contributed to BASMI.

Conclusion: All spinal mobility measures decrease with increasing age. Height significantly influences some spinal mobility measures, especially IMD and LSF. These factors have to be taken into account when assessing patients’ spinal mobility, and should be included in reference values for these measurements.

 

Table – Effect of age, gender, height and weight on spinal mobility measures
Measure	Univariable linear regression β (95% CI)	Multivariable linear regression β (95% CI)
Lateral spinal flexion (cm)
Age (years)	-0.15 (-0.17; -0.13)	-0.15 (-0.17; -0.13)
Gender (female vs male)	-0.50 (-1.23; 0.23)
Height (cm)	0.03 (0.00; 0.06)	0.03 (0.00; 0.07)
Weight (kg)	-0.01 (-0.04; 0.01)	-0.01 (-0.04; 0.02)
Intermalleolar distance (cm)
Age (years)	-0.46 (-0.42; -0.27)	-0.44 (-0.53; -0.36)
Gender (female vs male)	-1.05 (-3.92; 1.83)
Height (cm)	0.44 (0.33; 0.55)	0.42 (0.33; 0.52)
Weight (kg)	0.14 (0.05; 0.23)
Cervical rotation (degrees)
Age (years)	-0.35 (-0.42; -0.27)	-0.34 (-0.42; -0.27)
Gender (female vs male)	-4.13 (-6.43; -1.82)	-3.83 (-5.89; -1.77)
Height (cm)	0.12 (0.03; 0.21)
Weight (kg)	-0.03 (-0.10; 0.04)
BASMI (0-10)
Age (years)	0.03 (0.03; 0.04)	Significant interaction age X gender (see text)
Gender (female vs male)	0.21 (0.05; 0.38)
Height (cm)	-0.01 (-0.02; -0.00)
Weight (kg)	-0.00 (-0.01; 0.00)

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