Does height influence the assessment of spinal and hip mobility measures used in ankylosing spondylitis?

It is not known if height contributes to the variability in mobility measures in patients with ankylosing spondylitis (AS) and whether any measures should be reported corrected for height. We examined the contribution of height to the variability of mobility measures in patients with a diverse spectrum of AS disease.

We assessed the 9 mobility measures comprising the Bath AS and Edmonton AS Metrology Indices (BASMI and EDASMI) in a total of 205 patients. The contribution of height to the variability in mobility scores was analyzed descriptively according to tertiles of height, and also by combined probability scatter plots that combined each individual's height with the corresponding score for either the composite index or each of the 9 spinal mobility measures. Hierarchical (sequential) linear regression was used to assess the contribution of height to the variance in EDASMI and BASMI composite scores and individual measures, adjusted for age, disease duration, and the Bath AS Disease Activity Index.

Descriptive data and correlation analysis revealed significant differences related to height for both the EDASMI and the BASMI, particularly for EDASMI cervical rotation, EDASMI lumbar side flexion, chest expansion, lumbar flexion, and intermalleolar distance. Combined probability scatter plots showed that for a particular height there was a wide distribution of mobility scores and only intermalleolar distance showed some relation to height. Hierarchical regression analysis showed that height contributed significantly, although relatively minimally to the variance of both the EDASMI (3.1%; p

Body height has minimal effect on the variability of mobility scores in patients with AS. Disease-related factors predominate.