Normative values for the Bath Ankylosing Spondylitis Metrology Index in a UK population

Spinal mobility is assessed frequently in patients with AS/axial SpA using the BASMI to provide baseline measurement and monitor change over time. The interpretation of BASMI scores has been hindered by the absence of normative values. We aimed to obtain normative values for the BASMI in healthy men and women in a UK population. A cross-sectional study of 168 volunteers stratified by gender and age was completed. Exclusion criteria comprised factors potentially influencing spinal mobility. Each component of the BASMI was assessed, with the total score computed using the 10-point scoring system. Measurements were taken by physiotherapists following an agreed protocol. Data were summarized and analysed with age-specific centiles and CIs calculated. Total BASMI scores ranged from 0 to 4.4, with only 1.2% of the sample having a score of 0. The estimated median score for an individual age 25 years was 0.9, increasing with age to 2.1 for an individual age 65 years. There was a corresponding increase in component BASMI scores, which was more pronounced for some components than others. Our data indicate that it is unusual for healthy individuals to score zero on the BASMI, which has implications for the interpretation of scores, especially at baseline. The generation of normative values has the potential to inform clinical assessment of spinal mobility and assist patients in understanding how their spinal mobility compares with that of a healthy age-matched population.