Sundström B, et al. - In patients with long-standing well-defined ankylosing spondylitis (AS), researchers assessed the course of impaired spinal mobility. Data were analyzed for 232 patients with AS and 3849 clinical measurements from February 1980 to June 2016. After a 10-year disease duration, impaired spinal mobility in AS is common. A worse prognosis seemed to be associated with lateral spinal flexion below the 2.5^th percentile at 10 years. Findings suggested that fixed reference values in AS overestimated and should be avoided spinal mobility impairments.