Gait as predictor of physical function in axial spondyloarthritis: the prospective longitudinal FOLOMI (Function, Locomotion, Measurement, Inflammation) study protocol.

Axial spondyloarthritis (axSpA) is a chronic inflammatory rheumatic disease affecting predominantly sacroiliac joints and axial skeleton. axSpA progression being irregular and hardly predictable, identifying functional decline is particularly important in patient with axSpA to allow delivery of timely and targeted interventions. Pain, reduced range of motion or altered posture can have adverse consequences on gait. Although gait has previously been used as a sensitive measure of physical outcomes in elderly and pathological populations, to the best of our knowledge, no study has used gait as a predictor of physical function in patients with axSpA. The objective of our study is hence to determine if gait parameters measured in patients with axSpA could predict the evaluation at 18 months of physical function as assessed by the Bath Ankylosing Spondylitis Functional Index (BASFI). This is a prospective and longitudinal study. Sixty patients with axSpA and 30 healthy age- and sex-matched controls will be included. Patients should be aged 18-65 years at time of their first evaluation, followed at Grenoble Alpes University Hospital for axSpA or ankylosing spondylitis, able to walk 180 m without technical help and with stable treatment for at least 12 months. Clinical characteristics, BASFI, Bath Ankylosing Spondylitis Disease Activity Index (BASDAI), clinical and laboratory measurements of gait will be assessed during four visits (at baseline and at months 6, 12, and 18). Similar assessments will be performed once for the healthy control group. A linear mixed model at 6, 12 and 18 months will be constructed to answer to the first objective, with the BASFI as dependent variable and gait parameters as explanatory variables. The data collection started in August 2018 and will be completed with the inclusion and follow-up of all the participants. We believe that the combination of clinical and laboratory measurements of gait in patients with axSpA could strengthen the capacity to monitor disease's evolution and to predict changes in patients' physical function. Results of the present study could ultimately allow delivering targeted, timely, personalized interventions and treatment in patients with axSpA.Trial registration: The study was approved by local ethic committee (CPP Ile De France 1, RCB: 2017-A03468-45, date of agreement: July 17th, last version: V4.0, 2018, March 5th, 2019) and is retrospectively registered in Clinical trials (NCT03761212).