The aim of this study was to investigate in patients with early axial SpA which of the SMMs are most frequently impaired and in which order, which SMMs are most discriminative of different disease activity and severity states, and the use of SMMs over time and their relation to the mobility curves of healthy individuals.
We propose that mobility curves derived from healthy individuals could be used in the follow-up of patients with axSpA, in a similar approach to the use of growth curves for monitoring children’s growth. The assessment of SMMs within the same individual patient over time may raise some practical interpretation issues. However, only the discrimination between the axSpA subgroup and the other groups was analysed, leaving important questions regarding the value of measuring SMMs in patients with early axSpA unanswered. LSF has been shown to be the most impaired SMM in patients with early axSpA. A recent study analysed the impairment of spinal mobility in patients with chronic low back pain of short duration using the cut-offs defined in healthy subjects and compared patients with axSpA, possible SpA and no SpA. These age-adjusted ‘normal values’ allow the comparison of spinal mobility between patients and that of healthy subjects, which may guide clinicians when assessing the mobility of axSpA patients. SMMs as used for patients with axSpA have recently been investigated in healthy volunteers and percentile curves for these SMMs have been defined. Nevertheless, spinal mobility has been scarcely studied in the early phases of the disease and little is known on how the impairment in mobility across different measures behaves as compared with normal subjects. Spinal mobility has been mostly studied in cohorts of patients with radiographic axSpA (r-axSpA). īoth structural damage and inflammation are known to contribute to spinal mobility impairment. The BASMI is a composite index that includes LSF, mSchober, cervical rotation, tragus-to-wall distance (TTW) and intermalleolar distance (IMD). Several spinal mobility measures (SMMs) are recommended for the assessment of spinal mobility in patients with axSpA: chest expansion, modified Schober’s test (mSchober), occiput-to-wall distance (OTW) and either lateral spinal flexion (LSF) or the Bath AS Metrology Index (BASMI). Spinal mobility impairment is one of the central outcomes in axSpA and has been included in the core set of domains for the evaluation of patients with axSpA in clinical practice and trials, as defined by the Assessment of SpondyloArthritis international Society (ASAS). The natural history of axial spondyloarthritis (axSpA) is associated with a progressive restriction in spinal mobility. High variation of mobility measures impairs usage when monitoring individual axial spondyloarthritis patients over time. Spinal mobility assessment enables discrimination of cross-sectionally axial spondyloarthritis patients with worse disease activity and severity. 5.1 cm for LSF.Ĭross-sectional use of spinal mobility measures, at the group level, is informative in early axial spondyloarthritis. Smallest detectable changes were in general high, e.g. Reliability of SMMs was ‘fair’ to ‘good’ (inter-reader intraclass correlation coefficients (2, 1): 0.55–0.84 intrareader intraclass correlation coefficients (2, 1): 0.49–0.72). A high variability in SMMs within the same patient over time was observed, even when restricting the analysis to patients with low disease activity. 31% of LSF impairment in patients with Ankylosing Spondylitis Disease Activity Score (ASDAS) < 2.1 in ≥2/3 visits vs 49% in those with ASDS ≥ 2.1. LSF and Bath AS Metrology Index best discriminated between subgroups of patients (higher impairment in patients ever treated with biologics, with higher disease activity and presence of baseline syndesmophytes): e.g. If both (LSF and mSchober) were measured, 84% (DESIR) and 74% (SPACE) of the patients with impairment in ≥1 SMM would be captured. In 328 DESIR and 148 SPACE patients, lateral spinal flexion (LSF) and mSchober were the most impaired SMMs.