Objective: To determine whether the axial measures used in primary ankylosing spondylitis (AS) were reproducible for both AS and psoriatic arthritis (PsA) with axial disease.
Methods: A group of 20 rheumatologists from 11 countries with expertise in spondyloarthritis (SpA) met for a combined physical examination exercise to assess 10 patients with PsA with axial involvement (9 men, 1 woman, mean age 52 yrs, mean disease duration 17 yrs) and 9 AS patients (7 men, 2 women, mean age 38 yrs, mean disease duration 16 yrs). A modified Latin-square design was used. Measures included were occiput to wall, tragus to wall, cervical rotation, chest expansion, lateral spinal bending, modified Schober, and hip mobility. Data were analyzed using intraclass correlation coefficients (ICC) adjusted for order of measurements.
Results: The majority of the variance was contributed by the patients. There was no order effect. Observer effect was noted especially for chest expansion for both AS and PsA patients, and for the modified Schober in PsA. The ICC demonstrated very good to excellent agreement for most measures for both AS and PsA. Chest expansion provided only moderate agreement for AS and PsA.
Conclusion: Overall, measures of spinal mobility used in primary AS perform well with respect to interobserver reliability, and are equally reproducible when applied to PsA patients with axial involvement. Thus, these measures should now be evaluated in therapeutic trials of patients with PsA to determine sensitivity to change and concordance with other measures of structural damage.