This is a clinimetric study to validate the use of IMU spinal sensors to measure the range of spinal movement in a group of patients with axial spondyloarthritis.

One of the most important goals of therapy in axial spondyloarthritis is to improve and/or preserve spinal mobility. In the early stages of the disease, spinal stiffness is reversible but eventually the spine can fuse causing permanent loss of flexion. Traditional tests for spinal mobility using tape measures are inaccurate and do not capture many aspects of kinematics such as spinal rotation or speed of movement. There is also a need for wearable sensors to give patients feedback and encourage more regular exercise.

The investigators will be using IMU spinal sensors to measure spinal ROM in a group of 40 patients with axial spondyloarthritis. The investigators will be testing aspects of inter-rater and intra-rater reliability, comparing sensor reliability to the accuracy of the traditional tape measure test (BASMI).

Inclusion Criteria:

-Confirmed diagnosis of axSpA according to the ASAS criteria

Exclusion Criteria:

• Severe joint or spinal pain at the time of the study
• Severely restricted hip movement
• History of previous vertebral fracture
• History of previous spinal surgery
• Major scoliosis deformity
• Pregnancy

Each physiotherapist rater will have to independently attach the sensors to the participant's spine before testing, and no positioning marks will be left on the patient in between tests or between visits. They will work in different rooms and will not have access to earlier results.