Background Axial Spondyloarthritis (axSpA) patients have inflammation and/or structural damage in the lumbar spine that reduces their mobility and quality of life. The biomechanical features of axSpA have not been investigated in detail, but could prove to be a very important factor contributing to pain, stiffness and loss function. Myotonometry is being used to quantify stiffness muscles in a valid and reliable way.

Objectives To measure and compare the stiffness in the erector spinae muscles of axSpA patients and healthy subjects to analyse if there are any significant differences between them.

Methods 20 axSpa patients and 20 healthy subjects matched in age, BMI and sex, were recruited. The stiffness of the lumbar erector spinae (ES) muscles was assessed at L4–5 using myotonometry (MyotonPRO©) (figure 1). Measures were obtained twice in the left and right muscles, in a first test and five minutes later. PRO questionnaires, radiographic structural damage and metrology for axSpA were also assessed. Lumbar spinal mobility was also measured using an inertial sensor system (ViMove©).

Results No statistical differences were found between left and right muscles neither after five minutes, so the mean values were used for analyses. All muscular measures, except Decrement showed statistically significant differences between groups. The table shows results of muscular stiffness parameters analysed, statistical differences in all parameters between groups and correlations of these parameters with conventional metrology, patient reported questionnaires (only patients) and structural damage. For control subjects, the only significant correlation was between stiffness and age. However in the axSpA patients, the myoton readings correlated with mobility measures, especially with BASMI, frontal flexion (not extension), lateral flexion and rotation, measured with the inertial sensors system. Some correlations (p<0.05) were also found for BASFI and BAS-G but not for BASDAI or ASQoL.

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Abstract AB0868 – Figure 1

Conclusions axSpA increases lumbar muscle stiffness with respect to healthy individuals. Muscle stiffness, as measured by myotonometry, was related to loss of movement and this could be contributing to a loss of function independently of structural damage and inflammation in axSpA. These new outcome measures could be helpful for understanding the evolution of the disease and for the functional assessment.

Acknowledgements This study has been funded by Foreum, the XXI University of Cordoba Reearch Program and Junta de Andalucía (CS-S0029/2016).

Disclosure of Interest None declared