Biomechanical properties of low back myofascial tissue in younger adult ankylosing spondylitis patients and matched healthy control subjects

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Background:Ankylosing spondylitis is a degenerative and inflammatory rheumatologic disorder that primarily affects the spine. Delayed diagnosis leads to debilitating spinal damage. This study examines biomechanical properties of non-contracting (resting) human lower lumbar myofascia in ankylosing spondylitis patients and matched healthy control subjects.Methods:Biomechanical properties of stiffness, frequency, decrement, stress relaxation time, and creep were quantified from 24 ankylosing spondylitis patients (19 male, 5 female) and 24 age- and sex-matched control subjects in prone position on both sides initially and after 10min rest. Concurrent surface electromyography measurements were performed to ensure resting state. Statistical analyses were conducted, and significance was set at p<0.05.Findings:Decreased lumbar muscle elasticity (inverse of decrement) was primarily correlated with disease duration in ankylosing spondylitis subjects, whereas BMI was the primary correlate in control subjects. In ankylosing spondylitis and control groups, significant positive correlations were observed between the linear elastic properties of stiffness and frequency as well as between the viscoelastic parameters of stress relaxation time and creep. The preceding groups also showed significant negative correlations between the linear elastic and viscoelastic properties.Interpretation:Findings indicate that increased disease duration is associated with decreased tissue elasticity or myofascial degradation. Both ankylosing spondylitis and healthy subjects revealed similar correlations between the linear and viscoelastic properties which suggest that the disease does not directly alter their inherent interrelations. The novel results that stiffness is greater in AS than normal subjects, whereas decrement is significantly correlated with AS disease duration deserves further investigation of the biomechanical properties and their underlying mechanisms.HIGHLIGHTSLimited studies exist in the area of human resting muscle tone and its effects.The role of muscle properties in ankylosing spondylitis has not been studied.Few studies relate BMI, age, disease duration with muscle biomechanical properties.Disease duration alters low back elasticity and stiffness in ankylosing spondylitis.Relations between linear elastic and viscoelastic properties not altered by disease.

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