Figure 2PT force-elongation relationship in RA patients (n selleck SB203580 = 18) (a) and AS patients (n = 12) (b) and their respective matched controls. Results are presented as means �� SEM. Table 3Physiological data of RA (n = 18; 13 women) and AS (n = 12; 4 women) patients versus age- and sex-matched healthy controls. ACSA: anatomical cross-sectional area. Results are presented as mean �� SEM.3.4. Quadriceps Muscle Cross-Sectional Area and Muscle Specific ForceThere were no differences in quadriceps muscle force or CSA between RA and AS patients and their respective matched controls. Consequently, muscle specific force was not compromised for either patient groups (Table 3).4. DiscussionThis study is to our knowledge the first to investigate the physiological properties of patellar tendons in patients with stable RA or AS.

Compared to healthy age- and sex-matched controls, tendon stiffness in both patient groups is significantly reduced, and whereas the size of the PT was unchanged in RA, there was PT thickening in the AS group, resulting in pronounced reduction of YM. Despite preserved muscle force and size, these changes in tendon properties were accompanied by significant impairments in physical function. The reduction in PT stiffness is likely due to local and systemic effects of cytokines on the tendon, since proinflammatory cytokines are known to alter tendon structural characteristics in inflammatory arthropathies.

The main drivers of the local inflammatory process are TNF-��, interleukin-1 (IL-1) and IL-6 which produce proteolytic enzymes such as matrix metalloproteinases that lead to collagen destruction [32], and the proangiogenic vascular endothelial growth factor, which evokes synovial hyperplasia and infiltration of macrophages and T cells into synovium [14]. According to the different pathologies of RA and AS inflammatory molecules target primarily the enthesis in AS, whereas in RA tendon involvement is thought to be secondary through the proximity to inflamed synovium [10, 11]. Systemically circulating cytokines [33] could have an additional detrimental effect on the tendon in both RA and AS. In addition to the effects of inflammation, disuse can be a contributor to reduced PT stiffness due to chronic reduction of the loading of the tendons [4, 34]. In the current study, however, there were no differences Drug_discovery in habitual physical activity levels between the patient groups and their controls. It is therefore unlikely that disuse was causing the differences we observed in PT stiffness.Tendon mechanical properties are essential for proprioception and for the reflex responses involved in rapid adjustment of muscle tension to positional changes [3], as well as the storing of elastic strain energy which is key to efficient locomotion.