Objective: To investigate the passive properties of the plantar flexors muscle-tendon tissue in patients with the hypermobility type of Ehlers-Danlos syndrome (EDS-HT).
Methods: Twenty-five women with EDS-HT and 25 sex- and age-matched healthy control subjects participated in the study. Passive resistive torque (PRT) of the plantar flexors was measured with an isokinetic dynamometer during 2 standardized stretch protocols to obtain the passive muscle tension. Protocol 1 consisted of 4 continuous cycles to a predetermined angle of 10° dorsiflexion. Protocol 2 consisted of a slow stretch to the onset of pain. Torque, angle, and electromyography were simultaneously recorded during the tests. To take muscle thickness into account, muscle cross-sectional area (MCSA) was obtained with peripheral quantitative computed tomography. Stiffness of the Achilles tendon was assessed using a dynamometer in combination with ultrasonography.
Results: The results demonstrate a significantly larger maximal joint angle in the EDS-HT patients accompanied by a similar PRT compared to the control subjects (protocol 2), indicating a lower passive muscle tension in the patient group. PRT for the predetermined angle (protocol 1) was the same for both groups and there was no difference in MSCA. Furthermore, a significantly lower Achilles tendon stiffness was seen in the patient group than in the control group.
Conclusion: This study is the first to provide evidence for altered passive properties of the muscle-tendon unit in EDS-HT patients. These changes are thought to be associated with structural modifications in connective tissue.
Copyright © 2012 by the American College of Rheumatology.