Submitted on September 9, 2008
Revised on December 1, 2008
Accepted on December 27, 2008
Ultrasonic Evaluations of Achilles Tendon Mechanical Properties Post Stroke
Heng Zhao1, Yupeng Ren2, Yi-Ning Wu1, Shu Q. Liu1, and Li-Qun Zhang3*
1 Northwestern University
2 Rehabilitation Inst of Chicago/Northwestern University
3 Rehabilitation Institute of Chicago/Northwestern University
* To whom correspondence should be addressed. E-mail: l-zhang{at}northwestern.edu.
Spasticity, contracture, and muscle weakness are commonly observed post stroke in muscles crossing the ankle. However, it is not clear how biomechanical properties of the Achilles tendon change post stroke, which may affect functions of the impaired muscles directly. Biomechanical properties of the Achilles tendon including the length and cross-sectional area in the impaired and unimpaired sides of 10 hemiparetic stroke survivors were evaluated using ultrasonography. Elongation of the Achilles tendon during controlled isometric ramp-and-hold and ramping up then down contractions was determined using a block-matching method. Biomechanical changes in stiffness, Young's modulus, and hysteresis of the Achilles tendon post stroke were investigated by comparing the impaired and unimpaired sides of the 10 patients. The impaired side showed increased tendon length (6%, P=0.04), decreased stiffness (43%, P<0.001), decreased Young's modulus (38%, P=0.005), and increased mechanical hysteresis (1.9 times higher, P<0.001) compared to the unimpaired side, suggesting Achilles tendon adaptations to muscle spasticity, contracture, and/or disuse post stroke. In vivo quantitative characterizations of the tendon biomechanical properties may help us better understand changes of the calf muscle-tendon unit as a whole and facilitate development of more effective treatments.
