Evaluation of Achilles tendon stiffness during contraction usign strain sonoelastograpy

Schneebeli, Alessandro and Falla, Deborah and Del Grande, Filippo and Cescon, Corrado and Clijsen, Ron and Barbero, Marco (2018) Evaluation of Achilles tendon stiffness during contraction usign strain sonoelastograpy. In: Pysiotherapy UK Conference 2018, 19-20/10/2018, Birmingham.

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Purpose: To evaluate Achilles tendon stiffness using strain sonoelastography with an external reference material during an isometric ramp contraction. Methods and Materials: Ultrasound and strain sonoelastography examinations were performed on 37 healthy participants using a commercially available ultrasound system (MyLab ClassC, Esaote, Genoa, Italy) with a linear transducer (LA533) in the frequency range 3–13 MHz. Strain sonoelastography, using an external reference material made with Zerdine® (CIRS, Norfolk, VA, USA) with known elasticity properties, was performed in the longitudinal plane at the level of the medial malleolus. The experimental protocol was tested and validated in previously published work. The external reference material was used to provide a comparison between the examined tissue and a material with a known elasticity. Stiffness was computed according to the sonoelastography color scale as the strain ratios between the tendon and reference material. Sonoelastography images were captured during rest and during a series of isometric contractions of the gastrocnemius muscle at different force levels (0.5kg, 1kg, 2kg, 5kg, 10kg.) The mean and standard deviation of the strain ratios for all subjects across the different conditions were calculated and the Friedman test with post hoc pairwise comparison were used to determine the correlation between the different contraction levels. Results: No significant differences were found for Achilles tendon stiffness between men and women (p=0.6) or between the left and right Achilles tendon (p=0.5), therefore the data were pooled for further analysis. The mean (±SD) values for the strain ratio was 1.98 (±1.09) in a relaxed state and 1.32 (±0.63), 1.07 (±0.55), 0.83 (±0.37), 0.49 (±0.19) and 0.33 (±0.10) for the contractions with 0.5 kg, 1 kg, 2 kg, 5 kg and 10 kg respectively. Friedman test for related samples showed significance (p=0.000) and the post hoc pairwise comparison revealed significant differences (p<0.05) between all the contraction levels except for 0.5 kg – 1 kg (p=0.41); 1 kg – 2 kg (p=0.12) and 5 kg – 10 kg (p=0.12). Conclusion: Strain sonoelastography can be used to quantify changes in Achilles tendon stiffness during isometric contractions of the gastrocnemius muscle, with the lowering of the strain ratio between the tendon and the reference material indicating a constant increase of tendon stiffness during contraction. Further research can now extend these measures to people with Achilles tendinopathy. Implications: • Altered tendon stiffness due to tendon pathologies can be evaluated using the proposed imaging technique described in this study in which the tendon is put under load. • Sonoelastography may improve the evaluation of patients with Achilles tendinopathy by providing a quantitative assessment of the force-stiffness curve Key words: Strain sonoelastography; Achilles tendon; Musculoskeletal Acknowledgment: We thank the staff and students at the University of Applied Sciences and Arts of Southern Switzerland (SUPSI), for taking part in the study. We especially thank the Thim van der Laan Foundation, Landquart, Switzerland, for financial support.

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