Reliability of human achilles tendon stiffness measures using freehand 3-D ultrasound

Merza, E; Pearson, S; Lichtwark, G; Garofolini, A; Malliaras, P

Abstract

Achilles tendon (AT) stiffness is an important property of both human locomotor performance and injury mechanics. Freehand 3-D ultrasound (3-DUS) is a promising method for measuring stiffness of the Achilles tendon, particularly the free AT (2–6 cm proximal to calcaneus), which is commonly injured. The aim of this study was to investigate the test–retest reliability of freehand 3-DUS in measuring free AT stiffness in humans. The free Achilles tendon length of healthy participants (n = 10) was scanned on the same day on two consecutive occasions (1 h apart) during rest and isometric plantar flexion contractions at 20%, 40% and 60% of maximum force. The slope of the force–elongation curve over these force levels represented individual stiffness (N/mm). Relative reliability was assessed using the intra-class correlation coefficient (ICC), and absolute reliability was estimated with the standard error of measurement (SEM) and smallest detectable change. Systematic bias in stiffness measures was explored by comparing test and retest distributions and Bland–Altman plots. The test–retest reliability of free AT stiffness measured using freehand 3-DUS was excellent [ICC = 0.994, 95% confidence interval [CI]: 0.978–0.999)]. The mean stiffness values at test (361.83 N/mm [170.77]) and retest (364.98 N/mm [168.57]) did not significantly differ (p = 0.72), and the smallest detectable change was 52.14 N/mm. The Bland–Altman plot indicated the absence of systematic bias (95% CI: –22.18 to 15.88). Freehand 3-DUS provides reliable and precise measures of tendon stiffness and can be used to detect small changes in free AT stiffness in response to load or tendon pathology.

Citation

Merza, E., Pearson, S., Lichtwark, G., Garofolini, A., & Malliaras, P. (2021). Reliability of human achilles tendon stiffness measures using freehand 3-D ultrasound. Ultrasound in Medicine and Biology, 47(4), 973-981. https://doi.org/10.1016/j.ultrasmedbio.2021.01.002

• Journal Article Type: Article
• Acceptance Date: Jan 4, 2021
• Online Publication Date: Feb 15, 2021
• Publication Date: Apr 1, 2021
• Deposit Date: Apr 23, 2021
• Journal: Ultrasound in Medicine & Biology
• Print ISSN: 0301-5629
• Publisher: Elsevier
• Volume: 47
• Issue: 4
• Pages: 973-981
• DOI: https://doi.org/10.1016/j.ultrasmedbio.2021.01.002
• Publisher URL: https://doi.org/10.1016/j.ultrasmedbio.2021.01.002
• Related Public URLs: http://www.journals.elsevier.com/ultrasound-in-medicine-and-biology/
• Additional Information: Additional Information : ** Article version: AM ** Embargo end date: 15-02-2022 ** From Elsevier via Jisc Publications Router ** Licence for AM version of this article starting on 15-02-2022: http://creativecommons.org/licenses/by-nc-nd/4.0/ **Journal IDs: issn 03015629 **History: issue date 30-04-2021; published_online 15-02-2021; accepted 04-01-2021