Mechanotendography in Achillodynia shows reduced oscillation variability of pre-loaded Achilles tendon: a pilot study

Abstract

The present study focuses on an innovative approach in measuring the mechanical oscillations of pre-loaded Achilles tendon by using Mechanotendography (MTG) during application of a short yet powerful mechanical pressure impact. This was applied on the forefoot from the plantar side in direction of dorsiflexion, while the subject stood on the ball of the forefoot on one leg. Participants with Achilles tendinopathy (AT; n = 10) were compared to healthy controls (Con; n = 10). Five trials were performed on each side of the body. For evaluation, two intervals after the impulse began (0-100ms; 30-100ms) were cut from the MTG and pressure raw signals. The intrapersonal variability between the five trials in both intervals were evaluated using the arithmetic mean and coefficient of variation of the mean correlation (Spearman rank correlation) and the normalized averaged mean distances, respectively. The AT-group showed a significantly reduced variability in MTG compared to the Con-group (from p = 0.006 to p = 0.028 for different parameters). The 95% confidence intervals (CI) of MTG results were disjoint, whereas the 95% CIs of the pressure signals were similar (p = 0.192 to p = 0.601). We suggest from this work that the variability of mechanical tendon oscillations could be an indicative parameter of an altered Achilles tendon functionality.

Mechanotendography: description and evaluation of a novel method for investigating the physiological mechanical oscillations of tendons using a piezo-based measurement system

“…Thereof, four formerly in vivo recorded MTG-signals were converted into audio samples to produce signals close to real applications: three audio samples from in vivo recorded MTG-signals of the Achilles tendon after impact 30 (audioMTGAchilles_1, audioMTGAchilles_2, audioMTGAchilles_3) and one MTG-signal from the triceps brachii tendon during isometric muscle action of triceps brachii muscle at an intensity of 80% of the MVC (audioMTGtri). 3 The settings of the in vivo captured signals can be looked up in Schaefer & Bittmann 3,30 including the approvals of ethics committee (University of Potsdam, Germany; no. 37/2015, 64/2016) and informed written consent of all participants.…”

“…The 0.1s interval of audioMTGAchilles was chosen because the original MTG-signal was recorded during a short impact on the forefoot of the participant from plantar in direction of dorsiflexion, which generated the here relevant oscillation of the Achilles tendon in the 0.1s interval after impact. 30 The MTGtri-signal was originally recorded in vivo during a 10s isometric muscular interaction of two participants. 3 Since the sampling rate was 1000 Hz, 0.5s provide a sufficient long signal for the investigation of reliability.…”

“…That was one reason to choose the in vivo MTG-signals of the Achilles tendon after impact as base for the audio samples, which show higher frequencies. 30 Since the mechanical oscillations of muscles and tendons during pure isometric muscle activity are located in frequency areas below 30 Hz, [1][2][3] the audio replay by the subwoofer might reflect those frequency areas not as good as the original MTG-signals. This limited frequency response is especially visible by comparing the original MTG-signal of the triceps brachii tendon and the re-recorded audio MTGtri-signal using the subwoofer ( Figure 6).…”

“…The comparison of the here presented reliability results in the technical setting to measures of a recently conducted study in patients with Achillodynia lead to further assumptions. 30 The MTG of the Achilles tendon was measured during an impact on the forefoot from plantar in direction of dorsiflexion during one leg stance.…”

“…Patients with Achillodynia (n = 10) showed a significantly higher MCC and a significantly lower MD between the curves of five trials compared to healthy controls (n = 10). 30 In comparing those results with the here recorded audio trials, it is even more indicated that the oscillations of an affected Achilles tendon after impact in vivo behave similarly compared to the repetition trials ex vivo recording the same audio file (MCC: Achillodynia (in vivo): 0.85 ± 0.07 vs. audioMTGAchilles (ex vivo): 0.88 ± 0.13; MD: Achillodynia: 0.13 ± 0.03 vs. repeated audioMTGAchilles: 0.02 ± 0.03). In contrast, the healthy subjects in the Achilles tendon study showed a higher variability (lower MCC, higher MD).…”