Three‐dimensional morphology and volume of the free Achilles tendon at rest and under load in people with unilateral mid‐portion Achilles tendinopathy

Abstract

Mid-portion Achilles tendinopathy (MAT) adversely affects free Achilles tendon (AT) structure and composition. However, it is not known how these pathological alterations associated with MAT change the normal three-dimensional (3-D) morphology of free AT at rest and under load throughout the entire free tendon length. Here, we used 3-D ultrasound to examine the effect of unilateral MAT on free tendon 3-D morphology [length, cross-sectional area (CSA), anteroposterior (AP) diameter and mediolateral (ML) diameter] and volume at rest and during a submaximal (50%) voluntary isometric plantarflexion contraction bilaterally in individuals with unilateral MAT (n = 10) compared with a matched healthy control group (n = 10). The tendinopathic free AT had a greater CSA relative to the control tendons along the entire tendon length, which was mainly driven by a greater tendon AP diameter. Under load, the tendinopathic tendon experienced greater longitudinal and transverse strains than the control tendons. In contrast to the control tendons, which experienced a reduction in tendon CSA and ML diameter, bulged along the AP axis and behaved isovolumetrically under load, the tendinopathic tendon experienced a reduction in tendon CSA, AP diameter and ML diameter and an overall volume reduction. Overall, these findings suggest that the magnitude of longitudinal strain and volume change and the corresponding magnitude and direction of transverse strain under load are altered in MAT compared with normal tendon. These findings are indicative of a fundamental reorganization of the tendon matrix and alterations in tendon fluid content and distribution under load in tendinopathic tendon.

Influence of altered geometry and material properties on tissue stress distribution under load in tendinopathic Achilles tendons – A subject-specific finite element analysis

“…The resting free tendon's CSA in the present study was on average 31% greater for the tendinopathic compared to the healthy tendons, which is within the 20-66% range reported in other studies (Arya and Kulig, 2010;Nuri et al, 2017bNuri et al, , 2018. The mean free Achilles tendon volume was similarly greater in the tendinopathy group in the present study, although this volume difference relative to the healthy tendons only approached statistical significance (p = 0.07).…”

“…Previous studies reported that mid portion Achilles tendinopathy is characterised by tendon thickening (Arya and Kulig, 2010;Nuri et al, 2017bNuri et al, , 2018 and altered material properties (Arya and Kulig, 2010). This study quantified the relative contributions of tendon thickening and decreased material properties on tissue stress under load in tendinopathic compared to healthy Achilles tendons.…”

“…For a tendon of a given length, a lower stiffness would result in greater tendon strain under the same external load. A further adaptation in Achilles tendinopathy is tendon thickening, which increases the tendon cross-sectional area (CSA) by 20-66% (Arya and Kulig, 2010;Helland et al, 2013;Leung and Griffith, 2008;Nuri et al, 2017bNuri et al, , 2018Obst et al, 2018). Tendon thickening may therefore be an adaptation that at least partially compensates for the reduction in tendon stiffness, thereby protecting the tendon from high strains.…”

Ultrasonography effectiveness of the vibration vs cryotherapy added to an eccentric exercise protocol in patients with chronic mid‐portion Achilles tendinopathy: A randomised clinical trial

“…For this study, 61 patients with chronic mid‐portion AT (age: 41.2 ± 10 years) were recruited and divided into two groups: EE programme vibration training (n = 30) and EE programme combined with cryotherapy (n = 31) (Figure ). Participants’ inclusion criteria were as follows: aged between 18 and 65 years, having symptoms for at least 3 months, and having mid‐portion Achilles pain (2–7 cm proximal to insertion) on palpation . Exclusion criteria were a lower limb disease within the last 12 months, previous fracture or surgical intervention, any systemic disease, and past negative experiences with EE vibration and cryotherapy interventions.…”

“…Therefore, the contraction tendon surface is slightly lower in the proximal tendon areas at low intensity. Nuri et al 31 contraction in subjects with AT. Our study showed a CSA increase being positive the difference between contraction and at rest, supporting EE and hypertrophy theories.…”