Axial speed of sound is related to tendon's nonlinear elasticity

Abstract

Axial speed of sound (SOS) measurements have been successfully applied to noninvasively evaluate tendon load, while preliminary studies showed that this technique also has a potential clinical interest in the follow up of tendon injuries. The ultrasound propagation theory predicts that the SOS is determined by the effective stiffness, mass density and Poisson's ratio of the propagating medium. Tendon stiffness characterizes the tissue's mechanical quality, but it is often measured in quasi-static condition and for entire tendon segments, so it might not be the same as the effective stiffness which determines the SOS.The objectives of the present study were to investigate the relationship between axial SOS and tendon's nonlinear elasticity, measured in standard laboratory conditions, and to evaluate if tendon's mass density and cross-sectional area (CSA) affect the SOS level.Axial SOS was measured during in vitro cycling of 9 equine superficial digital tendons. Each tendon's stiffness was characterized with a tangent modulus (the continuous derivative of the true stress / true strain curve) and an elastic modulus (the slope of this curve's linear region).Tendon's SOS was found to linearly vary with the square root of the tangent modulus during loading; tendon's SOS level was found correlated to the elastic modulus's square root and inversely correlated to the tendon's CSA, but it was not affected by tendon's mass density. These results confirm that tendon's tangent and elastic moduli, measured in laboratory conditions, are related to axial SOS and they represent one of its primary determinants.

Lower material stiffness in rupture-repaired Achilles tendon during walking: transmission-mode ultrasound for post-surgical tendon evaluation

“…The axial transmission speed of ultrasound (TSOU) in tendon is proportional to its density and instantaneous material stiffness [45], which, in turn, is dependent on the applied load to the tendon [32]. Ultrasound transmission techniques take advantage of the relationship between TSOU and tendon biomechanics to afford a non-invasive method of quantifying properties of human tendon under dynamic loading conditions.…”

Reproducibility and feasibility of acoustoelastography in the superficial digital flexor tendons of clinically normal horses

“…16 Previous strain measurement techniques are poorly adaptable to veterinary medicine because of invasiveness, necessity for unrealistic levels of patient cooperation, expense, and specialized equipment requirements. Preliminary studies of noninvasive, sonographic methods for evaluation of tendon function in veterinary species have been based on elastography, 17 measurement of the axial speed of sound, [18][19][20][21][22] or acoustoelasticity. 23,24 These techniques currently offer the greatest potential for practical clinical application in horses with tendon injury.…”

Tendinopathy alters ultrasound transmission in the patellar tendon during squatting

“…Ultrasonic transmission techniques have the potential to provide direct non‐invasive estimates of human tendon loading. In vitro studies of animal tendon have demonstrated that the axial transmission of ultrasonic waves is governed by the elastic modulus and density of tendon and is a function of the tensile load to which it is exposed (Hoffmeister et al., ; Miles et al., ; Kuo et al., ; Pourcelot et al., ,b; Vergari et al., ,b,c). Recently, ultrasound transmission has also been shown to be a sensitive indicator of tendon injury in animal models and has been used to document the recovery of tendon properties following injury (Vergari et al., ,b,c).…”

“…In vitro studies of animal tendon have demonstrated that the axial transmission of ultrasonic waves is governed by the elastic modulus and density of tendon and is a function of the tensile load to which it is exposed (Hoffmeister et al., ; Miles et al., ; Kuo et al., ; Pourcelot et al., ,b; Vergari et al., ,b,c). Recently, ultrasound transmission has also been shown to be a sensitive indicator of tendon injury in animal models and has been used to document the recovery of tendon properties following injury (Vergari et al., ,b,c). Although ultrasound transmission is emerging as a potentially useful technique for the non‐invasive of measurement of tendon properties during dynamic activities, studies employing the technique in humans have been currently limited to measurement of the Achilles tendon during walking (Pourcelot et al., ,b; Wearing et al., ).…”

“…We specifically evaluated squatting as it is a common maneuver in volleyball and often used in rehabilitation of patellar tendinopathy (Kongsgaard et al., ). As degenerative change associated with tendinopathy is thought to impair collagen structure, alter tendon ground substance, increase fluid content, and lower the elastic modulus of the patellar tendon (Helland et al., ) and as ultrasonic velocity is highly correlated with these properties in tendon (Pourcelot et al., ,b; Crevier‐Denoix et al., ; Vergari et al., ,b,c), it was hypothesized that axial ultrasonic velocity, would be lower in patellar tendinopathy.…”