Feasibility of using a hand-held device to characterize tendon tissue biomechanics

<div><p>Objectives</p><p>To examine the feasibility of using the MyotonPRO digital palpation device in measuring the transverse stiffness of tendon tissue.</p><p>Design</p><p>Experimental study.</p><p>Methods</p><p>The MyotonPRO was used to measure the stiffness and related properties of ballistics gel in comparison with an external materials testing system (PCB electronics). The device was then used to measure the same properties of avian Achilles tendons before and after the removal of the overlying skin and subcutaneous tissue. Next, the test-retest reliability of the Achilles and patellar tendons was determined in humans. Finally, the stiffness of the Achilles tendon was measured before and after competitive running races of varying distances (10, 21 and 42 km, total number of athletes analyzed = 66).</p><p>Results</p><p>The MyotonPRO demonstrated a high degree of consistency when testing ballistics gel with known viscoelastic properties. The presence of skin overlying the avian Achilles tendon had a statistically significant impact on stiffness (p<0.01) although this impact was of very small absolute magnitude (with skin; 728 Nm ±17 Nm, without skin; Nm 704 Nm ±7 Nm). In healthy adults of normal body mass index (BMI), the reliability of stiffness values was excellent both for the patellar tendon (ICC, 0.96) and the Achilles tendon (ICC,0.96). In the the field study, men had stiffer tendons than women (p<0.05), and the stiffness of the Achilles tendon tended to increase following running (p = 0.052).</p><p>Conclusions</p><p>The MyotonPRO can reliably determine the transverse mechanical properties of tendon tissue. The measured values are influenced by the presence of overlying skin, however this does not appear to compromise the ability of the device to record physiologically and clinically relevant measurements.</p></div

Body mass index and collagen organization.

<p>The entire cohort (n = 66) was categorized as having a body composition that was normal (18.5 to 24.9, n = 24), overweight (25 to 29.9, n = 21) or obese (30+, n = 11).[<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0199645#pone.0199645.ref021" target="_blank">21</a>] Statin users are shown as open circles, controls are yellow. Obese individuals (comprising 5 male statin-users, 1 female statin user, and 5 male comparison participants,) demonstrated a reduced collagen organization (Kruskal-Wallis H = 7.4, df = 2, p = 0.02) compared to those of normal body weight.</p

Comparison of statin users and a comparison group of statin non-users.

<p>Comparison of statin users and a comparison group of statin non-users.</p

SP effect on activation of mitogen-activated protein kinases.

<p>Phosphorylated ERK1/2 in cultured human Achilles tendon cells at different time points after incubation with SP (10⁻⁷ M). The results clearly show that SP activates the phosphorylation of ERK1/2 over time in a biphasic course that peaks at 5 and 15 minutes of exposure. The activation by SP is effectively blocked when incubated simultaneously with the NK-1 R blocker (10⁻⁶ M; result at 5 min to the right). Beta(β)-actin is shown as a reference.</p

Cell viability after SP incubation and NK-1 R blocking.

<p>Analysis of viable tendon cells in human primary cultures after 24 hours of incubation with SP (10⁻⁷ M), without SP (control), and with SP and the NK-1 R blocker (10⁻⁶ M), as measured with crystal violet staining. The significant increase in viable cells seen after incubation with SP is effectively blocked with the NK-1 R antagonist. Error bars indicate standard deviation. *p<0.05; **p<0.01.</p

Effect of SP incubation on NK-1 R expression.

<p>Full-length glycosylated NK-1 R expression (Western blot) in cultured human primary tendon cells is lower in cells incubated with SP (10⁻⁷ M) for 4 hours (right) as compared to control cells (left).</p

NK-1 R in human primary Achilles tendon cells.

<p>Two clear bands of 80 kDa and 37 kDa, respectively, are shown. β-actin is shown as a reference.</p

Results of loading on gene expression.

<p>qPCR analysis for SP (<b>a</b>) and NK-1 R (<b>b</b>) mRNA, respectively, in cultured human primary Achilles tendon cells. The mean level of SP mRNA is significantly elevated after 2D-loading of the cultures, whereas the mean level of NK-1 R mRNA is significantly lowered after the loading. Error bars represent standard error of the mean. Level of significance: * p<0.05; **p<0.01 (Independent samples t-test).</p

Additional file 1 of Mild hypercholesterolemia impacts achilles sub-tendon mechanical properties in young rats

Supplementary Material

Metabolic activity after SP incubation.

<p>Incubating human tendon cells with SP (10⁻⁷ M) for 48 hours significantly increases their metabolic activity compared to incubation with pure cell culture media or PBS. The potency of SP as a proliferative factor is about half that of cell culture media with 10% fetal calf serum (FCS). As another positive reference, results from incubation with a cell culture medium with a serum-free growth factor (Q333) are shown. Results from MTS-assay analysis. Serum-free media set as standard to 1. Error bars represent standard deviation. **p<0.01.</p