Regional Elastic Properties of the Achilles Tendon Is Heterogeneously Influenced by Individual Muscle of the Gastrocnemius

Abstract

Background Anatomical studies and the mechanical property studies showed that there is a strong correlation between Achilles tendon (AT) elasticity and individual gastrocnemius muscle (the medial head of gastrocnemius (MG) and the lateral head of gastrocnemius (LG)) elasticity. Limited ankle dorsiflexion range of motion has been correlated with decreased flexibility of the MG/LG/AT complex. However, no studies have been conducted to examine the exact correlation between the Achilles tendon and the individual muscle of the gastrocnemius. Purposes The purposes of the present study were (1) to evaluate intra- and interoperator reliabilities of elastic property measurements in the gastrocnemius muscle-Achilles tendon complex by using the shear wave elastography (SWE) and (2) to examine the correlation between the regional elastic properties of the AT and the individual muscle of the gastrocnemius. Methods Twenty healthy subjects (mean age: 22.50 (3.02) years) were recruited in this study. The elastic properties of the AT and the individual muscle of the gastrocnemius were quantified using the SWE. Findings The SWE has comparatively high reliability in quantifying the elastic properties of the muscle-tendon range from good to excellent. The intraoperator ICC of the gastrocnemius muscle-Achilles tendon complex was 0.77 to 0.95, while the interoperator ICC was 0.76 to 0.94. The minimal detectable change (MDC) of the muscle was 1.72 kPa, while the AT was 32.90 kPa. A significant correlation was found between the elastic modulus of AT and the elastic modulus of the MG (r = 0.668 and p = 0.001 at the relaxing position and r = 0.481 and p = 0.032 at the neutral position). Conclusions The SWE has the potential to assess localized changes in muscle-tendon elastic properties, provide more intuitive relations between elastic properties of the muscle tendon and function, and evaluate the therapeutic effect of the muscle tendon. A significant correlation between the AT and the MG was found, and it may provide a new treatment idea (targeted to the tight muscle heads) for the clinical setting to treat subjects with AT disorders.

Influence of different knee and ankle ranges of motion on the elasticity of triceps surae muscles, Achilles tendon, and plantar fascia

“…The depth of the B-scan was 3.0 cm. For the AT, the Q-box diameter was defined by the thickness of the tendon, which was the distance between the superior and inferior borders of the AT 17 . For the MG, LG and SOL, the size of the regions of interest (ROIs) had to be set to 10*10 mm, and the diameters of the Q-box of muscle and muscle fascia were 5 mm and 1 mm, respectively 17 .…”

“…For the AT, the Q-box diameter was defined by the thickness of the tendon, which was the distance between the superior and inferior borders of the AT 17 . For the MG, LG and SOL, the size of the regions of interest (ROIs) had to be set to 10*10 mm, and the diameters of the Q-box of muscle and muscle fascia were 5 mm and 1 mm, respectively 17 . For the PF, the three quantification areas were located between the calcaneal insertion of the PF and 1 cm distal to its insertion, and the Q-box diameter was determined by the thickness of the fascia, which was defined as the distance between the superior and inferior borders of the PF [19][20][21]23 .…”

“…The ankle joint was fixed using a customized and movable ankle foot orthosis at a designated angle 25 . The measurement sites for the AT were 0 cm (AT0cm), 3 cm (AT3cm) and 6 cm (AT6cm) proximal to the calcaneal tuberosity 26 , while those for the MG and LG were defined as the proximal 30% of the lower leg length 17 . The SOL was measured in the distal half of the SOL for visualization of the distal SOL fascicles alone 27 .…”

“…The stiffness was measured with the SWE transducer positioned on the marks on the skin for the MG, LG, SOL, AT and PF with the ankle joint positioned at 25° of dorsiflexion (DF25°), in a neutral position (0°), or at 50° of plantar flexion (PF50°) and the knee fully extended or flexed to 90°. In addition, to reduce experimental errors, the participants were explicitly asked to keep their lower extremities fully relaxed throughout testing and to refrain from high-intensity exercise for 48 hours before testing 17,28 .…”

“…For example, our previous studies have shown that SWE is a valid and reliable tool for quantifying the stiffness of the gastrocnemius and AT. The intraclass correlation coefficient was 0.74 to 0.95 17 . In addition, Eby et al also demonstrated a positive significant correlation between muscle stiffness measurements obtained by SWE and stiffness measurements obtained by a material testing system 18 .…”