The positional effects of weight-bearing foot and ankle musculature on muscle stiffness using shear wave elastography.

BACKGROUND

Shear wave elastography (SWE), an ultrasound imaging method, assesses muscle tissue stiffness by measuring the speed of sound waves traveling through it, with faster speeds indicating greater stiffness. It is unclear whether differences in foot and ankle muscle stiffness depend on changes in loading volume. The purpose of this study is to assess stiffness changes of foot and ankle muscles between non-weight-bearing and weight-bearing positions.

METHODS

Sixty individuals (38F, age: 23.4 ± 3.20 yrs., weight: 74.9 ± 19.7 kg, height: 170.0 ± 8.70 cm) participated in this study. SWE measures were performed using an ultrasound scanner. Shear wave elastography mean velocity (m/s) values were recorded for the tibialis posterior, tibialis anterior, peroneal, and abductor hallucis muscles in both non-weight-bearing (sitting) and weight-bearing (standing) positions. Paired t-test was performed to analyze differences in muscle stiffness.

FINDINGS: A significant difference in muscle stiffness between non-weight-bearing and weight-bearing positions was found for tibialis posterior (p < 0.01, effect size (ES) = -0.97) and abductor hallucis (p < 0.01, ES = -1.08). No significant differences existed between positions for tibialis anterior (p = 0.43, ES = 0.12) and peroneal muscles (p = 0.13, ES = -0.16).

INTERPRETATION: Abductor hallucis and tibialis posterior muscles of the foot and ankle demonstrate significant increases in stiffness from a non-weight-bearing to weight-bearing task. Muscle stiffness of tibialis anterior and peroneal muscles is not dependent on these positions. Abductor hallucis and tibialis posterior may contribute to cushioning and support for the foot and ankle during weight-bearing tasks.