Ultrasound-tensiometry: A new method for measuring differential loading within a tendon during movement.

Area of Science:

• Biomechanics
• Musculoskeletal Ultrasound
• Tissue Mechanics

Background:

• Tendons transmit muscle forces to the skeleton, experiencing differential loading when multiple muscles attach.
• Tendon shear wave speed correlates with local tensile stress, suggesting wave speed variations can indicate uneven loading.
• Investigating differential tendon loading is crucial for understanding musculoskeletal function and injury.

Purpose of the Study:

• To determine if high-framerate ultrasound-based tensiometry can measure differential loading across a tendon.
• To validate the technique's ability to detect spatial variations in tendon wave speed corresponding to load.

Main Methods:

• Ultrasound-tensiometry was developed using high-framerate plane wave imaging (20 kHz) to track wave propagation in tendons.
• A finite element model, ex vivo porcine tendons, and in vivo human Achilles tendons were used to evaluate the technique.
• Shear wave speed was computed using a Radon transform of filtered displacement data.

Main Results:

• Wave speeds accurately reflected local tendon stress in silico and ex vivo, with higher loads showing increased wave speeds.
• In vivo, spatial variations in Achilles tendon wave speed correlated with differential subtendon loading during stretching and walking.
• The method demonstrated high spatial resolution (0.1 mm x 0.2 mm) and precision (±0.2 m/s).

Conclusions:

• High-framerate ultrasound-tensiometry successfully tracks spatial variations in tendon shear wave speed.
• This technique offers a promising tool for investigating local tissue loading within tendons.
• It may help delineate the specific contributions of individual muscles to overall tendon loading during movement.