Amputee locomotion: spring-like leg behavior and stiffness regulation using running-specific prostheses

Area of Science:

• Biomechanics
• Prosthetics
• Human Movement Science

Background:

• Carbon fiber running-specific prostheses (RSPs) enable individuals with lower extremity amputation (ILEA) to run.
• Able-bodied runners maintain constant leg stiffness (Kleg) and increase vertical stiffness (Kvert) with speed.
• Vertical stiffness (Kvert) is influenced by joint stiffness (Kjoint) and touchdown angles.

Purpose of the Study:

• To investigate stiffness regulation in ILEA runners using RSPs across various overground running speeds.
• To compare stiffness characteristics between intact and prosthetic limbs in ILEA runners.
• To understand the role of joint stiffness and angles in the spring-like function of the leg during running with RSPs.

Main Methods:

• Eight ILEA performed overground running at multiple speeds.
• Calculated Kleg, Kvert, and Kjoint from kinetic and kinematic data for both limbs.
• Analyzed joint-specific stiffness (Kankle, Kknee, Khip) and touchdown knee angle.

Main Results:

• Kleg and Kvert remained constant with increasing running speed for both limbs.
• Intact limbs demonstrated higher Kleg and Kvert compared to prosthetic limbs.
• No significant differences in Kankle, Kknee, or touchdown knee angle were found between limbs.
• Hip joints did not exhibit spring-like function; intact hip impact peaks suggest shock attenuation.

Conclusions:

• ILEA using RSPs exhibit distinct stiffness regulation strategies between their intact and prosthetic limbs.
• Differences in vertical stiffness regulation are primarily attributed to shock attenuation via the intact hip joint.
• Findings inform prosthetic design and rehabilitation for ILEA runners.