Sagittal and transverse ankle angle coupling can influence prosthetic socket transverse plane moments

Area of Science:

• Biomechanics
• Prosthetics
• Orthopedics

Background:

• The intact foot and ankle exhibit coupled motions between sagittal and transverse planes during gait.
• Current prosthetic feet lack this natural sagittal-transverse plane coupling.
• This limitation may affect prosthetic limb function and user experience.

Purpose of the Study:

• To investigate if a specific sagittal:transverse ankle angle coupling ratio can minimize peak transverse plane moments during prosthetic limb stance.
• To evaluate the effect of different coupling ratios on prosthetic limb biomechanics.

Main Methods:

• A novel torsionally active prosthesis (TAP) with a motor was used to simulate various sagittal:transverse coupling ratios (1:0, 6:1, 4:1, 3:1, 2:1).
• Eleven individuals with unilateral transtibial amputations walked in straight lines and circles at self-selected speeds.
• Primary outcome: peak transverse plane moment; Secondary outcomes: gait biomechanics and satisfaction.

Main Results:

• The 6:1 coupling ratio significantly reduced peak transverse plane moments compared to 3:1 and 2:1 ratios during specific walking conditions.
• No significant effects of coupling ratio were observed on secondary gait biomechanic metrics.
• Participant satisfaction was not significantly different across the tested coupling ratios.

Conclusions:

• A 6:1 sagittal:transverse ankle coupling ratio appears to minimize detrimental transverse plane moments in transtibial prostheses.
• This optimized coupling may not adversely affect propulsion, body support, or comfort.
• Future research will focus on developing passive prosthetic feet with fixed optimal coupling ratios.