Northwestern University Feinberg School of Medicine

Northwestern University Prosthetics-Orthotics Center

Development of an Equilibrium-Point Prosthetic Ankle Joint

Principal Investigators: Dudley S. Childress, PhD, and Steven A. Gard, PhD 

Project Director: Andrew H. Hansen, PhD 

Co-Investigators: Edward C. Grahn, Dilip Thaker, and Rebecca L. Stine, MS

Student Investigators: Ryan Williams, BS, and Brian L. Ruhe, MS

Funded by: National Institute on Disability and Rehabilitation Research (NIDRR)

Status: Completed


The ability to walk on different terrains is a distinct advantage that legged locomotion has over wheeled transportation. However, many features that non-disabled persons utilize on uneven terrain are not incorporated into prostheses and orthoses, making it difficult for persons who use these devices to walk on irregular surfaces. In particular, many prosthetic feet have rigid ankles that cannot adapt to different levels of surface inclination. This project will focus on the development of a prosthetic ankle joint that can adapt (without manual intervention) to different levels of walking surface inclination and shoes of different heel heights.

Our objectives include development of a working prototype and evaluation of the new device on level and non-level terrains. The working prototype will be tested against commercially available prosthetic feet. Performance goals include similar or superior walking of persons with amputations when using the prototype as compared to other feet on level surfaces, and superior function when using the prototype on inclined and declined surfaces. Performance will be assessed using walking speed, roll-over shapes, gait kinematics and kinetics, and subjective evaluation by the users. Gait measurements will also be compared with walking data from non-disabled persons.


Equilibrium-Point Prosthetic and Orthotic Ankle-Foot Systems, Devices, and Methods of Use, US 20100185301 A1.

Related Publications

Williams R, Hansen A, Gard S. (2009) Prosthetic Ankle-Foot Mechanism Capable of Automatic Adaptation to the Walking Surface. Journal of Biomechanical Engineering. 131(3):035002.

Hansen A, Childress D, Miff S. (2004) Roll-over Characteristics of Human Walking on Inclined Surfaces. Human Movement Science, Vol. 23, No. 6, 807-821.

Hansen A, Childress D, Miff S, Gard S, Mesplay K. (2004) The Human Ankle during Walking: Implications for Design of Biomimetic Ankle Prostheses and Orthoses. Journal of Biomechanics, Vol. 37, No. 10, 1467-1474.