Northwestern University Feinberg School of Medicine

Northwestern University Prosthetics-Orthotics Center

Effect of Roll-over Shape Arc Length on Gait of Transtibial Prosthesis Users

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

Project Director: Andrew H. Hansen, PhD

Co-Investigator: Margrit R. Meier, PhD

Student Investigator: Pinata H. Sessoms, MS

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

Status: Completed


Prosthetic feet that are commercially available have a wide range of mechanical properties, leading to differences in their roll-over shapes during walking. The arc length of the prosthetic foot's roll-over shape may be an important determinant of step length and loading properties on the contralateral limb. In particular, this study examines the hypothesis that shortening a prosthetic foot's arc length (in the forefoot section) will lead to increased loading and decreased step length on the contralateral limb. A shortened forefoot arc length is thought to create a "drop-off" effect at the end of single-limb stance phase as the person rolls to the end of the prosthetic foot's roll-over shape.


Previous work [1] has reported decreased loading to the sound limb when the Flexfoot prosthesis is used as opposed to other prosthetic feet. Our work suggests this difference comes as a result of the Flexfoot's long roll-over shape arc length [2]. In particular, we hypothesize that persons walking on feet with short effective foot lengths experience a "drop-off" effect at the end of stance on the prosthesis, leading to a shortened step length and a larger loading response on the sound limb [2,3].

The objective of this study was to systematically alter the arc length of the Shape&Roll Prosthetic Foot's roll-over shape to determine if step length and limb loading on the sound limbs of persons using transtibial prostheses were affected. The Shape&Roll Prosthetic Foot was chosen due to its design structure, which allows for easy adaptation of the arc length without interfering with other mechanical properties.


Subjects with trans-tibial amputations were recruited to participate in the study. Each subject used the socket from his or her own prosthesis. The Shape&Roll foot was connected to the socket and aligned by an experienced prosthetist. Gait analysis was performed with the person walking at slow, normal, and fast self-selected walking speeds. Next, a wedge cut was made in the foot to shorten its effective foot length and another gait analysis was performed. Lastly, a second wedge cut was made in the foot, and a third gait analysis was performed (see Figure 1). The prosthetic foot had a removable foot cover, was covered with a sock, and was placed inside a shoe, visually blinding the subjects to its alterations. The same alignment was used for all three conditions.

In the initial testing, subjects with unilateral trans-tibial amputations were recruited for testing. The study has been expanded recently to include persons with bilateral trans-tibial amputations.


The portion of this experiment that studies persons with unilateral amputations has been completed. Fourteen subjects finished the study and were included in data analyses. Shortening the roll-over shape arc length significantly increased the difference in first peaks of the vertical ground reaction forces, i.e. the sound limb loading peak became greater in magnitude as the roll-over shape arc length was decreased (see Figure 2). As the arc lengths of the roll-over shapes were reduced, the external ankle dorsiflexion moments in late stance were significantly reduced compared with those on the sound side (see Figure 3). Trends supported the idea that a shortened step of the sound limb would occur when roll-over shape arc lengths were shortened on the prosthetic side, but these trends were not statistically significant.


[1] Powers et al. (1994) Arch Phys Med Rehabil, 75:825-829.[2] Hansen et al. (2000) Prosthet Orthot Int, 24(3), 205-215.[3] Hansen et al. (2004) J Prosthet Orthot, 16(2), 41-45.

Related Publications

Hansen, A., Meier, M., Lambla, S., Sessoms, P., Childress, D. (2004). Effects of Prosthetic Foot Roll-over Shape Arc Length on Gait of Trans-tibial Prosthesis Users. 11th World Congress of the International Society for Prosthetics and Orthotics. Hong Kong, China, August 1-6.

Hansen, A., Meier, M., Sessoms, P., Childress, D. (2006). The Effects of Prosthetic Foot Roll-over Shape Arc Length on the Gait of Trans-tibial Prosthesis Users. Prosthetics and Orthotics International, Vol. 30, No. 3, 286-299.