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

Introduction

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.

Purpose

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.

Methodology

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.

Results

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.

References

[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.