Northwestern University Feinberg School of Medicine

Northwestern University Prosthetics-Orthotics Center

The Effect of Increased Prosthetic Ankle Motion on the Gait of Persons with Bilateral Transtibial Amputations

Principal Investigator: Steven A. Gard, PhD 

Student Investigator: Po-Fu Su, MS

Co-Investigators: Robert Lipschutz, CP and Todd Kuiken, MD, PhD, Rehabilitation Institute of Chicago

Funded by: National Institute of Child Health and Human Development (NICHD)

Status: Completed

Introduction

Increased ankle motion appears to improve the gait of persons with unilateral transtibial (TT) amputation, but the improvements are limited and inconsistent between studies [1,2]. The purpose of the study is to determine if the provision of prosthetic ankle motion in persons with bilateral TT amputations significantly improves their walking performance. The subjects in the study were divided into two groups based on etiology. The TRA group has their amputations due to trauma and the PVD group has their amputations due to peripheral vascular diseases. Comparisons of gait characteristics were made between the PVD and TRA groups, and with data from able-bodied (AB) subjects.

Clinical Significance

Analyzing the effects of increased prosthetic ankle motions in persons with bilateral TT amputations enables us to better identify the advantages and disadvantages of the prosthetic components because there are no compensatory actions from a sound leg. Our results may provide information for improving design of prosthetic ankles and feet, and help establish guidelines for prosthetists fitting persons with lower limb amputation.

Methodology

Data were collected from 12 people with bilateral TT amputations. The average age of the six TRA subjects was 45.7 years old and was 66.0 years old for the six PVD subjects. There were four phases in the study, each lasting a minimum of two weeks. Initially, subjects were fitted with Seattle LightFoot2 and walked with them for two weeks prior to the baseline gait analysis. Afterwards, subjects were randomly fitted with either the Endolite Multiflex Ankles (flexion unit) or Otto Bock Torsion Adapters (torsion unit) for the 2nd phase. Claimed by the manufacturer, the flexion unit mainly provides plantarflexion/dorsiflexion movement and the torsion unit provides up to 20° of internal and external rotations.

Endolite Multiflex AnklesOtto Bock Torsion Adapters

Endolite Multiflex Ankles(image taken from www.endolite.com)

Otto Bock Torsion Adaptors(image taken from www.ottobockus.com)

Subjects returned two weeks later for the 2nd gait analysis, after which they were fitted with the second set of ankle components. The protocol was repeated for the 3rd phase of the study. In the 4th phase, all the subjects walked with both of the ankle components. Three different freely-selected walking speeds were recorded. At the end of each gait analysis, questionnaires were administered to the research subjects to record their perceptions of walking with the different prosthetic configurations. Statistical analysis utilized a repeated measures with a factorial design comprising three walking speeds, four ankle configurations with one between subjects factor.

Results

The freely-selected walking speeds of the PVD were about 0.65 m/s compared to 1.05 m/s of the TRA group. When they walked at comparable speeds, the PVD and TRA groups displayed similar gait characteristics. The subjects exhibited symmetrical gait. The walking speeds, cadences and step lengths were not significantly different when the TT subjects walking with the four different ankle configurations. The TT subjects walking with the flexion unit had significantly greater sagittal plane ankle range of motion (see Figure 1). The torsion unit also significantly increased the transverse plane ankle range of motion (see Figure 2). However, the increased ankle motions did not significantly change the rotations of the knee, hip or pelvis. The flexion unit significantly increased the peak fore and aft ground reaction force (GRF) while the vertical GRF remained unchanged. Kinetics results also illustrated that walking with the flexion unit decreased the ankle moments, and increased the ankle power generation and absorption. However, the kinetics of the knee and hip were not affected by the different ankle configurations. From the results of the questionnaires, the TT subjects indicated that they liked the flexion and the torsion units about the same, but they preferred the combination of the two from among all the ankle configurations. Specifically, subjects indicated that the flexion unit was beneficial for going up/down stairs and inclines while the torsion unit assisted turning.

Figure1: Plot of left sagittal plane ankle peak-to-peak-value vs speed for the PVD, TRA and able-bodied subjects walking at various speeds with four different ankle configurations.
Figure 2: Plot of left transverse plane ankle peak-to-peak-value vs speed for the PVD, TRA and able-bodied subjects walking at various speeds with four different ankle configurations.

Discussion

The flexion unit increased both plantarflexion during the loading response phase of the gait and dorsiflexion during pre-swing. The TRA group even had greater sagittal ankle motion than the AB subjects at their freely-selected and fast speed. The increased dorsiflexion prior to toe-off decreased the distance between the GRF vector and the ankle joint center, resulting in smaller peak plantarflexor moments. The flexion unit also increased the energy storage/return at the ankle, which was reflected in greater ankle power absorption and generation. Although the torsion unit significantly increased the transverse plane ankle motion, the amount of increase was on average only about 1°. It was possible that the manufacturer's recommended setting of the stiffness of the torsion adaptor was too high. Another possible explanation was that TT subjects may have felt unstable walking with greater ankle transverse rotation, as they either adopted a walking pattern to avoid increased ankle transverse rotation or they requested the prosthetist adjust the torsion unit to be stiffer. Also, the increased ankle motion may not be used much for straight, level walking. Gait analysis on different floor conditions, or when the TT subjects performed task like turning, may further illustrate the advantage of the increased ankle motions.

References

[1] Hafner, B., et al. (2002). Clinical Biomechanics, 17, 125-344.[2] Lehmann, F., et al (1993). Arch Phy Med Rehabl, 74,1225-3.

Related Presentations and Publications

Gard S, Su P, Lipschutz R, Hansen A. Effect of prosthetic ankle units on roll-over shape characteristics during walking in persons with bilateral transtibial amputations. J Rehabil Res Dev. 2011;48(9):1037-48.

Gard S, Hansen A, Su P, editors. The effect of prosthetic ankle units on rollover shape characteristics during walking in persons with bilateral transtibial amputations. American Academy of Orthotists & Prosthetists 37th Academy Annual Meeting and Scientific Symposium; 2011 March 16-19; Orlando, FL.

Su P-F, Gard SA, Lipschutz RD, Kuiken TA. The Effects of Increased Prosthetic Ankle Motions on the Gait of Persons with Bilateral Transtibial Amputations. American Journal of Physical Medicine & Rehabilitation. 2010; 89(1):34-47.

Gard S, Su P, Lipschutz R, Kuiken T. The Effect of Prosthetic Ankle Units on the Gait of Persons with Bilateral Transtibial Amputations. Paper presented at: 13th ISPO World Congress; May 10-15, 2010; Leipzig, Germany.

Su P, Gard S, Lipschutz R, Kuiken T. Differences in gait characteristics between persons with bilateral transtibial amputations, due to peripheral vascular disease and trauma and able-bodied ambulators. Archives of Physical and Medical Rehabilitation. 2008; 89(7):1386-1394.

Su P, Gard S, Lipschutz R, Kuiken T. Gait characteristics of persons with bilateral transtibial amputations. Journal of Rehabilitation Research and Development. 2007; 44(4):491-501.