Presented at NACOB 98:
North American Congress on Biomechanics
Canadian Society for Biomechanics - American Society of Biomechanics

University of Waterloo
Waterloo, Ontario, Canada
August 14-18, 1998

KINETICS OF STAIR AMBULATION IN TRANS-TIBIAL AMPUTEES USING
THREE DIFFERENT PROSTHETIC FEET

H.J. Yack, D.H. Nielsen, D. Shurr
Physical Therapy Graduate Program, University of Iowa
Iowa City, IA 52242

INTRODUCTION

Bilateral lower limb kinetics were assessed in unilateral trans-tibial amputees in an effort to understand the strategies used to ascend stairs. The affect of three different prosthetic feet on these kinetics was also investigated.

REVIEW AND THEORY

In spite of the fact that stair ambulation is part of normal daily activities the associated kinetics have received only limited attention in the normal population and passing attention in the amputee population. Previous studies have identified the knee as having the dominant role in stair ascent (McFadyen & Winter, 1988) while others have reported more variability in strategies, with the hip playing an equally important role (Duncan et al., 1997). One study that examined trans-tibial amputees using different prosthetic feet, addressed the temporal aspects of stair ambulation and concluded that none of the feet were more advantageous (Perry et al. 1993). The purpose of this study was to assess the kinetics of stair ambulation in subjects with unilateral trans-tibial amputations. A secondary purpose was to identify the influence of prostheses with SACH (solid ankle cushioned heel), Flex-Foot and Re-Flex Vertical Shock Pylon (Re-Flex VSP) feet on the kinetics.

PROCEDURES

Informed consent was obtained from five physically active unilateral trans-tibial amputees (20 to 45 years of age) who participated in the study. Biomechanical analysis was performed as subjects ascended a three step staircase (18 cm riser, 25 cm tread, 76 cm width). As subjects approached the first step they stepped on a low riser (2.5 cm X 25 cm) that was positioned on the floor adjacent to the first step to ensure consistent kinematics as they stepped on the first stair. The first step was cutout (39 cm width) to allow for an isolated section that was bolted to the forceplate (Kistler). Subjects performed the gait activities using randomly selected SACH, FLEX or REFLEX prostheses. Three dimensional marker position data were obtained for individual gait cycles (Optotrack, Northern Digital Corp.) along with force plate data. These data were combined with anthropometric data in a 5 segment model to obtain kinematic and kinetic data (KinGait3, Waterloo) for 3 gait cycles on both sides. Intra- and inter- averages for kinematics and kinetics were calculated and assessed.

RESULTS AND DISCUSSION

POSITIVE WORK VALUES (j/kg) HIP
FLX RFX SAH
Involved
.531(.27)
 .500(.24) .703(.31) *
UnInvolved
.298(.14)
 .243(.14) .334(.17)

Table 1. Average normalized positive work values for the hip during the stance phase of stair gait. On the involved side SAH differed (p<.05) from FLX and RFX feet.

Figure 1. Ankle, Knee, and Hip powers during the stance phase of stair gait for the three prostheses on the involved (I) and uninvolved (U) sides.

The power curves show a marked difference between the involved (amputated) side and the uninvolved side with the amputees relying much more on hip powers to raise the center of mass of the body. This same trend is seen in the work values where, on average, approximately twice as much work is done by the hip on the involved side.

Differences were also seen in the hip powers as a function of the prosthetic foot that was used. Greater peak powers on both sides resulted when the SACH foot was used. These same trends can be seen in the work values where there is a 40% increase in the work values when using the SACH foot. Not evident from the averaged data are variations in strategies that resulted in one amputee sharing the work much more evenly between the knee and the hip.

The results of our study show that power patterns for unilateral trans-tibial amputee stair ascent are markedly different for the involved and uninvolved lower limbs. In addition, different prosthetic feet potentially influence the energy expended at the hip.

REFERENCES

Duncan JA, et al. Gait Posture 5:204- 210,1997.

McFadyen BJ, Winter DA. J Biomech 21:733-44, 1988.

Perry J, et al. J Rehab Res 30:137-143, 1993

ACKNOWLEDGMENTS

Partial support for this project was supplied by Flex-Foot, Inc.