MECHANICAL ENERGY RETURNED BY THE SACH AND SEATTLE LIGHT PROSTHETIC FEET IN ELDERLY WITH BELOW-KNEE AMPUTATION

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

MECHANICAL ENERGY RETURNED BY THE SACH AND SEATTLE LIGHT
PROSTHETIC FEET IN ELDERLY WITH BELOW-KNEE AMPUTATION

F. Prince ^1,2 , K. F. Zabjek ¹ and M. Raîche ¹
¹ Gait and Posture Laboratory, Sherbrooke Geriatric University Institute
² Department of Surgery, Service of Orthopedics, Faculty of Medicine,
University of Sherbrooke, QC, CANADA

INTRODUCTION

The total energy returned by the SACH and Seattle-Light (Seat-L) prosthetic feet was estimated in a population of elderly below knee amputees (EBKA). This in addition to an Index of Asymmetry and Abnormality (IAA) was quantified to estimate the utilisation of these two feet by an EBKA population when walking at natural speed.

REVIEW AND THEORY

Little research has identified a positive impact of an energy storing foot on the gait of EBKA's. Prince et al. (1994) attributed this to an inherent error in the model used for the estimation of the energy returned by prosthetic feet. A new technique was proposed to estimate the total energy stored and returned (Wdist) by any prosthetic foot.

Where Pdist is the power at the distal end of the leg, Fa and Va are respectively the force and velocity acting at this level and (leg is the angular velocity of the leg. Prince (1993) also proposed an Index of Asymmetry and Abnormality (IAA) which is based on the total work of the prosthetic and sound limbs of the EBKA in reference to the healthy elderly population (HE).

Where ASYM is the asymmetry factor, ABN PL and ABN SL are the abnormality factors for the prosthetic (PL) and the sound limb (SL) respectively.

The purpose of this study is to estimate the total energy returned by the SACH and Seat-L prosthetic feet and determine its impact on the gait of EBKA's.

PROCEDURES

Ten EBKA's aged 70.4 ± 9.5 years and 18 healthy elderly (HE) subjects aged 70.8 ± 7.0 years participated in this study. Selection criteria required that the EBKA's demonstrate sufficient locomotor potential to benefit from the Seat-L foot. The EBKA group had an initial gait evaluation with the SACH foot, followed by an eight session gait retraining program with the Seat-L foot. Upon completion of the gait program the EBKA's underwent a gait evaluation with the Seat-L foot. The gait of the 18 HE subjects was evaluated once to serve as a reference group. A seven segment inverse dynamics model (Waterloo 3D software) permitted the estimation of the muscle work done at the ankle, knee and hip, of the intact joints, as well as the prosthetic work of the SACH and Seat-L.

RESULTS

Following the gait retraining program specific to the Seat-L prosthetic foot, the EBKA's demonstrated significant increases in walking velocity (13%), cadence (6%) and stride length (10% PL, 8% SL). Figure 1 presents the energy returned by the Seat-L that was significantly greater than the SACH.

Figure 1: Total energy returned by SACH and Seattle-Light foot prostheses.

There was a significant decrease to the abnormality of the PL when the Seat-L was used, and a trend for a decrease on the SL. The asymmetry between the PL and SL increased, due to unequal changes to the SL and PL (See Table1).

SACH SEAT-L

Abnormality PL 39 (25)* 28 (20)*

Abnormality SL 24 (12) 16 (15)

Asymmetry 34 (18) 39 (21)

IAA 32 (17) 28 (12)

	SACH	SEAT-L
Abnormality PL	39 (25)*	28 (20)*
Abnormality SL	24 (12)	16 (15)
Asymmetry	34 (18)	39 (21)
IAA	32 (17)	28 (12)

Table 1: Index of Asymmetry and Abnormality (* p < 0.05).

DISCUSSION

The impact of the energy storing foot on gait is in contradiction to previous reports (Gitter, et al. 1991; Torburn et al. 1995). The amplitude of energy returned by the two prosthetic feet is comparable for the SACH and greater for the Seat-L to that previously estimated (Ehara et al. 1993; Prince et al. 1994). The difference in this data compared to previous research may be explained by the 2D vs. 3D model used for the calculation of the mechanical energy or the inverse dynamics vs. projection of vertical force used for moment calculation. The utilisation of the greater energy returned by the Seat-L foot is reflected by positive changes to the spatio-temporal gait parameters while the PL behaves closer to a limb of HE where abnormality decreased significantly. A specific gait retraining program for the Seat-L may be a prerequisite for optimal gait rehabilitation of elderly below-knee amputees. The IAA and total energy returned should be considered as additional factors in prosthetic foot evaluation and selection.

REFERENCES

Ehara Y. et al. Arch Phys Med Rehabil, 74, 68-72, 1993.

Gitter A. et al. Am J Phys Med Rehabil, 70, 142-148, 1991.

Prince F. et al. IEEE Trans Rehabil Eng, 2, 247-255, 1994.

Prince F., Ph.D. Thesis, Universit‚ de Montr‚al, 1993.

Torburn L. et al. J Rehabil Res Dev, 32, 111-119, 1995.

ACKNOWLEDGMENTS

Funding from Medical Research Council of Canada (MRC, MT-43434), Fonds pour Chercheurs et Aide … la Recherche (FCAR) is acknowledged. Scholarship awarded to FP from Fonds de recherche en sant‚ du Qu‚bec (FRSQ) is also acknowledged.