The Journal of the International Society for Prosthetics and Orthotics

The effect of prosthesis mass on the metabolic cost of steady-state walking was studied in ten male non-vascular trans-tibial amputees (TTAs) and ten non-amputee controls. The subjects underwent four trials of treadmill ambulation, with each trial performed for nine minutes at level grade and 76 m/min. Twenty minutes of seated rest followed each trial. During trials numbers one and two, TTAs ambulated without mass added to their prosthesis. During the third and fourth trials, either 454 or 907 grammes mass (1 or 21bs mass respectively) were randomly assigned and added to either the prosthesis or the leg of the non-amputee control. Subjects were blinded to the amount of mass added to their limb. Withingroup comparisons across the four trials showed significant differences in oxygen consumption (VO2) and heart rate (HR) between the two non "mass added" trials, but no effect for addition of mass. The V O 2 of TTAs was only 0.6ml/kg/min (4.7 percent) greater during walking following the addition of 907 grammes to the prosthesis than without mass addition at all, while HR averaged only 1.4 beats/min. higher under the same testing condition. Pearson-product moment correlations echoed these findings, as moderate, but in all cases, negative correlations were observed for associations among the All correspondence to be addressed to Robert S. Gailey, M.S.Ed., P.T., University of Miami, Division of Physical Therapy, 5th Floor Plumer Building, 5915 Ponce de Leon Boulevard, Coral Gables. Florida 33146, USA. Tel: +1 305 284-4535. Fax: +1 305 284-6128. factors of subject age, stump length, and prosthesis-shoe weight, and both VO 2 and HR. It was concluded that adding up to 907 grammes mass to a non-vascular TTA ' s prosthesis will not significantly increase the energy expenditure or HR at a normal walking speed, and that elevated energy cost of ambulation in repeated measures testing without mass added may reflect task familiarisation and not an added burden of prosthesis mass. Introduction An estimated 105,000 to 115,000 Americans lose a lower limb to amputation each year, with approximately 30,000 trans-tibial amputations being performed (Skinner and Effeney, 1985). Although the published literature lacks consensus concerning the distribution of causes for amputation in North America, it has been estimated that 70 to 90% are the result of disease, between 10 to 20% are for traumatic reasons, approximately 4% because of tumour, and 4% are congenital (Gailey et al, 1994; Ganguli et al., 1974; Smidt, 1990). Previous studies have reported that the metabolic cost of ambulation in trans-tibial amputees (TTA) is 15-55% higher than that of non-amputees, while ambulation velocity is 1040% slower (Gailey et al, 1994; Ganguli et al, 1974; Gonzalez et al., 1974; Huang et al, 1979; Pagliarulo et al, 1979; Waters et al, 1976 and 1988) (Table 1). It has been reported that traumatic TTAs walk at a faster pace while expending greater energy than vascular TTAs (Ganguli et al, 1974; Pagliarulo et al, 1979; Waters et al, 1976 and 1988). By comparison 10 R.S. Gailey, M. S. Nash, T. A. Atchley, R. M. Zilmer, G. R. Moline-Little, N. Morris-Cresswell and L.I. Sieben Table 1. Metabolic cost and velocity of amputee ambulation. non-amputee controls have an ambulation VO 2 ranging between 10.9-12.95 ml/kg/min at speeds between 60-99m/min (Blessey et al, 1976; Corcoran and Brengelmann, 1970; Gailey et al, 1994; Perry, 1992; Smidt, 1990; Waters et al, 1976 and 1988). (Table 2). The mean comfortable walking speed for non-amputee subjects is observed to be 76-80 m/min (Finely and Cody, 1970; Waters et al, 1976). In contrast the mean walking speed of TTAs is 71 m/min. approximately 10% slower than nonamputee subjects (Gailey et al, 1994; Pagliarulo et al, 1979; Waters et al., 1978). Many elements contribute to altered gait mechanics, slow walking pace and elevated energy cost of ambulation in amputees. Among the most critical of these elements are: 1) the degree of displacement of the centre of mass over the base of support in all three planes of motion (Engsberg et al, 1990; Peizer et al, 1969; Saunders et al, 1937); 2) asymmetry of motion secondary to an imbalance of the muscle group actions of the lower limbs (Mensch and Ellis, 1986; Skinner and Effeney, 1985); 3) diminished coordinated movement between the ankle and knee joints consequent to the loss of proprioceptive feedback and musculature of the prosthetic joints (Ganguli et al, 1974; Mensch and Ellis, 1986; Skinner and Effeney, 1985; Waters et al, 1976); 4) the inability of the prosthesis to simulate the normal biomechanics and functions of the anatomical ankle and foot (Fisher and Gullickson, 1978; Radcliffe, 1961) thus altering the normal biomechanics of locomotion (Fisher and Gullickson, 1978); 5) the influence of the prosthetic design on the mechanics of gait, which may cause the amputee to deviate from a normal gait pattern and increase energy expenditure during walking (Murphy and Wilson, 1962; Radcliffe, 1955, 1957 and 1 9 6 1 a , b ) ; 6) the loss of kinetic energy normally stored as potential energy in the anatomical limb during gait (Ehara et al, 1993; Ganguli et al, 1974; Gitter et al, 1991); 7) the loss of the skeletal lever arm, thus forcing proximal muscle groups acting on the remaining bone length to compensate for a longer lever arm and control the entire lower limb during the gait sequence (Ganguli et al, 1974; Gitter et al, 1991; Inman, 1967); 8) the loss of absolute amounts of contractile tissue mass, changes in insertion site, or altered functional capacity which will result in diminished potential strength (Eberhart et al, 1954; Ganguli et al, 1974; Klopsteg and Wilson, 1954; Winter and Sienko, 1988); 9) changes in body temperature regulation from loss of skin surface area which may disrupt the body 's natural homeostasis Table 2. Metabolic cost and velocity of normal ambulation Energy expenditure of trans-tihial amputees 11 (Levy, 1983). Interestingly, the mass of the prosthesis is surprisingly missing from this list. Both logic and a previous report (Inman, 1967) suggest that prosthesis mass should be included among the factors that influence energy expenditure and speed of ambulation in TTAs. However, the relationships among prosthetic mass, speed of ambulation, and energy cost of walking are not clearly defined. A recent report examined the effects of prosthesis mass on ambulation VO 2 in TTAs who used heavy prostheses operationally defined as greater than 2.27 kg and those who used light prostheses, defined as being of mass 2.27 kg or less. After controlling for stump length, age, speed of ambulation and baseline VO2, there was no significant difference in ambulation V O 2 between subjects who used high and low mass prostheses (Gailey et al, 1994). Additionally, no significant correlation was observed between prosthesis mass and either ambulation VO 2 or heart rate (HR), and the best predictors of the physiological responses to walking were the subjects' resting (i.e. pre-ambulation non-exercise) V O 2 , HR, and stump length. It is possible, however, that the findings of this study may have been influenced by its retrospective nature and cross-sectional design. Thus, the purpose of this prospective, randomised, control-design study was two-fold: 1) to compare the VO2 and HR of TTAs and non-amputee control at a steady state walking speed of 76 m/min and 2) to determine the effects of mass on VO 2 and HR when added to the limb of TTAs and non-amputee controls. Methods Subjects Subjects were ten mesomorphic males aged 24 to 52 years (x = 37.8 ± 10.4) with unilateral TTA. Ten non-amputee control subjects were matched with the TTAs for age (range = 23-51 years, x = 34.0±12.9 years), gender, and somatotype. The subjects with TTA were at least one year post-amputation from trauma or tumour but not vascular disease, while their intact limb was without injury or disability. All had a minimal stump tibial length of five centimetres and had used their current prosthesis for at least six months without skin irritation, pain, or other complication, the stump length was measured from the medial tibial plateau to the distal tibia. The prosthesis mass, both with and without the shoe, was recorded to the nearest gramme on a calibrated scale. Consent to undergo study was obtained from all subjects in accordance with the guidelines of the Institutional Medical Sciences Subcommittee for the Protection of Human Subjects. Descriptive characteristics of the subjects and their prostheses are shown in Table 3.