Gait Changes During Unilateral Load Carriage in Amputees

Background

Load carriage in the able-bodied population is fairly well studied because of military and industrial requirements. Kinetic, kinematic, and metabolic data have been presented for able-bodied populations (1,2,3,4,5). There are several activities of daily living or occupational activities that may require an amputee to carry a load unilaterally. Suitcases, grocery bags, cleaning buckets, briefcases, and occupational tasks may all restrict an individual to unilateral load carriage. Understanding the general effect of an unilaterally carried load on the gait of a trans-tibial amputee may assist practitioners and therapists in assessing individual amputees ability to cope with unilateral load carriage for activities of daily living and occupational tasks. Evidence supporting the ideal side of the body to for a unilateral amputee to carry a load may also be beneficial.

Studies of unilateral load carriage in the able-bodied have reported that subjects will selfselect a load that is about half of what they can carry in both hands, yet gait parameters may not be altered at such loads (2). Devita et al. reported that carrying loads on one side of the body causes an increase in trunk muscle activity and increased hip and knee joint moments on the contralateral side during single stance phase (3). It has also been shown that unilaterally carried loads of up to 20% body weight may have little difference on kinematic patterns in the able-bodied, but will result in significant increases in muscle activity (4). Gait changes have been reported in the able-bodied population at loads ranging from 20% to 50% body weight. Able-bodied subjects typically adapt to increased load by increasing cadence, decreasing stride length, and decreasing velocity (1).

Studies of unilateral load carriage in unilateral trans-tibial amputees have shown that energy expenditures are much higher than those of a matched able-bodied sample (6). A graded load carriage test among unilateral trans-tibial amputees using loads from 0 to 20 kg demonstrated the metabolic cost is not only higher, but rises faster with load compared to an able-bodied sample (7). No gait parameters were reported in either of these studies. Since metabolic cost is higher and rises faster in amputees than a matched group of able-bodied subjects, it may be reasonable to expect gait changes to occur in amputees at lower load levels than would be expected in the able-bodied population.

The purpose of this study is to examine the effect of unilateral load carriage on the gait of unilateral trans-tibial amputees. It is hypothesized that unilateral trans-tibial amputees will adapt to load carriage by increasing cadence, decreasing stride length, and decreasing velocity. It is hypothesized that as load increases the change in gait parameters will increase. Finally, it is hypothesized that loads carried on the sound side will have a greater impact than loads carried on the prosthesis side.

Methods

Fourteen healthy male trans-tibial amputees (10 right leg and 4 left leg) were recruited from the metropolitan Chicago area. The mean age of the subjects was 36.2 (ranging from 22 to 54 years old). The mean height of the subjects was 1.77 +-0.066 m and their average weight was 93 +-22.8 kg. Subjects were screened for vascular disease, diabetes, musculo-skeletal disorders other than amputation, normal range of motion and muscle strength, and chronic low back pain. Subjects were required to have been in a definitive prosthesis for at least one year and to be comfortable in their current prosthesis. Thirteen of the subjects wore prostheses fabricated and fit at the offices of Scheck and Siress Advanced Orthotics and Prosthetics.

All subjects volunteered and provided informed consent prior to participating. All data were collected on the same day using the GaitRite® [*Gaitrite is a product of MAP/CIR Inc. Haverton, PA.] electronic walkway (8). The GaitRite system consists of a portable 5.2 m walkway that records footfall patterns and spatio-temporal gait parameters through pressure-activated sensors. The participants were asked to wear comfortable walking shoes for the study. For all trials, the subjects were instructed to walk at a natural comfortable velocity beginning 1.5 m before the walkway and continuing for 1.5 m beyond the end of the walkway to allow for a steady state gait while on the walkway.

Three different load conditions (0%, 10%, and 20% body weight) were tested in 12 blocks of trials. The first block consisted of 10 trials with no load to establish a baseline. The second and third blocks consisted of six trials carrying a load of 10% body weight on the right side followed by four no load trials. Subjects were then allowed five minutes to rest. The next three blocks of trials consisted of four no load, six carrying 20% body weight from the right hand, and four no load trials respectively. Subjects were then allowed 20 minutes to rest. Blocks seven through 12 were the same as blocks one through six except that the subjects carried the load from the left hand. Each load carrying trial was preceded and followed by no load trials to verify that any changes in gait due to load carrying did not impact other load carrying trials. The same order of tests was used for each individual in order to randomize the side, prosthetic or sound, on which the load was first carried. Loads were composed of cast iron dumbbell weights, which were carried by hand in a durable canvas bag with a handle.

Velocity, cadence, stride length, sound side step length, and prosthesis side step length were analyzed. A one-way ANOVA was used to compare subject means for the gait parameters in the eight no load blocks. Data for each subject was set relative to the first block of trials to eliminate affect of individual subject gait parameters on the results. A two-way ANOVA for load (0%, 10%, and 20% body weight) and carriage side (sound and prosthesis) was conducted on the change in gait parameters relative to the initial no load block.

Results

Prosthetic design characteristics within the subject sample were as follows: Socket design: 12 total surface bearing, two patellar tendon bearing; Suspension: six silicon suction suspension with pin, five vacuum assisted suction suspension, one superacondylar wedge, one supra-patellar strap, one suspension sleeve; Foot: 11 dynamic response, three multi-axial. For the first block of ten no load trials subjects walked with a mean velocity of 123 +- 21 cm/s, cadence of 101 +- 6.6 steps/min, and stride length of 145 +-18 cm.

There was no significant difference for any of the variables between the blocks of no load trials. Carriage side did not have a significant effect on any of the variables, and there was no significant result for the interaction of load and carriage side. There was no significant change in walking velocity related to load. When carrying 10 percent body weight, subjects walked with a significantly increased cadence (1.8 steps/min, p < 0.01), shorter stride length (3 cm, p < 0.005), shorter sound side step length (2 cm, p < 0.005), and shorter prosthesis side step length (2 cm, p < 0.005) relative to the first set of no load trials. When carrying 20 percent body weight, subjects walked with a significantly increased cadence (3.3 steps/min, p < 0.001), shorter stride length (3.5 cm, p < 0.005), shorter sound side step length (2 cm, p < 0.005), and shorter sound side prosthesis step length (2 cm, p < 0.025) as compared to the 10 percent load trials. Plots for the sample means plus and minus one standard deviation for cadence, stride length, sound side step length, and prosthesis side step length relative to the mean for the initial no load trial are presented in figure 1.

Discussion

The purpose of this study was to examine the impact of unilateral load carriage on unilateral trans-tibial amputees. The hypothesis that velocity would decrease has been rejected, but the hypotheses that cadence would increase, and that stride length would decrease have been accepted. The hypothesis that changes in gait would be more pronounced with loads carried on the sound than on the prosthetic side was also rejected.

This is the first study known to these authors that has characterized the changes in gait in unilateral trans-tibial amputees during unilateral load carriage. Gait changes in this sample of transtibial amputees were detected at lower loads than what has been previously presented for ablebodied subjects (2,3,4). The evidence indicates that unilateral trans-tibial amputees adapt to unilateral load carriage in similar fashion to able-bodied subjects by increasing cadence and decreasing stride length. No change was detected in the velocity of the subject sample as load increased. Studies of able-bodied subjects disagree on the conditions under which individuals decrease walking velocity. It is also possible that subjects did not decrease their walking velocity in an attempt to avoid carrying the load for longer than necessary.

Ganguli reported no difference in energy expenditure of trans-tibial amputees based on the side of load carriage (6). Similarly this study found no difference in gait parameters when loads were carried on the sound side versus the prosthesis side. The available data is not able to make any suggestions about which side of the body may be best for healthy trans-tibial amputees to use for load carrying. It is entirely likely that other factors such as health of the existing joints (5,9) or the need for an assistive device may be more critical than the side of amputation for making recommendations on carriage side for individual amputees.

Studies of load carriage in trans-femoral, older, pediatric, diabetic, or disvascular populations should be conducted with matched able-bodied controls to further clarify the impact of load on the gait parameters of amputees. Studies comparing various feet or components during load carriage may also uncover evidence supporting the use of a specific class of prosthetic components for patients engaged in frequent lifting, manual labor, or load carrying.

Figure 1: Four plots presenting sample means and standard deviations for the change in cadence, stride length, sound side step length, and prosthesis side step length relative to the first block of no load trials. Blocks labeled (a) are significantly different than the no load trials. Blocks labeled (b) are significantly different than both the no load and 10 percent load trials.

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