Date Published: July 12, 2017
Publisher: Public Library of Science
Author(s): Benjamin J. Darter, Amy J. Bastian, Erik J. Wolf, Elizabeth M. Husson, Bethany A. Labrecque, Brad D. Hendershot, Alena Grabowski.
Locomotor adaptation enables walkers to modify strategies when faced with challenging walking conditions. While a variety of neurological injuries can impair locomotor adaptability, the effect of a lower extremity amputation on adaptability is poorly understood.
Determine if locomotor adaptability is impaired in persons with unilateral transtibial amputation (TTA).
The locomotor adaptability of 10 persons with a TTA and 8 persons without an amputation was tested while walking on a split-belt treadmill with the parallel belts running at the same (tied) or different (split) speeds. In the split condition, participants walked for 15 minutes with the respective belts moving at 0.5 m/s and 1.5 m/s. Temporal spatial symmetry measures were used to evaluate reactive accommodations to the perturbation, and the adaptive/de-adaptive response.
Persons with TTA and the reference group of persons without amputation both demonstrated highly symmetric walking at baseline. During the split adaptation and tied post-adaptation walking both groups responded with the expected reactive accommodations. Likewise, adaptive and de-adaptive responses were observed. The magnitude and rate of change in the adaptive and de-adaptive responses were similar for persons with TTA and those without an amputation. Furthermore, adaptability was no different based on belt assignment for the prosthetic limb during split adaptation walking.
Reactive changes and locomotor adaptation in response to a challenging and novel walking condition were similar in persons with TTA to those without an amputation. Results suggest persons with TTA have the capacity to modify locomotor strategies to meet the demands of most walking conditions despite challenges imposed by an amputation and use of a prosthetic limb.
Restoring a rudimentary walking ability in persons with a lower extremity amputation is a fundamental goal of physical rehabilitation. In the majority of instances, especially among younger individuals, this goal can be met. However, no device yet fully replicates the motor or sensory functions of the amputated structures. Walking performance is therefore altered, and the occurrence of undesirable outcomes is increased (e.g., biomechanical deviations, increased physiological energy cost for walking, increased risk for falling)[3–6]. These undesirable outcomes may become even more prominent and troublesome when faced with challenging walking conditions.
Demographic information (Table 1) for the 10 persons with a unilateral traumatic TTA (mean ± SD: 32.2 ± 6.9 yr, 1.79 ± 0.06 m, 90.1 ± 14.2 kg) and 8 persons without an amputation (27.5 ± 6.9 yr, 1.79 ± 0.05 m, 86.3 ± 13.3 kg) were statistically similar (all p>.17). The participants with TTA used their customary prosthetic limb consisting of a suction socket, with in most cases a sleeve suspension, and equivalent dynamic energy storing and return feet. Step length measurements for persons with TTA during treadmill acclimation resulted in equal numbers of participants with the prosthetic limb assigned to the slow (n = 5) and fast belts (n = 5) during the split adaptation condition. All participants completed the testing protocol without difficulty. However, prolonged handrail use was observed more frequently in persons with TTA during split adaptation walking. Kinematic data for the upper extremities indicated 4 persons without amputation released the handrails within the first 5 seconds of split adaptation walking, 3 others released the handrails by 80 second, and only 1 held on the entire time. Whereas, 1 person with TTA released the handrails with 5 seconds, 3 released by 80 seconds in, and 3 held on the whole time. Handrails were also used during tied post-adaptation walking. However, unlike the split adaptation condition, use was similar with 7 of 8 persons without amputation, and 8 of 10 persons with TTA releasing the handrails within the first 30 seconds.
Retaining an innate flexibility in motor control strategies for a wide range of walking conditions is an essential aspect of normal locomotor performance. Thus, the primary goal of this study was to evaluate the effects of a unilateral TTA on locomotor adaptability. Results suggest persons with TTA exhibited normal reactive accommodations, and as such were similarly perturbed as those without an amputation. Furthermore, the rates of locomotor adaptation and de-adaptation were similar between persons with and without an amputation, and for the sub-group comparison of persons with TTA based on belt assignment for the prosthetic limb. These findings suggest pathways and processes enabling locomotor accommodation and adaptation either do not depend on unaltered somatosensory feedback from the periphery, or compensations can be made to overcome the altered input.
Persons with TTA exhibit a locomotor adaptability similar to persons without an amputation despite altered somatosensory feedback and functional impairments imposed by use of a prosthetic limb. Therefore, persons with TTA likely have the capacity to modify locomotor strategies to meet the demands of most walking conditions. Our results may also have clinical implications for training interventions aiming to restore locomotor performance in persons with a lower extremity amputation. Split-belt walking has been previously used to correct step length asymmetry. In the current study the persons with TTA exhibited highly symmetric step lengths at baseline so adapting to a more symmetric pattern was not expected. Nevertheless, finding persons with TTA have a normal capacity to adapt locomotor strategies within a single session suggests a multiple session split-belt training program may also be effective for persons with TTA when significant step length asymmetry is present. Moreover, a normal adaptive ability suggests the training volume necessary to alter or acquire a new locomotor strategy is likely unchanged based solely on the presence of a transtibial amputation. In addition, patients may develop greater flexibility and an ability to rapidly change locomotor strategies if interventions that leverage adaptability are used during rehabilitation. Training in such a manner could help maintain stability and safety when faced with challenging walking conditions in everyday life.