Can external lateral stabilization reduce the energy cost of walking in persons with a lower limb amputation?
Introduction
Regaining walking ability is an important rehabilitation goal for lower limb amputees (LLA). Achieving this goal may be hampered by a significantly elevated energy cost of walking with a lower limb prosthesis, with reported increases between 9and 33% for transtibial, and 66 and 100% for transfemoral amputees [1], [2], [3]. While this increased cost of walking is well documented, its underlying causes are still poorly understood.
Previous research has associated the elevated cost of walking in LLA with compensatory strategies related to forward progression of the body. LLA compensate for the lack of ankle push-off power with increased mechanical work produced at the hip, which increases step-to-step transition costs [4]. Furthermore, particularly transfemoral amputees show vaulting, hip hiking and circumduction of the prosthetic leg to ensure foot clearance during swing in the absence of active ankle dorsiflexion and knee flexion, which supposedly comes with an extra metabolic cost [5]. However, correlations between these adaptations and the elevated energy cost of walking are moderate at best [4], [6], [7], suggesting a role for other factors, possibly not directly related to forward progression. One such factor could be the impaired balance control in LLA [8], [9]. While the energy demand of the motor responses associated with balance control is relatively low in healthy subjects, this cost might rise considerably as a result of compensatory strategies associated with the neuromuscular impairments in LLA, and thus contribute to the elevated energy cost of walking in LLA [1].
Especially in the frontal plane, the most unstable direction during walking, active feedback control appears necessary to ensure stability [10], [11]. Primary strategies for medio-lateral balance control are a stepping strategy, a lateral ankle strategy, and a hip strategy [12]. The stepping strategy provides gross balance control through adequate foot placement, while fine-tuning is accomplished by ankle inversion/eversion and hip abduction/adduction torques during stance. In LLA, the use of these strategies is hampered by reduced neuromuscular control to correctly place the foot, and a lack of control over the prosthetic ankle joint. Moreover, particularly in transfemoral amputees, the hip strategy is also often impaired due to atrophy and loss of control over the remaining muscles around the hip joint [13].
These impairments can be dealt with by taking wider steps to ensure a sufficient margin of stability [14]. Indeed, an increase in step width has been observed in LLA compared to controls, with larger increases for transfemoral amputees [12], [15], [16], [17]. Moreover, increased step width variability has been observed in LLA, indicating an increased reliance on the stepping strategy to compensate for the reduced ability to use an ankle and/or hip strategy [18], [19]. While these compensations may help ensure stability, previous work has demonstrated that increasing step width and step width variability adversely affects the energy cost of walking [20], [21] due to increased mechanical work to redirect the center of mass from side-to-side [20], [21], [22], or increased muscle activity to ensure adequate foot placement [23].
To estimate the contribution of medio-lateral balance control to the total energy cost of walking, the need for active balance control can be reduced artificially. To this end, Donelan et al. [24] constructed a set-up to externally stabilize subjects in the medio-lateral direction via stiff spring-like cords attached to the waist. In healthy subjects this resulted in significant reductions in step width and step width variability, with a concomitant reduction in energy cost of 3–7.5% [24], [25], [26], [27]. Since LLA, and especially transfemoral amputees, naturally take wider and more variable steps, it can be hypothesized that they will benefit more from external lateral stabilization than able-bodied controls, resulting in a substantially larger reduction in energy cost due to stabilization for LLA, particularly for transfemoral amputees.
The aim of the current study was thus to examine whether the increased energy cost of walking in LLA compared to able-bodied people is related to an increased effort for balance control. More specifically, we sought to examine whether external lateral stabilization leads to larger reductions in the energy cost of walking in transfemoral and transtibial amputees compared to able-bodied controls, and expected the largest reductions to occur in transfemoral amputees. Furthermore, we expected concomitant decreases in step width and step width variability.
Section snippets
Study population
Thirteen unilateral transfemoral amputees (TF), sixteen unilateral transtibial amputees (TT) and seventeen age-matched able-bodied controls (CO) agreed to participate. All amputees were experienced walkers who had completed their rehabilitation period and were able to walk 5 min on a treadmill. Subjects were excluded in case of contraindications for moderate exercise, or co-morbidities or medication use that could interfere with energy expenditure or balance control. Additional exclusion
Results
In each group one subject was unable to complete the protocol, for different reasons: soreness in the stump (TF), difficulty walking on a treadmill (TT) and dizziness (CO). Oxygen data for one subject (CO) were aberrant, therefore this subject was excluded, leaving a total of 12 TF, 15 TT and 15 CO subjects that were included in the analysis.
Discussion
The goal of this study was to investigate whether the increased energy cost of walking in LLA could partly be explained by impaired balance control, by evaluating the effect of external lateral stabilization in LLA and able-bodied subjects. Our hypothesis that external lateral stabilization would result in larger reductions in energy cost for LLA, especially for TF, was not corroborated by the results. The effect of stabilization on energy cost was small in light of previous studies with
Conflict of interest statement
We wish to confirm that there are no known conflicts of interest associated with this publication and there has been no significant financial support for this work that could have influenced its outcome.
Acknowledgements
This research was supported by a non commercial grant from OIM Foundation, Assen, The Netherlands (reference number 1104b).
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Energy expenditure in people with transtibial amputation walking with crossover and energy storing prosthetic feet: A randomized within-subject study
2018, Gait and PostureCitation Excerpt :Energy expenditure, the primary outcome of this study, was measured while participants with unilateral transtibial amputation walked at self-selected speeds on a treadmill. The range of comfortable walking speeds selected by participants varied (0.6–1.2 m/s), but were similar to speeds (0.68–1.07 m/s [4,21,24,25]) exhibited by people who use transtibial prostheses walking on a treadmill. Speeds were, however, generally lower than those adopted by individuals with transtibial amputation and healthy adults walking over-ground (1.1–1.2 m/s [2,3,19,24,26,27] and 1.0–1.7 m/s [2], respectively).