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Aim Ankle–foot orthoses are the standard of care for foot drop in cerebral palsy (CP), but may overly constrain ankle movement and limit function in those with mild CP. Functional electrical stimulation (FES) may be a less restrictive and more effective alternative, but has rarely been used in CP. The primary objective of this study was to conduct the first trial in CP examining the acceptability and clinical effectiveness of a novel, commercially available device that delivers FES to stimulate ankle dorsiflexion.
Method Twenty-one individuals were enrolled (Gross Motor Function Classification System [GMFCS] levels I and II, mean age 13y 2mo). Gait analyses in FES and non-FES conditions were performed at two walking speeds over a 4 month period of device use. Measures included ankle kinematics and spatiotemporal variables. Differences between conditions were revealed using repeated measures multivariate analyses of variance.
Results Nineteen individuals (nine females, 10 males; mean age 12y 11mo, range 7y 5mo to 19y 11mo; 11 at GMFCS level I, eight at level II) completed the FES intervention, with all but one choosing to continue using FES beyond that phase. Average daily use was 5.6 hours (SD 2.3). Improved dorsiflexion was observed during swing (mean and peak) and at foot–floor contact, with partial preservation of ankle plantarflexion at toe-off when using the FES at self-selected and fast walking speeds. Gait speed was unchanged.
Interpretation This FES device was well accepted and effective for foot drop in those with mild gait impairments from CP.
Cerebral palsy (CP) is the most common neuromuscular disorder among children.1 CP is a group of motor disorders resulting from a non-progressive injury during early brain development leading to impairments of movement and posture.2 Although the clinical presentation is heterogeneous, the ankle is the most commonly affected joint in individuals with CP who are ambulatory.3 Common impairments are insufficient ankle dorsiflexion during swing, or foot drop, and excessive plantarflexion during early to mid-stance. These abnormalities may cause standing and walking instability, and greater risk of tripping and falling.
Positional bracing is the current standard of care for individuals with CP who have limited ankle dorsiflexion. However, many people, particularly those with mild deficits, may choose not to wear orthoses because of the mobility restrictions they impose, or because of issues with comfort or cosmesis. By restricting ankle movement, orthoses may exacerbate muscle weakness and atrophy, leading to further loss of function over time.4 Functional electrical stimulation (FES) may be an effective alternative treatment for this population. In contrast to bracing, FES does not restrict motion, does produce muscle contraction, and thus has the potential to increase strength and motor control through repetitive neural stimulation over time.
The primary objective of this study was to conduct the first trial in CP examining the acceptability and effectiveness of a novel FES foot drop device on ankle motion and gait. We hypothesized that the FES device would be well accepted by children and adolescents with CP. We further hypothesized that it would be effective in increasing ankle dorsiflexion during swing and at initial foot–floor contact compared with the non-FES condition, while preserving ankle plantarflexion at toe-off, and that walking speed would be greater with the device.
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- What this paper adds
This study reports improvements in ankle dorsiflexion with partly preserved ankle plantarflexion during FES use in independently ambulatory individuals with CP. There was good acceptability of the FES device in this sample. Despite all participants having inadequate dorsiflexion during swing and at foot–floor contact without the device, few used an ankle–foot orthosis at the time they enrolled in this study, suggesting that positional bracing is not necessarily a well-accepted treatment option in this population. FES may be a more acceptable and more effective treatment alternative in individuals with CP who have mild gait impairments.
FES has not traditionally been considered a viable long-term treatment option in children because of concerns about tolerance, feasibility, and effectiveness. However, the current results dispute these concerns. The results here are generally consistent with a descriptive study by Durham et al.8 who reported that nine of 12 children with CP accepted the Odstock stimulator. Three of the nine did not use the device as often as suggested, but still wanted to continue wearing it after the study ended. The Odstock is another FES device for foot drop that includes a controller worn on the waist with lead wires to the stimulating electrodes on the leg and to a footswitch worn in the shoe. Factors limiting wear in their study were that the device was large, and the wires difficult for children to manage at school. The self-contained design of the device used in the current study may explain our slightly better acceptance rate. Our strategy of providing a high-level of family support as well as individually modifying the stimulation parameters may have also contributed to the high tolerance and acceptability. In fact, two participants who had trialed this same device in the past and did not use it long-term were successful with this comprehensive approach to encourage acceptability.
The current tolerance results are superior to the outcomes of Postans et al.9 who reported that six of 21 children did not tolerate electrical stimulation during their trial. However, they stimulated two large antigravity muscle groups in the lower extremities, which typically require higher amounts of stimulation to produce a functional contraction.
To our knowledge, this is the only trial so far in this population evaluating this novel device. Use of FES increased dorsiflexion during the swing phase of gait, as intended. The decrease in plantarflexion at toe-off, although not to a neutral ankle position as with an ankle–foot orthosis, may reduce push-off power and raises the question of whether the stimulation was perhaps delivered too early or too strongly at that point. The tibialis anterior typically becomes active before toe-off10 and stimulation is designed to mimic that. This observation of FES affecting ankle angle at toe-off may also reflect differences between the onset of muscle contraction from artificial electrical stimulation compared with preparatory activation from the central nervous system. Clinicians should be attentive to onset timing so as not to interfere with propulsion more than needed, recognizing the challenge of determining the optimal balance of force and timing for each patient.
Activation of the tibialis anterior and fibular muscles is the only option with this commercially available device. Others have investigated and reported some benefits of plantarflexor stimulation, with and without accompanying dorsiflexor stimulation, in those with CP or after stroke.11–16 The combination should be studied in larger trials with more rigorous study designs.
The observations of increased dorsiflexion during swing and improved foot–floor contact, with no change in spatiotemporal gait characteristics, are consistent with several other reports of FES in smaller samples of children with CP.8,9,13,14,17,18 The magnitude of change in dorsiflexion between the FES and non-FES conditions is also similar to that reported by Kesar et al.19 in a group of adults with post-stroke hemiplegia.
However, two different groups of adults with central nervous system lesions who used this same device demonstrated increases in walking speed, contrasting with our observations in the current sample.20 These increases in walking speed were 5.0% in the group with non-progressive lesions and 5.7% in the group with progressive lesions. A significant difference in walking speed between the FES and non-FES conditions was not present in earlier work by the same group in a smaller sample.21 All participants in those studies initially walked at a speed slower than 1.2 m/seconds, indicating perhaps greater gait impairment than participants in the current sample. When normalizing velocity for height, five of our 19 participants would not have met the inclusion criteria for the Stein studies because they walked too fast. Changes in walking speed might be less likely to occur in our sample because many already walked at a more functional speed.
Common factors in this population that may limit the amount of dorsiflexion achieved with stimulation, such as gastrocnemius muscle contracture and spasticity, should be considered when determining if FES could benefit individual patients. Further investigation should address several remaining questions. No direct comparison with an orthosis condition could be made as was originally planned in the current study because only one individual wore an ankle–foot orthosis at the time of initial FES use. However, this comparison would be valuable, and is recommended at least on an individual basis for clinical decision making with those individuals who do use a brace. The fact that only one participant was wearing an ankle–foot orthosis by the time of initial FES use (month 3), despite all having a history of previous orthosis prescription, suggests that ankle–foot orthoses may not be the best solution for this population. FES may be most appropriate for those children with mild CP, as in this study, who may feel overly constrained by an ankle orthosis, or for those who choose not to wear a brace because of issues with comfort or cosmesis.
We excluded those who had recent botulinum toxin injections because this would confound the study results, but the combination of FES with botulinum toxin injections may be particularly advantageous in this population, and should be investigated for added benefit. Additionally, it should be determined if optimal dosage parameters can be predicted based on individual characteristics, if FES can lead to increases in muscle size and strength, and if FES has neuroplastic effects on the central nervous system in children with brain injuries as has been shown in adults.22