Assistive ambulation devices for the ankle can bolster walking speed and safety and lessen the risk of injury to the joint. But which of 2 technologies is best for your patient?
By Hank Black, Lower Extremity Review June 2018
People with multiple sclerosis (MS) have difficulty walking: Gait impairment, including the reduced ankle dorsiflexion of foot drop, is one of the most common indicators of disability early in the course of this progressive autoimmune disease of the central nervous system, affecting approximately 75% of people with MS.
Assistive technology, such as ankle–foot orthoses (AFO) and functional electrical stimulation (FES), increases the safety of walking and the speed of ambulation (even then, only about one half of patients remain ambulatory 15 years after disease onset).[2,3] Assistive technology also reduces the risk of injury to the knee and ankle and reduces the effort of ambulation.
There are benefits of, and a downside to, both AFOs and FES. Knowledge of the literature, experience, ongoing refinements in technology, and careful assessment of the individual patient will help you select the device that holds most potential.
|Functional electrical stimulation|
|FES uses skin surface electrodes to provoke the peroneal nerve and stimulate the anterior tibialis muscle that controls ankle flexion. It utilizes either
Lower-extremity clinicians and many people with MS view FES as a promising alternative to an AFO; researchers are hard at work to solidify the science behind the technology. FES systems for MS have been prescribed in the United Kingdom since 2009, often covered by National Health Service insurance. In the United States, Medicare and most other insurers do not cover such devices for MS.[5,6] Advanced FES systems can cost $6,500 or more, according to several clinicians interviewed for this article. FES does not usually require adjustments to footwear.
|From the literature: Benefits of assistive ambulatory technology|
|A number of studies in recent years—most small and methodologically flawed, however—provide evidence of a beneficial effect of FES on the risk of falls and fear of falling,[7,8] energy cost of gait,[7,9-12] gait speed,[13,14] and functional mobility.[8,15 ]
Large trials of FES for drop foot in MS are rare; a 2015 trial of MS and drop foot included 187 participants and found a significant improvement in walking speed both initially and after 20 weeks (27% average improvement). Overall functional walking was maintained or improved in 95% of responders.
Linda (Miller) Renfrew PT MPhil, consultant physical therapist in MS at the Douglas Grant Rehabilitation Unit, Ayrshire Central Hospital, Ayrshire, Scotland, UK, and others have studied outcome measures with the MS population and assistive technology, in an effort to achieve more clarity in clinical decision-making. Speaking with LER, Renfrew said that “the most common outcome measure to assess with both FES and AFO has been gait speed. Whether it is the best, is still a matter of debate.” The debate hinges in part on the quality of psychometric properties.
Andreopoulou and colleagues  called for more, higher-quality studies of walking measures in a 2018 review of walking tests evaluating AFO and FES use in MS. The researchers found 20 walking measures in 41 studies. The most commonly used were the 10-meter walk test, gait kinematics, and the Physiological Cost Index. However, only 10 measures reported psychometric information (internal consistency and test–retest reliability). Strong evidence levels were found for the Multiple Sclerosis Walking Scale-12 and the timed 25-foot walk test, and moderate levels for the 6-minute walk test and the 10-meter walk test.
In a 2017 review of 19 studies involving 490 patients with MS who had foot drop on the effect of FES on gait speed, Miller and co-workers  found weakness for blinding in all studies, but clinically meaningful orthotic effects of FES in the 5-minute self-selected walk test.
Some of the same researchers, including Renfrew, delved further into the effects on gait speed as well as the oxygen cost of assistive technologies in the first randomized clinical trial  to compare initial orthotic effects of AFO and FES for this population. The trial included 78 participants, divided by modality of treatment and tested with and without their device.
Results showed that AFO reduced walking speed—more so in a fast-walking subset ( > 0.8 m/s), whereas FES increased speed in slow walkers ( < 0.8 m/s), but in not fast walkers. Miller and co-workers previously found this differential effect was dependent on self-selected walking speed.
The results of the Renfrew randomized clinical trial suggest that people with MS who walk slowly gain positive initial orthotic effects from FES but not from an AFO. This, the researchers say, may help patient compliance with FES by helping inform clinical decision-making and patient understanding. No effect was found on gait speed in the 25-foot walk test, a result attributed to very small changes observed in walking speed.
|Outcomes involving patients’ perception of exertion and other experiences with assistive ambulation technology are also helping frame discussions. Khurana and colleagues  employed several self-report questionnaires to help compare AFO and FES energy cost, efficiency, and effort in people with MS. In a preliminary, randomized, crossover study, researchers tested 20 subjects in 2 walk trials on different days (1 day with each device). Subjects then completed 3 questionnaires, the Fatigue Severity Scale, the Falls Efficiency Scale, and the Borg Scale of Perceived Exertion.
Results suggest FES may allow many patients to perform activities of daily living with less perceived fatigue. The researchers also saw a greater reduction in ambulatory exertion in patients who have had their diagnosis longer or have a greater fear of falling, which, they say, may have implications for identifying those who might best benefit from FES for improving decreased activity levels due to fatigue and foot drop. For patients with a rapidly progressive form of MS, the sudden worsening of foot drop may prohibit further use of FES as an assistive option.
Because investigation often leads to more product development, qualitative studies should complement traditional quantitative studies to gain a broader perspective, according to UK researcher Catherine Bulley PhD BSc (Hons). “There’s a growing recognition of the need to learn from the person who is experiencing services or equipment,” she said.
Bulley, a reader (professor) in physical therapy at Queen Margaret University School of Health Sciences, Musselburgh, Scotland, was part of a team investigating the impacts of AFO and FES on MS-associated foot drop. Among the team’s findings from 2 small focus groups was that both AFO and FES devices showed positive and negative aspects, but that most difficulties often were outweighed by improvements in quality of life, such as the ability to participate in activities.
“It can be easy for professionals to decide they are the expert,” Bulley said, “rather than, while linking to quantitative research, test products such as foot-drop footwear with the attitudes of patients, care-givers, family members, and others in mind, beginning in the early phases of design and continuing throughout.” Bulley is now engaged in evaluating the use of social media to communicate with end-users.
|Select, test, and fit an assistive device|
|Mobility early in the course of MS may not be highly affected by the disorder, and clinicians often get pushback when assistive technology is suggested. Peiting Lien, PT, who practices at The Johns Hopkins University, in a community outpatient center in Baltimore MD, said patients often express reservations about trying assistive devices because of cosmetic concerns. Eventually, however, patients come to terms with how such devices may benefit them.
“Most of our patients go for an AFO,” Lien said, “both because even custom orthoses are far cheaper than most FES devices, and it’s quicker to go through the fitting process.”
Lien’s clinic provides patients with a scorecard of the pluses and minuses of both types of devices and a trial of off-the-shelf AFOs of both static and dynamic design. Patients who are interested in pursuing FES are referred to a company representative for fitting because the clinic’s involvement is limited by the cost of purchasing successive generations of equipment and by time constraints for follow-up adjustments.
Some patients seek help from charitable organizations and foundations to pay for FES. Anna Berry PT, of the Andrew C. Carlos Multiple Sclerosis Institute at the Shepherd Center, Atlanta, GA, said patients may receive FES through a nonprofit funded by a grateful patient. “With this major advantage, most of our patients can walk out with an insurance-paid AFO as well as an FES, so they can switch to the AFO when needing additional stability, to rest their muscle from the electrical stimulation, or for convenience in traveling,” she said.
Depending on the patient’s disease status, the therapist explores his (her) understanding of ambulation in MS, as well as what kind of lifestyle they have and desire. The therapist also determines whether difficulty in dorsiflexion is the main reason for walking problems.
“Timing up the kinetic chain, such as weakness in hip flexors or hamstrings, or core instability, must be addressed first,” Lien said.
FES is contraindicated in pregnancy and epilepsy and when there is a history of cancer, Berry said. If a patient has a pacemaker, the manufacturer’s recommendations are followed. A history of ankle instability, such as from a previous sprain or a structural abnormality, may be a contraindication to FES, Berry added.
“We want to look at the patient holistically, including consideration of their type of work, lifestyle, fatigue level, and support system.”
Patient input is key, therapists say. Some patients cannot adjust to the intensity of electrical current or the complexity of the FES, or don’t have adequate use of their upper limbs to be able to wear it. Initial clinic visits include evaluation of muscle tone and ankle-joint range of motion and strength. A visual gait analysis is also performed: The PT observes the patient’s walking pattern, looking for weakness in the hip or knee. (Regarding the hip: Newer, multi-channel FES models may help with muscles controlling the knee, but neither an AFO or an FES helps hip weakness.) Manual evaluation of muscle tone is an essential part of the PT’s protocol, Berry said, because spasticity around the ankle joint, especially in the plantarflexor muscles, may be made worse with electrical stimulation of the targeted muscle.
An initial ankle stretch will determine if tone is going to fight against stimulation, according to Casie Turcotte PT, of the University of Maryland Rehabilitation & Orthopedic Institute, Baltimore, MD. FES usually will not alleviate drop foot in that case, although anti-spasticity injections may allow it to be effective afterward, she said.
FES also is inappropriate if range of motion is inadequate for the foot to dorsiflex. “The stimulation wants to pull the foot up, but without enough ROM, will end up pulling the foot out or in, usually out,” Turcotte said.
Speed and fatigue are determined by timed walk tests of varying length (with and without a device), which also provide the therapist the opportunity to further observe gait patterns. Subjective questionnaires, such as the Modified Fatigue Impact Scale and the Borg Scale of Perceived Exertion during an endurance test, also are used to evaluate fatigue. Turcotte’s group uses the 4-minute and 6-minute walk tests, as well as the Timed Up and Go, or TUG, test that assesses balance and fall risk. Timed tests inform the PT whether a person can ambulate sufficiently fast with a device to be safe at home (0.4 m/s)  or in the community (0.8 m/s).
Therapists do provide an exercise program for affected lower-extremity muscles. However, if a person with MS has zero muscle strength in the tibialis anterior, the peroneal nerve will not innervate it, Turcotte said, adding, “In that case, there’s no exercise I can give to simulate what the FES system does.”
For a trial of FES, therapists walk along with the patient to manually control the parameters of the device. During the trial, Turcotte asks herself several questions: “Do I need to stimulate a second sooner? Is the foot ‘slapping’ the ground after it lands, so I need to hold onto the stimulation a little bit longer? Should I increase the intensity to increase muscle recruitment?”
|Hank Black is a freelance medical writer based in Birmingham AL|
Source Lower Extremity Review
Pros and Cons of Functional Electrical Stimulation for MS-Related Foot Drop in Everyday Health