It is often said that technology drives innovation. If true, we should be in for an exciting ride in the field of rehabilitation over the next few decades. Miniaturized microelectronics, advanced robotics, sophisticated data processing systems, and new modalities of stimulating the peripheral and central nervous system are inspiring rehabilitation scientists and clinicians to probe novel methods for restoring function in individuals with neurological disorders. This chapter provides an overview of existing and emerging technologies that are beginning to cross over from the laboratory to the clinic. Their underlying assumptions are outlined, mechanisms of action discussed, and advantages and limitations highlighted. In some cases, FDA approval exists for these new technologies and their approved application is noted. While this chapter is not all-encompassing, since the field is moving so fast, this chapter focuses on those technologies that are most likely to enter the clinical domain of rehabilitation medicine in the near future.

Transcutaneous electrical nerve stimulation (TENS) refers to the use of electrical current to stimulate peripheral nerves with skin surface electrodes, typically for the purpose of reducing chronic neuropathic pain, either due to peripheral or central injury. The physiological rationale for TENS-induced pain relief is thought to be dose-dependent inhibition of nociceptive nerve transmission. Various studies have used a wide range of intensity, pulse width, frequency, duration, and patterning, rendering generalizations about the efficacy of TENS clouded. A recent Cochrane Review concluded that the quality of evidence in sham-controlled studies to date has been low, and no strong recommendations can be made for nonpharmacologic treatments (including TENS) for neuropathic pain.^1,2 Other uses of TENS include treatment of rotator cuff tendinopathy, but again, high-quality studies are lacking.³ While TENS is generally well tolerated, Table 94–1 lists common contraindications for electrical therapy in general.

Similar to TENS, functional electrical stimulation (FES) uses pulses of electrical current to stimulate peripheral nerves. However, the term FES is usually restricted to electrical stimulation of peripheral nerves innervating the muscle(s) of interest, resulting in muscle contraction.⁴ FES systems have been used primarily in individuals with central nervous system injury for both functional or therapeutic purposes. Electrodes are commonly placed on the skin surface overlying the target nerve. More invasive means of directly implanting stimulating electrodes via percutaneous insertion into the muscle belly, or nerve cuffs around specific peripheral nerves, can be more muscle-specific, but are much less common due to their invasive nature and limitation to short-term treatment (Fig. 94–1).

In practice, the application of electrical currents over a peripheral nerve is much more complex, since the action potentials generated in the nerve propagate centrally as well as distally in both afferent and efferent fibers.⁶ Thus, in addition to direct stimulation of the large axons of alpha motor neurons, the large Ia sensory afferent fibers from muscle spindles are activated, and can trigger the Ia reflex response. Also, as the intensity of the FES stimulus is increased, the normal orderly recruitment of axons with different fiber diameters is not followed. Large fibers are preferentially activated with the lowest electrical currents, and the muscles innervated by these large fibers are the most fatigable. Beyond its direct effects on muscle contraction and sensory afferent fibers, FES also results in changes in cortical excitability and may induce long-term neuroplasticity in central structures.

Despite caveats regarding the specificity of axons based on size or termination, in small laboratory-based studies under controlled conditions, FES has shown promise as a potential therapy in stroke, spinal cord injury, multiple sclerosis, peripheral nerve injury, spasticity, weakness, and muscle atrophy, and commercial systems are currently available. However, randomized-controlled trials using FES are relatively scarce, and thus, the level of evidence is limited. A recent review of FES for improving respiratory function after spinal cord injury found some support for its use in both acute and chronic settings.⁷ Further, observational and experimental studies using FES for foot drop in multiple sclerosis has shown positive effects on gait speed,⁸ but again, randomized-controlled trials are still forthcoming. Randomized trials using FES in stroke are also limited, but efficacy has been shown in treating post-stroke spasticity and in shoulder subluxation.^9,10

Hybrid systems employing FES stimulators coupled with orthotic devices have become more popular recently, especially for upper extremity control. Simpler, FES-only systems have more frequently been used for the lower extremity, such as for stance. While systems used most often clinically are relatively simple systems, rehabilitation scientists envision sophisticated systems in the near future that allow control of stimulation from central commands, in a so-called brain-machine-interface (BCI) hybrid.^5,6,11

The development of BCI-FES hybrid systems may be feasible soon, largely due to recent advancements in device miniaturization and next-generation signal processing systems. Most systems to date, however, have not successfully incorporated sensory feedback from muscles and joints to allow continuously smooth response trajectories characteristic of normal human movement. Future systems are likely to utilize fully implantable sensors and stimulators (Fig. 94–2).¹²

Augmentative and alternative communication (AAC) refers to various forms of human communication other than oral speech. Individuals that may be aided by assistive technologies for AAC range from persons with central nervous system injury, neurodegenerative disorders, developmental/intellectual disorders, autism spectrum disorder, and other patients with special health care needs, such as mechanically ventilated patients with tracheotomies. The current overview will be limited to neurodegenerative conditions, such as amyotrophic lateral sclerosis (ALS), primary progressive aphasia (PPA), and Alzheimer’s disease (AD).¹⁴

General communication support includes alterations of the person’s environment and supportive practices of institutions and caregivers. Other communicative systems rely on technological approaches that are rapidly advancing. “No-tech” AAC approaches, or those requiring no equipment, include vocalizations, tongue clicks, eye movements, partner-assisted scanning, and formal sign languages. Low-tech AAC approaches use non-computer-based equipment, such as alphabet boards, or other forms of communication boards and books. Partner-assisted scanning, a no-tech approach, might be supplemented with pointers that the individual uses to indicate choices, rendering this a low-tech AAC approach.

The most advanced AAC systems employ sophisticated sensors, digital processing schemes, and portable computers to aid in communication. Various speech-generating devices (SGDs) are in this class of high-tech AAC systems. The user can type or select words/pictures/phrases that the SGD reads aloud, employing either prerecorded natural speech or computer-generated text-to-speech algorithms. Depending upon the limitations of the user, letters, words, and phrases can be selected using the hands, feet, head, or eyes. However, many individuals, such as those with advanced ALS, have only rudimentary eye movements remaining that limit their ability to generate inputs to SGDs. In locked-in syndrome, even these rudimentary movements are lost. A major effort among various laboratories around the world is attempting to overcome this unmet need, developing systems that can generate outputs to either computer keyboards or SGDs via neural signals. These systems are typically called BCI communication access methods.

In principle, neural signals can be derived either from implanted electrodes into motor areas of the brain, or from electroencephalography (EEG) signals from the surface of the scalp. Clearly, noninvasive systems are the first choice, but are not entirely reliable for all users. BCI-hybrid systems for communication bear some similarity to the BCI systems mentioned above for stimulating skeletal muscle. Unique challenges accompany the application of BCI technology to communications disorders, as the system must be able to accurately detect either the position of the eye on a target (e.g., a letter), or extract information from the brain that is correlated with the user’s selection of the target. In individuals with compromised nervous systems, the cognitive demand to successfully execute the task can be challenging and may require substantial training.

While a large number of computational algorithms are still under development, the most common approach is to utilize a specific slow-wave in the user’s EEG pattern, the P3 wave.¹⁵ The P3 wave is a positive deflection in the EEG signal that occurs about 300 milliseconds after the presentation of a sensory stimulus. It is elicited in the process of decision-making, and thus, is related more to an individual’s own reactions to the stimulus rather than to the physical properties of the stimulus itself. The user focuses on rows and columns of letters, eventually focusing on the desired letter, and the P3 wave is detected. In certain individuals with ALS, the P300-based BCI speller was found to be quite useful in communication.¹⁶ However, not all individuals are able to successfully use BCI-spellers. Ongoing improvement in the design of such systems revolves around developing the optimal stimulus to evoke the P300 response (gray or color intensification, auditory stimuli), improving the signal-to-noise properties of EEG electrodes, and integrating P300 signals and eye-tracking information.

Wheelchairs, as well as other mobility assistive equipment, are often prescribed for patients with spinal cord injury, stroke, amputation, and obesity. Appropriate wheelchair prescription requires an extensive examination, including the patient’s musculoskeletal, neurological, and cardiopulmonary status, the patient’s height and weight, and the abilities of the patient to propel or drive a manual or powered wheelchair. The Rehabilitation Engineering and Assistive Technology Society of North America (RESNA) has recommended guidelines for a team evaluation approach, including a seating therapist, usually an occupational or physical therapist, and a rehabilitation technology supplier.¹⁷

The basic components of manual wheelchairs are standard, and vary little between brands. Some models employ options, such as anti-tippers, that prevent the wheelchair from tipping backward when the patient either attempts to stand, or attempts to propel the wheelchair up an incline. Also, while costly, lightweight and ultra-lightweight wheelchairs can be appropriate choices for stroke patients with hemiplegia. Likewise, sports-style wheelchairs may be appropriate for low-SCI patients due to their light weight and maneuverability. Recliner wheelchairs may be appropriate for high-cervical SCI patients who have limited trunk and head control. Tilt-in-space wheelchairs, typically tilting from −5 degrees to 50 degrees, are options for patients who sit in wheelchairs for long periods of time, and require caregivers for assistance (Fig. 94–3). These wheelchairs provide pressure relief and weight shifting, reducing the incidence of pressure ulcers, and providing appropriate positioning for proper respiration and digestion. Finally, while most powered wheelchairs utilize a joystick directing the wheelchair’s speed and direction, severely disabled patients may not be able to use them. In this case, other control mechanisms are appropriate, such as chin control, sip-and-puff, tongue control, or other similar devices.

There have been several advances in wheelchair design that have been driven by the interest in wheelchair sports.¹⁸ With the large number of younger patients who experience SCI, wheelchair sports allow these individuals to build strength and stamina, and improve their outlook on life. The general principles for sports wheelchair design include the use of lightweight materials but maintaining stiffness, minimizing rolling resistance, and improving the fit for the user. Computer-aided design has allowed wheelchairs to be customized and scaled to the user’s needs. Different designs exist for the various sports where wheelchairs are implemented, such as basketball, tennis, softball, rugby, and racing.

Finally, advances in robotic design has instilled interest in smart wheelchairs.¹⁹ These wheelchairs combine the technology contained within a standard power wheelchair with a computer and a set of sensors, often with a robotic base where the seat is attached. Smart wheelchairs can assist with navigation, obstacle avoidance, transporting the user between pre-defined locations autonomously, and other autonomous tasks, such as stair climbing. It has been suggested that between 60% and 90% of wheelchair users would benefit, at least some of the time, from a smart wheelchair.²⁰ Commercialization of smart wheelchairs may be difficult given efforts to contain Medicare costs.