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The science behind mobility devices for individuals with multiple sclerosis
Medical Engineering & Physics 24 (2002) 375–383 www.elsevier.com/locate/medengphy
Review
The science behind mobility devices for individuals with multiple sclerosis Brain T. Fay a,b,d,∗, Michael L. Boninger a,b,c a
c
Human Engineering Research Laboratories, A VA Center of Excellence, Highland Drive VA Medical Center, 7180 Highland Dr, Pittsburgh, PA 15206, USA b Department of Rehabilitation Science and Technology, University of Pittsburgh, 5044 Forbes Tower, Pittsburgh, PA 15260, USA Department of Physical Medicine and Rehabilitation, University of Pittsburgh Medical Center, 201 Kaufman Bldg, Pittsburgh, PA 15213, USA d Department of Kinesiology and Health Education, University of Texas at Austin, 222 Bellmont Hall, Austin, TX 78712, USA Received 4 March 2002; received in revised form 26 March 2002; accepted 15 April 2002
Abstract There is a growing body of research related to prescription of mobility devices. This research enables clinicians and clients to make clinical decisions related to mobility based on sound research. Unfortunately, there is little research investigating appropriate prescriptions in degenerative disorders such as multiple sclerosis (MS). In this article we will review the literature on mobility devices in MS and how it can be used to assist with clinical decision-making considering the progressive nature of this condition. In addition, we will review other research not conducted on individuals with MS that is relevant to this population. Finally we will present a call for future research that should help address this critical area. 2002 IPEM. Published by Elsevier Science Ltd. All rights reserved. Keywords: Multiple sclerosis; Mobility; Assistive technology; Wheelchair
1. Background There are currently between 250,000 and 300,000 people with MS in the United States [1]. Although the exact cause of this disorder is unknown, it likely involves a combination of genetic predisposition and environmental contacts, probably early in life. The underlying cause of disability is a loss of myelin, the fatty insulator surrounding the axon extensions of neurons and possibly axonal loss. This loss is due to attack by the individual’s immune system, but is restricted to the central nervous system. The course of MS is variable; however, the most common course is relapsingremitting, present in over 80% of individuals with MS [1]. In this form of MS, symptoms occur over a period of several days, stabilize and, with treatment, may improve. Unfortunately, over time there is usually a steady progression of worsening neurologic symptoms. One aspect
somewhat unique to MS is that symptoms not only vary between individuals, but in a single individual symptoms can vary from day to day and hour to hour. This variability of symptoms may be one reason for the lack of research on mobility devices for individuals with MS. MS is most commonly diagnosed in females in early adulthood. The symptoms of MS include fatigue, ataxia, weakness, sensory loss, spasticity, and others. An excellent review of the pathophysiology and treatment is present by Noteworthy et al. in the New England Journal of Medicine [2]. Although fulminate cases may result in death within months, the majority of individuals have near normal life expectancy. These statistics highlight the fact that the majority of individuals with MS live a significant portion of their lives with a mobility restriction that requires assistive technology intervention.
2. Mobility and quality of life Corresponding author. Tel.: +1 512 232 2684; fax: +1 512 471 8914. E-mail address: [email protected] (B.T. Fay). ∗
The symptoms of MS have a profound effect on mobility. Within 15 years of onset, 50% of individuals will require assistance with walking [2]. A 1983 study
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by Baum and Rothschild has demonstrated reduced mobility in the population with advanced MS [3]. Over 50% (⬎50%) of people with MS surveyed in this study required assistance both in and out of the home. The most common mode of assistance was a wheelchair. The help of another person and, more rarely, the use of a crutch or leg brace followed. Such work has demonstrated the need of mobility devices for people with MS. The ability to interact with one’s environment is often taken for granted, possibly due to the “recovery” following an exacerbation. The basic nature of personal mobility is that it allows people to interact in their environment and society. A greater ability to interact allows for more varied and stimulating contacts with family, friends, occupation and society. Given that humans are social beings, quality of life is closely correlated with mobility. Quality of life is dependent on the individual person’s perception of a disease and how it affects them. Given that MS is a progressively degenerative condition, differences in symptoms can vary widely from person to person. This variation in symptoms has been shown to affect individual attitude. Evers and Karnilowski [4] evaluated attitude as a function of disease state in a study of 243 people with MS. Using a scale of reasoned action [5], results demonstrated those individuals in remission were significantly more positive than persons with more progressed symptoms. Such an effect on attitude often affects measures of quality of life. Aronson [6] demonstrated this via a study in which persons with MS completed quality of life questionnaires and measures of physical disability. Reduced quality of life was associated with factors indicative of reduced mobility such as the inability to ascend stairs, fatigue and reduced social activity. Statistically validated scales exist to assist the clinician in assessing quality of life. The Functional Assessment of Multiple Sclerosis (FAMS) developed by Cella, et al. [7] brings together the multi-dimensional aspects of quality of life including physical functioning, social functioning and emotional well-being. Validation of this instrument has shown it to be prognostic of scales concerned with physical function and neurological impairment. Thus, the FAMS provides the clinician with a tool to use in developing an understanding of the person’s quality of life, relative to factors indicative of mobility. A test that can provide more general characterization of quality of life is the SF-36 [8]. This scale is more concerned with the perception of disease effects and is attuned to the early effects of multiple sclerosis [9].
3. Research concerning assistive technology in MS Extensive reviews of reference databases such as Medline, EI Compendix and PyscInfo concerned with
medical, engineering and psychological topics resulted in few studies directly related to the application of assistive technologies for people with MS. Instead, research concerning MS appears to be almost exclusively concerned with determining clinical treatment regimens and the cause of the disease. While some medical and therapy texts discuss the use of assistive technology with this population, the basis for any recommendations is not referenced to quantitative research. In one of the few studies identified, Perks, et al. [10] evaluated a population of manual wheelchair users in Scotland. It was found that 15% of manual wheelchair users had MS. Of these individuals with MS, a high percentage (59%) stated they did not feel their current wheelchair met their mobility needs. This resulted in difficulty moving about their home and outdoors. This study demonstrates the lack of appropriate mobility devices amongst a population of individuals with MS. Page, et al. [11] noted the incidence of MS in Scotland to be similar to that of the United States. Further investigation into the type of wheelchairs provided and used in the United States is required to verify the concerns found in Scotland. Given the lack of research activities concerning assistive technology for people with MS, health care professionals and researchers are best referred to relevant information in the body of work concerned with assistive technologies for other disabilities such as spinal cord injury (SCI) or cerebral palsy (CP).
4. Assistive technology research applicable to MS 4.1. Appropriate timing Since MS is a degenerative disease, the clinician should be mindful of the past clinical history of the client. An individual with the relapsing–remitting form that displays rare exacerbations may maintain the ability to walk for quite some time. Conversely, a person with the progressive form may require more active involvement of neurologists, physiatrists, physical therapists or occupational therapists in addressing the need for mobility. In addition to careful review of the client’s progression, the clinician should also consider the particular symptoms that are manifest, since these often vary between individuals with MS, in the case of spasticity and fatigue can vary depending on the time of day. Typical physical effects due to the progression of MS have been documented [12–14]. It is important to note demyelination can occur throughout the CNS and as a result there is no priority to motor control difficulties in any particular limb other than to say spasticity, ataxia and/or weakness proceed paralysis. Thus, the individual who reaches a point at which they are not able to walk with assistance may or may not be able to use a device
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such as a manual wheelchair. This is an important distinction when considering the following presentation of mobility interventions. Clinicians may benefit from the information provided by standardized disability scales tailored to MS. The Kurtzke Expanded Disability Status Scale (EDSS) [15] is an effective tool for obtaining a quick estimate of motor ability in people with MS [16] who are ambulatory. Recent work by Sharrack and Hughes [17] has developed the Guys Neurologic Disability Scale (GNDS) which is more responsive in characterizing mobility in both ambulatory and nonambulatory people with MS. The GNDS provides independent measures of function in various “domains” such as upper extremity function, lower extremity function, cognition, bowel and bladder function and others. This organization is of particular use to clinicians wishing to investigate a particular functional domain.
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tional electrical stimulation (FES). Since drop foot in MS results from damage to the central nervous system, the muscle is intact though it may be atrophied. Taylor, et al. [21] have investigated the use of a FES device known as the Odstock Dropped Foot Stimulator (ODFS). The ODFS provides stimulation to the common peroneal nerve and motor point of the tibialis anterior muscle. Stimulation is timed using a pressure switch placed in the shoe. In clinical trials, 21 individuals with MS were fitted with the ODFS and used the device for a period of 4.5 months. Changes in walking speed and effort were recorded in walking a 10-meter course. Results showed walking speed increased significantly (p⬍0.05) and effort decreased significantly (p⬍0.05). These results are promising, but do not address some of the downsides of FES raised by other studies such as rapid muscle metabolic exhaustion [22] and reduced ability to simulate the same motor point [23].
4.2. Gait modification 4.3. Appropriate cane usage and indications Normal human gait is a very efficient mode of mobility in which the weight of the trunk is balanced upon the pelvis via synchronized movement of the upper and lower extremities. Due to the efficiency of this activity, many people with MS are inclined to continue walking even when the operation of this synchronized system is disturbed. Research by Olgiati, et al. [18] has evaluated the relative contributions of symptoms common to the person with MS such as spasticity, ataxia and weakness. This work has shown the cost of walking via VO2 consumption to be increased by all three symptoms with a larger effect caused by spasticity but with contributions due to ataxia and weakness. Readers seeking a more extensive review of gait characteristics in MS are referenced to a review by Benedetti, et al. [19]. To test the effect of exercise on impaired gait, Rodgers, et al. investigated the effect of a six month aerobic training program on gait abnormalities in MS [20]. Results suggested a minimal effect on gait characteristics such as ankle dorsi/plantar flexion, knee flexion/extension and hip extension. Given these findings, exercise with a motor learning focus may be more applicable. When therapies do not help address gait difficulties, assistive devices may be of benefit. For example, devices exist to assist with “Drop Foot”, a common symptom of people with MS that interferes with normal gait. In drop foot, the dorsi-flexors of the ankle do not contract sufficiently to raise the foot during the swing-phase of gait. This results in the distal end of the foot contacting the ground. A common gait adaptation to address drop foot is to swing the foot out laterally during the swing phase. An effective clinical solution for drop foot is the use of an ankle–foot orthosis (AFO) which allows for dorsiflexion of the foot but not plantar-flexion. Another option that exists for the individual with MS is func-
When presented with ataxia and weakness, canes may provide a simple, but effective solution for the person with MS. Blount [24] provides a description of the mechanics of cane usage in a classic article. Herein, canes are described as an appropriate assistive gait device for persons with a variety of gait limiting concerns. Canes assist the individual in maintaining the even distribution of weight on the hips that is characteristic of normal human gait. This has the effect of reducing the effort of walking and prevents the development of repetitive strain injuries at the hip. Canes also provide a means of reducing falls. In a study of eight people with peripheral neuropathy and age-gender matched controls, Ashton-Miller, et al. [25] studied the response to frontal plane tilt of the floor surface to study participants as they performed a weight transfer task both with and without a cane. Perturbations were provided via two rapid changes in angle (±2° and ±4°) and performed with and without visual feedback. Results showed the fall rates of the case group to be significantly higher (p=0.036) than that of the control group when both groups were not using a cane and had visual feedback. Removing visual feedback caused falls in the case group to increase four times. Use of a cane in the hand contra-lateral to the weight transfer, caused a significant decrease in the number of falls in the case group and brought the fall rate below that of the control group when not using the cane. These studies demonstrate the scientific validity of cane use to address symptoms such as spasticity, ataxia, weakness and poor balance. Canes are an important assistive device for ambulatory individuals with MS given the increased cost of walking due to ataxia and weakness, the physics of cane use, and the prevention of falls found during cane use.
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However, the benefit of a cane is debatable without proper prescription. The Merck Manual of Diagnosis and Therapy [26] notes a properly sized cane should be held in the hand contra-lateral to the involved limb and provide 25°-elbow flexion when vertical. Gait should be initiated with the uninvolved limb, with the cane and involved limb following. Canes are also available with platform (4-leg) bases to provide greater stability for users with upper arm weakness or ataxia. It should be noted that canes are available in a wide variety of aesthetic designs which can allow for personal expression. 4.4. Use of walkers Persons with MS who experience continued lack of balance using a cane may find better stabilization by using a walker. Walkers provide increased stability due to the footprint of the four legs. In addition, walkers can be purchased with wheels, brakes and modified handgrips to aid in their effective use. Wheeled walkers may have two or four wheels. Braking of the wheeled walker may be automatic when sufficient weight is applied or may be activated via hand brake controls similar to a bicycle. Adapted handgrips can allow user-to-walker interfaces with large diameter tubing for individuals with reduced gripping abilities or with armrests for persons with non-functional hands. Walkers are typically foldable to aid in storage when traveling. 4.5. Appropriate manual wheelchair selection, configuration and training Part-time use or an exclusive move to wheeled mobility is required for individuals with MS who, despite interventions to address gait disturbances, are experiencing undo difficulty in balance or have fallen. Manual wheelchairs provide a wheeled option, but still allow for physical activity. It is important for the clinician to understand research, which has documented variables in the stability, physiology, propulsion, training and durability of the manual wheelchair prior to making recommendations. Work within the past 20 years has demonstrated the characteristics of the static [27] and dynamic [28] stability of the manual wheelchair. The static stability is described by the tendency of the wheelchair to tip to the rear, front and sides when at rest. Since most wheelchairs come with a standard size rear wheel, rearward stability is determined by the position of the rear axle relative to the user:wheelchair center of gravity [27]. Forward stability can be affected by the diameter of the front casters, but due to the small range in these values is similarly dependent on the user’s center of gravity. Side-toside stability can be influenced by the use of camber, which effectively increases the footprint of the wheelchair without largely affecting the center of gravity. Unfor-
tunately, increasing camber adds to the width of a wheelchair and can limit access to tight space. Determinants of dynamic stability are manifest largely in the same variables as static stability. However, depending on the user’s ability to manipulate the wheelchair, reduced stability has its benefits. For example, placing the rear wheel axle forward near the horizontal location of the center of gravity places more of the system’s weight over the rear wheel thus reducing the amount of energy required to propel the wheelchair and making wheelchair maneuvers such as a curb defying “wheelie” possible [28]. However, good motor control is needed to perform a wheelie and further to assure that ramps are negotiated safely in a chair with more weight over the rear wheels. An understanding of the physiology of manual wheelchair propulsion is important when considering persons with MS for a manual wheelchair. One of the benefits of a manual wheelchair can be the physical exercise it affords the user. Conversely, the amount and type of physical exercise a person with MS engages in can cause fatigue. A study by van der Woude, et al. [29] quantified physiologic variables of propelling a manual wheelchair on differing inclines. Mean oxygen consumption (VO2) and heart rate increased with increasing angle of inclination from a low of 0.59 l/min and 93 bpm on a level surface to 1.23 l/min and 125.5 bpm at an angle of 3°. Further research into physiologic limitations of individuals with MS is needed to determine if these values would limit manual wheelchair use. A growing body of literature exists on the proper configuration of the manual wheelchair, its use and the characteristics of the user. A stable seating surface is an initial concern in prescribing a properly configured wheelchair. Pressure measurement systems are available which allow the clinician to quantify the pressure at the user:seat interface. This allows for evaluation of seating systems that help reduce the interface pressure. This evaluation can be conducted during an examination so that a proper seating system can be chosen. This is of primary concern to individuals who remain in the wheelchair throughout the day since it can help to prevent the development of decubitus ulcers (pressure sores). In a study of wheelchair users with paraplegia, Boninger, et al. [30] investigated the relationship between pushrim forces, weight and median nerve injury at the wrist. This study demonstrated that weight of the user is significantly correlated with an increase in propulsive forces at the pushrim and the incidence of median nerve injury at the wrist. Recommendations are for manual wheelchair users to be vigilant in maintaining a healthy weight in consultation with their health care providers and for wheelchair users to be provided with lighter wheelchairs. It has been demonstrated via clinical data that approximately 50% of manual wheelchair users with spi-
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nal cord injury will develop repetitive strain injuries in either the wrist, elbow or shoulder within the first ten years of wheelchair use [31]. Although these injuries may not be as prevalent in MS clinicians should be aware of how wheelchair set up may affect risk of injury. Boninger, et al. [32] studied 40 wheelchair users with paraplegia to determine the effect of axle position on biomechanical factors of wheelchair propulsion which have been correlated with median nerve injury at the wrist. When propelling slightly greater than walking speed (2 mph), it was found that the horizontal distance between the shoulder of the user at rest and the axle was significantly correlated with the frequency of propulsion (p⬍0.01), the rate of rise of the propulsive force (p⬍0.05) and the push angle (p⬍0.05) at two speeds of propulsion. Frequency of propulsion may contribute to median nerve injury at the wrist since the hand is impacting the pushrim and experiencing micro-trauma. Similarly, the rate of rise of the propulsive force relates the magnitude of hand impact at pushrim contact. A greater rate of rise may cause increased micro-trauma. Lastly, the push angle relates the distance through which the propulsive force produces work. Shorter push angle input, less work to the system. These results are summarized in Fig. 1. Recommendations are to provide wheelchair users with adjustable axles that allow adjustment of the horizontal position according to the users abilities. Given the demonstrated issues surrounding manual wheelchair use, attempts have been made to develop protocols for training wheelchair users in healthy methods of wheelchair propulsion. One trainable characteristic of wheelchair propulsion is the manner in which the hand moves as it contacts the pushrim, propels the wheelchair and the returns to start another cycle. This motion is commonly termed “propulsion patterns” in the literature.
Fig. 1. Effects of manipulating the rear-wheel axle position of the manual wheelchair.
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In a recent study by Boninger, et al. [33], 38 subjects with paraplegia propelled a wheelchair while bilateral motion of the upper extremity and pushrim forces and moments were recorded. Results demonstrated the existence of four distinct propulsion patterns (Fig. 2). Statistical analyses were conducted to determine relationships between specific patterns and the force generated at the pushrim. Findings showed reduced frequency of propulsive strokes when a semi-circular propulsion pattern was used. In the semi-circular pattern, the hand follows the pushrim during the push phase of propulsion and then swings down below the pushrim as it moves back to engage the pushrim. This pattern led to a longer period of time spent in the push phase relative to the recovery phase. It was suggested that clinicians consider training wheelchair users in this style of propulsion in an effort to reduce the cumulative trauma imparted on the wheelchair user’s hand and wrist. In addition to concerns related to the user and user wheelchair interaction, wheelchair users should be confident of the structural integrity of their wheelchair. Failure of any component is more than an inconvenience for the wheelchair user. It is the limitation of their mobility. A series of standards have been developed by the American National Standards Institute (ANSI) and the Rehabilitation Engineering and Assistive Technology Society of North American (RESNA) in order to address these concerns [34]. Tests included in the standards protocol include the “curb drop” and “double drum” (Fig. 3). In the curb drop, the wheelchair is lifted 5.0 cm and dropped to the ground. In the double drum test, the wheelchair is placed two independent rollers (rear wheels on one roller and the front on the other). Each roller has two 1.0 cm high×2 cm wide slats which run from the center to the end of the roller and are positioned 180° out-of -phase. The rear drum turns at 1m/s whereas the front roller turns 5% faster so as to change the perturbations imparted to the chair over time. A study by Fitzgerald, et al. [35], performed the International Organization for Standardization (ISO) standards testing with three classifications of manual wheelchairs. The classes followed Medicare definitions of K1 (hospital-type), K4 (lightweight) and K5 (ultralight). The study performed the curb-drop and double-drum test on 25–K1 (hospital-type), 14–K4 (lightweight) and 22–K5 (ultralight) wheelchairs. Using ISO equivalent number
Fig. 2. Propulsion patterns of manual wheelchair propulsion as described by Boninger, et al. [33]. The gray line represents the path of a marker on the hand a an individual propels a wheelchair. The dark circle represents the pushrim of the wheelchair. The semicircular pattern was found to be most advantageous.
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Fig. 3.
The Curb Drop and Double Drum test stands.
of testing cycles, curb-drop and double-drum tests where expressed as a single variable and Kaplan-Meier survival curves were determined. The fatigue life of K5 (ultralight) wheelchairs was significantly greater (p⬍0.05) than both the K4 (lightweight) or K1 (hospitaltype) wheelchairs. Since ISO testing is based on a 5year life cycle, it was concluded that K4 (lightweight) and K1 (hospital-type) wheelchairs might not last the typical 3–5 year period expected by health insurers. A better investment may be in the K5 (ultralight) despite its initial high cost. These wheelchairs also have reduced rolling resistance making propulsion easier. 4.6. Power assisted wheelchairs A developing class of wheelchairs provides a power assist when desired, but allows the user to push the wheelchair as one would with a manual wheelchair. An example of the power assisted wheelchair is the JWII [2]. This wheelchair has a force/moment-sensing pushrim that provides an additional torque to the rear-axle proportional to the applied moment. Such devices have potentially important benefits such as enabling people normally provided with power wheelchairs to self-propel a wheelchair despite obstacles such as steep ramps. These potential benefits were recently demonstrated in a study of the JWII device [36]. Using the JWII, subjects demonstrated significantly lower oxygen consumption (p⬍0.0001) and heart rate (p⬍0.0001). Subjects completed some tasks significantly faster than with their personal wheelchair, but encountered difficulty transferring to/from the JWII and in disassembling the JWII for transport. Other brand options besides the JWII are available for purchase; however, research-based studies concerning these devices do not appear in the literature. For people with MS, the power-assisted wheelchair may prove to be a good compromise between the fatigue caused by using a manual wheelchair and the lack of exercise experienced in driving a power wheelchair.
4.7. Appropriate power wheelchair selection and configuration
The person with MS may need to move to a powered mobility solution given the degenerative nature of the disease. However, unlike other conditions such a quadriplegia, in which the user is solely dependent on the power wheelchair, persons with MS may be good candidates even when some ability to walk is still present. In this case, the power wheelchair is used to help limit fatigue. Power wheelchairs are available in a variety of designs. Each design is often available with a number of customization features. The basic designs have vastly different drive mechanisms characterized by rear-wheel, mid-wheel and forward-wheel drives [30]. These different types of power wheelchairs require training to learn the idiosyncrasies of the respective drive mechanisms. Rear-wheel drive power wheelchairs “feel” much like driving a car. Strengths of the rear-wheel drive include larger diameter drive wheels and intuitive control. Weaknesses include reduced maneuverability in tight spaces and reduced ability to climb over obstacles. Midwheel drive power wheelchairs are based on the premise that the center of gravity of the user is best placed over the drive wheels. This allows for improved maneuverability since these wheelchairs can turn on the vertical axis of the user. Weaknesses of mid-wheel drive wheelchair include the need for both front and rear tip casters that extend the length of the wheelchair and can cause the wheelchair’s drive wheels to become suspended off the ground when entering or leaving a steep incline. Mid-wheel drive wheelchairs also typically require a period of training to adapt to the sensation of being turned about one’s vertical axis. Front-wheel drive power wheelchairs provide for good obstacle climbing characteristics. They suffer from having the casters in the back of the wheelchair where they cannot be seen
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by the user which may complicate maneuverability of the wheelchair. Given the greater bulk of the power wheelchair and the advancement of the user’s disability, seating systems are often required. Similar to the systems mention previously for manual wheelchairs, the main goals are to provide comfort, function, and reduce the pressure between contacting surfaces of the user and wheelchair. Power wheelchair users may require more extensive adaptations to the seating system than do manual wheelchair users. Such adaptations can include inserts to aid in the positioning of the legs and trunk. Additionally, users with fatiguing conditions such as MS may benefit from a wide variety of headrests. Another important feature of power wheelchairs include tilt-in-space seats that allow the user to recline the back while the seat rotates upward at the same rate. This prevents significant shear forces between the user and the seat backrest. Tilt-in-Space wheelchairs are desirable because they allow the user to perform pressure relief to the buttocks and can aid in attaining and maintaining a proper seated position. The control interface can have a major effect on the success or failure of a power wheelchair as a mobility device. Basic controllers employ a proportional control scheme that monitors the displacement of a joystick. More elaborate programmable controllers allow for monitoring of the speed at which the joystick is displaced. The controller used has major implications for people with MS, since ataxia of the upper extremities is a concern in the later stages of the disease. Much like manual wheelchairs, ANSI/RESNA standards have been formulated to verify the integrity of the systems. Recent work by Algood, et al. [37] tested the power and control systems of five different wheelchair models using Section 14 of the ANSI/RESNA standards. Wheelchair vendors included in the study were Invacare, Sunrise Medical, Everest & Jennings, Permobil and Pride Mobility. The most common failure was with the battery connections and fuses that were not labeled properly (all models). Some wheelchairs failed when they were drivable with the battery charger plugged into the wheelchair but not the wall outlet (Sunrise Medical, Permobil). Additionally, one wheelchair did not provide for reverse polarity protection, which caused the controller to be damaged (Invacare). Another study by Vitek, et al. [38] investigated the static, impact and fatigue testing of three power wheelchairs of the vendors Invacare, Sunrise Medical, Everest & Jennings, Permobil and Pride Mobility. Three wheelchairs failed static tests of pushing a pulling on the footrests (Everest & Jennings), while three wheelchairs failed a static test of pulling up on the armrest (Sunrise Medical). One wheelchair failed the double drum test describe earlier (Everest & Jennings), while two wheelchairs failed the curb drop test (Permobil). As can be
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seen, ANSI/RESNA standards testing results can be an important piece of information in deciding which wheelchairs to recommend or purchase. Axelson, et al. [39] has authored an excellent text describing how to use these standards in purchasing a wheelchair. 4.8. Appropriate scooter selection and configuration Scooters are a popular mode of powered mobility amongst persons with MS. Commonly, an individual who is experiencing difficulties in gait, such as excessive muscular fatigue, will use a scooter as an energy conservation device so that walking is limited to short distances. Some users prefer the scooter to a manual wheelchair since upper extremity fatigue is not an issue. Scooters typically have either three or four wheels, with the rear wheels serving as the drive mechanism. Steering is accomplished via hand-bars that are intuitive to users who previously used a bicycle. Seating is provided in a chair having foam padding typical of a carseat. The backrest height ends at the level of the shoulder blades, which allows for unencumbered rotation of the trunk. Scooters are less desirable then power wheelchairs when considering dynamic stability. Standards testing comparing scooter and power wheelchair stability was completed by Rentschler, et al. [40] In this study, five front-wheel drive power wheelchairs, five rear-wheel drive power wheelchairs and five 4-wheel scooters were tested according to ANSI/RESNA wheelchair standards Section 2 (dynamic stability). This study demonstrated that front and rear-drive wheelchairs were significantly more stable than were scooters during dynamic braking tests on 6° and 10° slopes. It is important to note these test were conducted with a 4-wheel scooter and that 3wheel scooters would likely be more unstable. In general scooters are an options for individuals who retain trunk balance, upper extremity control and strength, and do not have a progressive course of MS. In scooters there is limited ability to modify the seat or provided additional functions such as tilt in space. In addition, the use of a tiller for steering requires good arm strength and joysticks are not an option. For these reasons scooters are a poor choice for individuals with advanced neurologic dysfunction. These limitations need to be considered in light of the progression of the disease.
5. Current and future research The mobility needs of people with MS are an important, real-life question. While concerns regarding inter-group variability are important, they should not preclude investigation of the science behind mobility. Instead, studies with carefully considered protocols and
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judicious choice of study variables and methods are required. Research into quality of life, determinants of activity levels, and appropriate mobility devices should be conducted. Such studies are required to determine the usage patterns of people with MS employing differing mobility devices as a function of disease progression. In the meantime clinicians need to rely on literature from other populations when assisting their patients in decisions related to mobility devices.
[15]
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[17]
[18]
Acknowledgements The US Department of Veterans Affairs Center of Excellence for Wheelchairs and Related Technology (grant #F2181C).
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a population-based study in Olmsted county, Minnesota. Neurology 1994;44:28–33. Kurtzke JF. Rating neurologic impairment in multiple sclerosis: an expanded disability status scale (EDSS). Neurology 1983;33:1444–52. Hohol MJ, Orav EJ, Weiner HL. Disease steps in multiple sclerosis: a simple approach to evaluate disease progression. Neurology 1995;45(2):251–5. Sharrack B, Hughes RAC. The Guy’s neurological disability scale (GNDS): a new disability measure for multiple sclerosis. Multiple Sclerosis 1999;5:223–33. Olgiati R, Burgunder JM, Mumenthaler M. Increased energy cost of walking in multiple sclerosis: Effect of spasticity, ataxia, and weakness. Archives of Physical Medicine and Rehabilitation 1988;69:846–9. Benedetti MG, Piperno R, Simoncini L, Bonato P, Tonini A, Goiannini S. Gait abnormalities in minimally impaired multiple sclerosis patients. Multiple Sclerosis 1999;5:363–8. Rodgers MM, Mulcare JA, King DL, Mathews T, Gupta SC, Glaser RM. Gait characteristics of individuals with multiple sclerosis before and after a 6-month aerobic training program. Journal of Rehabilitation Research and Development 1999;36(3):183–8. Taylor PN, Burridge JH, Dunkerley AL, Wood DE, Norton JA, Singleton C et al. Clinical use of the Odstock dropped foot stimulator: its effect on the speed and effort of walking. Archives of Physical Medicine and Rehabilitation 1999;80:1577–83. Levin O, Mizrahi J. EMG and metabolite-based prediction of force in paralyzed quadriceps muscle under interrupted stimulation. IEEE Transactions on Rehabilitation Engineering 1999;7(3):301–14. Mayr W, Bijak M, Girsch W, Lanmuller H, Rafolt D, Sauermann S, et al., Functional electrostimulation via implants: applications, limitations, perspectives. Interdisciplinary Aspects on Computers Helping People with Special Needs. 5th International Conference, ICCHP 1996. Osterreichische Computer Gesellschaft, Wien, Austria; 1996; 2 vol. 792 pp. p.311–17 vol.1. Blount WP. Don’t throw away the cane. Journal of Bone and Joint Surgery 1956;38-A(3):695–708. Ashton-Miller JA, Yeh M, Richardson JK, Galloway T. A cane reduces loss of balance in patients with peripheral neuropathy: Results from a challenging unipedal balance test. Archives of Physical Medicine and Rehabilitation 1996;77(6):446–52. The Merck manual of diagnosis and therapy, 16th edition. Rahway, N J: Merck Sharpe & Dohme Research Laboratories. 1993. Kirby RL, Ackroyd-Stolarz SA, Brown MG, Kirkland SA, MacLeod DA. Wheelchair-related accidents caused by tips and falls among noninstitutionalized users of manually propelled wheelchairs in Nova Scotia. Archives of Physical Medicine and Rehabilitation 1994;73(5):319–30. Cooper RA. Wheelchair selection and configuration. New York, NY: Demos Medical Publishing, 1998. van der Woude LHV, van Kranen E, Ariens G, Rozendal RH, Veeger HEJ. Physical strain and mechanical efficiency in hub crank and handrim wheelchair propulsion 1995;19(4):123–131. Boninger ML, Cooper RA, Baldwin MA, Shimada SD, Koontz AM. Wheelchair pushrim kinetics: Body weight and median nerve function. Archives of Physical Medicine and Rehabilitation 1999;80(8):910–5. Gellman H, Sie I, Waters R. Late complications of the weightbearing upper extremity in the paraplegic patient. Clinical Orthopedics and Related Research 1988;233(8):132–5. Boninger ML, Baldwin MA, Cooper RA, Koontz AM, Chan L. Manual wheelchair pushrim biomechanics and axle position. Archives of Physical Medicine and Rehabilitation 2000;81(5):608–13. Boninger ML, Souza AL, Cooper RA, Fitzgerald SG, Koontz AM, Fay BT. Propulsion patterns and pushrim biomechanics in
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manual wheelchair propulsion. Archives of Physical Medicine and Rehabilitation. [In Press]. American National Standards Institute. American nationals standards for wheelchairs-volume1: requirements and test methods for wheelchairs (including scooters). New York, NY: American National Standards Institute, 1998. Fitzgerald SG, Cooper RA, Boninger ML, Rentschler AJ. Comparison of fatigue life for three types of manual wheelchairs. Archives of Physical Medicine and Rehabilitation. [In Press] Cooper RA, Fitzgerald SF, Boninger ML, Prins K, Rentschler AJ, Arva J et al. Evaluation of a pushrim-activated, power-assisted wheelchair. Archives of Physical Medicine and Rehabilitation 2001;82:702–8. Algood SD, Cooper RA, Rentschler AJ, Vitek JM, Ammer WA, Wolf EJ. Power and control system testing of five different types
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of power wheelchairs. Proceedings of the 2001 RESNA Annual Conference. Reno, NV. 22–26 June 2001. [In Press] [38] Vitek JM, Cooper RA, Rentschler AJ, Algood SD, Ammer WA, Wolf EJ. Static, impact, and fatigue testing of five different types of electric powered wheelchairs. Proceedings of the 2001 RESNA Annual Conference. Reno, NV. 22–26 June 2001. [In Press] [39] Axelson P, Minkel J, Chesney D. A guide to wheelchair selection: how to use the ANSI/RESNA wheelchair standards to buy a wheelchair. Washington, DC: Paralyzed Veterans of America. 1994. [40] Rentschler AJ, Cooper RA. A comparison of the dynamic and static stability of power wheelchairs versus scooters. Proceedings of the 21st Annual Conference of the Engineering in Medicine and Biology Society. 13–16 October 1999. Atlanta, GA.
Review
The science behind mobility devices for individuals with multiple sclerosis Brain T. Fay a,b,d,∗, Michael L. Boninger a,b,c a
c
Human Engineering Research Laboratories, A VA Center of Excellence, Highland Drive VA Medical Center, 7180 Highland Dr, Pittsburgh, PA 15206, USA b Department of Rehabilitation Science and Technology, University of Pittsburgh, 5044 Forbes Tower, Pittsburgh, PA 15260, USA Department of Physical Medicine and Rehabilitation, University of Pittsburgh Medical Center, 201 Kaufman Bldg, Pittsburgh, PA 15213, USA d Department of Kinesiology and Health Education, University of Texas at Austin, 222 Bellmont Hall, Austin, TX 78712, USA Received 4 March 2002; received in revised form 26 March 2002; accepted 15 April 2002
Abstract There is a growing body of research related to prescription of mobility devices. This research enables clinicians and clients to make clinical decisions related to mobility based on sound research. Unfortunately, there is little research investigating appropriate prescriptions in degenerative disorders such as multiple sclerosis (MS). In this article we will review the literature on mobility devices in MS and how it can be used to assist with clinical decision-making considering the progressive nature of this condition. In addition, we will review other research not conducted on individuals with MS that is relevant to this population. Finally we will present a call for future research that should help address this critical area. 2002 IPEM. Published by Elsevier Science Ltd. All rights reserved. Keywords: Multiple sclerosis; Mobility; Assistive technology; Wheelchair
1. Background There are currently between 250,000 and 300,000 people with MS in the United States [1]. Although the exact cause of this disorder is unknown, it likely involves a combination of genetic predisposition and environmental contacts, probably early in life. The underlying cause of disability is a loss of myelin, the fatty insulator surrounding the axon extensions of neurons and possibly axonal loss. This loss is due to attack by the individual’s immune system, but is restricted to the central nervous system. The course of MS is variable; however, the most common course is relapsingremitting, present in over 80% of individuals with MS [1]. In this form of MS, symptoms occur over a period of several days, stabilize and, with treatment, may improve. Unfortunately, over time there is usually a steady progression of worsening neurologic symptoms. One aspect
somewhat unique to MS is that symptoms not only vary between individuals, but in a single individual symptoms can vary from day to day and hour to hour. This variability of symptoms may be one reason for the lack of research on mobility devices for individuals with MS. MS is most commonly diagnosed in females in early adulthood. The symptoms of MS include fatigue, ataxia, weakness, sensory loss, spasticity, and others. An excellent review of the pathophysiology and treatment is present by Noteworthy et al. in the New England Journal of Medicine [2]. Although fulminate cases may result in death within months, the majority of individuals have near normal life expectancy. These statistics highlight the fact that the majority of individuals with MS live a significant portion of their lives with a mobility restriction that requires assistive technology intervention.
2. Mobility and quality of life Corresponding author. Tel.: +1 512 232 2684; fax: +1 512 471 8914. E-mail address: [email protected] (B.T. Fay). ∗
The symptoms of MS have a profound effect on mobility. Within 15 years of onset, 50% of individuals will require assistance with walking [2]. A 1983 study
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by Baum and Rothschild has demonstrated reduced mobility in the population with advanced MS [3]. Over 50% (⬎50%) of people with MS surveyed in this study required assistance both in and out of the home. The most common mode of assistance was a wheelchair. The help of another person and, more rarely, the use of a crutch or leg brace followed. Such work has demonstrated the need of mobility devices for people with MS. The ability to interact with one’s environment is often taken for granted, possibly due to the “recovery” following an exacerbation. The basic nature of personal mobility is that it allows people to interact in their environment and society. A greater ability to interact allows for more varied and stimulating contacts with family, friends, occupation and society. Given that humans are social beings, quality of life is closely correlated with mobility. Quality of life is dependent on the individual person’s perception of a disease and how it affects them. Given that MS is a progressively degenerative condition, differences in symptoms can vary widely from person to person. This variation in symptoms has been shown to affect individual attitude. Evers and Karnilowski [4] evaluated attitude as a function of disease state in a study of 243 people with MS. Using a scale of reasoned action [5], results demonstrated those individuals in remission were significantly more positive than persons with more progressed symptoms. Such an effect on attitude often affects measures of quality of life. Aronson [6] demonstrated this via a study in which persons with MS completed quality of life questionnaires and measures of physical disability. Reduced quality of life was associated with factors indicative of reduced mobility such as the inability to ascend stairs, fatigue and reduced social activity. Statistically validated scales exist to assist the clinician in assessing quality of life. The Functional Assessment of Multiple Sclerosis (FAMS) developed by Cella, et al. [7] brings together the multi-dimensional aspects of quality of life including physical functioning, social functioning and emotional well-being. Validation of this instrument has shown it to be prognostic of scales concerned with physical function and neurological impairment. Thus, the FAMS provides the clinician with a tool to use in developing an understanding of the person’s quality of life, relative to factors indicative of mobility. A test that can provide more general characterization of quality of life is the SF-36 [8]. This scale is more concerned with the perception of disease effects and is attuned to the early effects of multiple sclerosis [9].
3. Research concerning assistive technology in MS Extensive reviews of reference databases such as Medline, EI Compendix and PyscInfo concerned with
medical, engineering and psychological topics resulted in few studies directly related to the application of assistive technologies for people with MS. Instead, research concerning MS appears to be almost exclusively concerned with determining clinical treatment regimens and the cause of the disease. While some medical and therapy texts discuss the use of assistive technology with this population, the basis for any recommendations is not referenced to quantitative research. In one of the few studies identified, Perks, et al. [10] evaluated a population of manual wheelchair users in Scotland. It was found that 15% of manual wheelchair users had MS. Of these individuals with MS, a high percentage (59%) stated they did not feel their current wheelchair met their mobility needs. This resulted in difficulty moving about their home and outdoors. This study demonstrates the lack of appropriate mobility devices amongst a population of individuals with MS. Page, et al. [11] noted the incidence of MS in Scotland to be similar to that of the United States. Further investigation into the type of wheelchairs provided and used in the United States is required to verify the concerns found in Scotland. Given the lack of research activities concerning assistive technology for people with MS, health care professionals and researchers are best referred to relevant information in the body of work concerned with assistive technologies for other disabilities such as spinal cord injury (SCI) or cerebral palsy (CP).
4. Assistive technology research applicable to MS 4.1. Appropriate timing Since MS is a degenerative disease, the clinician should be mindful of the past clinical history of the client. An individual with the relapsing–remitting form that displays rare exacerbations may maintain the ability to walk for quite some time. Conversely, a person with the progressive form may require more active involvement of neurologists, physiatrists, physical therapists or occupational therapists in addressing the need for mobility. In addition to careful review of the client’s progression, the clinician should also consider the particular symptoms that are manifest, since these often vary between individuals with MS, in the case of spasticity and fatigue can vary depending on the time of day. Typical physical effects due to the progression of MS have been documented [12–14]. It is important to note demyelination can occur throughout the CNS and as a result there is no priority to motor control difficulties in any particular limb other than to say spasticity, ataxia and/or weakness proceed paralysis. Thus, the individual who reaches a point at which they are not able to walk with assistance may or may not be able to use a device
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such as a manual wheelchair. This is an important distinction when considering the following presentation of mobility interventions. Clinicians may benefit from the information provided by standardized disability scales tailored to MS. The Kurtzke Expanded Disability Status Scale (EDSS) [15] is an effective tool for obtaining a quick estimate of motor ability in people with MS [16] who are ambulatory. Recent work by Sharrack and Hughes [17] has developed the Guys Neurologic Disability Scale (GNDS) which is more responsive in characterizing mobility in both ambulatory and nonambulatory people with MS. The GNDS provides independent measures of function in various “domains” such as upper extremity function, lower extremity function, cognition, bowel and bladder function and others. This organization is of particular use to clinicians wishing to investigate a particular functional domain.
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tional electrical stimulation (FES). Since drop foot in MS results from damage to the central nervous system, the muscle is intact though it may be atrophied. Taylor, et al. [21] have investigated the use of a FES device known as the Odstock Dropped Foot Stimulator (ODFS). The ODFS provides stimulation to the common peroneal nerve and motor point of the tibialis anterior muscle. Stimulation is timed using a pressure switch placed in the shoe. In clinical trials, 21 individuals with MS were fitted with the ODFS and used the device for a period of 4.5 months. Changes in walking speed and effort were recorded in walking a 10-meter course. Results showed walking speed increased significantly (p⬍0.05) and effort decreased significantly (p⬍0.05). These results are promising, but do not address some of the downsides of FES raised by other studies such as rapid muscle metabolic exhaustion [22] and reduced ability to simulate the same motor point [23].
4.2. Gait modification 4.3. Appropriate cane usage and indications Normal human gait is a very efficient mode of mobility in which the weight of the trunk is balanced upon the pelvis via synchronized movement of the upper and lower extremities. Due to the efficiency of this activity, many people with MS are inclined to continue walking even when the operation of this synchronized system is disturbed. Research by Olgiati, et al. [18] has evaluated the relative contributions of symptoms common to the person with MS such as spasticity, ataxia and weakness. This work has shown the cost of walking via VO2 consumption to be increased by all three symptoms with a larger effect caused by spasticity but with contributions due to ataxia and weakness. Readers seeking a more extensive review of gait characteristics in MS are referenced to a review by Benedetti, et al. [19]. To test the effect of exercise on impaired gait, Rodgers, et al. investigated the effect of a six month aerobic training program on gait abnormalities in MS [20]. Results suggested a minimal effect on gait characteristics such as ankle dorsi/plantar flexion, knee flexion/extension and hip extension. Given these findings, exercise with a motor learning focus may be more applicable. When therapies do not help address gait difficulties, assistive devices may be of benefit. For example, devices exist to assist with “Drop Foot”, a common symptom of people with MS that interferes with normal gait. In drop foot, the dorsi-flexors of the ankle do not contract sufficiently to raise the foot during the swing-phase of gait. This results in the distal end of the foot contacting the ground. A common gait adaptation to address drop foot is to swing the foot out laterally during the swing phase. An effective clinical solution for drop foot is the use of an ankle–foot orthosis (AFO) which allows for dorsiflexion of the foot but not plantar-flexion. Another option that exists for the individual with MS is func-
When presented with ataxia and weakness, canes may provide a simple, but effective solution for the person with MS. Blount [24] provides a description of the mechanics of cane usage in a classic article. Herein, canes are described as an appropriate assistive gait device for persons with a variety of gait limiting concerns. Canes assist the individual in maintaining the even distribution of weight on the hips that is characteristic of normal human gait. This has the effect of reducing the effort of walking and prevents the development of repetitive strain injuries at the hip. Canes also provide a means of reducing falls. In a study of eight people with peripheral neuropathy and age-gender matched controls, Ashton-Miller, et al. [25] studied the response to frontal plane tilt of the floor surface to study participants as they performed a weight transfer task both with and without a cane. Perturbations were provided via two rapid changes in angle (±2° and ±4°) and performed with and without visual feedback. Results showed the fall rates of the case group to be significantly higher (p=0.036) than that of the control group when both groups were not using a cane and had visual feedback. Removing visual feedback caused falls in the case group to increase four times. Use of a cane in the hand contra-lateral to the weight transfer, caused a significant decrease in the number of falls in the case group and brought the fall rate below that of the control group when not using the cane. These studies demonstrate the scientific validity of cane use to address symptoms such as spasticity, ataxia, weakness and poor balance. Canes are an important assistive device for ambulatory individuals with MS given the increased cost of walking due to ataxia and weakness, the physics of cane use, and the prevention of falls found during cane use.
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However, the benefit of a cane is debatable without proper prescription. The Merck Manual of Diagnosis and Therapy [26] notes a properly sized cane should be held in the hand contra-lateral to the involved limb and provide 25°-elbow flexion when vertical. Gait should be initiated with the uninvolved limb, with the cane and involved limb following. Canes are also available with platform (4-leg) bases to provide greater stability for users with upper arm weakness or ataxia. It should be noted that canes are available in a wide variety of aesthetic designs which can allow for personal expression. 4.4. Use of walkers Persons with MS who experience continued lack of balance using a cane may find better stabilization by using a walker. Walkers provide increased stability due to the footprint of the four legs. In addition, walkers can be purchased with wheels, brakes and modified handgrips to aid in their effective use. Wheeled walkers may have two or four wheels. Braking of the wheeled walker may be automatic when sufficient weight is applied or may be activated via hand brake controls similar to a bicycle. Adapted handgrips can allow user-to-walker interfaces with large diameter tubing for individuals with reduced gripping abilities or with armrests for persons with non-functional hands. Walkers are typically foldable to aid in storage when traveling. 4.5. Appropriate manual wheelchair selection, configuration and training Part-time use or an exclusive move to wheeled mobility is required for individuals with MS who, despite interventions to address gait disturbances, are experiencing undo difficulty in balance or have fallen. Manual wheelchairs provide a wheeled option, but still allow for physical activity. It is important for the clinician to understand research, which has documented variables in the stability, physiology, propulsion, training and durability of the manual wheelchair prior to making recommendations. Work within the past 20 years has demonstrated the characteristics of the static [27] and dynamic [28] stability of the manual wheelchair. The static stability is described by the tendency of the wheelchair to tip to the rear, front and sides when at rest. Since most wheelchairs come with a standard size rear wheel, rearward stability is determined by the position of the rear axle relative to the user:wheelchair center of gravity [27]. Forward stability can be affected by the diameter of the front casters, but due to the small range in these values is similarly dependent on the user’s center of gravity. Side-toside stability can be influenced by the use of camber, which effectively increases the footprint of the wheelchair without largely affecting the center of gravity. Unfor-
tunately, increasing camber adds to the width of a wheelchair and can limit access to tight space. Determinants of dynamic stability are manifest largely in the same variables as static stability. However, depending on the user’s ability to manipulate the wheelchair, reduced stability has its benefits. For example, placing the rear wheel axle forward near the horizontal location of the center of gravity places more of the system’s weight over the rear wheel thus reducing the amount of energy required to propel the wheelchair and making wheelchair maneuvers such as a curb defying “wheelie” possible [28]. However, good motor control is needed to perform a wheelie and further to assure that ramps are negotiated safely in a chair with more weight over the rear wheels. An understanding of the physiology of manual wheelchair propulsion is important when considering persons with MS for a manual wheelchair. One of the benefits of a manual wheelchair can be the physical exercise it affords the user. Conversely, the amount and type of physical exercise a person with MS engages in can cause fatigue. A study by van der Woude, et al. [29] quantified physiologic variables of propelling a manual wheelchair on differing inclines. Mean oxygen consumption (VO2) and heart rate increased with increasing angle of inclination from a low of 0.59 l/min and 93 bpm on a level surface to 1.23 l/min and 125.5 bpm at an angle of 3°. Further research into physiologic limitations of individuals with MS is needed to determine if these values would limit manual wheelchair use. A growing body of literature exists on the proper configuration of the manual wheelchair, its use and the characteristics of the user. A stable seating surface is an initial concern in prescribing a properly configured wheelchair. Pressure measurement systems are available which allow the clinician to quantify the pressure at the user:seat interface. This allows for evaluation of seating systems that help reduce the interface pressure. This evaluation can be conducted during an examination so that a proper seating system can be chosen. This is of primary concern to individuals who remain in the wheelchair throughout the day since it can help to prevent the development of decubitus ulcers (pressure sores). In a study of wheelchair users with paraplegia, Boninger, et al. [30] investigated the relationship between pushrim forces, weight and median nerve injury at the wrist. This study demonstrated that weight of the user is significantly correlated with an increase in propulsive forces at the pushrim and the incidence of median nerve injury at the wrist. Recommendations are for manual wheelchair users to be vigilant in maintaining a healthy weight in consultation with their health care providers and for wheelchair users to be provided with lighter wheelchairs. It has been demonstrated via clinical data that approximately 50% of manual wheelchair users with spi-
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nal cord injury will develop repetitive strain injuries in either the wrist, elbow or shoulder within the first ten years of wheelchair use [31]. Although these injuries may not be as prevalent in MS clinicians should be aware of how wheelchair set up may affect risk of injury. Boninger, et al. [32] studied 40 wheelchair users with paraplegia to determine the effect of axle position on biomechanical factors of wheelchair propulsion which have been correlated with median nerve injury at the wrist. When propelling slightly greater than walking speed (2 mph), it was found that the horizontal distance between the shoulder of the user at rest and the axle was significantly correlated with the frequency of propulsion (p⬍0.01), the rate of rise of the propulsive force (p⬍0.05) and the push angle (p⬍0.05) at two speeds of propulsion. Frequency of propulsion may contribute to median nerve injury at the wrist since the hand is impacting the pushrim and experiencing micro-trauma. Similarly, the rate of rise of the propulsive force relates the magnitude of hand impact at pushrim contact. A greater rate of rise may cause increased micro-trauma. Lastly, the push angle relates the distance through which the propulsive force produces work. Shorter push angle input, less work to the system. These results are summarized in Fig. 1. Recommendations are to provide wheelchair users with adjustable axles that allow adjustment of the horizontal position according to the users abilities. Given the demonstrated issues surrounding manual wheelchair use, attempts have been made to develop protocols for training wheelchair users in healthy methods of wheelchair propulsion. One trainable characteristic of wheelchair propulsion is the manner in which the hand moves as it contacts the pushrim, propels the wheelchair and the returns to start another cycle. This motion is commonly termed “propulsion patterns” in the literature.
Fig. 1. Effects of manipulating the rear-wheel axle position of the manual wheelchair.
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In a recent study by Boninger, et al. [33], 38 subjects with paraplegia propelled a wheelchair while bilateral motion of the upper extremity and pushrim forces and moments were recorded. Results demonstrated the existence of four distinct propulsion patterns (Fig. 2). Statistical analyses were conducted to determine relationships between specific patterns and the force generated at the pushrim. Findings showed reduced frequency of propulsive strokes when a semi-circular propulsion pattern was used. In the semi-circular pattern, the hand follows the pushrim during the push phase of propulsion and then swings down below the pushrim as it moves back to engage the pushrim. This pattern led to a longer period of time spent in the push phase relative to the recovery phase. It was suggested that clinicians consider training wheelchair users in this style of propulsion in an effort to reduce the cumulative trauma imparted on the wheelchair user’s hand and wrist. In addition to concerns related to the user and user wheelchair interaction, wheelchair users should be confident of the structural integrity of their wheelchair. Failure of any component is more than an inconvenience for the wheelchair user. It is the limitation of their mobility. A series of standards have been developed by the American National Standards Institute (ANSI) and the Rehabilitation Engineering and Assistive Technology Society of North American (RESNA) in order to address these concerns [34]. Tests included in the standards protocol include the “curb drop” and “double drum” (Fig. 3). In the curb drop, the wheelchair is lifted 5.0 cm and dropped to the ground. In the double drum test, the wheelchair is placed two independent rollers (rear wheels on one roller and the front on the other). Each roller has two 1.0 cm high×2 cm wide slats which run from the center to the end of the roller and are positioned 180° out-of -phase. The rear drum turns at 1m/s whereas the front roller turns 5% faster so as to change the perturbations imparted to the chair over time. A study by Fitzgerald, et al. [35], performed the International Organization for Standardization (ISO) standards testing with three classifications of manual wheelchairs. The classes followed Medicare definitions of K1 (hospital-type), K4 (lightweight) and K5 (ultralight). The study performed the curb-drop and double-drum test on 25–K1 (hospital-type), 14–K4 (lightweight) and 22–K5 (ultralight) wheelchairs. Using ISO equivalent number
Fig. 2. Propulsion patterns of manual wheelchair propulsion as described by Boninger, et al. [33]. The gray line represents the path of a marker on the hand a an individual propels a wheelchair. The dark circle represents the pushrim of the wheelchair. The semicircular pattern was found to be most advantageous.
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Fig. 3.
The Curb Drop and Double Drum test stands.
of testing cycles, curb-drop and double-drum tests where expressed as a single variable and Kaplan-Meier survival curves were determined. The fatigue life of K5 (ultralight) wheelchairs was significantly greater (p⬍0.05) than both the K4 (lightweight) or K1 (hospitaltype) wheelchairs. Since ISO testing is based on a 5year life cycle, it was concluded that K4 (lightweight) and K1 (hospital-type) wheelchairs might not last the typical 3–5 year period expected by health insurers. A better investment may be in the K5 (ultralight) despite its initial high cost. These wheelchairs also have reduced rolling resistance making propulsion easier. 4.6. Power assisted wheelchairs A developing class of wheelchairs provides a power assist when desired, but allows the user to push the wheelchair as one would with a manual wheelchair. An example of the power assisted wheelchair is the JWII [2]. This wheelchair has a force/moment-sensing pushrim that provides an additional torque to the rear-axle proportional to the applied moment. Such devices have potentially important benefits such as enabling people normally provided with power wheelchairs to self-propel a wheelchair despite obstacles such as steep ramps. These potential benefits were recently demonstrated in a study of the JWII device [36]. Using the JWII, subjects demonstrated significantly lower oxygen consumption (p⬍0.0001) and heart rate (p⬍0.0001). Subjects completed some tasks significantly faster than with their personal wheelchair, but encountered difficulty transferring to/from the JWII and in disassembling the JWII for transport. Other brand options besides the JWII are available for purchase; however, research-based studies concerning these devices do not appear in the literature. For people with MS, the power-assisted wheelchair may prove to be a good compromise between the fatigue caused by using a manual wheelchair and the lack of exercise experienced in driving a power wheelchair.
4.7. Appropriate power wheelchair selection and configuration
The person with MS may need to move to a powered mobility solution given the degenerative nature of the disease. However, unlike other conditions such a quadriplegia, in which the user is solely dependent on the power wheelchair, persons with MS may be good candidates even when some ability to walk is still present. In this case, the power wheelchair is used to help limit fatigue. Power wheelchairs are available in a variety of designs. Each design is often available with a number of customization features. The basic designs have vastly different drive mechanisms characterized by rear-wheel, mid-wheel and forward-wheel drives [30]. These different types of power wheelchairs require training to learn the idiosyncrasies of the respective drive mechanisms. Rear-wheel drive power wheelchairs “feel” much like driving a car. Strengths of the rear-wheel drive include larger diameter drive wheels and intuitive control. Weaknesses include reduced maneuverability in tight spaces and reduced ability to climb over obstacles. Midwheel drive power wheelchairs are based on the premise that the center of gravity of the user is best placed over the drive wheels. This allows for improved maneuverability since these wheelchairs can turn on the vertical axis of the user. Weaknesses of mid-wheel drive wheelchair include the need for both front and rear tip casters that extend the length of the wheelchair and can cause the wheelchair’s drive wheels to become suspended off the ground when entering or leaving a steep incline. Mid-wheel drive wheelchairs also typically require a period of training to adapt to the sensation of being turned about one’s vertical axis. Front-wheel drive power wheelchairs provide for good obstacle climbing characteristics. They suffer from having the casters in the back of the wheelchair where they cannot be seen
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by the user which may complicate maneuverability of the wheelchair. Given the greater bulk of the power wheelchair and the advancement of the user’s disability, seating systems are often required. Similar to the systems mention previously for manual wheelchairs, the main goals are to provide comfort, function, and reduce the pressure between contacting surfaces of the user and wheelchair. Power wheelchair users may require more extensive adaptations to the seating system than do manual wheelchair users. Such adaptations can include inserts to aid in the positioning of the legs and trunk. Additionally, users with fatiguing conditions such as MS may benefit from a wide variety of headrests. Another important feature of power wheelchairs include tilt-in-space seats that allow the user to recline the back while the seat rotates upward at the same rate. This prevents significant shear forces between the user and the seat backrest. Tilt-in-Space wheelchairs are desirable because they allow the user to perform pressure relief to the buttocks and can aid in attaining and maintaining a proper seated position. The control interface can have a major effect on the success or failure of a power wheelchair as a mobility device. Basic controllers employ a proportional control scheme that monitors the displacement of a joystick. More elaborate programmable controllers allow for monitoring of the speed at which the joystick is displaced. The controller used has major implications for people with MS, since ataxia of the upper extremities is a concern in the later stages of the disease. Much like manual wheelchairs, ANSI/RESNA standards have been formulated to verify the integrity of the systems. Recent work by Algood, et al. [37] tested the power and control systems of five different wheelchair models using Section 14 of the ANSI/RESNA standards. Wheelchair vendors included in the study were Invacare, Sunrise Medical, Everest & Jennings, Permobil and Pride Mobility. The most common failure was with the battery connections and fuses that were not labeled properly (all models). Some wheelchairs failed when they were drivable with the battery charger plugged into the wheelchair but not the wall outlet (Sunrise Medical, Permobil). Additionally, one wheelchair did not provide for reverse polarity protection, which caused the controller to be damaged (Invacare). Another study by Vitek, et al. [38] investigated the static, impact and fatigue testing of three power wheelchairs of the vendors Invacare, Sunrise Medical, Everest & Jennings, Permobil and Pride Mobility. Three wheelchairs failed static tests of pushing a pulling on the footrests (Everest & Jennings), while three wheelchairs failed a static test of pulling up on the armrest (Sunrise Medical). One wheelchair failed the double drum test describe earlier (Everest & Jennings), while two wheelchairs failed the curb drop test (Permobil). As can be
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seen, ANSI/RESNA standards testing results can be an important piece of information in deciding which wheelchairs to recommend or purchase. Axelson, et al. [39] has authored an excellent text describing how to use these standards in purchasing a wheelchair. 4.8. Appropriate scooter selection and configuration Scooters are a popular mode of powered mobility amongst persons with MS. Commonly, an individual who is experiencing difficulties in gait, such as excessive muscular fatigue, will use a scooter as an energy conservation device so that walking is limited to short distances. Some users prefer the scooter to a manual wheelchair since upper extremity fatigue is not an issue. Scooters typically have either three or four wheels, with the rear wheels serving as the drive mechanism. Steering is accomplished via hand-bars that are intuitive to users who previously used a bicycle. Seating is provided in a chair having foam padding typical of a carseat. The backrest height ends at the level of the shoulder blades, which allows for unencumbered rotation of the trunk. Scooters are less desirable then power wheelchairs when considering dynamic stability. Standards testing comparing scooter and power wheelchair stability was completed by Rentschler, et al. [40] In this study, five front-wheel drive power wheelchairs, five rear-wheel drive power wheelchairs and five 4-wheel scooters were tested according to ANSI/RESNA wheelchair standards Section 2 (dynamic stability). This study demonstrated that front and rear-drive wheelchairs were significantly more stable than were scooters during dynamic braking tests on 6° and 10° slopes. It is important to note these test were conducted with a 4-wheel scooter and that 3wheel scooters would likely be more unstable. In general scooters are an options for individuals who retain trunk balance, upper extremity control and strength, and do not have a progressive course of MS. In scooters there is limited ability to modify the seat or provided additional functions such as tilt in space. In addition, the use of a tiller for steering requires good arm strength and joysticks are not an option. For these reasons scooters are a poor choice for individuals with advanced neurologic dysfunction. These limitations need to be considered in light of the progression of the disease.
5. Current and future research The mobility needs of people with MS are an important, real-life question. While concerns regarding inter-group variability are important, they should not preclude investigation of the science behind mobility. Instead, studies with carefully considered protocols and
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judicious choice of study variables and methods are required. Research into quality of life, determinants of activity levels, and appropriate mobility devices should be conducted. Such studies are required to determine the usage patterns of people with MS employing differing mobility devices as a function of disease progression. In the meantime clinicians need to rely on literature from other populations when assisting their patients in decisions related to mobility devices.
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Acknowledgements The US Department of Veterans Affairs Center of Excellence for Wheelchairs and Related Technology (grant #F2181C).
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