Internationally, the average incidence of spinal cord injury (SCI) approaches approximately 30 per 1 million inhabitants annually, while the annual prevalence is 485 per 1 million.1,2 In the United States, SCI occurs at a rate of approximately 12 000 new cases per year.3,4 Most individuals who sustain SCI are left with complete or partial loss of motor function of their lower extremities and often impairments extend to their upper extremities as well.3,4 Spinal cord injury is a worldwide concern, and from the time of injury, survivors of SCI make lifelong efforts toward recovery of function and mobility.
Functional recovery plays a vital role after SCI. The amount of functional recovery is largely correlated with the severity of the injury (eg, complete vs incomplete) and the level of the injury,5 with lesser severity and lower level of injury associated with greater recovery of function. Most studies report that functional recovery takes place in the first 3 months and can continue as far as 1 year postinjury, albeit at a slower rate.5 Improvements in function, however, continue beyond 1 year after injury in some individuals.6–10
Despite the functional improvements obtained with locomotor rehabilitation therapy,8,9,11–15 many persons with incomplete SCIs remain with significant residual disability even after rehabilitation. Alternative rehabilitative techniques have been studied to determine whether they might be more effective than traditional therapies; however, results have been dependent on the specific technique or therapy used and outcomes have been inconsistent between studies.6,16 Advances in technology have allowed the use of robotic devices to assist with retraining of standing, transfer, and walking tasks for individuals with partial function of the lower extremities.17–20 Partial body weight support treadmill training systems have been widely studied in populations of persons with SCI, with mixed results.17–22 Moreover, many of these body weight–supported systems can be costly, all consist of large workstations, and the mechanics of the device confine the use to a rehabilitation gymnasium. Furthermore, difficulties in the complicated and timely process of fitting a user in the device, often necessitating 2 therapists and/or a trained technician or aide, have hindered their acceptance and use in the rehabilitation setting.
Wearable robotic systems potentially provide support and assistance to paretic limbs in functional tasks, thereby allowing users an opportunity to increase the amount of practice they receive in standing and gait tasks. Compared to large, treadmill-based systems, wearable devices can be less costly, and much easier to don/doff. Moreover, while large workstation gait systems limit training to the rehabilitation gymnasium, a wearable device permits training to occur in more natural environments and in tasks other than gait training, such as sit-to-stand transition tasks. Some of these wearable devices also allow for training over and around obstacles and in various terrains, and many of these systems can be used in the ascent and descent of stair training. These features potentially make these devices a more practical and flexible option for therapists in a rehabilitation setting. At least 2 companies are developing bilateral lower extremity powered braces (Ekso Bionics, Berkeley, California, and Argo Medical Technologies, Yokneam Ilit, Israel), although their utility in this population remains to be studied.
The subject of this case is a 22-year-old woman with an incomplete SCI (American Spinal Injury Association Impairment Scale class D, level C5) due to a motor vehicle accident 4 years before initiating the intervention described in this report. She sustained fracture of the odontoid process and the C5 and C6 vertebrae, with residual tetraparesis. At the onset of intervention, she primarily used a power wheelchair for mobility but was able to stand with the assistance of a rolling walker and perform limited locomotor tasks, including walking approximately 15 m with the use of a rolling walker. She was able to independently transfer in and out of her wheelchair with upper extremity assistance, and to independently control her power wheelchair, using a standard joystick. Prior to her accident, she was active in sports. The individual had been receiving both physical and occupational therapy before beginning the intervention discussed in this case study; however, according to her report, she had not experienced any recent gains in function. She had received a trial of body weight–supported treadmill-based locomotor training early in her rehabilitation course but had not received this training in the months prior to the onset of training with the robotic knee orthosis (RKO) device. Her primary goal at the time of examination was to increase independence and endurance with walking in order to more easily navigate her college campus and not to require the use of her wheelchair at social events. She had no known medical issues other than the history of SCI. The individual provided informed consent for participation in the study, approved by the Columbia University Medical Center institutional review board.
EXAMINATION AND EVALUATION
Neurologic examination was completed before the onset of training. This examination revealed decreased motor function in all 4 extremities, with asymmetric motor impairments, the right side more affected than the left. Motor examination showed left upper limb strength 4/5 throughout, with right upper limb strength 3/5 throughout with increased tone noted in elbow and wrist flexion on the right. Left lower extremity strength was 4/5 throughout, right lower extremity strength 3/5, except ankle dorsiflexion, which was 3-/5. Increased tone was noted in bilateral lower extremities in knee extension and plantar flexion, greater in the right than in the left. Sensation was present but reduced (score of 1 in ASIA/ISCoS Impairment Scale) in all 4 extremities to light touch. All findings were consistent with the ASIA/ISCoS Impairment Scale, class D.23
Despite the participant's ongoing therapy up to the point of participation in this study, functional deficits persisted. At the time of intervention, the participant did require the use of her upper extremities to successfully transition to a standing position from sitting, for which she used her rolling walker. She was also observed to have residual gait limitations including decreased ability to perform heel to toe during gait, decreased step length bilaterally, poor control of the right knee with dynamic weight-bearing activities with occasional hyperextension, decreased stance time on right during gait tasks, and overall slow gait velocity as well as poor endurance. These deficits required the participant to rely on the use of her wheelchair for locomotion of long distances, and on her rolling walker for increased safety and to minimize her risk of falls with shorter distance tasks. Furthermore, the participant's availability to participate in this study was limited to 7 visits. On the basis of these evaluation findings and the limited time available to participate in a training program, it was determined that the patient would benefit from training in a wearable RKO that provides user-initiated assistance to knee extension during weight-bearing activity as well as resistance in knee flexion.
Standardized functional outcome measures used in this case study included the 6-Minute Walk Test to measure endurance,24 the Berg Balance Scale to assess balance,25,26 the Timed Up & Go (TUG) Test to measure functional mobility,24 and the 10-Meter Walk Test to assess short-duration walking speeds.24,27 (See Table 1 for baseline and final values.) All gait outcome measures used in this report have previously demonstrated high interrater reliability in a population of individuals with SCI and the Berg Balance Scale in a population of elderly individuals.24–26,28–30 Outcome measures were recorded at baseline and reassessed upon completion of the 7-session intervention period by a physical therapist not otherwise involved in the training regimen. The rater did not have access to baseline outcome scores at the time of posttherapy measurement. All measured outcomes are reported in this case study.
DESCRIPTION OF DEVICE
The RKO we used (Tibion Bionic Technologies, Sunnyvale, California) is a device designed for individuals with neurologic impairments and residual gait deficits.31 The device relies on multiple sensors, including 4 force sensors within a footplate that is worn in the user's shoe, which detect the amount and timing of weight-bearing through the foot. Other sensors measure joint angle at the knee, the extension force provided by the device's actuators, which, in combination with the footplate sensors, provide feedback to the device's central processing unit.
The central processing unit creates a model of the user's activities (including sit-to-stand transitions, gait on level surfaces, and stair climbing/descent). Data from foot sensors, combined with the user-initiated extension motion at the knee joint, activate the device. Algorithms determine when the user requires increased assistance to complete the functional task, and activate the RKO to provide this assistance. A user interface allows a trained therapist to control set parameters including the amount of assistance (to extension) and resistance (into flexion) the device provides, the minimal force required for device activation, and the range-of-motion limitations for each user. These parameters can be manually updated over the course of therapy. The device is untethered from any cords and contains its own battery power source sufficient for approximately 2 to 3 hours of use. Velcro straps secure the device to the user's lower extremity. It can be used interchangeably among multiple users (with appropriate infection control measures as indicated), and each device can be easily configured to service either the right or left lower extremity32 (Figures 1a and b).
The device permits functional training in various environments and may thus facilitate generalizability of learning. It has been used primarily as a rehabilitation training tool for people with unilateral lower extremity neurologic deficits. While most individuals with SCI have bilateral lower extremity paresis, some individuals with Brown-Sequard syndrome or asymmetric involvement of the lower extremities may be good candidates for gait retraining with this device. The footplate sensors, which activate the device, facilitate users to increase weight bearing through the affected lower extremity, and the resulting knee extension assistance the device provides yields increased control of the affected lower extremity, thus potentially improving balance, user confidence on the affected lower extremity, and overall enhancing gait. The model of the user's activities created by the processor is designed to assist with gait and stair-climbing tasks. The operation and use of the device require an accompanying therapist or assistant to aid in donning/doffing the device and to set and update training parameters, such as the amount of assistance and/or resistance the device gives to the user's movements. Parameters are easily updated throughout the session via a user interface located directly on the device. When the exercise mode of the device is deactivated, the device is passively backdriveable, which not only is a safety feature but also allows the therapist to position the lower extremity to maximize benefit for a particular activity, such as to accept more weight bearing in a sit-to-stand transition activity or to ascend steps with a step-over-step pattern.
Training was performed by an experienced physical therapist trained in the use of the device. The subject participated in 7 training sessions, each approximately 1 hour in duration over a 2-week time period. The RKO was worn only on the weaker33 lower extremity throughout each session of the intervention.
Each RKO-assisted training session was 50 minutes in duration. Approximately 10 minutes of time was devoted to sit-to-stand training with semitandem stance without the assistance of the upper extremities. Twenty minutes of each training session was allotted for gait training with verbal and tactile cues to correct for posture, increase weight bearing on right lower extremity, increase bilateral foot-floor clearance, and increase eccentric control of the right lower extremity, and foot placement sequencing in gait tasks on a solid surface and over obstacles. It is noteworthy that the individual did not require the use of her rolling walker for the entire gait training portion of the program. Following the gait training activities, the participant then performed 10 minutes of balance activities including weight shifts in the anterior/posterior direction and in the medial/lateral direction with sustained weight shifts over the more involved lower extremity. Finally, the individual performed 10 minutes of stair training including step-ups with each lower extremity with verbal and manual cues for controlled ascent/descent. Sessions were progressed to participant tolerance by self-report of fatigue. Manual assistance was given as needed for balance and additional cueing by the therapist and reduced over the course of the training. The participant was monitored for obvious signs of fatigue (excess sweating, racing heart rate, pallor) and by self-report. She was given rest breaks as needed and by request during the intervention. She was undergoing no other therapy or intervention during the course of this study.
Despite the device being bulky and weighing approximately 4 kg (8 lb), the participant had no complaints about the device during the course of her training, and there were no obvious restrictions in her gait caused by the device. No adverse events occurred during the intervention. The therapist was able to don/doff the device, while the participant was seated in her wheelchair. The participant was not required to stand or transfer out of her wheelchair prior to the initiation of the therapy. The device itself took approximately 5 minutes to don/doff. It required an additional 5 minutes to program parameters on the initial training session; however, these parameters were stored within the device for future use, thereby facilitating a more rapid setup for future training sessions. With the device in place, the participant did not require the use of her upper extremities for assistance with transitioning from sitting to standing.
On completion of training, the participant demonstrated improvements in the 6-Minute Walk Test and the Berg Balance Scale. The change in the Berg Balance Scale represents an improvement from “walking with assistance” to “independent” in the descriptive functional categories developed by Berg et al26 and, due to the grade of the change, is indicative of a true functional change at a 95% confidence interval. However, because of the range of the participant's scores, no conclusion can be drawn as to whether this improvement would lead to a reduced fall risk. Conversely, the TUG test data demonstrated increased time from baseline to posttraining with increases in time also noted in 10-Meter Walk Test times (see Table 1). All measurements were taken without the device.
Furthermore, at conclusion of training, the participant was able to transition from sitting to standing from her wheelchair without the assistance of her upper extremities, however, and demonstrated no other change in functional mobility.
Robotic therapies for individuals with spinal cord injuries have previously been largely limited to partial body weight support systems in training over a treadmill, specifically for locomotor training.19,34,35 Furthermore, limited carryover has been demonstrated in functional tasks after training with these devices.20 A wearable device such as the Tibion Bionic Leg (Tibion Bionic Technologies, Sunnyvale, California) is less costly, easy-to-don/doff, and simple-to-manipulate exercise parameters and can be used over varying terrains with various mobility tasks, thereby potentially yielding more generalizable training effects and increasing the device's usability in a rehabilitation setting.
This case study describes the clinical decision-making process related to the selection of an overground robotic locomotor training approach and discusses the practical use of this novel device in an individual with a chronic, incomplete cervical SCI. We describe the practical application of this device for mobility training, including sit-to-stand transition training, gait training, balance training, and stair training. We demonstrate the outcomes of mobility training. Overall, the use of the device was well received by the participant as well as the treating therapist. The device proved easy to use and quick to set up. It was also easily adjustable throughout the course of the training sessions, and the participant subjectively reported that the device was comfortable to wear. In contrast to other devices, the therapist was able to perform gait training in various environments, including over and around obstacles, on varying terrains, and use the device in stair training with the participant involved in this case study.
From a functional perspective, the participant showed improvements in gait endurance by an increase in 6-Minute Walk distance after limited training. She also demonstrated improvements in balance as demonstrated with an increased score of the Berg Balance Scale. Similarly, results of an earlier study,31 using the same RKO for training in a population of subjects who had survived stroke, showed 12% gains in the 6-Minute Walk and 13% gains in the Berg Balance Scale posttraining, which gains were sustained at a 3-month follow-up interval.
The individual involved in this case study did not demonstrate improvements in functional mobility as would have been reflected by decreased time to complete the TUG test, nor were improvements noted in the 10-Meter Walk Test for short-duration gait speed. In the prior study of RKO training with survivors of stroke,31 subjects demonstrated improvements in both the TUG test (21% improvement) and 10-Meter Walk Test (7.5% improvement), which were not observed in this case. One potential explanation for the differences in these findings may be an inadequate number of training sessions with the device, while the user in this case study was able to demonstrate a more functional gait pattern, she may not have had sufficient practice in the new pattern as to improve time measures on a short duration task. Subjects with stroke who were involved in the previous study participated in a 6-week training program (eighteen 1-hour training sessions) with the RKO, whereas the participant referred to in this case study was limited by her availability to seven 1-hour training sessions. It is also possible that improvements in short-duration gait speeds are gained later in training, and the training protocol used in this report was not sufficiently long to demonstrate maximal gains.
In addition to differences in duration of training between the subject of this case and prior subjects with stroke,31 there were also differences in the extent of impairment. Subjects with stroke in the prior study had unilateral deficits, whereas the participant reported here had bilateral deficits, perhaps limiting the effectiveness of the RKO. This individual used the device only on her weaker33 lower extremity throughout the duration of the training; however it could be argued that she would require bilateral training with the device, or alternating training with the device from one lower extremity to the other, to demonstrate more pronounced gains, or gains in short-duration tasks such as the TUG Test and 10-Meter Walk Test. This method of training was not considered because of the limited time the subject had available.
Finally, the participant involved in this case study had a lower level of functional independence with gait tasks than the subjects who participated in the prior study. Use of the device in training made it unnecessary for the participant to require the use of her rolling walker to complete all gait training tasks, and a portion of the gait training did occur without the use of her rolling walker. The severity of her limitations might require increased training time with the RKO to demonstrate improvements in all functional outcome measures. Other explanations include a lack of emphasis during the training sessions on gait speed or a fundamental lack of responsiveness of these impairments to robotic training of this type. A pattern suggestive of somewhat-slower gait speed and mobility performance but with improved endurance of the participant was noted. It is possible that a delay of initiation could mask improvements on short duration gait tasks, but a definite conclusion cannot be drawn from this individual case.
The device itself poses a low safety risk, with a number of safety features included and shut-off buttons located directly on the device itself in the event that a malfunction occurs. It is noteworthy that even though a number of safety features have been listed, the device is novel and has had limited testing with this neurologic clinical population, thus always raising concern of hazardous device-user interactions. There were no adverse events that occurred during the course of the training reported in this case. Larger studies are needed to confirm safety in this population, however.
There are several limitations of this case study. As a single case, it is not possible to determine whether outcomes resulted from the training intervention, the robotic device, or other time or environmental factors. A randomized study with comparison groups is required to determine a treatment effect. A single physical therapist, trained in the use of the RKO, conducted all training sessions with the participant. Outcome measurements were measured by 2 different physical therapists uninvolved in the training program in an effort to reduce bias; however, the interrater reliability of their assessments was unknown, and no blinding was feasible. Reassessment was completed on the same day as the last session; therefore, fatigue may have affected the results.
The RKO used in this case study was used as part of a short-duration physical therapy training program for an individual with chronic incomplete SCI. The device was easy to use, parameters were easily adjusted, and the device was well tolerated by the participant. Modest gains were noted in balance and gait endurance, while declines were noted in a timed test of functional mobility and in short-duration gait speed. Larger controlled studies are needed to determine whether this training approach is effective in restoring mobility in individuals with asymmetric lower limb paresis from SCI.
The authors thank Randy B. Kolodny, PT, DPT, who provided data collection.
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balance; gait; robotics; spinal cord injury