Virtual Reality in Gait Rehabilitation

Nigel W. Tierney1; Jessica Crouch1; Hector Garcia2; Martha Walker3; Bonnie Van Lunen4;Gianluca DeLeo5; George Maihafer3; Stacie Ringleb2

1 Department of Computer Science, Old Dominion University, Virginia USAntierney@cs.odu.edu, jrcrouch@cs.odu.edu

2 Virginia Modeling Analysis and Simulation Center, Old Dominion University, Virginia USA3 Department of Physical Therapy, Old Dominion University, Virginia USA4 Department of Exercise Science, Old Dominion University, Virginia USA

5 Department of Medical Laboratory Sciences, Old Dominion University, Virginia USA

AbstractThis paper describes an innovative approach to gait rehabilitation via a system that combines the use oftraditional and advanced rehabilitation techniques with a virtual reality (VR) training environment. The VR-Gait system that has been developed consists of VR software that generates and displays a dynamicurban environment on a large high definition television mounted in front of a treadmill. The treadmill ispaired with an overhead suspension device that can provide a patient with partial weight support. Inertialtracking is used to actively monitor a patient’s posture during a training session and prompt auditory cuesthat encourage a patient to maintain correct walking posture. This project aims to demonstrate thatimproved gait rehabilitation can be accomplished using a VR environment composed of widely available,relatively inexpensive, and unobtrusive hardware components. This project will also have the capability toimprove medical decision-making by providing objective guidelines for patient progress and projectedfunctional outcome. A validation study with stroke patients is currently ongoing.

1. INTRODUCTIONGait disabilities are a serious problem that affectmillions of people and are accompanied byexorbitant costs. A multitude of causes lead to gaitdisability including stroke, limb amputation,traumatic brain injury, spinal cord injury, cerebralpalsy, and progressive neurological disorders.This paper describes an innovative approach togait rehabilitation via a system that combines theuse of traditional and advanced rehabilitationtechniques with a virtual reality (VR) trainingenvironment. The goal of this approach is to helppatients achieve their maximum functionalcapacity as efficiently as possible. The firstpopulation targeted by this work is stroke patients;however, the results of this project could beapplicable to the wider group of individuals withgait disabilities from other causes.

According to the American Stroke Association(ASA), approximately 700,000 individuals eachyear are diagnosed with a stroke. Of theindividuals who survive up to 90% of them reportone or more disabilities [6]. Also according to theASA, the direct cost of strokes in the United Statesis estimated at 37.3 billion dollars, due to manycontributing factors including the loss of ability towork and direct patient care.

As seen in Figure 1, during stroke rehabilitation itis common for patients to practice motor skills andcompensatory strategies for daily living activities,including ambulation, within a clinical setting. Thehope is that skills gained in a clinical environmentwill generalize to the patients’ home environments.

Figure 1: Current clinical gait rehabilitation for apost stroke patient

The traditional approach to rehabilitation is laborintensive limited in intensity and duration ofrepetitions and its carryover outside of therehabilitation setting is uncertain.

Virtual reality technology can help address theselimitations by allowing the development of low-costtraining environments consistent with a client'shome environment. Furthermore, virtualenvironments are adaptable and can affordpatients the opportunity to practice under a varietyof simulated circumstances.The difficulty level of the training scenarios can beadjusted by varying the speed and slope of thetreadmill, the complexity of tasks, and the amountof body weight support. A VR system can alsogive the patient immediate feedback onperformance, which is an important component oflearning [16]. While skilled therapy will always bea part of rehabilitation, the use of VR-enhancedtreadmill training may be a cost-effective way toincrease patient motivation to practice walkingunder different simulated conditions. To studythese issues, a new VR-enhanced treadmillsystem with partial body weight suspension hasbeen developed. The remainder of this paper is organized asfollows. Section 2 reviews previous work relatedto VR-enhanced rehabilitation and training.Section 3 describes the methods employed tocreate the VR-Gait system, and section 4 outlinesthe ongoing validation study. Conclusions andfuture work are discussed in section 5.

2. PREVIOUS WORKExtensive research has been conducted toexamine the efficacy of VR-enhanced training andrehabilitation. In particular, virtual trainingenvironments have been successfully used inteaching both decision-making skills and physicalskills [9],[11],[14],[15]. More specific to strokerehabilitation, a previous study has shown that astroke patient’s use of a paretic arm can beimproved through the use of a virtual trainingenvironment that delivers visual and auditory cues[6].

Yeh, et al., also performed insightful research onupper extremity motor training for post-strokerehabilitation using a VR-enhanced environment[18]. The system implemented a “Static ReachingTask” environment in which the subject wouldreach for virtual 3D objects. This system usedshutter glasses to display a 3D environment, andused a tracking device attached to a subject’shand to support interaction with the environment.Although not in the area of gait rehabilitation, thisresearch indicated that VR could be useful instroke rehabilitation.

Wellner, et al., performed studies on gaitrehabilitation by pairing the use of a rehabilitationgait robot “Lokomat” with a virtual environment, tostudy obstacle crossing improvement [17]. The“Lokomat” system is designed to help subjectswith spinal cord injuries; however, the system thatwas developed could also be used for post-stroke

gait rehabilitation. “Lokomat” has a haptic (activetouch) interface which can simulate obstacleswithin the VR environment. In this system the VRenvironment also contains an avatar that providesevent-driven, auditory and visual cues. Testing onspinal cord injury or stroke victims had yet to becompleted at the time of publication, but positivefeedback was provided by healthy test subjectsregarding the visual and audio feedback and theobstacle force feedback.

Closely related to our work is a previous project ongait training that tested two post-stroke patientsusing a combined treadmill and VR system. Thisstudy found that the subjects’ abilities to increasetheir speed and to walk on a slight slope weregreatly improved by the VR-enhanced training [5].However, this research did not incorporate partialweight support or examine the efficacy of thesystem for patients who were unable to walkcompletely independently.

Fung, et al., performed studies on gait training forstroke patients by using a treadmill mounted on a6-degree-of-freedom motion platform with amotion-coupled VR environment [7]. The 6-degree-of-freedom system provided the uniquefeature of simulated turning within theenvironment. This system contained an overheadharness, but it was not used in the study. Thissystem also provided auditory and visual cues aspositive/negative feedback. Subjects wererequired to wear 3D stereo glasses to visualize thevirtual environment. Test results from this projectdemonstrated improved gait speed with training.

The VR-Gait system presented in this paper buildson these earlier results and aims to demonstrateimproved gait rehabilitation using a VRenvironment constructed of widely available,relatively inexpensive, and unobtrusive hardwarecomponents. If this system provides demonstrablebenefits for gait rehabilitation, it could be easilyreplicated and deployed in a variety of clinicalsettings.

3. METHODSThe VR-Gait system consists of VR software thatgenerates and displays a dynamic urbanenvironment on a large high definition televisionmounted in front of a treadmill. The treadmill ispaired with an overhead suspension device thatcan provide a patient with partial weight support.Research has shown that the use of partial weightsupport in gait training not only acts as a safetydevice to protect a patient from falling, but it alsoenables subjects to practice walking with a morenormal pattern and at a higher speed [2]. The VRprogram includes an interactive graphical userinterface (GUI) that allows the physical therapist toconfigure the virtual environment and recordinformation about each training session. Inaddition to moving cars and pedestrians, the VR

environment includes an avatar that acts as avirtual walking partner during the training session.During a session the avatar offers auditoryencouragement and advice to improve thesubject’s morale and to deliver feedback onproper posture. Walking posture is monitored viaa small inertial tracking device mounted on a hatworn by a patient during training.

The multidisciplinary team responsible for creatingthis system has a wide range of expertise.Computer science, engineering, modeling, andsimulation capabilities were required to developthe VR environment, interactive GUI, and the datarecording and analysis tools. Physical therapistscontributed to the design and evaluation of thesystem, and are conducting the evaluation studywith stroke patients. Physician collaborators haveassisted with patient recruitment.

3.1 HardwareThe hardware components which are involved increating the VR-Gait system are an inertialorientation tracking device, a high definition TV, acomputer terminal, a programmable treadmill, andan overhead suspension device. The inertialorientation tracking device is an IntersenseInertiaCube2, with 3-degree of freedom trackingand a 180Hz update rate. The InertiaCube2 isplaced on a cap that a subject wears on his or herhead. The tracking system determines whether asubject is maintaining correct posture, lookingdown, or leaning to one side; leaning is a commonproblem for stroke patients. The 51 inch SharpAquos high definition television is mounted on astand in front of the treadmill and acts as thedisplay for the VR environment. The computerrunning the VR software and GUI is a Windows™Vista PC, containing an Intel® Core™ 2 DuoProcessor E6700 (4MB L2 Cache, 2.66GHz, 1066FSB), 2GB of 667MHz memory, and a 256MBnVidida GeForce 7900 GS video card. Theprogrammable treadmill is a Biodex Gait Trainer 2.The overhead suspension device, BiodexUnweighing System, provides weight support forthe patient and has a patient weight capacity of360lb (163kg).

3.2 Interactive GUI & Data CollectionThe GUI provides the entry point into the VRprogram environment. As seen in Figure 2, theGUI accepts as input the user’s personalinformation, the base speed at which to run theprogram and a selection of simulation scenarioswhich vary in speed and length. The GUI acts as adata collection tool as it stores the information ofeach session for each individual patient in aMicrosoft® Excel™ spreadsheet. The GUI canalso be used to trigger early termination of the

Figure 2: Interactive GUI to enter into simulationcontaining input boxes for data storage on the

right & environment variables settings on the left

simulation. The GUI was developed using VisualBasic.

3.3 The VR Walkthrough EnvironmentThe VR walkthrough environment is a 3dimensional (3D), interactive linear milieu thatsubjects walk through. It simulates a cityscapecreated using the high performance graphicstoolkit OpenSceneGraph, the 3D characteranimation library Cal3D, the character animationtoolkit ReplicantBody, and 3D modeling programAutodesk’s 3D Studio Max.

As seen in Figure 3, the cityscape is made up of aseries of blocks. Four blocks are rendered oneach side of the road at any given time. As a blockpasses behind the subject’s viewpoint, that blockis deleted, and a new block is created at the endof the remaining three blocks. This ensures thatthe rendered scene is four blocks deep at alltimes; however, it results in a pop-up effect. Thepop-up effect is controlled through the use ofsimulated fog that hides objects in the distanceand eases them into the visible scene graduallyand realistically.

Each block contains a straight road with an arrayof 3D car models driving up and down the road.The order of buildings and car models is randomlygenerated each time the simulation is run, thusguaranteeing a different visual experience foreach training session.

Located at each side of the virtual road is a seriesof 3D city buildings and other miscellaneous 3Ditems such as trees and signs that are randomlyselected from a list of 3D models. A footpath islocated on each side of the road. The scenecamera moves down the left footpath, simulating

Figure 3: Screenshot of the block walkthroughwith the avatar located on the left

the subject’s walking motion. Also located on andnear the footpaths is a selection of 3D charactermodels that are walking, waiting at corners, andinteracting with other characters.

The city blocks continue to appear through the fogwhile the simulation runs; however, when the timefor the simulation ends or the GUI is used toinitiate the early termination, a call will be made fora final block to appear. The final block contains aselection of tree models, signifying the end of theurban environment, and a model of the “Arc deTriomphe,” signifying the “triumphant” completionof the simulation. The display of the final blockacts as a positive and encouraging methodinforming the subject that he or she hassuccessfully completed a session.

3.4 Avatar & Inertial TrackerEmbedded within the VR environment is a virtualfriend/avatar that provides support and feedbackfor the subject within the system. A series ofrecorded auditory cues are triggered upon theperformance of certain events. These includecongratulatory messages when certain milestonesare achieved and warning messages when thesubject is looking down or leaning. Some of theseauditory cues are triggered by the inertial tracker.

3.5 System IntegrationThe VR-Gait system combines many successfulfeatures that have been shown to be associatedwith motor learning and successful gait training.These include progressive decrease in bodyweight support using the overhead suspensiondevice and repetitive practice and positivefeedback on performance using the VRenvironment and inertial tracker. As seen in Figure4, all the equipment has been successfully put inplace for the system.

Figure 4: A subject on a treadmill connected tothe overhead suspension device, wearing a

baseball hat with the inertial tracker attached, andlooking at the VR environment on the monitor

4. VALIDATION STUDYThe investigation into the success of this system iscurrently underway. It involves the testing of up to20 patients who have had a stroke. The EasternVirginia Medical School (EVMS)

Institutional Review Board (IRB) has grantedapproval to perform testing on human subjects,allowing recruitment of the patients to begin. Thevalidation study is designed to determine whetherthere are significant changes in objectivemeasures of gait and functional gait performance.

Each patient must meet a certain set of criteria tobe included in the study. These criteria are:

�Be 18 years of age or older

�Have had a stroke within the previousyear

�Be able to ambulate independently with orwithout an assistive device for at least20ft, but still deem that there is room forimprovement

�Have adequate cognitive ability toparticipate in the study (a mini-mentalstate examination score of 24 or above)

�Be safe to exercise at low to moderatelevels

�Adequate ability to hear VR audio, see VRimages, and follow physician commands

Table 1: Sample Progression of Training Speedand Duration

Week/Time Warm-Up Training

Cool-Down

Week 1 10 min

1.0 X 3 min

1.0 X+0.53 min

1.0 X 4 min

Week 2 12 min

1.2 X 2 min

1.4 X 8 min

1.2 X 2 min

Week 3 15 min

1.4 X 2 min

1.6 X 11 min

1.4 X 2 min

Week 4 20 min

1.6 X 2 min

2 X 14 min

1.6 X 4 min

Each patient will follow a testing storyline thatsimulates the patient walking through a cityscape,where they are greeted and accompanied by anavatar acting as the patients’ “friend.” The table ofprogram times and speeds can be seen in Table1. Where the maximum time is 20 minutes (min),and ‘X’ is the speed at which a patient walks 20feet without assistance during the functional gaitassessment (FGA). The overhead suspensiondevice starts with 40% body weight supported.The length of time spent walking and the speed ofwalking gradually increase across sessions, andthen the percent of body weight supporteddecreases by 10% each week. Each subject willprogress according to this protocol unless he orshe shows signs of exercise intolerance. If thereare signs of exercise intolerance, the subject willmove to a lower level of exercise for the nexttraining session. If the signs of intolerance indicatethat the subject has become medically unstable,the subject will discontinue the intervention and bereferred for medical treatment.

Each patient will undergo a functional gaitevaluation prior to testing, and parameters ofperformance will be recorded during trainingsessions to track progress. Training will beconducted over 12 sessions or until a subject canwalk for 30 minutes at 3mph with 0% weightsupport assistance, whichever comes first. Asubject may also discontinue the training sessionby requesting that the session be discontinued.When either the 12 training sessions have beencompleted or the patient can walk for 30 minutesat 3mph with 0% weight support assistance, thepatient will be re-tested using the functional gaitassessment tool. Patients will also be asked fortheir subjective comments on training with the VRsystem. All testing and interventions are beingperformed at the Old Dominion University Schoolof Physical Therapy Research Laboratory.

5. CONCLUSIONS & FUTURE WORK

Although the initial research is being conducted onstroke patients, the VR-Gait system could be usedto treat any of the multiple gait disability causingailments mentioned in Section 1 above. Eventhough each area of gait rehabilitation may requiresome specific fine tuning of the system, the overallfunctionality of this system could be useful for allareas of gait disability.

Application with the amputee population is astrong possibility. Increased motivation andparticipation might be achieved by adding thegaming element of a scoring system, which wouldbe particularly appealing to younger patients, suchas young soldiers coming back from war.

The loss of vision on one side is a commonsymptom of stroke patients. This motivates futureimplementation of interactive events anddistractions in the VR environment in thehemisphere with diminished vision to stimulatedevelopment of a compensatory head-turninghabit.

The implementation of visual obstacles within theVR environment along with sensors to track theleg motion is another avenue of possible futureextension. While the use of a simulatedenvironment in rehabilitation is mainly a treatmenttool, it also will aid in medical decision making inpatient progress and prognosis. When the systemis fully developed it can be made intelligent, takinginto account the patient’s abilities in terms ofdistance, speed, weight bearing, and movementresponses so that the decision of when and howmuch to advance the program’s difficulty isautomatic and based on patient performanceparameters. Once a database of patient useparameters and endpoints has been established,the system could track a patient’s starting pointand the trajectory of progress in the first fewtreatments and predict the probable endpoint.Predicting a patient’s functional abilities andlimitations will help the patient, family andhealthcare providers make decisions about thefuture. This information may also be used topredict who will not benefit from continuedtreatment so that resources are used most wisely.

6. ACKNOWLEDGEMENTSThe authors thank the Old Dominion UniversityOffice of Research for supporting this project.

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