Harvard and MIT Rehabilitation Engineering Center with Prof. Robert W. Mann (1987)
MANN: I'm Professor Robert W. Mann, and I want to introduce you to the Harvard University Massachusetts Institute of Technology Rehabilitation Engineering Center. We are funded by a grant from the National Institute on Disability and Rehabilitation Research. Our focus is quantitative functional assessment. This videotape will introduce you to several of our ongoing projects.
The mobility facility in MIT'S Newman Laboratory for Biomechanics in Human Rehabilitation provides a state-of-the-art environment for the human movement research. A pair of electro-optical cameras are used to acquire kinematic data from human subjects. These cameras are capable of automatically digitizing the image position of point sources of infrared light. Triads of infrared light emitting diodes serve as the light sources. Arrays of these diodes are mounted on the body segments being studied.
As you see here, the set up for a typical gait experiment includes a total of four arrays mounted on the pelvis, thigh, shank, and foot segments. Track, a software package developed at MIT, first computes the three-dimensional position of each triad, then uses the known position of each triad with respect to a local body reference frame to compute the full six degree of freedom position and orientation of each segment.
Studies requiring temporal data of foot-to-floor reaction forces make use of the Kistler force platform embedded in the laboratory floor. A Silicon Graphics Iris workstation, running software developed at MIT, may be used to display collected data. As shown here, the upper left hand corner of the display shows an anthropomorphic figure having polyhedron segments which correspond to array segments defined during data collection.
The other three quadrants of the display show plots representing relevant anatomical angles. The measured foot-floor reaction force is displayed as a line segment having a length proportional to the force magnitude. A full gate experiment starts with the subject walking through the cameras intersecting fields of view with the instrumented foot stepping on the force platform.
Currently only one full gait stride may be viewed, but development is underway for an expanded system which will be capable of observing several consecutive gait strides. Those data is processed and displayed on the Iris workstation. The operator may rotate the figure to most any desired angle to study qualitatively the observed motions.
Simultaneously the operator may refer to the anatomical angle plots to obtain quantitative data of interest. Other types of lower extremity motions are also readily studied with this method. Note the long axis rotations of thigh relative to pelvis and shank relative to thigh. Most other gait analysis systems cannot acquire and display this sort of data. The squat demonstrates large excursions of the respective lower extremity joints.
In addition, bilateral data may be displayed and similarly studied. This data was collected at the Biomotion Laboratory of the Massachusetts General Hospital, a replica of the MIT Track system, with two cameras on each side of the subject and two force plates in the laboratory floor.
An example of quantitative functional assessment is a collaborative effort of the Massachusetts Institute of Technology and the Massachusetts General Hospital, which has made it possible for the first time to measure pressures in the hip of the living human. This accomplishment has had major impact on hip surgery, rehabilitation protocols, and on our understanding of how human joints function and fail.
This unique device serves the same role as a standard femoral head replacement implant. Microelectronics in the metal ball transmit the pressures measured at thin diaphragms in atmosphere which contact the acetabular cartilage in the hip socket. The metal sphere replaces the femoral head of the hip which has been damaged by injury or disease.
When implanted, the metal stem is cemented inside the femoral bone, and the radio transmitter is powered by an externally worn coil which creates a harmless, painless electromagnetic field inside the thigh. Graphical display of the data can be varied. Examples to follow show the patient walking, stair climbing, and rising from a chair.
During walking, the hip pressure and motion were recorded in the Biomotion Laboratory at MGH, which uses the MIT Track system. Computer graphics display the hip and leg motion. The force vector at the Kistler force platforms are also shown.
Pressures in the hip socket are recorded at locations 1 through 10. Their corresponding pressures are listed. The magnitude and direction of the hip pressure vector during walking is displayed by the lines emanating from the socket. The maximum pressure during walking occurs in the superior region of the hip.
Stair climbing is a more strenuous activity. Here we see the 3D graphic representation of the motion displayed by the computer. Again notice the force plate vector as the patient transfers load to the first step. The locations of highest pressure are shifted towards the posterior region of the socket, and the magnitudes are higher as compared with walking. During climbing, the maximum pressures traverse the posterior superior region of the socket.
The most stressful activity measured thus far is rising from a chair, particularly a low chair. Maximum pressures of nearly 3,000 pounds per square inch were recorded, more than doubling the pressures seen with running or jumping. This pressure is 100 times the typical automobile tire pressure.
The location of this maximum pressure was directly posterior. During rising from the chair, the magnitude of pressure starts high and is directed posteriorly, then rapidly decreases as the upright position of the subject is reached.
The third anniversary of the implantation of this prosthesis occurs during this RESNA meeting. The woman subject has been served admirably with an excellent hip replacement, and the data flow continues unabated and perfect.
NARRATOR: In the Newman Lab, Professor Neville Hogan and his students are developing the next generation of cybernetic controllers for artificial limbs. The true measure of effectiveness for a prosthesis control scheme is the amputees performance. To ensure the participation of amputees in the research, a facility has been developed for emulating, in hardware, any prosthesis design.
This facility consists of a high-performance artificial elbow that is worn by an amputee who controls it via the digital computer. The computer can be programmed to determine the way the prosthesis responds to the amputees commands. This provides a powerful vehicle for studying prostheses.
Proposed designs may be evaluated in a side-by-side comparison simply by reprogramming the computer. Because the goal of this research is to restore the functional capability of the upper limb, at present an amputee's ability to perform common activities of daily living is being evaluated. Many common functional tasks such as opening a door or pulling out a drawer are difficult to perform using existing cybernetic prostheses.
To study this problem, we are investigating a simple but representative task, turning a crank. The crank task requires of the amputee many important skills, namely postural stabilization, multi-joint coordination and constraint accommodation. In addition, the task is fully quantifiable. All pertinent motions and forces can be measured from both the crank and the prosthesis.
NARRATOR: In Newman Laboratory , Professor Will Durfee and his students are interested in the problem of how you control electrically stimulated muscle to restore useful function, such as hand grasp or gait. This work is done primarily through experimental studies which include stimulation of able-bodied and spinal-cord-injured subjects as well as stimulation in animal models.
When a quadriplegic's forearm muscles are stimulated to restore rudimentary grasp, the subject must somehow command the level of stimulation to control the grasp force. Current clinical systems monitor shoulder motion as the command channel, where raising the shoulder closes the hand, and lowering the shoulder opens the hand.
In this project Professor Durfee and graduate student Tom Moriano are examining the quality of various potential command channels, including shoulder motion. They have chosen to study this by instrumenting the potential command channel site on the able-bodied or spinal-cord-injured subjects and simulating the electrically stimulated hand grasp on an Amiga personal computer.
Here you see an able-bodied subject seated in a chair which restricts upper body movement. Joysticks are attached to the subject's shoulder to monitor motion. The subject's hand controls the computer mouse. On the computer display screen appears an animated picture of a hand which the subject is controlling in an attempt to grasp the cup, lift it off the table, and place it on the opposite table.
The subject controls the position of the animated hand by moving his shoulder up and down. Although the subject is just playing a complex video game, in fact, the system is an approximation to an electrically stimulated grasping system for quadriplegics. The advantage of the simulation system is that parameters can be easily changed to explore new command modalities. The results of this research should lead to a better understanding of appropriate means for spinal cord injured subjects to control electrically stimulated systems.
What you are seeing is the beginning of a project which is concerned with restoring gait in paraplegics. Jeff Hausdorff, a graduate student, is measuring the knee torque of an able-bodied subject when the quadriceps are electrically stimulated. He has applied surface electrodes from a commercial stimulation unit to the able-bodied subject, and is stimulating at increasing levels of amplitude.
Normally the torque is recorded by an instrument connected to the ankle by a cable, but here the leg is allowed to move. You can see how the leg moves up and down as Jeff manipulates the strength knob on the stimulator. The ultimate goal of this project is to determine if a combination of advanced orthotic bracing combined with electrical stimulation has the possibility of restoring gait of sufficient quality to be accepted by the spinal cord injured.
NARRATOR: In the US alone, it has been estimated that there are over one million people who are unable to speak due to neuromotor disability. This population includes people with cerebral palsy, head injury, ALS, and other conditions. The growing array of non-vocal communication systems available for them presents a formidable challenge to the clinician charged with making an optimal prescription.
In response to this need, Dr. Cheryl Goodenough-Trepagnier at Tufts New England Medical Center and Dr. Michael Rosen at MIT with their colleagues and students have developed the Tufts-MIT Prescription Guide. This computer-based system prompts a sequence of assessments and questionnaire entries.
From the data it establishes which devices in its database a client could use and calculates two scores for each device which are predictive of how well it will be used. One score is referred to as benefit. It is designed to be an index of the extent to which the features of a device meet the communication needs and constraints of a client. It is expected, therefore, to be predictive of his or her satisfaction.
Client data for this calculation is entered by the clinician in the form of answers to the needs questionnaire. Because a non-vocal client is not in general qualified to consider directly the technological features of communication systems, the questions are expressed in terms of the human and environmental circumstances and preferences which define the client's communication.
In order to derive the benefit score, the 155 answers are operated on by a knowledge-based system which transforms them into a profile representing the presence or absence of needs for device qualities, such as wearable portability and a minimal receiver mental load. Comparison of this profile with a needs met profile for each device results in calculation of benefit.
The other prescription criterion score calculated for each device is referred to as motor-determined maximum rate or MDM rate. It is an estimate of the limit imposed by the client's residual motor ability on the number of words per minute he or she could communicate with the device once it has become thoroughly familiar. The assessment data on which this index is based is obtained by means of special purpose test equipment rather than trial use of actual communication devices.
CLINICIAN: You ready? Okay, everything's. Ready. All set. Ready, go.
NARRATOR: In this scene the assessment for keyboard devices is being used. The switch closure time data acquired via the computer interface is used to derive a closed form model of the dependence of the client's movement time on the task parameters. This model is then applied to the language menu and physical characteristics of each device in the database to calculate the time which would be required to compose a standard corpus of text. MDM rate is calculated from that total.
CLINICIAN: Well okay.
NARRATOR: Each component of the motor assessment is intended to tap the specific motor abilities which determine the rate at which a client could use a particular class of devices. We saw that the assessment for keyboard-like devices requires the client to ultimately close pairs of switches whose location, size, force, and travel vary from task to task as quickly as possible.
CLINICIAN: There will be eight boxes. The fourth one is going to be filled in. That's your target. And when the cursor arrives at the one that's filled in, you're going to click the switch a the back of your head. Right? All right. Let's do it.
NARRATOR: In this scene, the client will be assessed for his ability to use scanning communicators, that is, those which can be controlled by a single switch used to interrupt the devices sequential presentation of its language menu. The clinician can repeat this assessment and is prompted to do so with any apparently appropriate type of switch at any body site he or she feels might be optimal for speed and ease of use.
The software establishes values of four response times from the acquired data. These results are used along with files on scanning devices from the system's database to establish the greatest scanning rate at which each device could be used. From that value, the time to compose the standard text and MDM rate are derived.
For some clients a potentially advantageous approach to device control is placement of several switches at body sites where useful motor acts are available. This kind of interface applies to encoded devices, that is those which allow a selection of a language item by means of a sequence of selections from among a small number of switches.
CLINICIAN: Okay Louie. What you have to do on this task is we have to hit between the back of your head, the switch on the back of your head and one to your left as fast as possible until the computer tells you to stop. You'll hear the little beeps like you did before. So are you ready?
NARRATOR: The switch closure timing data acquired by the computer is processed to prepare a table containing the average closure to closure times for all pairs of switches. For each device in the database which can be operated in this manner, another file is available which contains the frequencies of occurrence of all switch pairs as they occur in composition of the standard text. MDM rate is calculated by combining the timing data with the frequency data.
CLINICIAN: There it goes.
NARRATOR: A variety of outputs is available to the clinician at the end of the procedure. Shown here is an example of the summary output which lists all devices the client is capable of using along with the value of MDM rate and benefit for each. The prescriptive decision is made on the basis of these quantitative indices of the match of client to device. Refinement and evaluation of the system are in progress in the laboratory and at several clinical sites.