BioMed Central
Page 1 of 15
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Journal of NeuroEngineering and
Rehabilitation
Open Access
Research
Smart portable rehabilitation devices
Constantinos Mavroidis*, Jason Nikitczuk, Brian Weinberg, Gil Danaher,
Katherine Jensen, Philip Pelletier, Jennifer Prugnarola, Ryan Stuart,
Roberto Arango, Matt Leahey, Robert Pavone, Andrew Provo and
Dan Yasevac
Address: Department of Mechanical & Industrial EngineeringNortheastern University360 Huntington Avenue, Boston MA 02115, USA
Email: Constantinos Mavroidis* - mavro@coe.neu.edu; Jason Nikitczuk - jasonn@coe.neu.edu; Brian Weinberg - shwagg01@yahoo.com;
Gil Danaher - gdanaher@coe.neu.edu; Katherine Jensen - kjensen@coe.neu.edu; Philip Pelletier - ppelleti@coe.neu.edu;
Jennifer Prugnarola - jprugnar@coe.neu.edu; Ryan Stuart - rstuart@coe.neu.edu; Roberto Arango - robaran@yahoo.com;
Matt Leahey - mleahey@coe.neu.edu; Robert Pavone - pavone.r@neu.edu; Andrew Provo - provo.a@neu.edu;
Dan Yasevac - yazy33@hotmail.com
* Corresponding author
Abstract
Background: The majority of current portable orthotic devices and rehabilitative braces provide stability, apply precise
pressure, or help maintain alignment of the joints with out the capability for real time monitoring of the patient's motions
and forces and without the ability for real time adjustments of the applied forces and motions. Improved technology has
allowed for advancements where these devices can be designed to apply a form of tension to resist motion of the joint.
These devices induce quicker recovery and are more effective at restoring proper biomechanics and improving muscle
function. However, their shortcoming is in their inability to be adjusted in real-time, which is the most ideal form of a
device for rehabilitation. This introduces a second class of devices beyond passive orthotics. It is comprised of "active"
or powered devices, and although more complicated in design, they are definitely the most versatile. An active or
powered orthotic, usually employs some type of actuator(s).
Methods: In this paper we present several new advancements in the area of smart rehabilitation devices that have been
developed by the Northeastern University Robotics and Mechatronics Laboratory. They are all compact, wearable and
portable devices and boast re-programmable, real time computer controlled functions as the central theme behind their
operation. The sensory information and computer control of the three described devices make for highly efficient and
versatile systems that represent a whole new breed in wearable rehabilitation devices. Their applications range from
active-assistive rehabilitation to resistance exercise and even have applications in gait training. The three devices
described are: a transportable continuous passive motion elbow device, a wearable electro-rheological fluid based knee
resistance device, and a wearable electrical stimulation and biofeedback knee device.
Results: Laboratory tests of the devices demonstrated that they were able to meet their design objectives. The
prototypes of portable rehabilitation devices presented here did demonstrate that these concepts are capable of the
performance their commercially available but non-portable counterparts exhibit.
Conclusion: Smart, portable devices with the ability for real time monitoring and adjustment open a new era in
rehabilitation where the recovery process could be dramatically improved.
Published: 12 July 2005
Journal of NeuroEngineering and Rehabilitation 2005, 2:18 doi:10.1186/1743-
0003-2-18
Received: 19 March 2005
Accepted: 12 July 2005
This article is available from: http://www.jneuroengrehab.com/content/2/1/18
© 2005 Mavroidis et al; licensee BioMed Central Ltd.
This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/2.0
),
which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
Journal of NeuroEngineering and Rehabilitation 2005, 2:18 http://www.jneuroengrehab.com/content/2/1/18
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Introduction
During the last several decades a great deal of work has
been undertaken for developing devices to accelerate
recovery from injuries, operations and other complica-
tions. Many successful devices and methods have come
out of this work. This included a general division of the
recovery process into several phases.
In the early stages of therapy, passive rehabilitation is
often a preferred method for reducing swelling, alleviating
pain, and restoring range of motion. This consists of mov-
ing the limb with the muscles remaining passive and often
involves devices such as Continuous Passive Motion
(CPM) machines. The next stage of rehabilitation is often
an active-assistive movement phase, which involves using
external assistance to assist the muscles in moving the
joint in order to reestablish neuromuscular control. Vari-
ous different methods are presently used for this purpose,
including various braces, orthoses, and large machines.
The final stages aim at returning an individual to normal
activities via resistance exercises that are usually focused at
regaining muscle strength. Isokinetic machines are well
known, ideally suited systems for achieving this final goal.
In this paper we present a compilation of several new
developments in the area of portable and smart rehabili-
tation devices, being developed by the Northeastern Uni-
versity Robotics and Mechatronics Laboratory. The
devices that will be presented in this paper are:
a) a transportable continuous passive motion device ide-
ally suited for nearly any aspect of the earlier rehabilita-
tion stages of the elbow,
b) an electro-rheological fluid based device for resistance
exercises and control of the knee;
c) an electrical stimulation and biofeedback device for
active-assistive exercises of the knee.
The presented devices span across all three of the men-
tioned phases in rehabilitation and exhibit many advan-
tages over current technology. All three devices have been
developed to increase the efficiency in rehabilitation exer-
cises while remaining compact and portable. In each case,
the capabilities of present technology have been taken
into consideration and each device is designed to have
similar characteristics. The most notable difference how-
ever, between this new breed of rehabilitation devices and
currently used equipment is their highly adaptive, versa-
tile and reprogrammable nature. Computer control is
intrinsic to the design of each device presented in this
paper and is a central theme behind their operation. This
makes for highly effective tools for a wide range of appli-
cations. More specifically, the advantages of our advanced
orthotics can be divided into four main categories: cost,
portability, real-time abilities, and versatility.
Cost
The designed advanced rehabilitation devices resolve sev-
eral issues with cost with present-day technology. Every
initial feasibility prototype fell just short of $2,000 to
build. With all the electrical and sensory components that
need to be added to each device for a final functional and
marketable product, it is estimated to cost approximately
$,3500. A state of the art, computer controlled Isokinetic
Machine, such as the Biodex System 3 Pro, can be bought
for over $40,000. Clearly, direct cost comparisons warrant
the use of advanced rehabilitation devices over the com-
parable rehabilitation machines. Indirectly, the smaller
size of the advanced rehabilitation devices also brings
down costs by eliminating concerns with storage, porta-
bility, and weight. Rehabilitation machines are inherently
large and require a permanent or semi-permanent set-up.
The facility able to house such a device along with the per-
sonnel required for operating them is at a large economi-
cal disadvantage to smaller facilities using these much
more compact advanced rehabilitation devices. Numer-
ous devices, at an overall lower cost than a single
machine, could be stored in something as simple as a
closet. The devices themselves could easily be transported
by the patients for use at home as well, saving time and
money in the costly trips to specialized facilities.
Portability
The most important feature of such a device is the fact that
it is a portable and wearable form of rehabilitation. The
compact and lightweight characteristics of these advanced
rehabilitation devices allow them to be used in an average
chair, while standing, or perhaps even during ambulatory
motion. Their application is limited by only the user's
abilities, meaning weaker patients can use it for resistive
exercises while stronger patients can use it for both weight
training as well as proper gait training. Equally notewor-
thy is the new capability for patients to take the device
with them and exercise on their own time, from the com-
fort of their own home or office, or for use during their
every day routines. All exercises being recorded, a physical
therapist could simply download the data remotely and
analyze the effectiveness and efficiency of the device,
without ever needing the patient to revisit the medical
facility.
Real-Time Abilities
The ability of rehabilitation machines to function in real-
time, is what separates them from their less efficient coun-
terparts, the conventional orthotics. The inclusion of this
feature is intrinsic to the utilization of compact advanced
actuators and smart sensors in our portable and smart
rehabilitation devices. They are easily computer
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controlled, and can react in the order of milliseconds.
With such controllability, a rehabilitation regime can be
perfectly tailored to each patient's individual needs very
easily. Ideally, with closed loop control, feedback from
the sensors would allow a computer to calculate the effi-
ciency of each specific exercise and alter them in real-time
accordingly to achieve optimal levels of rehabilitation.
Versatility
Probably the most unique advantage of these devices
arises from their versatility. With comparable abilities to
modern day rehabilitation machines and similar func-
tionality to several different types of these machines, the
all-encompassing nature of these advanced orthotics
alone makes them equally as versatile. However, due to all
their additional strengths and advantages, including size,
portability, and real-time computer control, the applica-
tions of these devices goes above and beyond those of the
competing technologies. In the area of rehabilitation,
these advanced orthotics could be a valuable tool in the
development of new rehabilitation exercises and regimes.
With complete control and tunability of the device, any
type of complex algorithm defining the motion or resist-
ance of the patient's knee could be easily implemented.
Whole new concepts in rehabilitation or weight training
could potentially be developed using this device as a
research instrument, providing all the force and feedback
necessary for any type of investigation. For more compli-
cated medical disabilities, for instance in the case of gait
correction in stroke patients, both analysis and imple-
mentation of newly developed methods could also be eas-
ily performed. Other potential applications, showing the
extreme versatility of this device, include virtual reality
simulations and athletic training, such as in rowing and
weight-lifting.
Portable continuous passive motion elbow
device
Overview
A transportable elbow rehabilitation device for use
throughout the entire process of rehabilitating patient's
with severe elbow trauma was designed, built, tested and
optimized. The apparatus has three settings – passive,
active and bracing. The device consists of a D.C. motor,
gearbox, encoder, clutch and brake located in a portable
unit, attached through a flexible shaft to an absolute
encoder located on an elbow brace. In the passive setting,
the device moves the forearm about the elbow joint to
regain the range of motion. It acts as a "smart" continuous
passive motion machine because constant sensor feed-
back enables the device to push to the patient's maximum
range of motion during each cycle. Torque and speed of
the passive movement is controlled through the current
and voltage, respectively, drawn by the motor. In the
active setting, variable resistance is applied using the
brake. Both settings are controlled, monitored and
recorded using a LabVIEW program on a personal compu-
ter, with specific protocol defined by a physician, physical
therapist or athletic trainer. Currently available CPM
machines are not transportable, do not sense the patient's
range of motion and do not allow for an active setting. By
combining three different functions (active mode, passive
mode and bracing) of the device into one transportable
unit, the next generation of elbow rehabilitation devices
was created.
Significance and Background
Following surgery, stroke or other injury to the elbow, a
patient's range of motion is reduced due to trauma expe-
rienced at that location. Increasing the user's range of
motion is the first step in a full recovery. This is accom-
plished through passive motion, where the patient's fore-
arm is actively forced to flex and extend, followed by
strength training. At this point, most doctors or physical
therapists begin to use a continuous passive motion
(CPM) machine. A CPM machine moves the forearm
about the elbow joint to regain the patient's range of
motion. Unfortunately, current CPM machines often
involve a complicated set up, are non-portable, and are
most importantly inefficient. Their inefficiency arises
from their inability to recognize when the user's range of
motion has increased. The machine must be continuously
monitored and manually reset to further increase the
range of motion. A related concern is the possibility of
forcing the patient's arm past his or her range of motion
resulting in further damage to the joint. The range of
motion can only be increased in very small increments
and movement about the elbow is nonproductive once
the preset range is achieved. There are several patents cov-
ering the range of elbow rehabilitation devices [1-6]. Sev-
eral companies such as Breg, Dyna Splint, Ultra Flex,
Biodex CPM and the Bledsoe Extender Arm Brace have
products out on the market that immobilize the injury
and prepare the elbow for rehabilitation [7-12]. However,
the only portable devices that are available provide either
spring tension against an elbow contracture to achieve
increased motion or locking mechanisms to restrict
motion and prevent further injury. There are currently no
commercially available devices that are portable and pro-
vide the passive motion required in the beginning stages
of elbow rehabilitation.
Design and Prototype
A wearable and portable CPM device that senses increases
in the patient's range of motion and simultaneously
increases its range of motion has been developed in our
laboratory. The patient's torque and motion limits are
inputted into a computer interface. The program then
monitors and controls all of the components of the
device, progressively increasing the user's range of motion
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about the joint within the torque and motion range.
Through sensory input, the computer senses when the
user's muscular resistance has reached its limit and signals
a reversal in direction of motion, allowing for maximum
range of motion to be reached quickly and efficiently,
without harm to the patient.
This new transportable elbow rehabilitation device also
safely and efficiently assists throughout the rest of the
entire rehabilitation process, including bracing the joint
and building muscle mass. The device has adjustable set-
tings for each stage of rehabilitation. The passive motion
setting, as mentioned, uses constant sensor feedback that
enables the device to progressively increase the user's
range of motion. The device is also capable of applying
variable resistance about the elbow joint to build muscle
mass once the patient's ideal range of motion has been
achieved. This mode is very similar to Isokinetic
machines. Finally, the device is also capable of acting as a
simple brace: either locking in place to prevent the user
from moving his or her arm, or disengaging entirely to
provide mediolateral support. The combination of all
three modes with adjustable settings within each mode,
allows this device to be utilized through the entire rehabil-
itation process for a variety of elbow injuries.
The elbow device is lightweight, easily programmable and
transportable. A CAD rendering of the device and its com-
ponents can be seen in Figure 1.
The device can be split into two subsystems. The first is the
brace worn by the patient. It is designed around an Ortho-
merica Prime Elbow System brace and includes an optical
encoder, for measurements of position and velocity and
an attachment point for a flexible shaft. This flexible shaft
connects the brace to the second subsystem, a tabletop
drive assembly unit that provides the functionality of the
device. It houses a DC motor, an electrically controlled
clutch and magneto-resistive fluid brake and is designed
to fit in a backpack. The flexible shaft allows the user to
move freely while the device is in use and easily detaches
from the brace, providing the patient with a protective
elbow brace to continue daily routines when not in use.
The motor-gearbox combination provides the passive
exercise motion for the patient to increase his or her range
of motion. A current limiter set in the motor control box
ensures that the patient does not exceed his or her range
of motion. The current measurement is converted to
torque resistance in the computer and once the prepro-
grammed limit is exceeded; the motor direction is
reversed
Between the motor and flexible shaft is the electrically
controlled clutch. It serves mainly as a safety feature for
the patient. It disengages if the user hits the stop switch, if
the current exceeds the motors limited levels, or when the
active feature is in use. This active feature functions with
the use of a magneto-resistive fluid (MRF) brake. The
brake is manufactured by Lord Corporation and features a
simple yet rugged design, high torque, and quiet opera-
tion. It provides smooth, controllable resistance to the
patient for building muscle and tissue strength in the
elbow joint. The MRF brake and motor in-line assembly
can also be used in combination. This provides the user
with an extra impulse of motion after they have used the
resistive feature to their maximum range of motion or
active-assistance.
The device was constructed for feasibility analysis. Figure
2 shows the full assembly. The device has a mobility range
of 155 degrees. The motor, gearbox (1:134 gear ratio), and
clutch combination was found to be capable of producing
10 N·m of torque. The MR brake was found to have a
maximum resistive torque capability of 5.6 N· m. All
CAD rendering of portable elbow deviceFigure 1
CAD rendering of portable elbow device.
Table 1: Elbow Device Design Summary
System Characteristics:
Range of motion (0° being full extension) ± 77.5°
Continuous Passive Motion capabilities 10 N·m
Isokinetic capabilities 5.6 N·m
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these performance characteristics can be found listed in
Table 1.
The motor, encoder, brake, and clutch are controlled
through a LabVIEW 7.0 program on the PC. The user inter-
face is simple, and utilizes tab controls that allow the user
to select either the active or passive setting. In the active
setting, the user inputs the resistive torque required for
exercise and can see a real-time plot of the joints position
and resistance level. Inputs in the passive setting include
the number of repetitions, speed, and minimum and max-
imum angles. The user can view real time plots of position
and torque being applied to their joint during the exercise
routine. The graphic user interfaces for the passive motion
can be seen in Figure 3.
Electro-rheological fluid based knee resistance
device
Overview
This device aims to demonstrate the feasibility of using
Electro-Rheological Fluid (ERF) actuators in orthotics, cre-
ating a new breed of rehabilitation devices. ERFs are fluids
that experience dramatic changes in rheological proper-
ties, such as viscosity or yield stress, in the presence of an
electric field. Using the electrically controlled rheological
properties of ERFs, compact actuators with an ability to
supply high resistive torques in a controllable and tunable
fashion, have been developed. This study involves the
design, fabrication and testing of an ERF based knee
orthotic device and the innovative ERF actuators it uses.
The knee orthotic is achieved through a standard brace
design with a polycentric hinge and gear system. Coupled
to this are two Flat-Plate ERF actuators, given that name
for their characteristic set of parallel flat plates allowing
for actuation of the fluid. The overall knee orthotic system
is designed to resist up to 25.4% of an average human
knee's torque abilities and be controlled in real-time. The
goal of this work is to provide a much more efficient
means of rehabilitation over the average orthotic, while
matching the proficiency of rehabilitation machines, all
in a smaller, simpler, and more cost efficient design.
Significance and Background
An orthotic device by strict definition is a specialized
mechanical device that supports or supplements weak-
ened or abnormal joints or limbs. The majority of these
devices can be categorized as passive, meaning the resist-
ance or support they provide is not changed in real time.
The Sports Medicine Committee of the American Acad-
emy of Orthopedic Surgeons has further classified these
types of braces, specifically used for the knee, into four
categories: prophylactic, rehabilitative, functional and
patellofemoral. All provide stability, apply precise pres-
sure, and/or help maintain alignment of the knee joint at
set constants.
Some of the more innovative designs allow torsion to be
applied at the knee joint and new technology has further
improved their efficiency by allowing the torque to be
adjusted. However, the lack of real-time abilities is a sig-
nificant downside for these devices that limits their over-
all effectiveness in rehabilitation. The inclusion of active
components has been a widely accepted method of
improving upon this deficiency.
This seemingly small addition has considerable draw-
backs though. The application of traditional active ele-
ments increases the overall size, cost, weight, and other
related characteristics. Equally important are the concerns
with control and sensory feedback, which would also be
considered necessary with the addition of active compo-
nents. All these combined, along with the obvious goals
of making the systems as efficient and beneficial to an
individual during rehabilitation as possible, force their
designs to go beyond that of a portable orthosis, and more
so a machine.
In terms of rehabilitation, the most effective methods
known today are these rehabilitation machines. They are
commonly used for rehabilitating and strengthening
patients, subjects, and athletes while providing
quantitative measurements of their performance. They
provide high resistive and sometimes assistive forces,
while providing a unique tailoring of the rehabilitation
regime to nearly any individual. This ability dramatically
increases their proficiency as a rehabilitation tool. Their
services have been limited to primarily only physical ther-
apy offices though, as a direct result of their shear size,
weight, and cost.
Electro-rheological fluids (ERFs) are fluids that experience
dramatic changes in rheological properties, such as viscos-
ity, in the presence of an electric field. Willis M. Winslow
first explained the effect in the 1940's using oil disper-
sions of fine powders [13]. The fluids are made from sus-
pensions of an insulating base fluid and particles on the
order of one tenth to one hundred microns (in size). The
volume fraction of the particles is between 20% and 60%.
The electro-rheological effect, sometimes called the Wins-
low effect, is thought to arise from the difference in the
dielectric constants of the fluid and particles. In the pres-
ence of an electric field, the particles, due to an induced
dipole moment, rearrange into a more organized manner,
or form chains along the field lines. These chains alter the
ERF's viscosity, yield stress, and other properties, allowing
the ERF to change consistency from that of a liquid to
something that is viscoelastic, such as a gel. ERF's gener-
ally respond to changes in electric fields in a matter of
only a millisecond or two. Good reviews of the ERF phe-
nomenon can be found in [14,15].
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Portable elbow device: full assemblyFigure 2
Portable elbow device: full assembly.
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Control over a fluid's rheological properties offers the
promise of many possibilities in engineering, especially
actuation and control of mechanical motion. Devices that
rely on hydraulics can benefit from ERF's quick response
time and reduction in device complexity. Their solid-like
property in the presence of a field can be used to transmit
forces over a large range and have found a number of
applications. A list of many engineering and practical
applications of ERFs can be found in [16]. Our team has
developed several prototypes of ERF-based linear and
rotary actuation elements [17,18], which can apply con-
trollable resistive forces and torques such as the Flat Plate
(FP) rotary actuator concept which is the primary compo-
nent of the ERF actuated knee orthosis described below.
Design and Prototype
The ERF knee device possesses the ability to accurately
provide large resistive forces with full real-time control
while remaining completely portable and wearable. These
characteristics make it an ideal apparatus for several appli-
cations. For active rehabilitation exercises it replaces the
need for overly cumbersome and reasonably outdated
machines, by remaining a lightweight portable system
that is capable of all the same forces, control, and more.
Similarly, it replaces the need for large weight-lifting
machines. For gait-training purposes, such as in stroke
patients with hyperextension difficulties, it is a viable clin-
ical device. Through the sensors embedded in the device,
computer closed-loop control, and clinical training these
disabilities are overcome by providing real-time resistance
that limits motion and supports the weight of the user, to
retrain a proper gait. Additionally, the portability of the
device adds a whole new dimension to rehabilitation and
exercising in general, where the patient is now able to take
a powerful isokinetic machine home, to work, on vaca-
tion, or wherever else they may travel.
The design of this innovative device consists of three
major subsystems – an ERF based resistive actuator, a gear
system, and the structural brace frame. The ERF based
resistive actuators, which provide a bias force to the knee
joint, simulating whatever forces desired, consist of
multiple parallel rotating electrode plates and they are
called Flat Plate resistive actuators. They are attached via a
gear system to a standard brace as seen in the CAD render-
ing of Figure 4.
Several circular copper plates (shown in Figs. 5a and 5b)
are located parallel to each other, on a fixed axis. On a par-
allel, concentric axis, are another set of copper plates,
which lie parallel and alternate with the fixed plates. The
latter set of plates can rotate relative to the fixed plates,
and the small gap between the plates contains ERF. Apply-
ing an electric field across the gap causes the fluid proper-
ties to change (in a matter of milliseconds), resulting in an
increase in yield stress. The change physically alters the
fluid from the consistency of thin oil to that of a thick gel.
This property is used to control the resistive forces of the
ERF FP actuator. The copper electrode plates with an inner
and outer radius, r
i
and r
o
, respectively and a gap of d
between plates can be seen in Figure 5a. Based upon the
dimensions of the variables r
i
, r
o
, and d the design of the
FP resistive actuator can be adjusted to produce a device
Passive motion graphical interfaceFigure 3
Passive motion graphical interface.
CAD rendering of electro-rheological fluid based knee orthosisFigure 4
CAD rendering of electro-rheological fluid based knee
orthosis.
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capable of the resistive torques needed for any
application. Figure 5b shows the assembly of a multiple
Flat-Plate ERF element in CAD.
The entire ERF assembly is housed in a casing that seals in
the fluid and attaches to a gearbox. The gearbox transmits
and multiplies the torque output of the FP resistive actua-
tors while supporting them on the frame. The brace frame
is an off-the-shelf knee brace with all the features neces-
sary for the device. It boasts a polycentric hinge, comfort-
able strapping method, and a lightweight, rigid frame.
Included in the design were optical encoders for measur-
ing angle, speed, and acceleration of the knee.
(a) Electrode plates (b) Internal assembly of the FP ERF resistive actuatorFigure 5
(a) Electrode plates (b) Internal assembly of the FP ERF resistive actuator.
(a) (b)
Table 2: ERF Based Knee Device Design Summary
Actuator Parameters:
Gap size (d) 1.0 mm
Inner Radius (r
i
)20.0 mm
Outer Radius (r
o
)45 mm
Number of Plates 17
Actuation Voltage 4.25 kV
Maximum Actuator Torque 9.17 N·m
System Characteristics:
Gear Ratio 1:1.67
Torque Produced by Device 30.16 N·m
Components of the brace's ERF FP actuatorFigure 6
Components of the brace's ERF FP actuator. Fabri-
cated case with o-ring seal (top left); CNC machined elec-
trodes with rapid prototyped mounts (top right); fabricated
rotating shaft with steel output shaft and commuter installed
(bottom left); actuator shaft with rotating plates attached
(bottom right).
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An initial prototype of the design was built for feasibility
analysis. The final actuator was rapid prototyped using a
3D Systems Viper 2000i
2
machine. It was bench tested and
was found to produce a maximum resistive torque of 9.16
N·m. A Don Joy 4TITUDE™ knee brace was donated by
the company Don Joy Orthopedics, slightly disassembled
and machined to allow for attachment of the gearbox and
actuator. A gear ratio of 1:1.67 was used resulting in an
overall device resistance of approximately 30.16 N·m.
The final system successfully demonstrated an accurate
and easy controllable system for resisting knee motion. In
Table 2 a summary of the device characteristics and the
Close up views of the ERF actuated braceFigure 7
Close up views of the ERF actuated brace. Fabricated gearbox (left); Inner hinge (center left); Attached Actuator casing
made with slots so inside plates are visible (center right); Fabricated actuator attached, filled with fluid, and encoder mounted
(right).
First version prototype of the ERF driven knee rehabilitation orthosisFigure 8
First version prototype of the ERF driven knee rehabilitation orthosis. Left actuator casing is made with slots so
inside plates are visible, right actuator is filled with fluid.
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actuator parameters can be found. Below are several
images of the prototype and close-ups of some of the indi-
vidual parts (Figs. 6, 7, 8).
So far tests were performed to verify the capabilities of the
actuators. Since two identical actuators were used, the
verification of one of these actuators would be theoreti-
cally as accurate as creating a duplicate of a human knee
joint for the purpose of testing the whole device. The aver-
age torque output of the actuator at each voltage was
plotted and compared to the predicted theoretical equa-
tion's results. Figure 9 was the result and the two plots
show a very close resemblance. The accurate results there-
fore suggest that the proposed system is capable of the
forces desired.
Electrical stimulation and biofeedback knee
device
Overview
A knee brace that can be used in multiple stages of reha-
bilitation by using various therapy techniques was devel-
oped by our team. Following knee surgery most patients
experience muscle atrophy and in some cases nerve dam-
age. To overcome these problems physical therapists have
turned to the use of electrical stimulation (E-Stim) and
biofeedback (EMG) as the preferred methods of
treatment. These forms of therapy help to increase the
range of motion of the knee and improve neuromuscular
re-education. By incorporating these units, along with a
rotary encoder, into a post-operative brace it is possible to
monitor the progress of the patient in a unified computer
Theoretical vs. experimental torque of final designed/fabri-cated actuator for ERF driven knee rehabilitation orthosisFigure 9
Theoretical vs. experimental torque of final designed/fabri-
cated actuator for ERF driven knee rehabilitation orthosis.
Theoretical Torque vs Experimental Torque
0
1
2
3
4
5
6
7
8
9
10
00.511.522.533.544.5
Electric Field [kV/mm]
Torque [N m]
Theoretical
Experimental
Schematic of the smart knee braceFigure 10
Schematic of the smart knee brace.
Control Box
PC & Labview User Interface
Post-Operative
Brace
Rotary Encoder
E-stim Pad
Brace Support
EMG Pad
Control Box
PC & Labview User Interface
Post-Operative
Brace
Rotary Encoder
E-stim Pad
Brace Support
EMG Pad
Journal of NeuroEngineering and Rehabilitation 2005, 2:18 http://www.jneuroengrehab.com/content/2/1/18
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controlled setting. It also allows the patient to perform the
rehabilitation while walking in a stable brace which pro-
motes proper gait. A graphical user interface was built in
LabView to monitor the various sensing units of the bio-
feedback knee brace.
Significance and Background
During physical therapy, an articulated controlled motion
and exercise is crucial in a successful physical therapy
process. Controlled motion benefits the ligaments, bones,
and soft tissue and prevents them from becoming degen-
erative. Resistance exercises help build muscle mass and
restore functionality to the limbs. Devices such as the two
previously mentioned are ideal for these two cases. Alter-
native systems exist however, that use very different
methods for overcoming the same aspects in
rehabilitation. These include electronic stimulation and
biofeedback.
Electrical Stimulation (E-Stim) is a rehabilitative treat-
ment that stimulates nerves by sending an electrical cur-
rent through the skin. In knee surgery rehabilitation the E-
Stim is typically used to activate the muscles around the
knee for the purposes of neuromuscular re-education. In
the early post-operative stages the E-Stim is used for active
rehabilitation, where it stimulates the motor nerves of
muscles without the patient's effort. In the secondary
stages of therapy the E-Stim is used in active-assisted
motion, where patient uses their muscles along with the
external stimulation to move the joint. E-Stim can also be
used while exercising muscles as well.
Biofeedback implemented by EMG is a device that moni-
tors muscle activity. The feedback provides valuable infor-
mation regarding progress and muscle performance. The
data from this device allows therapists to gain a better
understanding of how the patient is responding to the
treatment. This means that the therapy can be better tai-
lored to the individual.
Following knee surgery many patients experience muscle
atrophy and in some cases nerve damage. To overcome
these problems, physical therapists have turned to the use
of electrical stimulation and biofeedback as the preferred
methods of treatment. These forms of therapy help to
increase the knee range of motion as well as reduce pain,
swelling, and total recovery time.
Design and Prototype
A knee brace combining electrical stimulation with the
sensory information from biofeedback and other sensors
Graphical controls interface for the electrical stimulation and biofeedback knee deviceFigure 11
Graphical controls interface for the electrical stimulation and
biofeedback knee device.
Electrical stimulation and biofeedback knee deviceFigure 12
Electrical stimulation and biofeedback knee device.
Journal of NeuroEngineering and Rehabilitation 2005, 2:18 http://www.jneuroengrehab.com/content/2/1/18
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has been developed as shown schematically in Figure 10.
The information from the biofeedback and a rotary
encoder are fed to a computer. The computer compares
the EMG information to the data it receives from the lin-
ear encoder. If it detects a bio-signal being sent from the
brain to the leg, but there is no motion in the brace, the E-
Stim is triggered to assist the patient. All information
gathered by the sensors is presented to the operator within
a graphical interface, where it is also possible to adjust the
settings for proper customizing of the exercises (see Figure
11 for a screen capture of this interface).
The flexibility and computer control of this device results
in a valuable autonomous tool for a variety of
rehabilitation exercises. The system, as described, can be
used in place of or in conjunction with any exercise
involving passive rehabilitation or active-assisted (the two
earlier post-operative rehabilitation stages). With the
addition of the foot switch, which is placed under the sole
of the patient's shoe, the system can be used to aid in
walking and regaining proper mobility. When pressure is
exerted on the switch, it triggers the electrical stimulation
on the quadriceps as well as the tibialis anterior, to assist
in such situations as with those who suffer from foot drop
due to nerve damage. Furthermore, the system boasts the
added benefits of allowing the patient to perform the
walking exercises while wearing a stable brace (promoting
Control box for the electrical stimulation and biofeedbackdeviceFigure 13
Control box for the electrical stimulation and biofeedbackdevice.
Journal of NeuroEngineering and Rehabilitation 2005, 2:18 http://www.jneuroengrehab.com/content/2/1/18
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a more proper gait) and establishes an easy way to moni-
tor their progress.
A prototype was developed to demonstrate the proposed
concept as shown in Figure 12. This prototype uses a Don
Joy TROM knee brace as a frame for the device. The
padding for this brace was adapted to allow the e-stim and
EMG electrodes to be adhered to the proper locations on
the leg. Polyethylene brace supports were also added to
the upper and lower sections of the brace. This adds
stability and makes the brace significantly easier to put on.
In addition, the hinge on the brace was modified so that a
1/4" diameter shaft rotates with the lower section of the
brace. A Renco rotary encoder was attached to this shaft so
that the angle and velocity of the knee brace could be
determined. The wiring from the e-stim, EMG and the
rotary encoder is covered by a custom wiring conduits
located along the rails of the brace. Once the wiring leaves
the brace it is hooked up to a control box, which houses
all of the electronics. This includes the ProComp Infiniti
biofeedback unit, the Respond II e-stim unit, as well as
two solid state relays. This control box is also connected
to a personal computer. Figure 13 is a picture of the con-
trol box with the components labeled.
A graphical user interface in Labview is responsible for
controlling the response of the system (see Figure 11). The
information from the EMG biofeedback and the rotary
encoder are fed to a computer via Labview. The computer
will then compare the EMG information to the data it
receives from the rotary encoder. If it detects a signal being
sent from the brain to the leg, but there is no motion in
the brace, the e-stim will be triggered to assist the patient.
This will help re-educate the neuro-muscular system. This
information will be presented to the operator with a
graphic interface. By controlling the operation of the e-
stim through adjustable set points in the lab view program
the physical therapist will be able to apply the device
throughout the entire rehabilitation process.
The device was tested to ensure all the components were
coordinated correctly. The test subject was instructed to
perform a steady extension of the knee as shown in Figure
14. In the testing, the subject attempts to do seated leg
extensions with the help of the brace. In this exercise the
subject sits on the edge of a table and attempts to extend
their lower leg horizontally. When the subject reaches a
point where they can't extend their leg any further under
their own power, the EMG biofeedback senses this data.
Then the logic in the controls will compare the readings
with the information from the rotary encoder. If the EMG
signals are above the threshold this is set and the rotary
encoder is stationary then the e-stim is triggered. The e-
stim causes the quadriceps to contract helping the subject
to achieve full extension. Since we were testing on a
healthy subject, the threshold was set to a low value so
that the e-stim was triggered in the middle of the exercise.
Figs. 15a–d shows the results of one of these tests. Once
reaching his maximum point, the EMG unit is seen detect-
ing the muscle trying to move with no movement
registered by the encoder. This triggered the E-Stim device
and current was sent to the muscle, forcing the muscle to
complete the extension movement. All processes worked
correctly setting the ground work for a very versatile and
efficient system.
Conclusion
The designs of the three systems described involve the
meshing of standard, mechanical solutions and novel,
new age ones. Besides being innovative the devices were
all designed with a few key factors in mind. Compactness
and portability were desired to compete with present day
equipment that is currently quite large, permanent, and
tedious to set-up and use. This was obviously met in each
case, where all three devices are wearable, can be trans-
ported easily and involve computer control that simplifies
their use significantly. Finally, the prototypes of portable
rehabilitation devices presented here did demonstrate
that these concepts are capable of the performance their
commercially available but non-portable counterparts
exhibit. After proving this feasibility, analyzing the effi-
ciency of these devices is the next obvious phase.
All three devices will be undergoing redesigning and con-
struction to optimize their operation in order to proceed
to human testing. Collaborations with large companies
have been established for the development of specialized
Human subject wearing the instrumented biofeedback knee deviceFigure 14
Human subject wearing the instrumented biofeedback knee
device.
Journal of NeuroEngineering and Rehabilitation 2005, 2:18 http://www.jneuroengrehab.com/content/2/1/18
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braces for these projects. Additionally, collaborations and
arrangements are already in place for human testing at
Spaulding Rehabilitation Hospital located in Boston,
Massachusetts. If these tests are successful, they will open
the door to a new era in rehabilitation where the recovery
process could be dramatically improved through the use
of a whole new breed of rehabilitation devices.
Acknowledgements
Special thanks to Paul Canavan and Sue Lowe, of the Northeastern Univer-
sity Physical Therapy Department; Doctors Joel Stein and Paolo Bonato, of
the Spaulding Rehabilitation Hospital in Boston MA; and Dr. Peter Gerbino
of Children's Hospital in Boston MA, for their advice and input on the
projects.
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Test on quadriceps muscles (extension)Figure 15
Test on quadriceps muscles (extension). (a) Position; (b) Velocity; (c) EMG Biofeedback; (d) Electrical stimulation.
0
20
40
60
80
100
120
140
160
180
200
0
1.32
2.64
3.96
5.28
6.6
7.92
9.24
10.6
11.9
13.2
14.5
15.8
17.2
18.5
19.8
21.1
22.4
23.8
25.1
26.4
27.7
Time [Seconds]
Position [Degrees]
Position
-25
-20
-15
-10
-5
0
5
10
15
20
0
1.32
2.64
3.96
5.28
6.6
7.92
9.24
10.6
11.9
13.2
14.5
15.8
17.2
18.5
19.8
21.1
22.4
23.8
25.1
26.4
27.7
Time [Seconds]
Velocity [Degrees/Sec]
Velocity
(a) (b)
-6000
-4000
-2000
0
2000
4000
6000
8000
10000
12000
0
1.32
2.64
3.96
5.28
6.6
7.92
9.24
10.6
11.9
13.2
14.5
15.8
17.2
18.5
19.8
21.1
22.4
23.8
25.1
26.4
27.7
Time [Seconds]
EMG Biofeedback [
P
V]
EMG Biofeedback
0
0.5
1
1.5
2
2.5
0
1.32
2.64
3.96
5.28
6.6
7.92
9.24
10.6
11.9
13.2
14.5
15.8
17.2
18.5
19.8
21.1
22.4
23.8
25.1
26.4
27.7
Electical Stimulation Triggered [1=no, 2=yes]
Electrical Stimulation
Triggered
(c) (d)
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