An Intelligent System for Knee and Ankle Rehabilitation

An Intelligent System for Knee and Ankle Rehabilitation
World Academy of Science, Engineering and Technology
International Journal of Medical, Health, Biomedical, Bioengineering and Pharmaceutical Engineering Vol:7, No:8, 2013
An Intelligent System for Knee and Ankle
Dimitar Karastoyanov and Vladimir Monov
International Science Index, Biomedical and Biological Engineering Vol:7, No:8, 2013
Abstract—The paper is concerned with the state examination as
well as the problems during the post surgical (orthopedic)
rehabilitation of the knee and ankle joint. An observation of the
current appliances for passive rehabilitation devices is presented. The
major necessary and basic features of the intelligent rehabilitation
devices are considered. An approach for a new intelligent appliance
is suggested. The main advantages of the device are: both active as
well as passive rehabilitation of the patient based on the human patient reactions and a real time feedback. The basic components:
controller; electrical motor; encoder, force – torque sensor are
discussed in details. The main modes of operation of the device are
Keywords—Ankle, knee, rehabilitation, computer control.
HERE is an increasing trend in using robots for medical
purposes. One specific area is the rehabilitation. The
percentage of persons suffering from muscular weakness of
the lower limb can oscillate between 0.05% and 1% of the
total European population; during 2006 by the statistics it is
reported in Bulgaria have been done 59700 manipulations of
the lower extremities (0.7% of the population). There are some
continuous passive motion commercial (CPM) machines used
for rehabilitation purposes. However, these machines have
limited use because of their insufficient motion freedom. In
addition, these types of machines are not actively controlled;
they have not feedback and therefore cannot accommodate
complicated exercises required during rehabilitation.
With this study we proposed a new intelligent mechatronic
system which can accomplish active and passive knee and
ankle rehabilitation based on feedback force control. Here an
intelligent computer control structure with four degree of
freedom mechanical system is proposed.
During the past 3 decades, continuous passive motion
(CPM) devices have become a generally accepted part of post
surgical treatment to promote healing and regeneration of joint
cartilage. CPM machines for rehabilitation in the clinic or
home are used post operatively to prevent joint stiffness after
Total Knee Replacement, ACL repair, Femur Fractures, closed
manipulation of the knee or shoulder. In 1970, Robert B.
V. Monov is with the Institute of Information and Communication
Technologies, Bulgarian Academy of Sciences, 1113 Sofia, Bulgaria (phone:
+359 2 979 2474; fax: +359 2 870 7273; e-mail: [email protected]).
D. Karastoyanov is with the Institute of Information and Communication
Technologies, Bulgarian Academy of Sciences, 1113 Sofia, Bulgaria (e-mail:
[email protected]).
International Scholarly and Scientific Research & Innovation 7(8) 2013
Salter, MD, PhD, a Toronto orthopedic surgeon, together with
a succession of research fellows, first investigated the
biological effects of CPM on healing and regeneration of
articular tissues in rabbits [1]. Later, Salter and his colleagues
began applying this basic research to human patients. They
found that nine selected patients "have been relatively free of
pain, have maintained the increased motion gained at
operation, and have accepted the application of CPM well"
As described by O'Driscoll and Giori, Salter's basic premise
is that "because immobilization is obviously unhealthy for
joints, and if intermittent movement is healthier for both
normal and injured joints, then perhaps continuous motion
would be even better." However, because patients could not be
expected to move their injured joints continuously for hours at
a time, the movement would, of necessity, be passive. "He
also believed that CPM would have an added advantage,
namely that if the movement was reasonably slow, it should be
possible to apply it immediately after injury or operation
without causing the patient undue pain [2].
According to Hammesfahr and Serafino, CPM "is one of
the primary methods for decreasing the deleterious effects of
immobilization and can deliver orthopedic, neurological, and
even circulatory benefits to the patient. Immobilization, in
turn, can create deleterious sequelae of physiological and
functional impairments [3].
Through the years, CPM devices have been created for most
of the major joints of the upper and lower extremities, but they
appear to be most frequently prescribed for post surgical use
in injuries of the knee or shoulder. CPM is generally provided
through devices mechanically designed to bend and flex joints
at a given rate for several hours
Motion and stress are important for the maintenance of
normal connective tissue and the healing of injured connective
tissue. Motion enhances blood flow and decreases pain.
Passive motion involves movement of a joint without active
contraction of muscle groups. It is used to maintain range of
motion (ROM) and flexibility in joints in the early
postoperative and rehabilitative period after surgery or injury
when active movement might disrupt the repair process or is
too painful to perform. Continuous passive motion is a
rehabilitation technique that involves introduction of
progressive passive range of motion (PROM) to an extremity
through an externally applied force.
Here are presented a few of the different CPM device:
Danninger, Kinetec, Mckelor, Ormed, Optiflex. Generally the
International Science Index, Biomedical and Biological Engineering Vol:7, No:8, 2013
World Academy of Science, Engineering and Technology
International Journal of Medical, Health, Biomedical, Bioengineering and Pharmaceutical Engineering Vol:7, No:8, 2013
CPM devices operate separately for the knee only or the ankle
The Kinetec Spectra Knee CPM for knee patients (Figs. 1
and 2) can now be addressed with a carriage that
accommodates all patients, age 8 to 80.
Kinetec Performa Knee CPM equipped with a reliable,
smooth and quiet screw-drive transmission. Standard features
include seven speed settings, manual set-up mode,
programmable muscle stimulation and adjustable force
settings. Its UL-approved computerized hand control is
completely waterproof, and its built-in pediatric capability
eliminates the need for costly attachments for children and
shorter adults.
The Optflex and McKelor (Figs. 3 and 4) have an
innovative, sleek upper carriage which produces a very
durable and comfortable CPM, extended range of motion
within a compact design that is capable of accommodating
patients with limb lengths up to 106mm.
Fig. 3 OptiFlex Knee CPM
Fig. 4 McKelor DC Knee CPM
Fig. 1 Kinetec Spectra Knee CPM
Fig. 2 Kinetec Performa Knee CPM
International Scholarly and Scientific Research & Innovation 7(8) 2013
Many researchers have developed different rehabilitation
devices. For example, Krebs et al. have developed and have
been clinically evaluating a robot-aided neuro rehabilitation
system called MIT-MANUS [4]. This device provides
multiple-degree of freedom (DOF) exercises of upper
extremities for stroke patients. They are not actively controlled
and do not incorporate any feedback from the patient during
the motion. Also, the patient’s reactions during the exercises
need to be taken into consideration to change and control the
exercises actively as a real physiotherapist will do. This can
only be done with intelligent devices which can decide the
type and pace of exercises based on the patient’s complaints
and reactions during the physiotherapy.
This paper is focused on the development and testing of
a new type of controllable complex (active and passive)
knee and ankle rehabilitation device with online feedback.
Here an intelligent control structure with four degree of
freedom mechanical system is proposed. It can make flexionextension for the knee joint, plantar flexion-dorsiflexion,
abduction-adduction and inversion-eversion movement for the
ankle joint. This manipulator is driven by appropriate actuator
for each joint (for instance stepper or DC motor, voice coil
International Science Index, Biomedical and Biological Engineering Vol:7, No:8, 2013
World Academy of Science, Engineering and Technology
International Journal of Medical, Health, Biomedical, Bioengineering and Pharmaceutical Engineering Vol:7, No:8, 2013
actuator etc.) and controlled by a microcontroller using
force/torque with online feedback and position sensor
The key features of the device will include: a compact
design with highly tunable force/torque capabilities, control
circuitry, sensors, and real-time closed loop computer control
for optimizing rehabilitation exercises. Algorithms for
synthesising appropriate control of the knee and ankle joints
will also be developed.
The mechatronic system will operate in two modes;
learning and therapy. The control technique is selected for the
force control which aim is to specify the relationship between
position and force. Proposed intelligent controller structure is
used to tune the parameters and can modify itself according to
the reactions of the patient.
A continuous passive motion (CPM) device in some cases
is not suitable for active physical therapy. For example, during
the rehabilitation process, patients sometimes move their
extremities suddenly due to reflexes. On conventional
machines like CPM, don’t respond in this kind of situations
and continue the given cyclic motion. If a reflex causes a
patient’s leg move while the machine is operating, an
improper load results and can damage the patient’s muscle or
tendon tissue [5].
Because of these disadvantages, there is a need to create a
new intelligent device which can accomplish the
rehabilitation of extremities based on the patient’s
complaints and the online feedback during rehabilitation
The aim of the project is to enhance the intelligent control
and sensor technology to be applied in an innovative, accurate
and easy to use rehabilitation system. This will improve the
quality of the rehabilitation and the postoperative process.
The rehabilitation system will perform the flexion–
extension motions for the knee rehabilitation. It can make
flexion-extension, plantar flexion-dorsiflexion, abductionadduction and inversion-eversion movement for the ankle
joint. The device has to be designed for both left and right
lower limb. In addition, it can be adjusted for different limb
International Scholarly and Scientific Research & Innovation 7(8) 2013
The devices mechanical structure will use the classical
methods for fixation the knee and ankle.
The rehabilitation device must have the following main
- Automatic anatomically correct alignment,
- Feedback force control to evaluate and limit the amount
of force,
- Speed control: from 40º/minute to 145º/minute
- Effective passive mobilization of the joint;
- Multi-Mode operation – active, passive and their
combination during every cycle, pause in flexion or
- Adjustable in length from small children to large adults.
- Remote control with digital display allowing easy
adjustment of all parameters - range of motion, speed,
pause and timer;
- Large range of motion: knee -3° to 130°; ankle plantar
flexion 40° dorsiflexion 30° internal rotation 30° external
rotation 30°;
- Patient and user safety: The patient can stop and reverse
the unit at any time; The movement reverses if the load is
The system hardware for controlling the manipulator is
shown on Fig. 5. System hardware will consist of a stepper
motor with its driver, force/torque sensor and controller for
measurement of force and torque data that come from therapist
and patient. Position data will be taken by encoder emulation.
Autonomous control system is developed for obtaining and
visualizing of human motion data. The developed system is
consisted of sensing, data acquisition and graphical user
interface (GUI). A microcontroller transfers recorded data
during each cycle to the PC via RS485 interface.
The complete autonomous system consists of four primary
components - sensing, data acquisition, communication and
friendly oriented software for interpretation of the data.
Sensing involves the devices that interact with the physical
world and give information about it. Data acquisition gathers
and digitizes the information from the sensors.
Communication takes this data and makes it available through
the RS-485 lines. Once the data is transferred, a variety of
different interpretations are possible with PC. A graphical user
interface will be created to visualize downloaded data.
World Academy of Science, Engineering and Technology
International Journal of Medical, Health, Biomedical, Bioengineering and Pharmaceutical Engineering Vol:7, No:8, 2013
International Science Index, Biomedical and Biological Engineering Vol:7, No:8, 2013
Fig. 5 System Hardware Block Scheme
The proposed control system will be designed and tested.
External sensors and encoders measure knee and ankle joint
position in real-time and send signals to the microcontroller.
These sensors data are used in every step of the control
algorithm in order to optimize the force and position during
the motion.
The microcontroller serves a few different functions. For
communication, it job is to collect sensor data and create a
serial bitstream. In order to get all of the data needed, we had
to coordinate all of the different features of the
microcontroller: analog and digital I/O as well as A/D
conversion. For each individual sensor, efficient code was
written for the processor to integrate all of the data into a
single serial stream.
In order to fulfill more complex functions for passive and
active rehabilitation, an intermediate controller is provided. In
view of the requirements to this controller (speed, enough
input-outputs, communication capabilities, coding, tools for
coding), we have chosen a microcontroller of the company
Freescale/former Motorola/ from the family MC9S12А with
the following characteristics: 16 bitCPU, working frequency
up to 25 MHz, 64 КВ flashEEPROM, 4 КВ RAM, 1 КВ
International Scholarly and Scientific Research & Innovation 7(8) 2013
EEPROM, 29 digitalinput-outputs, 2 х 8 10 bitanalogchannels,
serial peripheral interface /SPI/. Taking into account the price,
we have chosen the microcontroller MC9S12A32. The
structure of this family is shown in Fig. 6.
A. Intelligent Controller
The mechatronic system will be controlled by an intelligent
controller which will incorporate the preloaded data about the
patient and provide an interface for information flow between
the manipulator and patient.
The TMC428 (Trinamic Motion Control Ltd.) is a
miniaturized low cost and high performance stepper motor
controller for up to three motors – Fig. 7. It integrates all real
time critical tasks in reliable, dedicated hardware: An
integrated motion ramp profile generator as well as an
adaptable micro step sequencer with micro step RAM table.
Advanced stop- and reference switch handling allows
precise and fast referencing as well as on-the-fly position
checking. Automatic motor current control gives high motor
dynamics while saving energy. The interrupt output can
generate precise position pulses.
International Science Index, Biomedical and Biological Engineering Vol:7, No:8, 2013
World Academy of Science, Engineering and Technology
International Journal of Medical, Health, Biomedical, Bioengineering and Pharmaceutical Engineering Vol:7, No:8, 2013
Fig. 6 Intermediate controller
The TMC423 adds encoder functionality to the TMC428.
Evaluation Boards, application notes, spreadsheets for
parameter calculation, C code examples and schematics are
available in order to support short design-in times.
A. Main Characteristics
unique miniaturized stepper motor controller realized as
low power 0.35μm CMOS device
up to three stepper motors with up to 64 times micro
full step frequencies up to 20 kHz
driver status information read back for μC
power down mode
B. Interface
SPI μC interface; easy-to-use protocol for μC; serial 4wire driver interface (SPI); step-/direction output
The TMC423 is a triple incremental encoder input chip,
which interfaces to any SPI compatible controller. It integrates
24 bit counters – one for each encoder – to provide a high
position resolution without CPU interaction. The TMC423 is
intended as a companion chip for the TMC428 but not limited
to this. Both ICs together enable the realization of a motion
control system of three axes with encoder feedback. This
provides position verify caution or stabilization by
implementation of some additional software. Further, the
TMC423 allows dynamic resolution adaptation for direct
comparison of encoder counters with motors using different
micro step resolution.
All encoder counters can be latched synchronously, or
whenever a null channel event occurs, providing a position on
strobe holding function. The TMC423 also provides a
International Scholarly and Scientific Research & Innovation 7(8) 2013
step/direction output with programmable signal shaping for
the TMC428 as well as a multiplexer function for the
TMC428 reference switches. Additionally, the TMC423 can
drive an LED matrix and read out a switch matrix, to support
systems with keyboard user interaction.
C. Main Characteristics
incremental encoder interface for three 2 or 3 channel
TMC428 step / direction interface extension
TMC428 reference switch interface
TMC428 interrupt de-multiplexer
control of LED 6 x 4 Matrix; control of key 6 x 4 matrix
D. Interface
- SPI interface to microcontroller
We intend to use convenient controller electronic with a
range of appropriate motor torques. The PD-110-42 offers
three motor torque options and can be controlled via RS232,
RS485, CAN or IIC interface (Fig. 8). The power supply,
interface and the multipurpose I/Os can be connected with
small JST connectors. The PD-110-42 comes with the PC
based software development environment TMCL-IDE for the
Trinamic Motion Control Language (TMCL). Using
predefined TMCL high level commands like „move to
position“ or „constant rotation“ a rapid and fast development
of motion control applications is guaranteed. Communication
traffic is kept very low since all time critical operations, e.g.
ramp calculation are performed on board. The TMCL program
can be stored in the on board EEPROM for stand-alone
operation. The firmware of the module can be updated via the
World Academy of Science, Engineering and Technology
International Journal of Medical, Health, Biomedical, Bioengineering and Pharmaceutical Engineering Vol:7, No:8, 2013
International Science Index, Biomedical and Biological Engineering Vol:7, No:8, 2013
serial interface. With the Stall Guard feature it is possible to
detect motor overload or motor stall.
The system has two main stages: learning and therapy.
Fig. 7 Three Axis Stepper Motor Controller Block Scheme
Fig. 8 Stepper Motor 42mm with Intelligent Electronics and Serial Interface
Through user interface, physiotherapist will be able to
select exercise mode covering information regarding exercises
and patient extremities. Some exercise modes may not need
learning process. In these modes, physiotherapist will enter
exercise information to start the system for therapy. According
to the selected mode, necessary parameters will be taken from
the knowledge base.
In the exercise modes that need learning process, the
physiotherapist and the mechatronic system will be
marked it. During the rehabilitation process, the realized
forces that arise and position data are taken by parameter
estimation unit to estimate control parameters. Estimated
parameters (inertia, stiffness, velocity), desired force and
position data are conveyed to the knowledge.
In therapy stage, the mechatronic system will perform
therapy motion instead of physiotherapist or the other
therapeutic exercise devices. Using force and position sensors,
the reactions that come from the knee will be taken by
feedback to the manipulator and these data are received by
rule base and the system tunes the forces or stop the
rehabilitation process, if requires.
According to the patient reactions during the
rehabilitation process, the intelligent controller will
International Scholarly and Scientific Research & Innovation 7(8) 2013
evaluates the situation. These conditions will be monitored
by force and position sensor.
The system security is controlled by both hardware (limit
switches) and software if the motion of manipulator is
increased over the limits.
The characteristics for assessing knee and ankle
performance are associated with:
• More sophisticated and efficient rehabilitation of the
knee and ankle joints;
• Automatic examination and calibration procedures
reducing the human errors;
• Advanced sensor and feedback based control
(compliance, force, interactive dynamic control)
providing a reliable and safe human-machine interaction;
• Data acquisition and sophisticated computer evaluation
based on clinical experience, allowing an accurate,
o The proposed rehabilitation system consists of the
following modules and components:
• Safety electromechanical system for realization of the
World Academy of Science, Engineering and Technology
International Journal of Medical, Health, Biomedical, Bioengineering and Pharmaceutical Engineering Vol:7, No:8, 2013
Sensory system (motion sensors, force sensors, wire
position sensors) collecting the information about actual
knee motion and providing the feedback for the control
• Control system for the force/torque and position in each
• Rehabilitation planning and programming system (user
• Visual and auditory feedback system with user and patient
The rehabilitation system will be developed as a stand-alone
module that can be integrated with various rehabilitation
devices and subsystems.
Salter RB, Hamilton HW, Wedge JH, et al. Clinical application of basic
research on continuous passive motion for disorders and injuries of
synovial joints: a preliminary report of a feasibility study. J Orthop Res.
O'Driscoll SW, Giori NJ. Continuous passive motion (CPM): theory and
principles of clinical application. J Rehabil Res Dev. 2000:37;179-188.
Hammesfahr R, Serafino MT. CPM: The key to successful
rehabilitation. Orthopedic Technology Review. 2002;3(2).
Stone KR, Walgenbach AW, Freyer A, Turek TJ, Speer DP. Articular
cartilage paste grafting to full-thickness articular cartilage knee joint
lesions: a 2- to 12-year follow-up. Arthroscopy. 2006;22:291-99.
Lum P.S., Burgar C.G., Van der Loos H.F.M. (1999), Proc Int. Conf. On
rehabilitation Robotics: 235-239
International Science Index, Biomedical and Biological Engineering Vol:7, No:8, 2013
The system is expected to be a very useful one for
supporting the knee rehabilitation and restoration of motor
functions. This safe, reliable and dynamically controlled
device will support the patients to autonomously perform the
knee recovery training from the early rehabilitation stage on
the new quality level.
The realization combines the following medical and
technical activities:
• Planning, programming and realization of the repetitive
functional knee training taking into account
biomechanical patterns as well as specific patient
disorders and disabilities (dislocations, spasticity, muscle
strength, etc.);
• Programmable and dynamically controlled flexionextension, pronation-supination and adduction-abduction
motions on the lower limb joints;
• Assessing and supporting the own initiative, efforts and
will of the individual. Quantitative measurements of
patients motor-functions (limb motion, forces, mechanical
work etc.) needed to assess and document rehabilitation
outcome and improve therapeutic approaches.
• Storage of patient data to study the progress of
• Minimum alteration of the loads and pressures applied to
the lower extremities during the active/ passive mode;
• Minimal maintenance and medical staff exertion;
• The system will be designed to support the knee
restoration of the various patient groups with orthopedic
disorders, such as complicated fracture-dislocations (with
open fixations), simultaneous surgery at both extremities
(e.g. total knee replacement and high tibialostheotomy),
total hip replacement or bedridden elderly patients with
multiple pathologies, (cardiac or pulmonary disorders).
The research work reported in the paper is partly supported
by the project AComIn “Advanced Computing for
Innovation”, grant 316087, funded by the FP7 Capacity
Programme (Research Potential of Convergence Regions).
International Scholarly and Scientific Research & Innovation 7(8) 2013
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