Continuous Passive Motion Hand Rehabilitation

1
Continuous Passive Motion Hand Rehabilitation Matt
hew Byrne2, Aaron Hadley1, Jennifer Hornberger1,
Jonathan Webb2 Advisors Bert Lariscy, Crystal
Bates Departments of 1Biomedical Engineering
and 2Mechanical Engineering, Vanderbilt
University, Nashville TN
BACKGROUND
PROTOTYPE REVISION AND TESTING
DISCUSSION

• Continuous Passive Motion (CPM) is a method of
  rehabilitation following injury or surgery.
• CPM aims to prevent the buildup of scar tissue
  and limit the pain induced from using muscles
  after surgery by mechanically moving injured body
  parts and preventing further joint damage.
• Hand CPM devices are typically used in injuries,
  including ankylosis of joints, finger
  dislocation, joint tissue replacement, and
  sprained finger joints.
• The devices are used from 48 hours after surgery
  to six weeks after surgery, for an average of
  8-10 hours a day.
• CPM devices are marketed towards physical therapy
  clinics and post-operative individuals.
• Approximately 75,000 patients per year require
  the use of a hand CPM.

• Alpha
• Small copper rings were placed on a black knit
  glove. On each of the fingers, pieces of plastic
  tubing were affixed on the palm and reverse side
  of the hand. A guide wire was fed through tubing
  to pull the fingers to full flexion and
  extension.
• The tubing used proved to be too large to allow
  for the complete closure of the hand. The guide
  wire was found to be too stiff, thus a more
  flexible string should be used.
• Beta
• A strip of fabric was sewn onto the finger to
  serve as a track which would hold the string to
  the finger as the string is contracted.
• The fabric was found to be overly flexible, and
  bunched up at the joints during flexion.
• Gamma
• Five small plastic rings were sewn on each side
  of the glove at specific joint locations such
  that the tension of the string would produce the
  desired range of motion.
• This model provided the desired range of motion
  in both flexion and extension, and the use of
  nylon line proved to be sufficiently strong,
  thin, and flexible. This series of rings can be
  sewn on any of the fingers for use.

The string and pulley prototype meets most of our
design goals. It begins in an open palm and
provides the anatomically correct finger motion.
The device can be set to run at a variety of
speeds and ranges of motion. This model is
also easy to put on, lightweight, and
unrestrictive. However, the methods
for controlling the motor prevent portability.
It has the potential to be made more portable by
minimizing the computer motor control system. The
device, with the manufacture of additional
gloves, is adaptable to both the left and right
hand as well as to different hand sizes. The
current prototype only works for one finger but
could be easily expanded with additional strings
and motors. The thumb could be incorporated to
the prototype as well. However, in this design
controlled thumb motion would be achievable in
only one axis of motion. The patient also has the
ability adjust the speed and range of motion of
the CPM as well as the ability to return the
device to the starting position if too much pain
is experienced. The single-finger prototype was
produced for about 105. Expansion to include the
other three fingers would increase the cost to
about 330. Assuming a 40 markup, the product
could be sold for 465. Even taking into
consideration the costs of modifications to
upgrade the prototype the device should still be
able to be sold for well under 2500, half the
price of existing hand CPM devices.
PROBLEMS WITH EXISTING DEVICES

• All fingers are mechanically forced into the same
  movement, preventing individual fingers from
  rehabilitating to their possible full range of
  motion.
• Motion is restricted to either the fingers or the
  thumb, but no systems incorporate both aspects of
  the hand.
• The weight and bulk of the devices restrict
  patients daily activity and comfort.
• The system setup is complex, requiring multiple
  people to attach the CPM to the hand and to set
  up the initial movement criteria.
• Average device costs are high. Rental
  600/month, Ownership 3,000-7,000

CONCLUSION
DESIGN GOALS
This prototype is an improvement on existing hand
CPM devices. It provides the much needed ability
to control the speed and range of motion in the
movement of individual fingers. This will enable
better customization of rehabilitation
therapy, allowing patients to maintain the range
of motion in less injured or non-injured fingers.
Increased comfort, ease of use, and decreased
weight will help to increase patient compliance
and decrease the patients recovery time.
The decreased cost will make CPM therapy an
option for more patients, resulting in a larger
market.
Fig. 2 Beta (ring) and Gamma (middle)
Fig. 3 Gamma Prototype, final design

• Develop a new process that allows for all fingers
  to move independently, providing greater
  customization of rehabilitation.
• Incorporate the thumb into the design in at least
  one dimension of movement .
• CPM system should be lightweight (less than 1 lb)
  and portable for use at home.
• The device should be adjustable to multiple users
  and have a starting position at an open palm.
• Range of Motion in each finger Flexion 270o
  Hyperextension -15o
• Variability of speed and force application in
  each finger
• Speed Range Minimum 2 deg./sec.
  Maximum 54 deg./sec.
• Reduce the cost of production in the hand CPM.
• Other factors that were not necessary but a
  desired result in the design were that the
  device has a long battery life (1 day), does not
  restrict daily tasks, is easily operated and
  controlled, is simple to put on, and does not
  intimidate the patient.
• In all of these design goals, safety is an
  underlying criteria.

Fig.1 Alpha Prototype
MOTOR DEVELOPMENT

• Two chief methods were considered for moving the
  strings
• McKibben muscles are small rubber-wound tubes
  that contract when inflated. This idea was
  rejected because McKibben muscles must be
  attached to a large compressor, have inconsistent
  motion, and frequently rupture.
• Servomotors would allow small rotating discs to
  wind up the strings at the specific desired
  speed, allowing for very precise lengths and
  ranges to be obtained.
• Motor
• A simple servomotor was obtained, which was
  altered to obtain full control over rotation. A
  spool with a 41 ratio was attached to the
  servomotor shaft in order to wind the strings for
  the front and rear sides of the hand
  simultaneously. The front string can be shortened
  4 inches while the rear is lengthened 1 inch by
  the same motor.
• A separate motor for each finger would be
  required for the desired outcome of independent
  finger motion.
• Control
• The motor can be manually controlled remotely
  with the digital proportional radio control that
  came with the motor.
• The output signal to the motor was measured and
  replicated with LabVIEW, allowing the motor to be
  controlled with a computer. In this way, the
  computer can be used to run the CPM through a
  flexion and extension cycle.
• The available equipment does not, however, allow
  the desired degree of precision in speed and
  range, but exploring other programming languages
  and motor systems may.

FUTURE WORK

• Improve precision and capabilities of the
  computer program that controls the motor.
• Find more durable materials for long-term use
• Incorporate additional fingers and possibly the
  thumb.
• Condense motors and system for motor control.
• Incorporate goniometers to monitor joint angles
  and enable more precise control of range of
  motion.
• Add additional safetly features.

INITIAL DESIGN OPTIONS

• Magnets were rejected because a large current is
  needed to induce a strong magnetic field,
  hindering power source portability also the
  magnetic force varies, creating speed control
  issues.
• Memory Metals were rejected because there is
  precision uncertainty and possible fatigue stress
  causing permanent undesirable deformation. The
  temperature dependence range is also too high for
  human touch.
• Inflatable Tubes were rejected due to size and
  weight of required compressors.
• Strings and Pulleys, similar to the Mechanical
  Engineering departments artificial hand, could
  replicate the movement of tendons within the
  hand. Tracks along finger would reinforce the
  linear motion while a force pulled on the strings
  to move them. This idea was chosen because of its
  innovation and feasibility..

ACKNOWLEDGEMENTS
Thanks to Bert Lariscy, Vanderbilt University
Electrical Engineering masters graduate, and
Crystal Bates, Occupational Therapist, for their
help in the human factors and ideation process of
the hand CPM design.
Fig. 4 sketch of mechanical tension
for desired motion
Fig. 5 Inside the servomotor
Fig. 6 The 41 spooling attachment