Continuous Passive Motion Hand Rehabilitation

Design Team Project Sponsors: Group Members: Bert Lariscy, Vanderbilt University EE graduate Crystal Bates, Occupational Therapist Jim Lassiter, MCN Chief Occupational Therapist Group Members: Jonathan Webb ME Matthew Byrne ME Jennifer Hornberger BME Aaron Hadley BME

CPM Devices Continuous Passive Motion is a method of rehabilitation following injury or surgery. Its main aim is to increase movement of the joints while preventing overextension or further damage and to prevent the buildup of scar tissue.

CPM Market Injuries Typical surgeries where CPM is needed post operatively: ankylosis of joints dislocation of fingers and wrist sprain and strain of wrist joints tissue replacement at hand joints

Sales Market Primary Clients: 1) Physical Therapy Clinics 2) Post-Operative Individuals 155,000 physical therapy jobs in the United States Approximately 75,000 patients per year in need of care Ownership Costs: $3,000-$7,000 Rental Costs: $600/month Product is used for six weeks or less after surgery, typically for 8-10 hours a day.

Design Problem Problems with current CPM device: All fingers forced into same movement thumb not a part of the system heavy and bulky complex, difficult to set up and use

Design Goals Safety is of primary concern. It is necessary to make a completely new design that will incorporate independent finger motion, so as to allow for greater customization of rehabilitation. If possible, the thumb should be incorporated into the design in at least one dimension of movement. It must also be lightweight and portable, so that a patient can treat themselves at home.

Design Goals Following the evaluation of the comparison chart, the following ranking of design objectives was obtained. The following parameters are not necessary, but desirable in the final design. Clearly, the portability aspect of the device is the most important to meet patient needs, especially considering the heavy daily usage by patients.

Design Specifications Starting Position – open palm Range of Motion (ROM) -15 degrees (Hyperextension) to 270 degrees (Flexion) Speed of Motion Minimum of 2 degrees/second to a maximum of 54 degrees/second Speed to be set by physician based on rehabilitation plan

Mechanical Tension A series of small pulleys and strings will be used to move the fingers. These strings would be placed on the palm and back of the hand. Each finger and even each joint could be moved independently. A computer would control the length of the strings to set the desired position and allow for tension response.

ME Department’s Artificial Hand The ME Department’s artificial hand uses similar tendon-like cables. Tension returns the finger to an extended position. The “tendons” are inside the finger, but for our CPM model the strings would have to be outside the body.

Prototypes Alpha – Simple black knit glove with copper rings for mounting points. Plastic tubing with inner metal cord for flexion. (green picture to right) Beta – sewn black sleeve onto golf glove, one plastic mounting ring at finger tip. Gamma – four plastic mounting rings sewn in, fishing line for flexion.

Power Supply - McKibben muscles Contractile devices operated by pressurized air (force equivalent ~1kg at 3 bars) When actuated with a supply of compressed air, can contract up to 40% of the original length. Very lightweight because the main element is a thin membrane Highly compliant and flexible without any significant hysteresis, however precision control may be an issue. Applicability will be tested upon part arrival. Planning meeting with Center for Intelligent Systems (Cognitive Robotics Lab)

Power Supply - Motors Attaching the string to the spinning shaft of a motor will provide for a controllable tension in the pulley system. Motors demand only a battery power source to operate and are highly precise. The desired motion is a constant rotation in the forward and reverse directions, and the control mechanisms (on/off, forward/reverse) of this motion are being researched. Servo-motors, Stepper Motors, and Synchronous Motors are being compared for optimal use in the CPM pulley system.

Future Directions Decide on mechanical power supply Integrate power supply with model Test prototypes Revise Prototype