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: fingers not allowed independent motion 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

Previously Explored Techniques Magnetic fields can control joints of individual fingers though adjusting the induced current of an electromagnet wrapped around individual finger joints. Problems: 1.) A large current is needed to induce a strong magnetic field, hindering power source portability. 2.) The magnetic force varies with the square of the magnetic field, creating speed control issues. Shape Memory Alloys maintain the ability to deform and reform their shape when exposed to certain temperatures, and this property could be used to move the finger joints. 1.) Precision uncertainty and fatigue 2.) Temperature dependence range is too high for human touch. Magnetic Field Memory Metals

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.

Inflation Initial inflation of the air/fluid-filled bladder adjustable to fit all hand sizes. Each finger attached to one of five individual compartments to allow different ROM for each finger Rate of inflation controlled through strain gauges and pressure sensors. Problems feedback so device will stop if there is too much resistance ROM not as large as existing devices Air supply source

Future Directions Order materials Calculate forces necessary to move fingers. Submit prototype design for outside production by March 1st. Test prototype Revise Prototype