1. Continuous Passive Motion Hand Rehabilitation Matthew Byrne 2, Aaron Hadley 1, Jennifer Hornberger 1, Jonathan Webb 2 Advisors: Bert Lariscy †, Crystal Bates † Departments of 1 Biomedical Engineering and 2 Mechanical Engineering, Vanderbilt University, Nashville TN 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. 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. 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: 270 o Hyperextension: -15 o 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. 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 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 department’s 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.. 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. BACKGROUND PROBLEMS WITH EXISTING DEVICES 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 patient’s recovery time. The decreased cost will make CPM therapy an option for more patients, resulting in a larger market. 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. PROTOTYPE REVISION AND TESTINGDISCUSSION CONCLUSION FUTURE WORK INITIAL DESIGN OPTIONS 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 4:1 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. MOTOR DEVELOPMENT Fig.1 – Alpha Prototype Fig. 2 – Beta (ring) and Gamma (middle)Fig. 3 – Gamma Prototype, final design Fig. 5 – Inside the servomotor Fig. 4 – sketch of mechanical tension for desired motion Fig. 6 – The 4:1 spooling attachment 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.