MALCOLM: Improving Pediatric Cerebral Palsy Rehabilitation (Rice University)

Jessica Joyce, Kurt Kienast, Jennifer Desmarias, Leslie Miller, Lawrence Lin, and Allison Post

ABSTRACT

Effective rehabilitation devices for wrist strengthening in pediatric spastic cerebral palsy patients will generate force measurements given all patient postures to track progress after corrective surgery. However, current devices focus primarily on range of motion of the wrist rather than isometric contraction and cannot accurately measure the forces exerted by a specific set of muscles. Development of a device that allows for multi-axial force measurements to provide a more accurate assessment of wrist strength via visual feedback would give patients and doctors the ability to assess rehabilitation progress after surgery.  This assessment is important for the advancement of the treatment of CP.

EXECUTIVE SUMMARY

Effective rehabilitation devices for wrist strengthening of pediatric spastic cerebral palsy (CP) patients measure wrist extensor forces given various postures to track recovery after corrective surgery. However, current devices primarily measure range of motion of the wrist, which is not indicative of muscle strengthening and cannot accurately assess the forces exerted by specific wrist muscles. The Rice University senior design team, Rice Helping Hands (RHH), aims to develop a device that measures force in multiple axes will provide a more accurate assessment of wrist strength and give patients and doctors the information from a graphical interface to assess rehabilitation progress after surgery. The needs for the device stem from:

• CP’s negative impact on wrist function
• Desire to accurately measure the strength of the extensor muscles both pre- and post-surgery
• Patients’ need to be engaged during treatment through the use of a graphical interface

RHH is working with an orthopedic surgeon, Dr. Gloria Gogola, from Shriner’s Hospital for Children to address the constraints of the device, which include:

• Portability to aid the doctor or the clinician in moving the device from one location to another
• Adjustability to fit pediatric patients of all sizes and postures
• Mechanical specificity to isolate the wrist extensors for testing
• Measurement accuracy to determine the magnitude of force exerted by the patient regardless of direction
• Graphical interface to engage patients and provide force measurements for the clinician

RHH has identified the following design objectives for the users:

• Comfort
• Ease of use with minimal medical training
• Ease of sterilization between patients

The team has created a design for the overall device which has five major components (force sensor, arm restraint, stand, hand restraint, GUI) that are being constructed simultaneously. The most significant advancement has been the construction of the Maltese cross for the force measurement device. The team built the core block design, applied eight strain gauges in a quarter Wheatstone Bridge configuration, and secured the electrical components. The team has tested the device and determined a calibration matrix to determine the patient’s applied force. The team visited the CP clinic at Shriner’s Hospital, tested the entire device on patients with CP, and has had success in meeting the design objectives.  The team has also performed a market analysis and projects a potential $2.5 million in profits in the first year the device is marketed.

BACKGROUND

Rice Helping Hands (RHH) has tasked with designing and developing a wrist rehabilitation device for pediatric patients with spastic cerebral palsy (CP) by Dr. Gloria Gogola, an orthopedic pediatric surgeon at Shiner’s Hospital in Houston Texas.

Design Constraints

The design of the RHH device must accomplish the following:

(1)         Accurately measure wrist extensor contractile force

(2)         Allow isometric contractions only

(3)         Engage the patient in a visual game

(4)         Provide muscle strengthening rehabilitation and diagnosis/assessment

(5)         Be portable and movable by one individual

(6)         Adjustable for patients age 6-14

Cerebral Palsy

CP can significantly affect a child’s limb function [4]. Proper limb function is critical for performance in everyday tasks such as using eating utensils. Children with spastic CP have difficulty performing everyday tasks due to improper muscle balance, specifically an imbalance in flexor-extensor action [5]. In normal physiology, the extensor and flexure muscles are able to easily and seamlessly alternate contraction and relaxation in order to control limb movement [2, 5]. An example of this balance occurs in the wrist. The wrist extensors contract during the upward-lifting motion of the wrist, and the flexors contract during the downward motion of the wrist. Children with spastic CP tend to have spastic wrist flexors. This spastic flexed state causes underdevelopment of the extensors [3]. This flexor-extensor imbalance results in dysfunction in everyday tasks.

Rehabilitation for Patients

Rehabilitation research shows that muscle strength has a direct correlation with performance in everyday tasks [1]. Spastic CP patients exhibit weak muscle strength that causes lower force output magnitude and control of the muscles to perform [4]. Rehabilitation therapy to strengthen weak muscles profoundly impacts function in everyday tasks [1], and is therefore a desirable approach for rehabilitation of spastic CP patients. However, current devices do not meet the needs of the CP clinic at Shriner’s Hospital (see Appendix A).

RESULTS

We have developed a rehabilitation system aimed at strengthening the wrist extensor muscles of spastic CP patients, through a visually engaging game interface that offers data capture for post-therapy assessment and diagnosis by a physician. Our solution comprises five subsystems: force measurement, hand restraint, arm restraint, stand, and graphical interface. The force measurement subsystem is a custom-designed 3-axis load cell that we have named multi-axis load cell object loading mechanism (MALCOLM). The load cell utilizes a core block Maltese cross configuration to be explained in the following section. The hand restraint is a splint designed by Dr. Gloria Gogola, an orthopedic surgeon at Shriner’s Hospital, the client for the project. The arm restraint is a semicircular cylindrical PVC pipe lined with two particle-filled vacuum bags to contour to the patient’s forearm. The stand is a table with storage space for all parts and lockable wheels for maneuverability. The graphical interface is an interactive visual display for both the patient and clinician that will be displayed on a portable electronic tablet.

An overview of the device

Our final design is picture in Figure 1.  As pictured, the steel frame is fitted with aluminum cantilever beams, each with two strain gauges attached for measurement of compression and tension. These strain readings will then be collected by the National Instruments DAQ, and our digital interface will convert these readings into a force based on a calibration matrix.

Arm Restraint

The arm restraint is a PVC half-pipe that is mounted with Velcro straps for easy fitting and adjustability for each patient’s arm (see Figure 2: Arm restraint with Velcro straps and vacuum bags.).  The arm restraint is further stabilized with vacuum bags. These bags can be changed out, depending on the size of the patient’s arm for added comfort and ease of use. The arm restraint is fixed to the table via a television mount purchased from McMaster-Carr.  This television mount allows for simple adjustability of the height and angle of the arm restraint and is secured in place by one knob. Additionally the arm restraint is mounted on a track on the table to allow for the device to be used by both left handed and right handed patients.

Arm Restraint uses velcro and vaccum bags

Table

The table for the RHH device is a custom table (see Figure 3: Custom table to house the components of the RHH device.). The table top is a 13 inch by 30 inch by 2 inch sheet of clear acrylic with rounded edges.  The legs are 10 in high hollow cylinders of aluminum with locking 5 inch wheels and castors.  The handle to provide mobility is a machined hollow aluminum cylinder, as shown in the figure below. Additionally, the tabletop has been modified so the Maltese cross multi-axis load cell MALCOLM is recessed into the table and covered with an acrylic box to protect the electronics and wires attached. This table meets the criteria for stability during testing and adjustability for pediatric patients, as well as mobility in the clinic setting.

The custom built table for the RHH device

Tablet and GUI

On top of the table is the tablet that acts as our user interface for the device. The user interface caters to both the patient and the clinician. For the patient, the interface will display a video game that aids in strengthening of the wrist extensors. The video game will display a child-engaging image following the shape of several preset functions such as a sine wave or a step function. This task is meant to increase both maximum force output and control of the wrist extensors. For the clinician, the interface will display a set of controls where the clinician can specifically tailor the patient’s rehabilitation experience. The clinician can input the patient’s personal information and rehabilitation parameters. The rehabilitation parameters are parameters that will adjust the patient’s rehabilitation session based off of their rehabilitation progress. For example, the clinician can input the patient’s maximum force output and a percentage of this force for the repeated exercise. This parameter will adjust the amplitude of the preset functions such that the exercise of following the function is physically possible.

The Graphical User Interface that RHH has designed

Budget & Market Analysis

Spastic cerebral palsy affects over 350,000 children in the United States alone, and contributes to almost $2 billion in healthcare costs according to the CDC.  Our device will drastically reduce healthcare costs by improving the diagnostic capacity of doctors, therefore improving the quality of each patient’s rehabilitation plan.  While our device is targeted towards children with cerebral palsy, the market could easily be expanded to those suffering from other neurological disorders, such as those suffering from spinal cord injuries or strokes, more than doubling our market.  With a low manufacturing cost, the potential for investment return and profit is great.

Our target buyers are hospitals and other health care providers.  With almost 6,000 registered hospitals in the United States according to the AHA, we could sell that many units over the course of three to five years.

We determined the lowest cost production method for the proposed 6,000 units would be injection molding for the custom parts. The table below describes the cost for manufacturing one unit. The cost of producing one prototype for our device, $2500, is significantly reduced in mass production, as demonstrated by the table. Cost reduction is realized in the streamlining of our electrical interface with NI instrumentation and user interface, which can be easily combined into one unit, as well as the mass manufacturing of the machined components of our device. Funding for our prototype is provided by Rice University’s Oshman Engineering Design Kitchen.

Table 1: Total cost for one unit based on components.

With the production cost estimated at only $200 for 1 unit and the proposed retail price $600, the first round of production would yield $2,520,000 in profits. However, with the proposed modifications to allow the device to be used for in-home rehabilitations, the market for our device could reach many millions of dollars.

REFERENCES

1. Damiano DL and Abel MF. Functional Outcomes of Strength Training in Spastic Cerebral Palsy. Arch Phys Med Rehabil. 1998 Feb; 75: 119-125.
2. Guyton, Arthur and John Hall. Textbook of Medical Physiology. 11^th ed. 2006.
3. Johnston MV. Encephalopathies. In: Kliegman RM, Behrman RE, Jenson HB, Stanton BF, eds. Nelson Textbook of Pediatrics. 19th ed. Philadelphia, Pa: Saunders Elsevier; 2011.
4. Valvano J and Newell KM. Practice of a Precision Isometric Grip-Force Task by Children with Spastic Cerebral Palsy. Dev Med & Child Neur. 1998; 40: 464-73.
5. Wehbe, Marwan A. “Anatomy of the Extensor Mechanism of the Hand and Wrist.” Hand Clinics 11.3 (1995): 361-66.

APPENDIX A

Appendix A: Comparison of Existing Devices Using Design Criteria