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Student Projects
Contact Information
Rice University, Department of Bioengineering
Team Members | Faculty Advisor(s) |
Shuai “Steve” Xu | Maria Oden, PhD |
Matthew D. Miller | Gloria Gogola, MD |
Neel A. Shah | |
Caterina C. Kaffes | |
Jennifer D. Cieluch |
Primary Email Address: stevexuster@gmail.com
Primary Telephone Number (include area and country code): 909-964-7006
Project Information
List all parts (hardware, software, etc.) you used to design and complete your project:
· OMEGA LCL-010 load cell (Stamford, CT)
· Custom amplification and filtering circuitry
· 9 volt battery
· Green L.E.D.
· Switch
· PVC pegboard
· Nylon pegs
· Velcro finger strap
· Steel threaded bolt
· Metallic eye-bolt
· Helicoil
· Plastic enclosure
· NI’s CF-6004
· HP iPAQ PDA
· NI’s LabVIEW 8.6 Mobile Module
Describe the challenge your project is trying to solve.
Intrinsic hand muscles are of high clinical value. In the United States, the yearly cost of treating upper extremity disorders was estimated at $18 billion (1). For children, the hand is the most frequently injured part of the body (2). Beyond blunt trauma, the assessment of intrinsic hand muscle strength (IHMS) is necessary for diseases as widespread as rheumatoid arthritis (3), diabetes (4) and median/ulnar nerve injuries (5).
The manual muscle test (MMT) is the most common clinical test to assess intrinsic hand muscle strength (6-8). However, the 5-point grading scale of the MMT exhibits low validity, poor reliability and inherent subjectivity (9-11). Pinch and grip devices serve as an additional proxy for IHMS (12, 13) but these measurements are dominated by extrinsic muscles of the forearm (14, 15). Several hand-held devices have been reported in the literature to specifically measure IHMS. The Intrins-o-meter (16) and the Rotterdam Intrinsic Hand Myometer (17) require extensive clinician involvement and force patients into contorted positions (18) that lead to high interobserver error ranging from 37-52% (19). Ultimately, IHMS can be used to aid medical decision making (20), evaluate the relative benefits of surgical interventions (1, 17) and track rehabilitative progress (21, 22).
Describe how you addressed the challenge through your project.
THE CHALLENGE: The project was initiated at the request of Dr. Gloria Gogola, an orthopedic surgeon specializing in the upper extremities at Shriners Hospital for Children in Houston, TX. The global objective of the project is to develop a novel device, which we will refer to as PRIME (Peg Restrained Intrinsic Muscle Evaluator) that can accurately and efficiently measure the intrinsic hand muscles for a wide range of patients.
In selecting design strategies, we outlined key objectives in terms of design criteria for our device. The design criteria focused optimizing the three main characteristics of portability, clinical utility and device sensitivity. In Table 1, PRIME’s specific design criteria are listed in detail.
Solutions considered: Several proposals were outlined after discussions with orthopedic surgeons and hand therapists. These devices are listed in Table 2. Using a decision tree, we ranked our possible designs using our most important design criteria without weighting. This allowed us to eliminate proposal E as a possible design. We implemented a Pugh matrix to select the final design. The results showed us that a final design combining the pegboard in proposal A with the load cell of proposal B would best meet the design criteria.
Final design description of PRIME: The completed device is shown in Figure 1. PRIME is a self-contained, battery powered device that is capable of sensing forces up to 10 lbs ± 0.025 lbs (Figure 1). The prototype is described in three components: the pegboard base, the force transducer enclosure and the display unit.
The pegboard baseprovides structural support while minimizing excess hand movement: The custom PVC pegboard measures 2 feet in length, 1 foot in width and ½ inch in thickness. The holes are drilled in a staggered design one inch apart. Rounded pegs are a novel and rapidly adjustable method to restrain excess hand movement to improve accuracy, isolate individual fingers for highly specific testing and minimize clinician involvement. Locking the movement of the hand grants two key benefits. First, true isolation of individual intrinsic finger strength can be obtained. Second, the numerous placement holes for the plastic pegs allow for greater flexibility and rapidity in testing. Finally, PVC is a light, safe and easy to clean material.
The force transducer enclosure is a self-contained module of PRIME: Shown in Figure 2, the force transducer enclosure (FTE) includes an OMEGA (Stamford, CT) LCL-010 load cell, custom circuit board and a 9 volt battery. Chosen for its high sensitivity, the OMEGA LCL-010 senses forces from 0 to 10 lbs at a resolution of 0.25%. The load cell outputs to a custom developed circuit board (Figure 3) where an AD620 instrumentation amplifier augments the voltage output of the load cell (Equation 1). A voltage regulator and voltage divider ensure that the voltage given to the load cell and instrumentation amplifier is constant. The signal then enters an active low pass filter to eliminate any high frequency noise above 28 Hz (Equation 2).
The voltage difference between Vout+ and Vout- is capped at 3.5 volts protecting the subsequent circuitry from damage. A D-15 output plug collects the outputs of the load cell for force measurement and the battery life of the 9 volt battery. A switch controls the power for PRIME. In addition, a LED provides visual cue of PRIME’s activation.
Interface between the FTE and pegboard base maximizes ease of use: The interface between FTE and the peg board base is made through a custom sleeve that allows for free rotation and height adjustment about the vertical axis (Figure 4). A helical nut allows the metallic bolt to fit tightly into the PVC board. This configuration confers several advantages. First, the vertical position of the FTE can be easily adjusted. The clamp firmly holds the FTE at a specific height. Secondly, the FTE can swivel 360° about the metallic bolt. The clinician can easily accommodate PRIME to meet various hand sizes and morphologies. Also, this connection strategy enables the measurement of intrinsic strength of the thumb which improves upon previous devices. Furthermore, this interface drives the symmetry of the peg board. By rotating the FTE, the clinician can measure intrinsic hand muscle strength in both hands without forcing the patient into new or awkward positions. To interface between the FTE and a patient’s physician, a Velcro strap is employed. The Velcro strap is a low-cost, adjustable and highly effective method to interface between a patient’s individual finger and the metallic eye-bolt connected directly to the load cell (Figure 1). In addition, the Velcro strap eliminates the risk of slippage.
Display unit utilizes National Instrument’s technology and a PDA: A National Instrument’s (Austin, TX) CF-6004 CompactFlash Data Acquisition Unit was used to sample analog voltage signals through the D-15 output directly from the FTE. The sampling rate is set at 10,000 Hz. The CF-6004 is placed within a HP iPAQ hx2000 PDA with a CompactFlash II slot. A custom user interface (Figure 5) developed using LabVIEW™ mobile module continuously samples voltage, automatically calculates peak force, displays the value on a digital gauge and warns of low battery. See Figure 6 and 7 for a detailed description of the underlying code.
Tabbed browsing allows the clinician to input critical patient data and export it in .txt format for further analysis. The underlying program architecture is composed of the two components; one loop controls voltage sampling from the load cell and battery and the second loop handles data storage and export regarding the patient’s information. A new file is generated every testing session and automatically named by the patient’s medical record number and a time stamp (Figure 8).
The advantages of the NI CF-6004 and PDA display include highly accurate sampling, ultra-portability and minimal technical expertise for operation. LabVIEW™ is a powerful programming language that is capable of generating executables that run on any mobile platform. The ability to store data in a standardized format is critical for scalability.
PRELIMINARY VALIDATION RESULTS: PRIME’s technical characteristics and testing protocol allow it to accurately and repeatedly measure intrinsic hand muscle strength. Calibration produced a linear fit with a r2 > 0.99 (Figure 9), indicating high confidence in extrapolated force measurements.
Test-retest was used to measure single observer repeatability. In this scenario, one observer measured the small finger abduction strength of a single subject five times with enough time to recover between tests. Comparing the force standard deviation to the mean yielded a coefficient of variation of 1.8% (Table 3). To determine interobserver repeatability, the small finger abduction strength of a single subject was measured by three trained observers and one untrained observer (Table 4). The coefficient of variation for all four observers was found to be 6.7%. The coefficient of variation for trained observers was only 1.4%. These values suggest that PRIME allows for highly repeatable measurements for a single observer-subject combination as well as for multiple observers testing the same subject.
A survey was implemented to measure clinician interest and satisfaction with PRIME on a visual analog scale from Strongly Agree to Strongly Disagree for various statements. Overall, feedback from nurses and doctors at Shriners Hospital for Children™ in Houston was highly positive (Figure 10). This reflects PRIME’s ability to generate physician buy-in. In addition, PRIME was tested with actual pediatric patients in a small focus group (n=3). The patients were capable of following directions and comfortably completing the various tests.
COMMERCIAL POTENTIAL: A recent patent search did not reveal potential competitors in the commercial space. Without question, any major hospital in the United States which sees a substantial case load of hand injuries and orthopedic cases would be interested in PRIME. With over 1,100 members, the American Association for Hand Surgery provides a small sample of surgeons, hand therapists and nurses who focus on hand injuries. Considering the one million of Americans who suffer hand injuries each year and the prevalence of neurodegenerative complications such as spinal cord injury, we hope to reach a market size in the 8 figures within five years.
We envision PRIME to reach the market via 510(k) notification for the FDA; PRIME can be considered as substantially equivalent to approved force transducers on the market. To ensure reimbursement, we will demonstrate PRIME’s role as a critical technology in a host of diseases and illustrate its potential to serve as a measurement for comparative effectiveness research. By investigating IHMS before and after interventions, PRIME can guide appropriate treatment and reduce unnecessary surgeries.
CONCLUSIONS: PRIME is driven by a pressing clinical need. Without question, this device holds value for countless patients suffering from hand injuries and various neuromuscular diseases. The design of PRIME, powered by NI technology, will continue to maximize usability and deliver high quality clinical data. We are undergoing institutional approval from Shriners Hospital for Children™ to conduct a full validation study for PRIME v1 for publication in a peer-reviewed journal by the start end of the summer. A provisional patent has been filed and we hope to push forward to further commercialization.
APPENDIX of TABLES and FIGURES
Design Objective | Design Estimate | Target Criterion |
Weight of less than 8 kg | Sum masses of components | W < 8 kg |
Volume less than 0.125 m3 | Calculate perimeter of base * height | V < 0.125 m3 |
Durable for repeated use of up to 1 year | Fatigue testing and accelerated use for Y time | Y > 1 year |
Test requires < 10 minutes per hand | Time the lag from the test start to data readout | T < 10 min |
Interobserver error under 10% | Collect data with different users for one patient | 5% F1<F2< 5%F1 |
Cost for prototype development < $2,000 | Sum costs for each component | C < $2,000 |
Clear display either in LCD or computer interface | Various users agree is disagree about the display clarity | > 75% agree |
Device rated from 0-8 lbs | Use known weights to determine range | S from 0.1-150 N |
Calibration must take less than 1 hr | Time the lag from non-calibrated to fully calibrated mode | Tcal < 1 hr |
Costs less than $100 per use | Sum costs for each test including wear and tear | Cuse < $100 |
Store data in convenient format for EXCEL analysis | Test the compatibility of data readout with EXCEL | Compatible w/ EXCEL |
Uses commercially available batteries, U.S. 120V AC outlet or USB plug | Test the operation of the device with each of these power supplies | Compatible w/ sources listed |
Less than 1 in 100,000 uses where patients suffer from physical harm | Measure the adverse patient reaction after widespread adoption of device | Injuries < 1 per 100,000 uses |
Table 1. The design criteria were established to create an appropriate framework for the development of the device. Our prototype has succeeded in the meeting all of the design criteria we have tested for thus far. Further validation is still required within an actual hand clinic.
Title | Description | |
A | Bending Peg Board Strain Gauge System | The device implements bending pegs with embedded strain gauges in order to record forces created from movements of fingers and thumb against the bendable peg. The pegs are placed in strategic located on top of the peg board. |
B | Wrist Strapped Single Loop Load Cell System | The device implements one loop that is connected to a load cell in order to record forces created from the movement of the finger or thumb against the loop. The wrist is strapped to the device in order to limit movements. |
C | Peg Board Spring Sensing Optical System | The device implements a camera in order to record the amount of displacement created when the finger or thumb pushes against the spring-loaded block. The block would be painted in a contrasting color to the rest of the device, so that its movements would be easily tracked and analyzed. |
D | Self-Contained Strain Gauge Device | This device included a reference rod that is attached to the forearm of the patient. This would allow the device to be “self-contained” on the patient. A loop strap would be attached to the reference rod and interface with the patient’s fingers. A built in strain gauge of the reference rod will be the force transducer unit. |
E | Hand Muscle Imparted Fluid Turbidity Assay | The device employs a dilitant fluid in order to measure the forces created from the movements of the finger and thumb while submerged in the fluid. The viscosity change of the fluid due to the specific finger movements can be tracked and correlated to force. |
Table 2. The various design proposals attempted to encompass a wide range of techniques. The proposals were determined from brainstorming sessions, a thorough review of the literature and discussions with clinicians and engineers. A decision tree and Pugh analysis led us to select components of proposals A and B.
Equation 1: The equation used to determine the amplification factor. We have a gain of 1000 from the AD260 chip.
Equation 2: The OP07 based low pass active filter has a cutoff frequency of 28 Hz where R is the resistive value in Ohms, C is capacitance in Farads. This filter significantly attenuates any signals with frequencies above 28 Hz. This eliminates the interference of 60 Hz noise and other disturbances.
Test-retest | Force (N) |
Test 1 | 14.66 |
Test 2 | 14.96 |
Test 3 | 14.35 |
Test 4 | 14.70 |
Test 5 | 14.99 |
Average | 14.703 ± 0.26 (standard deviation) |
Table 3: Single observer test and retest indicates that PRIME is capable of reproducing IHMS measurements for a given patient with high precision. Coefficient of variance is calculated by dividing the standard deviation by the mean (1.8%). Conversion to lbs can be done internally by the program.
Interobserver | Force (N) |
Observer 1 (trained) | 16.642 |
Observer 2 (trained) | 16.34 |
Observer 3 (trained) | 16.80 |
Observer 4 (not trained) | 17.16 |
Overall Average | 16.60 ± 0.34 (standard deviation) |
Table 4: The coefficient of variance for the interobserver test is less than 2% for all operators. Preliminary results indicate that PRIME confers significant advantages over existing devices in interobserver precision.
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