Specific Aim
The project aims to design an electric goniometer for rehabilitation and monitoring purposes after hand surgery. Flexor tendon injury has been a big problem for hand surgeons. Limited blood flow through fingers often leads to poor hand recovery quality. Some tendon repair failures are due to the suture or knot rupture. It is reported that tendons without stress may have up to 50% lower strength of the repair between the first and third weeks.1 Furthermore, adhesion of the tendon with surrounding tissues will result in restricted finger joint flexibility. Thus, hand rehabilitation is critical in hand function recovery. In practice, hand therapists provide instructions for helping patients do finger exercises after the surgery. They teach patients to do the finger curling exercise and measure the angle of each joint with a goniometer. However, it is optimal for patients to do exercises and get feedback not only during appointments with the therapist but also at home. This consideration leads to the issue that exercise quality at home is not guaranteed. Moreover, it is impractical for doctors and therapists to constantly keep track of how much a patient uses his finger every day. If the tendon is under too much stress and too frequent stimulation, the risk of rupture will significantly increase. On the other hand, if the fingers after surgery are barely exercised, it is not beneficial for the recovery of the hand.2
Thus, for post‐hand‐surgery patients, there is a need for a wearable wireless goniometer with compatible software for better and easier monitoring and assessment of the postsurgery hand rehabilitation for patients to use without the assistance of hand therapists. We aim to work with a team of hand surgeons and therapists at Washington University in Saint Louis medical school to develop a solution for an easier way to monitor the process of post-hand-surgery rehabilitation.
Proposed Solution
A real-time PIP joint goniometer is proposed, which is designed based on the cooperation of multiple gyroscope/accelerometer sensors. This kind of sensor is a 3-axis sensor that can calculate the forces in the X, Y, and Z directions based on the measured spatial acceleration. Then, the forces in the 3D space can be converted into a 3D angle measurement, and the orientation of the sensor can also be derived. The original gyroscope/accelerometer sensor is that measurements of tilt angles are precise only under static conditions. If the sensor is constantly moving, there may be motion distortions to the signal. A system consisting of multiple sensors can be used to measure the relative motion between the sensors. Our solution is based on the integration of two identical gyroscope/accelerometer sensors in a single system. One is used as a baseline sensor, and the other sensor is used to generate the relative angular position relative to the baseline sensor. In this way, algorithms can be developed to calculate the PIP joint angle based on the relative angular position difference between the two sensors, which are expected to avoid motion distortions effectively.
Previous studies have shown a promising ability to conduct measurements of tilt angles based on the gyroscope/accelerometer sensor. In the following figure 1 (a), the 6-axis sensor first collects information about translational and angular accelerations. In figure 1 (b), when the sensor is tilted, the acceleration information can be converted into angle information, and the combination of X, Y, and Z angles can be used to reconstruct a rotational model in the 3D space3. Specifically, the X, Y, and Z angles are obtained, the equation of the bottom surface of the sensor can be calculated in a manually modeled space, and the normal vector of the surface can be used for the tilt angle estimation.
In our design of the system, the spatial positions of the two sensors and 6 angle components, including X1, Y1, Z1, X2, Y2, and Z2, are measured. A rotation of the coordinate system is computed based on the data collected by the baseline sensor, and the data collected by the other sensor are registered into the new coordinate system. Thus, similar procedures can be followed for the measurements of the tilt angle of the sensor after the registration, and the tilt angle measured in the new system should equal the PIP joint angle. Overall, this normalization process increases the spatial stability of the measurements and simplifies signal processing.
We proposed to use a finger-mounting sleeve for the sensor module. The first approach is to 3D print a mounting sleeve that exactly fits the finger size and shape of the subject. The outcome of 3D printing depends on the printing material available. soft material can fit finger shape better and provide more comfort to the patients whereas rigid plastic sleeve requires an additional layer of soft cushion to fit the shape. The makerspace in Juber hall on Danforth campus has the capability for 3D printing, we will reach out to them regarding the material choices and 3D printing costs.
There is an alternative way to use soft fastening cable straps to fix the accelerometers. The proposed structure of this mounting device is composed of three parts: the strap, the glue sticking the accelerometer board to the strap, and the accelerometer itself. An additional 3d-printed board might also be placed between the strap and the accelerometer in order to counter possible instabilities. This mounting device is adjustable to fit different sizes of fingers, and soft straps will not be hard for patients to put on.
Figure 1: (a) the measurement axes of the 6-axis gyroscope/accelerometer sensor; (b) example tilts of the sensor 3.
Proposed Budget
The prototype comprises of two finger mounting parts and two Gyro/Accelerometer sensor modules, each containing a Bluetooth unit, a rechargeable battery unit, and a Gyro/Accelerometer sensor. The Gyro/Accelerometer sensor modules are purchased from MBIENTLAB (https://mbientlab.com/pricing/). To mount the sensors, we are going to use the MMS Skin Adhesive Kit, which costs around $150 per kit. The app for sensor signal acquisition is available for free.
The finger mounting part is expected to be 3D printed using the 3D printer provided by the course instructor. Alternatively, we can use adhesive from the sensor kit. The estimated cost of the prototype, including two sensor modules and additional components, is approximately $300-400.
| Item Name | Item Description | Total price | Link | Number |
| Metamotions (MMS) | Durable, wearable, rechargeable, powerful Gyro/Accelerometer sensor modules | $ 272 | PCB with case: https://mbientlab.com/store/metamotions/ | 2 |
| 3D printed Mounting sleeve | 3D printing using the maker space from engineering school (used for mounting and/or encasing purposes) | N/A | Direct funding from MakerSpace in Mckelvey Engineering school | N/A |
| Double side tape | Attach the PCB board to the mounting part | $ 15 | https://a.co/d/2gEUGuO | 1 |
| Fastening strap sleeve | Used for fixation purposes (intended to be applied surrounding the finger to serve as the fixation element of mounting platforms) | $ 18 | https://a.co/d/jcwk6Qz | 1 |
| Fastening strap | An alternative solution for fixation purpose | $ 24 | https://a.co/d/5j4JdeB | 1 |
| Silicone Cushion | Used for adhere our mounting component with patient skin | $ 24 | https://a.co/d/eiRsbUZ | 2 |
| Silicone ring | Fixation solution | $ 20 | https://a.co/d/0Ct5Exg | 2 |
| 407 Silicone glue | Use for adhere silicone ring | $ 30 | https://a.co/d/ev0iflw | 3 |
| Price in total: $ 403 |
Reference
[1] Thorne, C. H., Gurtner, G. C., Chung, K. C., Gosain, A., Mehrara, B. J., Rubin, P., & Spear, S. L. (2013). Grabb and Smith’s Plastic Surgery (7th ed.). Lippincott Williams and Wilkins.
[2] Chung, Kevin. Grabb and Smith’s plastic surgery. Lippincott Williams & Wilkins, 2019.
[3] Admin. (2022, September 17). Measure tilt angle using MPU6050 gyro/Accelerometer & Arduino. How To Electronics. Retrieved December 4, 2022, from https://how2electronics.com/measure-tilt-angle-mpu6050-arduino/