The PIPJ Exoskeleton

What it does

The PIPJ Exoskeleton mainly works as a stable and static support, but the slider mechanism adds passive and active motion guides to prevent contractures. Plus, the plates' variations make it a fixator for surgical procedures and splint for other treatments.

Your inspiration

The PIPJ is one of the most vulnerable joints in the human body to injuries due to having limited tolerances to angular, axial, and rotational stresses. In addition, the PIPJ is in an unprotected position and has a long moment arm. In the country, the common rehabilitation technique for PIPJ injuries is by using static finger fixators which are inexpensive, less complicated, and faster to attach. However, because of its resolute static nature, these compromise with finger contractures, which are complications of a joint losing some of its range of motion and most of the time also acquiring deformities to the digit where the injury happened.

How it works

The key mechanism of the device is to allow the injured finger to curl, and to do this, one end of the Slider must be in tangent with the PIPJ's circular path. Then, the finger fixator can return to its static state by simply misaligning the Slider's head with the PIPJ when the finger is at rest. To accommodate passive motion or when the patient can control their finger’s curling through the device, the head of the Slider must be pushed to one end of the Slot while simultaneously rotating the Pole to let its protrusion hit the top part of the Slot and initialize flexion. Pushing the Slider more results in further curling of the finger, and vice versa. In the latter parts of recovery, active motion starts by aligning the Slider's head to the PIPJ under it. Then, through the finger’s flexion and extension, the entire mechanism just follows. In this scheme, the finger’s motion has little to no help from the fixator.

Design process

From a series of interviews from orthopedic surgeons, the essential attributes that define the product’s purpose and general features were identified. These include providing an early range of motion and displacing the “bulkiness” of the design which are necessary for restoring the mobility and maintaining the regular shape of the hands. Moreover, the necessary surgical cuts must be limited to prevent the patient from complications and risks thus the use of medical-grade pins to also keep the plates in position. The first iteration of the device uses a hinge that connects the arms of the plates. The flexion of the finger can then be activated by using a screwdriver to turn the hinge. This was later improved by implementing a slotted design to account for the length change when the middle phalanx supinates with flexion due to asymmetry in the PIPJ. It is then equipped with a gear at one end to activate the finger's flexion and extension. A spring is also added in the middle part to put constant tension on the PIPJ aiding in recovery. It was later identified that the device does not bend by just pushing the arms together. Thus, the pole and its protrusion were incorporated in the design to initialize the curling of the finger as well as a means of the patient to control the device.

How it is different

Unlike most readily available finger fixators, the device offers static, passive, and active functions to help bring back an injured hand’s natural range of motion. To accommodate a multitude of hand sizes, multiple plates were fabricated based on the common ring sizes. The current dimensions of the other parts are from the prevalent index, middle, and ring finger lengths from Filipino anthropometric data. This means the device can be reused except for the plates that make direct contact. The plates were also specially designed to cater the commonly used 1.1, 1.4, and 1.6 mm-thick medical pins in hand operations. For testing, the way the plates are installed on a patient’s finger is revised to one that uses straps akin to a splint. Unknowingly, this widens the scope of our project from a finger fixator to be only administered through surgery to a splint that is also applicable for post-recovery treatments and other medical cases that do not need open surgeries.

Future plans

After consulting with hand surgeons during the testing phase of the device, their suggestions are taken into consideration for the future plans of the project which are having a built-in protractor or some marker to tell the degree of the finger’s flexion and a mechanism that can stop the flexion of the finger at specific angles. Another is a design development for the plates that gives more provision to the surgeon in terms of its placement. Aside from these, fabricating the device using medical-grade steel makes the device stronger allowing further redesigns to make the device smaller and the mechanism smoother.

Awards

The Anti-Contracture Finger Fixator and Splint received funding (Top 3) from the James Dyson Foundation Project Capstone Project Grant among the projects of the UPD BSME Class of 2024. It was also selected as one of the three representatives of the UPD DME in the upcoming Undergraduate Project Competition 2024.