Development of a Thumb Metacarpophalangeal Joint Splint

Abstract

In daily life, we are constantly using our hands to do everything that is important to us. The thumbs play a critical role in this and losing stability of your thumb leads to a reduced Quality of Life. There are numerous conditions that can lead to joint problems in the thumb that negatively affect its stability, like rheumatoid arthritis, osteoarthritis, hypermobility, and dislocation injuries.
In this graduation project, a personalized thumb splint is developed which improves the stability of the metacarpophalangeal (MCP1) joint of thumb. Creating personalized products is not easily viable, so the design workflow for Ultra Personalized Products and Service Systems is used. In this project, that means making use of patient specific 3D scans to create a modifiable design template of a thumb splint. The template needs to be parametrically adjustable to facilitate the production through digital fabrication methods, like 3D printing.
The thumb splint is intended for patients who have mild joint laxity symptoms, meaning that the splint must prevent hyperextension of the MCP1 joint, but allow as many other movements of the hand as possible. This optimizes the patient’s hand function. An elaborate exploration of the current thumb splinting market reveals deficiencies in existing solutions such as the splint slipping off too easily, causing painful pressure, being too bulky or too limiting. In this project, steps are taken to standardize a thumb splint design and create a data-driven workflow, allowing the evaluation and improvement the product performance.
Different scanning positions and additive manufacturing methods were used to produce over 100 thumb splinting prototypes. Each one provides new insights to improve the fit, comfort, effectiveness, security, and appearance of the splint. This led to a final splint design where all the research and prototyping insights are combined.
The result is a splint made of Multi Jet Fusion printed PA12 (nylon). It is modelled on a scan in a new position: a thumb in opposition. It features a hinge which allows more flexion of the thumb, extension to a specified maximum and makes sure the splint stays snugly in place on the skin. It is well secured to the hand, does not cause painful pressure points, and facilitates almost all thumb movements except for (hyper-)extension of the MCP1 joint beyond 180°. Parametric design rules were formulated to adjust the fit to any user, based on their 3D scan, wherein the thumb is in an opposed position.
Potential users were involved in the design process at four different moments to gain insights about criteria priorities and finally evaluate the ergonomics and performance of the splint. The final evaluation revealed that the splint functions as intended and has promising value. The viability of the new design was also evaluated with different orthopedic and fabrication experts. While there is room for further detailing and optimization before implementation, the proposed thumb splinting architecture shows a promising step in the standardization of a solution for people who suffer joint laxity in the MCP1 joint.