Design of a Distal Radius Fracture Immobilisation Device

Abstract

Immobilisation devices are commonly used for the treatment of extra-articular distal radius fractures. However, conventional immobilisation devices such as plaster casts and fibreglass casts may lead to complications and discomfort. Another disadvantage of present-day conservative fracture treatment is that the casts have to be replaced after one or two weeks when the swelling subsides. In this thesis, an alternative distal radius fracture treatment device was designed, prototyped and evaluated. The main goal of this design was to make the immobilisation device adaptable to swelling while fitting most patients.

The device was designed using a three-step iterative design process and four successive iterations. The steps that were performed in each iteration were setting the requirements, generating solutions and evaluating and deciding. The development of the design was done in the following steps: generating design directions, developing a conceptual design, embodiment of the design and detailing the design. A prototype of the device was created to demonstrate the device's functionality. The design and the prototype were evaluated using diverse methods. Ten healthy volunteers provided feedback after wearing the device, an orthopaedic surgeon offered his expert opinion and several aspects were assessed using calculations and literature. After the prototype was made and evaluated with healthy participants an additional iteration was done to improve the function of the design.

In the first stage, 16 design directions were generated, and the three most promising design directions, the Cushioned Clamp, the Filled Sleeve and the Friction Slots were selected. In the next stage, these design directions were further developed into conceptual designs. The Cushioned Clamp was chosen as the best solution. The Cushioned Clamp consists of interconnected rings around the forearm, wrist and hand with pads that can be adapted in height. In the next step, an embodied design was made. This design had a large offset on the arm and therefore the rings were made adjustable during the detailing phase. Also, the usability of the device was improved. The final design is a device with three adjustable rings with pads that can separately be adjusted for swelling of the limb. The rings are connected with telescopic mechanisms. With a few additional size parts, the single immobilisation device can be adapted to fit 90\% of the adult population. The device was prototyped using aluminium, SLA-printed Form Tough 1500 and Draft Resin, FDM-printed PLA and foam. The prototype allowed too much movement of the wrist, this was addressed and solved after the tests with healthy volunteers. The device is reusable, which reduces waste as less material is used and disposed of. Furthermore, the device is waterproof which reduces skin complications and improves hygiene. The device allows thumb movement which improves the hand function. Furthermore, the mass of the device is 437~grams, which is less than a conventional plaster cast. Volunteers were generally satisfied with the device and the device is quick in application. The medical experts shared concerns about comfort, robustness and applicability for different fracture types. During the improvement phase, several aspects of the device were discussed and improvements were made. Most importantly, additional telescopic mechanisms and connections were designed to prevent movement in the device. Further, the comfort, X-ray permeability and play in the prototype were addressed.

The device is adjustable and adaptable to swelling while allowing skin ventilation. Further, good hand function, a sustainable design and clean applications are advantages of this design. However, the functionality of the design and the prototype can be improved by reducing play and improving robustness. Furthermore, the comfort of the device can be increased by making the device more compact and distributing the pressure better.