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Case study: Hand orthosis 2017-05-19T11:11:43+00:00

Case study: Hand orthosis

Lateral epicondylitis (tennis elbow) is a common disorder. Dr de Lint developed a new principle to treat severe cases of this disorder using a hand orthosis. This orthosis should allow the wrist to flex while applying an external wrist extension force on the palm of the hand. A custom made brace was used to test the working principle. Our task in this project was to develop a commercial product that can be manufactured in series and that should maintain the original working principle. The result is shown here and the results of a clinical trial, carried out with this new orthosis, can be found in this article, published in Clinical Orthopedics and Related Research.

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Stage 1: Explore

The first step in the project was to analyses the dynamic forces that must act on the hand in order to obtain the desired result. Once this is defined, the location, height and direction of reaction forces needed to obtain equilibrium in all positions of the hand where defined.

Second step in this stage is to develop a configuration that will apply all forces and is suitable for serial manufacturing. It was decided to develop a construction kit that can be assembled by the orthotist and adapted to the individual patient.

Stage 2: Design

In this stage several models where developed. Within our approach we develop various models, with a focus on the functionality of the design. It was  decided to replace the actuator of the original custom made brace, which was an elastic band, with the memory metal super elastic springs on both sides or the hand. In this configuration the point of rotation of the wrist is not hindered. Typically for the design of orthosis user requirements and techical specifications evolve along with the progression of the subsequent models. In every model these requirements and specifications where updated.

Stage 3: Engineer

Once the concept is developed to such extend that all functional requirements are met, the engineering stage starts. In this case various processes where incorporated in the product, from injection molding, sheet molding to manufacturing and bending of the memory metal springs. These manufacturing processes where developed along with the product itself.

Stage 4: Validate

In the validation stage various mechanical tests where performed. Especially the fatigue properties of the memory metal springs deserved attention. Special test set ups where developed to test the force-displacement curve over a high number of cycles. Part of the validation stage was a clinical trial. This trial was very successful, however because of the pain relieve which the patients experienced they started to use their hand much more then expected. Therefore the fatigue demand for the spring was much higher as expected.
It was decided to carry out a redesign consisting of a special support for the spring to enable to load the complete spring evenly. This resulted in a much higher fatigue strength of the device which appeared to be sufficient.

Stage 5: Transfer

The first series where manufactured by BAAT, later the customer took over the manufacturing chain and process control. The product is still on the market and distributed by various companies:

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