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Case study: Knee Orthosis Joint 2017-05-19T11:11:43+00:00

Case study: Knee Orthosis Joint

Patients who are not able to control their knee joint usually receive a brace to support them during walking and standing. The conventional braces fixate the leg in a straight position and as a consequence the patient has to walk with a stiff leg. This is not only inconvenient for the patient; it also gives an abnormal walking pattern and could lead to increased wear of the hip joint.

For this project, the user input was defined as follows: There is a need for a joint that enables the patients to have a normal walking pattern. This joint should block while the patient’s leg is in the vertical standing position and it should automatically unlock when the patient’s leg is in the swing phase.


Stage 1: Explore

There were two main constraints defined: The functionality must be achieved without the need of electronics and all functionality must be concentrated in the joint to be able to use it with standard brace components. Furthermore, gravity was identified as a promising working principle.

Starting from this point, we generated a concept that indeed relied on gravity with respect to the locking mechanism. A functional model was produced to show that the idea indeed could work. In fact, it was possible to build a strong IP position with this working principle. Within this phase, we were also able to define a set of technical specifications that this concept should fulfil in order to function properly.

Stage 2: Design

In this step all possible bottle necks are addressed by means of design calculations and testing of the most critical parts. In this case it was important to find a way to transfer the high loads without affecting the locking mechanism. The influence of the dynamic forces on the locking mechanism during walking was another topic to test. Then the reliability of the system was an important aspect to be considered. For all aspects we have created verification steps and test set ups in order to proof that the main issues can be covered in the design.

Stage 3: Engineer

In this phase our focus was to finalize and fully detail the design. In this case an important question was to select the most economical production method: casting or machining. Particularly in this project the challenge was to optimize the assembly of the locking mechanism and optimize the tolerances for some specific parts.

Stage 4: Validate

This product was classified as a class I product, however, a severe validation process was carried out to prove safety and efficacy. When the product blocks unexpectedly the patient could fall and break his leg.

The standard ISO tests where not sufficient to prove safety and therefore, specific validation tests were developed and performed. An important set up was to test the orthosis joint by imitating a real walking pattern. In this way we were able to evaluate the long term performance of the system before actually bring it on the market.

Stage 5: Transfer

This last step was a very important one. In this project the customer took care of all CE mark activities. Our job in this phase was mainly to start up to transfer the manufacturing process properly to their subcontractors.