Design and implementation of a test stand for in-vivo force measurement on a flexor tendon

Abstract

Carpal Tunnel Syndrome (CTS) is a compression of the median nerve in the region of the wrist. Symptoms include pain and numbness in the supplied fingers and can greatly restrict affected individuals in their everyday lives. To lower the number of people suffering from CTS, guidelines and ergonomic standards have been established. These currently lack a scientific model considering all influencing factors. A musculoskeletal model, currently developed at the Center for Integrated Neuroscience Tübingen, Germany, simulates all the known risk factors. To verify the model, one important parameter was chosen. This parameter is the contact force between the Flexor Digitorum Superficialis (FDS) III tendon and the surrounding tissue. The aim of this thesis is therefore, to create a test stand which makes it possible to measure the resulting force in an in-vivo situation.The workflow started with planning the construction by creating a list of requirements. Furthermore, a functional model was built to develop a reliable measurement procedure and to correct design errors. In a pilot study the response of electromyographic signal to a range of loads on the FDS III was tested on six probands. Possible designs were constructed and finally the most promising approach was built. Lastly the setup was improved and tested for performance in in-vitro situations.With the final setup one is able to position different angles in the wrist and measure resulting forces with a quickly adjustable force sensor. The in-vitro measurements show good precision and accuracy in lower angles with a Standard Deviation (SD) of 0.15 N at a mean of 3.68 N. For angles at 60° the design of the test measurements led to high transverse forces, which resulted in a deviation from expected results. Measurements with sheep tendons showed stable holding of the tendon with the attached surgical hook and had a good precision. In conclusion it can be said that a solid measurement setup was constructed and tested within the scope of this thesis. The ease of use and simple design not only allow measurements to be taken quickly, but also safely during surgery. Repeatability was improved during different in-vitro tests, which can be seen in a SD decrease from 1.06 N to 0.45 N. Performance in higher angles is to be expected better in in-vivo situations, which will be looked at in the planned cadaveric tests at the BG Clinic Tübingen, as part of the Eberhard Karls Universität Tübingen.