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SPIKE Fixture

Introduction

Very few research endeavors have been undertaken to build a fixture which will dynamically move all the bones of the shoulder to collect data on moment arms and forces. This information would be very valuable for doctors in evaluating and repairing shoulder injuries. Most research in this area involves fixing the motion of one of the bones and moving the others. This presents an opportunity for our team to build a fixture which will dynamically move the shoulder bones and measure moment arms of the given muscle groups.

Project Objectives:

Develop a prototype shoulder fixture by May 2010 which will dynamically measure moment arms of broad muscles or tendons given a position of the humerus or scapula.

regressionThere are several specifications that we aim to do with our fixture:
(a.) Create a stable base and preserve the structural integrity of the cadaver
(b.) Provide for the full range of motion of the humerus
(c.) Control the motion of the scapula and clavicle
(d.) Build a fixture that is moveable and modular

We want this fixture to be able to accurately measure moment arms and compare our values with theoretical models of moment arms calculations. We want our data to also closely resemble regression equation models, shown in figure 1.

Because we will be measuring moment arms of the broad muscles with this fixture, we will need to create artificial muscles because cadaver muscles are too stiff to use due to rigor mortis. We will approximate the broad muscles with wires. The problem, however, with using wires is that they tend to cross over each other and do not stay where they need to. Consequently, we are attempting to encase the wires in a gel-like substance that mimics the properties of live human muscle. gelOne possibility being considered right now is ballistics gel. We will be making several different mixtures and testing material properties so that they will match up with those of human muscles.

(1)Figure taken from de Groot, J.H., & Brand, R. (2001). A three-dimensional regression model of the shoulder rhythm. Clinical Biomechanics, 16(9), 735-743.
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