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Illustrative project: shoulder simulator

Simulating and understanding how the shoulder moves

The workings of the human shoulder are not yet fully understood. To help gain new insights into the mechanisms by which it functions, the ZHAW School of Engineering’s Institute of Mechanical Systems has developed a physiological shoulder simulator. The device can also be used as a dummy for testing the stability of implants and prosthetic devices.

Winter sports accident statistics show that the shoulder and upper arm are the second most common injury sites. That is hardly surprising given that the shoulder, with its 27 muscles and five joints, plays an essential part in practically every movement or posture. Yet, even in the 21st century, the workings of the human shoulder are not yet fully understood. That is why the Institute of Mechanical Systems (IMES) has designed and built an experimental shoulder simulator.

«Because our simulator functions like a real shoulder, it can be subjected to the same physical strains and tests as its human counterpart. That provides insights into how easily particular movements can make the shoulder unstable.»

Dr. Daniel Baumgartner, Project Manager

Making the strains placed on joints visible

Using the physiological simulator, it is possible to replicate shoulder movements and the strains placed on the shoulder in a realistic way. Electric motors are used to simulate strains on the shoulder muscles. They can twist the upper arm and use weights to raise it, thus making it possible to analyse the various forces at work in these movements.

What muscular forces do various arm movements activate? What forces are exerted on the joints between the upper arm and the shoulder blade? “Because our simulator functions like a real shoulder, it can be subjected to the same physical strains and tests as its human counterpart. That provides insights into how easily particular movements can make the shoulder unstable.”

Providing insights for both surgery and industry

The insights gained from this fundamental research are useful in a number of areas, shoulder surgery being but one example. Operations involving prosthetic shoulders have not so far been as successful as those involving artificial knees or hips. A collaborative project between the ZHAW and the Balgrist Hospital in Zurich is proving beneficial to the doctors involved, as it helps to reduce the risk that patients undergoing shoulder operations suffer permanent impairments to their freedom of movement. The shoulder simulator can also be used to test the structural robustness, load-bearing capacity and functional characteristics of joint implants and prosthetic joints under realistic conditions. One company has already had its joint implants tested on the simulator for that purpose. “Surgical interventions carried out on artificial bone still provide a better representation of a real operation than can be achieved with computer simulation and they also yield better experimental results,” explains  Baumgartner. “It would not be acceptable that an implant screwed into real bone begins to loosen after 10,000 arm movements.”

«If we can transfer that real data to the simulator, we will be able to determine precisely what muscular exertion is needed to raise the arm and what forces that exerts on the joint itself.»

Dr. Daniel Baumgartner, Project Manager

Working with individual movement data

At present, the shoulder simulator still operates with target values determined by the computer. In the medium term, it should even be possible to transfer movement data from individual patients directly to the simulator. “Each individual has his or her own characteristic movement processes,” says Baumgartner. “If we can transfer that real data to the simulator, we will be able to determine precisely what muscular exertion is needed to raise the arm and what forces that exerts on the joint itself.” Such an approach would make it possible to calibrate operations and implants even more precisely to the specific needs of each individual patient.

At a glance

Participating institutes and centres:

Project partner:

Financing: Nationalfonds SNS

Project status: finished