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Pneumatics power innovative shoulder joint test rig

13 November 2015

Pneumatics distributor, Thorite supplies Newcastle University research team with components for a new rig that is capable of testing all types of reverse shoulder prostheses.

Reverse shoulder joint replacement is an increasingly common surgical intervention. However there are concerns in relation to such procedures, with novel designs of reverse shoulder prostheses continuing to appear on the market. Many claim to offer improvements over older designs but such assertions are difficult to validate when there is no agreement as to how such implants should be tested in the laboratory - or even if such testing is necessary. 

In order to permit appropriate laboratory testing of all types of reverse shoulder prostheses a novel, multi-station test rig has been designed by Dr Simon Smith and built under the direction of Professor Tom Joyce in the School of Mechanical and Systems Engineering at Newcastle University. The team was aided in this work by Thorite's North Shields sales and service centre team who supplied a variety of pneumatic actuators for the rig, which is capable of applying motion in three axes to test the prostheses.

Known as The Newcastle Shoulder Wear Simulator, it uses three Thorite-supplied Norgren pneumatic cylinders with integral position encoders to move five prosthetic shoulder joint units simultaneously in the flexion-extension, abduction-adduction (arm raising and lowering) and internal-external rotation axes.

Axial loading is applied to each artificial shoulder joint using an SMC pneumatic cylinder, the compressed air to these five cylinders being supplied from an SMC proportional valve via a manifold - again from Thorite - which also supplies the sixth static control station.

The axial loading cylinders are double acting and back pressure serves as an air spring to remove loading on the prostheses, as required. The simulator is programmed in LabVIEW and two instrument controllers are used to control the pneumatic system. Closed loop feedback is used for the three motion axes, while open loop feedback is used to control the loading, which has been demonstrated to be highly reliable. Professor Joyce concludes:

"The shoulder simulator can be important in several ways. Firstly, it can allow weaknesses in current designs of reverse shoulder prosthesis to be pinpointed and fed back to the designers and manufacturers so that the implants can be improved. Secondly, the performance of different designs of reverse shoulder prosthesis can be compared in the simulator and this data shared with interested scientists, clinicians, patients and engineers.

“Thirdly, the simulator will permit novel designs of reverse shoulder prosthesis to be tested in the laboratory prior to implantation in human subjects. Together, all of these benefits offer opportunities to improve artificial shoulder joints for the increasing number of patients requiring such implants."

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