Experimental study on a new non constrained total shoulder prosthesis

We designed a new non constrained total shoulder prosthesis and examined it biomechanically. In order to adapt the shoulder prosthesis for the Japanese, fifty skeletal and one hundred radiographs shoulder joints of Japanese were measured. In radiographs we also measured curvature radius of the humeral head and glenoid fossa. We studied force analysis to elucidate the stability of gleno humeral joint using Rigid Body Spring Model. The result on this study indicate that to lengthen the glenoid surface and to make it near the same radius head and glenoid the joint stability will become stable. Our total shoulder prosthesis consist of a cobalt alloy humeral component, a cobalt alloy glenoid component and a high density polyethylene++ outer head put over a small head of humeral component. The glenoid component have two variations. One is for anatomical replacement and its central angle is 78 degrees. The other is for poor function of rotator cuff and its central angle is 110 degrees. The results of biomechanical experiments showed possibility and advantages of our non constrained total shoulder prosthesis being put into clinical practice.