Shoulder Simulator Wear Test of Five Contemporary Total Shoulder Prostheses With Three Axes of Rotation and Sliding Motion

Shoulder joint replacement generally utilizes ultra-high molecular weight polyethylene (UHMWPE) as a bearing surface. Long term survival of such implants is recognized to be limited by wear of the UHMWPE. Commercially available JRI 42 mm diameter VAIOS Total shoulders were wear tested in diluted bovine serum for five million cycles in a unique Shoulder Wear Simulator. Five Total shoulders were subject to rotational and translational motion, and loading, to replicate the “Mug to Mouth” activity of daily living. A sixth Total shoulder was subject to loading only in a control station. Wear was measured gravimetrically and surface roughness was measured with a non-contacting profilometer. Mean wear rate of the UHMWPE components was 21.5 ± 5.4 mm3/million cycles. The humeral heads roughened, from 19 ± 3 nm Sa to 43 ± 13 nm Sa over the five million cycles of the test, while the UHMWPE glenoid components became smoother, from 959 ± 230 nm Sa to 77 ± 17 nm Sa. This is the first reported wear test of multiple samples of a commercially available Total shoulder in a dedicated shoulder simulator.