Saturday, October 15, 2016

Does the prosthetic humeral head articular surface wear?

Surface and form alterations in retrieved shoulder hemiarthroplasty

These authors studied 13 retrieved and 3 new shoulder hemiarthroplasties to analyze whether the metallic articular surface of retrieved shoulder hemiarthroplasties is different from new implants. . The implant was the Synthes Epoca humeral head made of chrome cobalt alloy (Co-28Cr-6Mo). The retrieved implants had been in place for an average of 600 days. The surface roughness was measured on different sites of the surface (dome of the head and the rim). The implants were further measured using a coordinate measuring machine to gain information on volumetric wear and geometric alterations. The surface was analyzed with a scanning electron microscope to see marks of wear.

They found that the maximum surface roughness on the retrievals was significantly increased in comparison to unused implants. The images show a 25,000 times magnification of an unused implant (above) and a used implant (below).

They did not measure volumetric wear on these retrieved prosthetic humeral head components.

Here is a figure showing the shape deviation in a retrieved implant.

Their data on shape deviation is shown below.

Even the new components are not completely uniform!

Comment: This is an interesting study showing that one the hardest metal prosthetic joint surfaces can wear in the articular environment of the shoulder. It would be of interest to know the surface characteristics of humeral heads retrieved after total shoulders were similar or different than those shown here for retrieved hemiarthroplasties.

While there may be concern about the effect of these surface irregularities on glenoid wear, it is for sure that the metal prosthetic surface is smoother than that of the arthritic humeral head.