Sunday, July 17, 2016

Corrosion in modular humeral components

Fretting and Corrosion in Modular Shoulder Arthroplasty: A Retrieval Analysis

These authors point out that adverse effects caused by metal debris and subsequent elevated serum metal ion levels have been reported for total hip arthroplasty, but that the corrosion at taper junctions in retrieved anatomic shoulder arthroplasty implants has not been well studied. 

They compared the corrosion in cobalt-chromium and titanium alloy stems and correlated the observations with clinical data in 36 retrieved hemiarthroplasties and total shoulder arthroplasties.

Substantial corrosion was present on 27 of the 36 heads (75%) and 29 of the 36 stems (81%). 

Significantly greater corrosion was seen in mixed metal combinations where Ti stems were used compared to the same metals using CoCr stems. For the CoCr heads there was a tendency of increased corrosion when combined with Ti stems compared to the combination with CoCr stems.

Stemless designs showed somewhat less corrosion at the taper junction than stemmed designs.

From their data it was not possible to determine if corrosion can lead to adverse clinical reactions or cause failure of shoulder arthroplasties.

Comment: Tribocorrosion is a material degradation process due to the combined effect of corrosion and wear. This article prompts us to inspect all retrieved modular humeral implants, looking for evidence of this process. There are good arguments for using chrome-cobalt humeral heads and titanium stems, so that more data needs to be collected on the clinical importance of the amount of tribocorrosion that takes place before there is concern about their use.