Although there are many benefits of head-neck modularity used in total hip arthroplasty, a speaker here highlighted the risk of mechanically assisted crevice corrosion at the head-neck junction.

 

"There is much ado. This is not about nothing," Joshua J. Jacobs, MD, said in his presentation at the Current Concepts in Joint Replacement Winter Meeting. “There is a real phenomenon here. The question is the prevalence.”

 

Jacobs reported on two published studies in which patients with modular tapers were revised for adverse local tissue reaction (ALTR) secondary to corrosion at the head-neck junction. The patients had increased serum metal ion levels and ALTRs similar to those seen in patients with metal-on-metal bearings. The first study included 10 patients with all metal-on-polyethylene bearings of different designs. Jacobs noted that most had 32-mm heads or smaller and most symptoms occurred at 4 years postoperatively. “Revision to a ceramic head with a titanium sleeve resulted in resolution of their high cobalt levels and, in all but one case, resolution of their symptoms,” Jacobs said.

 

The second study included 11 patients with either metal-on-polyethylene or ceramic-on-polyethylene bearings with a single-stem design that has since been recalled. Patients presented with pain as their primary symptom nearly 8 months after their index procedures. Researchers found large fluid collections and ALTRs. The serum cobalt levels in these patients were 19 times higher than one would see in a normal control group of patients with metal-on-polyethylene bearings, Jacobs said.

 

"This does give us some insight of the etiology of these adverse local tissue reactions that have been reported around metal-metal bearings, but now also around metal-poly bearings with corrosion at modular junctions," Jacobs said. “It is related to the summation of the debris released from bearing surfaces and modular taper junctions through so-called tribocorrosion mechanisms — that is, combined tribology, the mechanical process of wear and corrosion, which is an electrochemical process.”

 

He continued, “Interestingly, adverse local tissue reactions have only been reported in association with modular junctions involving a cobalt-chromium alloy component, and while corrosion does occur to titanium and titanium junctions, we have not seen the same sort of soft tissue response; however, titanium necks may be more susceptible to fracture.”

 

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