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Non-articular metal surfaces may be a greater source of ions vs component interfaces in THA
Compared with neck-stem or head-neck interfaces, passive corrosion of exposed non-articular metal surfaces may be a greater source of serum metal ions following total hip arthroplasty, according to results of this prospective randomized study.
Researchers randomly assigned 50 patients who underwent primary total hip arthroplasty (THA) to receive either a metal-on-metal (MoM) bearing with an all cobalt-chromium shell or a metal-on-polyethylene (MoP) bearing with a titanium shell. Final analysis included 24 patients in the MoM group and 23 patients in the MoP cohort. Both groups had a mean age of 60.2 years. Median head size in the MoM group was 46 mm vs. 32 mm in the MoP group. Median acetabular component sizes for the groups were 54 mm and 52 mm, respectively.
Results showed significantly higher levels of median serum chromium and cobalt in the MoM group at both 1 year and 2 years. However, researchers found serum titanium levels were similar between the MoM and MoP groups at 1 year and significantly higher in the MoP group at 2 years. Chromium, cobalt and titanium serum levels increased significantly from baseline and remained consistent at 2 years in the MoM group, with the exception of chromium which had a significant increase from 1 year to 2 years, according to researchers. In comparison, serum chromium levels remained unchanged from baseline to 2 years and serum cobalt and titanium increased significantly at 1 year in the MoP group.
According to multiple regression analysis, head size was a significant predictor of chromium and cobalt levels. – by Casey Tingle
Disclosures: Gofton received honorarium for course lectures and training, and payment for publication of SuperPATH papers from Microport; received unrestricted institutional research support from DePuy Synthes; and received payment for research from Smith & Nephew. Please see the full study for a list of all other authors’ relevant financial disclosures.
Perspective
Back to TopFemoral stem modularity in both primary and revision total hip systems has been advanced as a methodology of providing increased flexibility to the reconstructive hip surgeon. Restoration of normal biomechanics, leg length inequality and proximal femoral deformity are pathologies that are corrected by their employ. However, the construct of the modular connection at the stem-neck junction has been associated with fracture and increased serum ion levels particular to the materials employed.
This randomized study investigated the use of titanium-titanium neck-stem junctions particular to a series of 25 MoM and 25 MoP articulations measuring their respective chromium, cobalt and titanium serum ion levels.
The authors conclude titanium serum ion levels were similar in the first and second years of the study and, more importantly, not associated with any adverse local tissue reactions (ALTR). It is interesting, in this regard, that large heads have been associated with increased frictional torque at the stem-neck junction, contributing to increased debris generation, which seemed minimized particular to the titanium serum ion levels in this study. Their comparison of titanium serum ion levels to those associated with non-modular titanium femoral stems previously reported (Omler GW, and colleagues) were similar. The absence of ALTR is a relevant observation for their employ in hip reconstruction.