Study: Cobalt Levels and Pseudotumor Characteristics Vary du
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This study examines cobalt levels and psuedotumor characteristics in a non-recalled modular femoral prosthesis. A Study was conducted to determine relationships between serum cobalt levels and pseudotumors following modular and metal-on-metal (MoM) total hip arthroplasty (THA), the location and size of pseudotumors, and changes to pseudotumor grade over time.

Researchers retrospectively evaluated a cohort of 190 primary THAs implanted with a dual modular femoral stem by one surgeon. 117 THAs used a cobalt-chromium modular neck (CoCrMN) component and non-metal-on-metal articulation, 63 THAs had a titanium neck component and MoM articulation, and 10 had a titanium neck component and polyethylene liner. Serum ion levels were recorded for all patients. Pseudotumor grade and location were measured by musculoskeletal-trained radiologists.

--Cobalt levels did not correlate to time after index arthroplasty.

--In the CoCrMN group, cobalt levels were elevated in 11 of 19 patients with pseudotumor compared to 14 of 19 in the MoM group.

--Pseudotumors were more often located lateral to the hip joint in the CoCrMN group compared to anteromedial following MoM arthroplasty.

--In CoCrMN THAs, pseudotumors were visualized in 12 of 51 initial MARS MRIs within 40 months compared to 5 of 66 performed later.

In conclusion, the characteristics of psuedotumors differ between CoCrMN patients and MoM patients. Normal levels of serum cobalt do not exclude the occurrence of pseudotumor, and the follow-up of patients with the CoCrMN prothesis should include routine MARS MRI.