Introduction: The purpose of this study was to retrospectively evaluate blood metal ion levels and leukocyte profiles in patients with modular dual-mobility hip implant (MDM) during a postoperative follow-up up to 2 years.
Methods: We recruited 49 patients in a retrospective cohort study and had postoperative follow-up up to 2 years. Blood concentrations of chromium (Cr), cobalt (Co) and serum cytokines were measured. Flow cytometry was used to quantify the subpopulations of leukocytes, including CD14+ and CD16+ monocytes, CD3+ T lymphocytes, CD19+ B lymphocytes, CD4+ Helper T-cells and CD45+RA memory vs. naïve T-cells.
Results: Clinical performances of implants were good during 2 years of follow-up. Cr levels were normal in all patients and only detectable in 1 patient (1.4µg/L, ref < 5.0µg/L). Co levels were mildly elevated in 4 patients at 1 year (mean 1.375µg/L, range 1.2-1.7µg/L, ref < 1.0µg/L) and in 2 patients at 2-year follow-up (both 1.2µg/L). Interestingly, Co level observed in 3 patients at 1 year converted to undetectable at their 2-year follow-up. Percentages of B cells, T cells and their subpopulations were within normal levels. There was no increase of CD16+ inflammatory monocytes.
Discussion: With the recent introduction of MDM systems there is potential for metal ion release from the interface between the acetabular shell and CoCr liner. Clinical results have been good and metal levels undetectable or within acceptable ranges at 1-2 years. There was no evidence of activated immune response, as manifested by constant circulating leukocyte profiles and no increase of CD16+ inflammatory monocytes.
Keywords: CD14+ monocyte; CD16+ monocytes; Cobalt and chromium; MDM System; metal ions; metal-on-metal.