Metal Ion Release, Clinical and Radiological Outcomes in Large Diameter Metal-on-Metal Total Hip Arthroplasty at Long-Term Follow-Up

Abstract

Total hip arthroplasty (THA) with metal-on-metal (MoM) bearings have shown problems of biocompatibility linked to metal ion release at the local level causing an adverse reaction to metal debris (ARMD) and at a systemic level. The aim of this study was to evaluate clinical and radiological outcomes, and metal ion concentrations in the blood and urine of patients who underwent THA with the LIMA Met-Met hip system. Patients with ceramic-on-ceramic (CoC) bearings were included as a control group. In this study, 68 patients were enrolled: 34 with MoM THAs and 34 with CoC THAs. Patients were evaluated clinically (Harris Hip Score, SF-36) and radiologically at a median of 7.4 years after surgery. Whole blood and urinary cobalt and chromium levels were also assessed. Both types of implants were comparable in terms of clinical and functional results. Ion levels were significantly higher in the MoM group compared with CoC group 7 years after surgery. No correlations were found between metal ion levels and patient demographics, functional and radiological outcomes, and prosthesis features. Patient monitoring is thus advised to establish if prosthesis revision is necessary, especially in the case of MoM THA.

Keywords: ceramic-on-ceramic; chromium; cobalt; metal-on-metal; total hip arthroplasty.

Figure 1

Local and systemic toxicity of metal-on-metal (MoM) metal debris. Metal debris, released from the implant by corrosion or wear, causes local periprosthetic alterations called adverse reaction to metal debris (ARMD), mediated by different types of cells including macrophages, osteoclasts, giant cells, dendritic cells and lymphocytes. Tissue alterations can cause osteolysis (induced by osteoclasts and macrophages) at the bone-level, or pseudotumor formation and aseptic lymphocyte–dominated vasculitis-associated lesions (ALVAL) at the soft tissue-level. Periarticular metal debris can be disseminated to different organs through circulatory and lymphatic systems causing systemic toxicity.

Figure 2

Flowchart summarizing patients involved in the study: (a) MoM, metal-on-metal bearing; (b) CoC, ceramic-on-ceramic bearing. FU = follow-up.

Figure 3

F.A., 81-year-old female, Metal-on-Metal Total Hip arthroplasty for primary arthrosis, right hip X-ray. (a) Post-operative follow-up, one month (b) Post-operative follow-up, 7 years (24 months after recruitment).

Figure 4

V.D., female, 58 - year-old, Ceramic-on-Ceramic Total Hip arthroplasty for femoral neck fracture, right hip X-ray: (a) Post-operative follow-up, one month (b) Post-operative follow-up, 5 years (24 months after recruitment).

Figure 5

Scatter dot plot (median with interquartile range) of metal ion levels in MoM and CoC groups. Cobalt ion level in whole blood (a) and urine (b). Chromium ion level in whole blood (c) and urine (d). Urinary values are expressed as μg/g of creatinine. Dotted lines represent the laboratory upper limits of the normal range in the general population for cobalt and chromium in whole blood (1 and 0.5 µg/L, respectively). Dotted red lines represent the safety threshold of 7 µg/L for Co and Cr in whole blood. In urinary levels normalized to creatinine (b and d), dotted lines represent the normal values of CoU < 2 µg/g and CrU < 0.05 according to the National Institute for Research and Safety (Institut national de recherche et sécurité (INRS)). Dotted red lines represent the safety threshold of 30 µg/L for Co and 31 for Cr in urine.