Retrieval analyses of total hip replacements

Metal ion release was assessed in 31 patients with loosening of total hip replacements (THR). Three types of alloys were used for these prostheses: stainless steel (9/31), Ni-Cr-Mo (5/31) and Co-Cr (17/31). The exposure periods were from 2 to 15 years.Intracellular deposits were observed in macrophages, fibroblasts, histiocytes and numerous multinucleated giant cells. X-ray microprobe analyses by energy dispersive spectrometry (EDS) on ultrathin sections revealed the presence of elements contained in the alloys (Ni, Cr, Fe, Mo) and of additional elements, in particular P, CI, Ca and S. Co was only detected in wear particles. Metal distribution in tissues and body fluids was related to the alloys used. Stainless steel THR induced the lowest metal concentrations, Ni-Cr-Mo alloys showed high increases of Ni and Cr. Co-Cr alloys induced very high Co levels: 100- to 400-fold concentrations in body fluids and 600- to 1000-fold concentrations in tissues with respect to normal upper levels. The metal clearing was studied in three patients with Co-Cr-THR. Two years after removal, only Ni reached normal values. The sometimes alarming high concentrations should lead to a systematic follow up and surveillance of patients.