Dosages sanguins de métaux chez 48 patients porteurs d’une prothèse totale de hanche en chrome-cobalt à couple métal-polyéthylène

Abstract

Purpose of the study Component wear and dissemination of wear debris, particularly with metal-on-metal combinations, is the predominant long-term complication of total hip arthroplasty. The purpose of our work was to search for metal particles released when using the metal-on-polyethylene combination by analyzing serum levels of chromium (Cr), cobalt (Co), nickel (Ni), and molybdium (Mo) in patients with a metal-on-polyethylene chromium-cobalt total hip arthroplasty. We compared the observed levels with those observed in a control population and studied changes as a function of signs of loosening. Material and methods During a thirty-month period, 53 patients with degenerative hip disease underwent total hip arthroplasty. The same implant, PVL ®, being used for all hips. Forty-eight patients were available for analysis at a minimum follow-up of 32 months. Results of the clinical and radiological examination of the operated hip were recorded. Serum metal levels were assayed by mass spectrometry on total blood samples. Patient activity was determined with the Devane classification and hip function with the Postel-Merle-d’Aubligné score; walking distance was recorded in kilometers. Signs of prosthetic loosening were identified on plain radiograms (AP and lateral views) searching for femoral and/or acetabular lucent lines, cement fracture, granuloma. The control group included 56 patients scheduled for total hip arthroplasty. Non-parametric statistical analysis was used to search for correlations between the clinical, radiological, and biological parameters. Results At mean 44 months follow-up, 17% of the patients had a fair or mediocre function score and 37% had radiological signs of femoral component loosening. Serum cobalt increased significantly in the implanted group (serum cobalt ≥ 0.60 μg/L in 50% of patients) compared with the control group (serum cobalt ≥ 0.60 μg/L in 9%) (P < 0.001, Mann-Whittney test). Increased serum cobalt was highest in patients with radiographic signs of loosening. This significant difference was not found for other metals. Patient activity, hip function, and follow-up were not correlated with serum levels. Discussion Serum cobalt appears to be a good biological marker of prosthetic function although intra- and inter-individual variations are influenced by assay technique, metal ion solubility, and metal dissemination in the organism. The metal-on-metal combination does not appear to be the only friction couple which increases the serum level of metal ions. Our results do not allow defining a time of latency between onset of radiographic signs and increased serum levels.