INTRODUCTION: Metal-on-metal alloarthroplasty of the hip is gaining popularity in order to avoid complications associated with polyethylene wear. On the other hand, metal-on-metal articulations release metal ions, the biological effects of which remain unclear. Genetic and immunological changes have been associated with increased metal ion levels in arthroplasty patients. We intended to study the outcome after metal-on-metal arthroplasty of the hip with a focus on the toxicologically and immunologically relevant metal ions chromium, cobalt, nickel, and manganese.

PATIENTS AND METHODS: A prospective, randomised study was designed where all patients received a cemented arthroplasty of the hip, either with a metal-on-metal bearing (Metasul ®; 28 patients) or with a metal-on-polyethylene bearing (Protasul ®, 26 patients). Only patients with primary osteoarthritis of the hip and without other metallic implants were included (mean age 65 years, range 45–74). Follow-up was performed after a minimum of two years. Clinical outcome was measured by the Harris hip score and the SF36, and radiographic analysis was undertaken by plain radiography. Metal ion concentrations in patient serum were analysed by high-resolution plasma mass spectrometry.

RESULTS: It was found that the clinical outcome was almost identical in both groups with respect to Harris hip score and SF36, and radiographic signs of osteolyses or loosening did not occur in any group. In the metal-on-metal group, chromium concentrations increased 4.1 fold and cobalt concentrations increased 7.6 fold when compared to preoperative values (p< 0.05; Wilcoxon Mann Whitney Test), whereas nickel and manganese concentrations did not change significantly. In the metal-on-polyethylene group, no significant increase in the concentration of any ion occurred.

DISCUSSION: In conclusion, metal-on-metal and metal-on-polyethylene arthroplasties of the hip provide equal clinical and radiographic outcomes in the medium term, but the concentrations of chromium and cobalt increase considerably after metal-on-metal arthroplasty. Importantly, the allergogenic and previously not assessed ions nickel and manganese show no significant changes in the medium term after any type of hip alloarthroplasty. To our knowledge, this is the first study that addresses manganese and nickel concentrations in a prospective, randomized setting, and our patients will be followed further with respect to possible immunological and genetic changes.