MRI findings, metal ion levels and clinical outcome of a complete series of large metal on metal THA: what's really going on?

INTRODUCTION:: Metal-on-metal (MoM) large head total hip arthroplasties (THAs) were discontinued early after their introduction because of the high number of failures due to adverse reaction to metal debris (ARMD). Aim of this study is to report the clinical outcome at a mid-term follow-up (FU) of a series of large-head MoM THA.

METHODS:: In this prospective study, 25 hips (24 patients, 3 males, 21 females, mean age 62.44 years) who have undergone primary THA with large head (diameter ⩾36 mm) MoM prosthesis were evaluated. Each patient underwent a standard follow-up after surgery, that included blood tests with metal ion levels (Co and Cr), x-ray of the pelvis, metal artifact reduction sequence magnetic resonance imaging (MARS-MRI) and clinical evaluation.

RESULTS:: At an average follow-up of 7.3 years, 4 hips have been surgically reviewed: 2 for causes not related to ARMD (1 heterotopic ossification and 1 periprosthetic fracture); the other 2 on the same patient (bilateral) with ARMD, who was eventually found to be allergic to nickel. Increased metal ions, osteolysis and severe MRI alterations were found in patients with ARMD. Asymptomatic alterations at MRI were found in 8 patients. Harris Hip Score improved after surgery from a mean of 51 points to a mean of 90 points ( p < 0.01).

CONCLUSIONS:: The findings of this study show that not all the patients with MoM THA will develop clear symptoms of ARMD at mid-term follow-up. Patients should be closely monitored following protocols such as that proposed in the European Consensus Statement.