How to Interpret Metal Ions in THA.

Abstract

Modern total hip arthroplasty has seen an unfortunate increase in proportional implant failures secondary to adverse local tissue reactions (ALTRs) secondary to wear of metal-on-metal (MoM) bearings and mechanically assisted crevice corrosion (MACC) related to corrosion at implant junctions and tapers. The purpose of this study is to describe the appropriate choice of metal ion testing and evaluation of those levels to identify failed total hip arthroplasty implants containing cobalt and chromium. When presented with an arthroplasty of concern, the surgeon must determine what metal ion levels to obtain and then incorporate those levels into a treatment algorithm. Patients with painful hip arthroplasties are evaluated for chromium and cobalt by obtaining whole blood and synovial metal levels. Synovial fluid cobalt had the highest correlation with ALTR compared with the other tests, with a threshold of 19.75 ng/ml, with a specificity of 89%, if the cobalt-to-chromium ratio is greater than 1.4 ng/ml in a metal on polyethylene hip, with a sensitivity of 95%. The interpretation of whole blood metal ions is a key component of the algorithm in treating the symptomatic hip arthroplasty but is not to be used in a vacuum.