Blood metal ions after hybrid metal-on-polyethylene Exeter-Trident total hip replacement

Metal-on-metal total hip replacements (THRs) with large femoral heads have been associated with elevated levels of cobalt (Co) and chromium (Cr), which have been attributed to high levels of wear at the articular surface. Our unit recently published data showing a significant increase in the mean levels of Co ions in patients with a 36-mm diameter femoral head with the metal-on-polyethylene Trident-Accolade system. The aim of this study is to assess the levels of Co and Cr in the Exeter-Trident hybrid system, as similar findings would raise concern over the V40 taper trunnion.

The study included 83 patients (45 male and 38 female with a mean age of 75.6 years) who received Exeter-Trident hybrid metal-on-polyethylene THRs. The patients were then divided into two groups according to the diameter of the femoral head used-38 patients in the 28-mm group (control), and 45 in the 36-mm (experimental) group. Serum levels of blood Co and Cr were analysed for all recruited patients.

In the control group (28-mm femoral head) all Co and Cr values were normal (under the abnormal threshold), as were the experimental group (36-mm femoral head). The data values were below <10 nmol and <40 nmol for Co and Cr, respectively.

Since the National Joint Registry (NJR) states that the Exeter femoral stem is the commonest cemented femoral stem prosthesis used in the UK, we found it imperative that these results are documented given the corresponding findings in the Trident-Accolade system in our previous study. This study provides relative reassurance that the issue does not lie with the V40 taper trunnion, but raises suspicion that the issue may be with the titanium Accolade stem with large diameter femoral heads.