Introduction

Comparative studies examining Fixed-Bearing (FB) and Mobile-Bearing (MB) Total Ankle Replacement (TAR) designs have demonstrated similar results and successful long-term outcomes for both. To date there has been no study directly comparing FB and MB designs of the same prosthesis. We present the first prospective randomised trial comparing patient satisfaction, functional outcomes and radiographic results of the Salto Talaris Fixed-Bearing and the Salto Mobile-Bearing Total Ankle Replacement in the treatment of end-stage ankle arthritis.

Introduction and aim: We have previously shown an association between whole blood metal ions and reduced CD8+ T cells in patients with unilateral metal on metal (MOM) hip resurfacings. Our aim was to substantiate this controversial finding with a follow up cohort of larger numbers of patients before further immunological investigation.

Method: We measured lymphocyte subset counts and whole blood Cobalt and Chromium in 2 groups of patients: a Birmingham hip resurfacing group (n=100); and a metal on polyethylene MOP hip arthroplasty group (n=34). Metal ions were measured using inductively-coupled mass spectrometry (ICP-MS) with a Dynamic Reaction Cell (DRC). The detection limit was 10 parts per trillion. All hip components were well fixed, clinically and radiologically.

Results: Cobalt and chromium levels were significantly elevated in the MOM resurfacing group compared to the MOP group (p< 0.0001). There was a statistically significant decrease in the MOM resurfacing groups’ level of CD8+cells (T cytotoxic) (p=0.005) when analysed by a Mann-Whitney U test. There was no significant difference between levels of CD4+ (T helper cells), CD19+ (B cells) and CD16/56+ (Natural Killer cells). A threshold level of blood cobalt and chromium ions for depression of total numbers CD8+ T cells was observed.

Conclusions: This follow up cohort of 100 MOM hip resurfacing patients has replicated the association of reduced CD8+ T cells and raised metal ion levels observed in our founder cohort. This was specific to CD8+ T cells. We are now more certain that this association needs further detailed immunological investigation.

Introduction: We have previously shown an association between whole blood metal particles from unilateral metal on metal (MOM) hip resurfacing and reduced CD8+ T cells (JBJS Br April 2006). There are no reported clinical effects of these findings. Certain patients maybe at high risk of developing clinical effects; one such group is patients with bilateral hip resurfacings. There are no published studies of bilateral hip resurfacings. Our aim was to investigate the association between whole blood metal ions and reduced CD8+ T cells in a follow up cohort of bilateral MOM hip resurfacings.

Method : Peripheral blood samples were analysed from patients with bilateral MOM hip resurfacings (n=25), unilateral hip resurfacings (n=34) and metal on polyethylene (MOP) hip arthroplasty (n=34). Samples were analysed for: lymphocyte subsets (FACS analysis); whole blood cobalt and chromium ion levels (using inductively-coupled mass spectrometry). Xrays revealed all hip components were well fixed.

Results : When compared to patients with standard MOP hip replacements there was a 30% reduction in both the bilateral and unilateral resurfacing groups’ level of CD8+ cells (T cytotoxic) (p=0.010). All other lymphocyte subgroups were not significantly different. There was evidence of a threshold effect of raised metal ions and reduced CD8+ T cells but no evidence of a dose-response relationship.

Conclusions : Bilateral MOM hip resurfacing is associated with a reduced CD8+ T cell count when compared to MOP hip arthroplasty. This association is not significantly different from the levels seen after unilateral MOM hip resurfacing.