Vincent P. Galea

Mid-term changes in blood metal ion levels after Articular Surface Replacement arthroplasty of the hip

Aims Our first aim was to determine whether there are significant changes in the level of metal ions in the blood at mid‐term follow‐up, in patients with an Articular Surface Replacement (ASR) arthroplasty. Secondly, we sought to identify risk factors for any increases. Patients and Methods The study involved 435 patients who underwent unilateral, metal‐on‐metal (MoM) hip resurfacing (HRA) or total hip arthroplasty (THA). These patients all had one measurement of the level of metal ions in the blood before seven years had passed post‐operatively (early evaluation) and one after seven years had passed post‐operatively (mid‐term evaluation). Changes in ion levels were tested using a Wilcoxon signed‐rank test. We identified subgroups at the highest risk of increase using a multivariable linear logistic regression model. Results There were significant increases in the levels of metal ions for patients who underwent both MoM HRA (Chromium (Cr): 0.5 parts per billion (ppb); Cobalt (Co): 1.1 ppb) and MoM THA (Cr: 0.5 ppb; Co: 0.7 ppb). In a multivariable model considering MoM HRAs, the change in the levels of metal ions was influenced by female gender (Co: Odds Ratio (OR) 1.42; p = 0.002 and Cr: OR 1.08; p = 0.006). The change was found to be irrespective of the initial level for the MoM HRAs, whereas there was a negative relationship between the initial level and the change in the level for those with a MoM THA (Co: OR ‐0.43; p < 0.001 and Cr: OR ‐0.14; p = 0.033). Conclusion The levels of metal ions in the blood increase significantly over the period until mid‐term follow‐up in patients with both a MoM HRA and those with a MoM THA. We recommend that the levels of metal ions be measured most frequently for women with a MoM HRA. While those with a MoM THA appear to stabilise at a certain level, the accuracy of this trend is not yet clear. Vigilant follow‐up is still recommended.

Risk factors for mid-term revision surgery in patients with articular surface replacement total hip arthroplasty

Introduction: This study assessed the associations between gender and implant survival, as well as adverse local tissue reaction (ALTR), in patients with articular surface replacement (ASR) XL total hip arthroplasty (THA). Secondly, we sought to report the differences between genders in metal ion levels and patient reported outcome measures (PROMs) in these patients. Methods: 563 unilateral ASR XL THA patients were enrolled in a multicentre follow-up study at a mean of 6.4 years after index surgery. All patients had blood metal ion levels and PROMs obtained annually, and a valid anteroposterior pelvis radiograph. A sub-set of patients from a single centre had annual MRI performed and were analysed for the presence of moderate-to-severe ALTR. Results: 60 hips (11%) were revised during the study period. The only variables found to be associated with revision surgery in patients with unilateral THA were VAS pain (hazard ratio [HR], 1.35; p<0.001) and elevated cobalt metal ion levels (HR, 1.05; p<0.001). No variables assessed were found to be associated with prevalence of ALTR. Chromium concentrations were greater in female patients than males, while cobalt levels were similar between genders. Males reported higher HHS, EQ-5D and UCLA scores than females. Conclusions: Both males and females with metal-on-metal THA implants should be followed with equal vigilance as gender does not appear to be associated with poor outcomes, such as revision surgery and presence of ALTR.