Mild or moderate renal insufficiency does not increase circulating levels of cobalt and chromium in patients with metal-on-metal hip arthroplasty.

AIMS: To determine whether there is any association between glomerular filtration rate (GFR) and blood cobalt (Co) and chromium (Cr) levels in patients with metal-on-metal (MoM) hip arthroplasty. PATIENTS AND METHODS: We identified 179 patients with a unilateral 36 mm diameter head as part of a stemmed Summit-Pinnacle MoM hip arthroplasty. GFR was calculated using the Modification of Diet in Renal Disease formula. RESULTS: Normal renal function (GFR ≥ 90 ml/min/1.73 m2) was seen in 74 patients. Mild renal insufficiency (GFR 60 to 89 ml/min/1.73 m2) was seen in 90 patients and moderate renal insufficiency (GFR 30 to 59 ml/min/1.73 m2) in 15. There was no statistical difference in Co and Cr levels between patients with normal renal function and those with mild or moderate renal insufficiency. No correlation was seen between creatinine and blood metal ion levels or between GFR and blood metal ion levels. Linear regression analysis did not show any association between Co and Cr levels and GFR. CONCLUSION: We did not find any association between GFR and blood metal ion levels. Consequently, the accumulation of Co and Cr in blood due to renal insufficiency does not seem to be a major risk in patients with mild or moderate renal insufficiency. Cite this article Bone Joint J 2017;99-B:1147-52.

Repeated metal ion measurement in patients with bilateral metal on metal (ASR™) hip replacements.

BACKGROUND: Blood metal ion measurements have become a cornerstone in the surveillance of metal-on-metal (MoM) hip replacements. Interpretation of these levels in patients with bilateral MoM hip replacements, however, is challenging. We therefore asked (1) if there is a clinically significant change in whole blood (WB) Co or Cr levels in repeated WB assessment in patients operated on with bilateral ASR hip replacements, and (2) what proportion of patients has WB Co or Cr level below the previously established safe upper limits (SUL) (Co<5.0µg/L, Cr<7.4µg/L) in the repeated WB metal ion assessment. HYPOTHESIS: We hypothesized that there is a significant difference between repeated Co and Cr level measurement performed within one year±4 months interval in patients with bilateral ASR hip replacements. MATERIALS AND METHODS: We identified all patients (n=139) who had received bilateral ASR hip replacements (278 hips). Patients (n=76, 152 hips) who had undergone two blood metal ion measurements within eight to sixteen months' time interval were included in the study analysis. Study cohort included 38 patients with bilateral ASR hip resurfacings (mean age 53 years, median follow-up 4.6 years, median femoral diameter 51mm) and 38 patients with bilateral ASR XL total hip replacements (mean age 60 years, median follow-up 3.6 years, median femoral diameter 49mm). RESULTS: There was no significant change in Co and Cr levels between the repeated measurements in the HR cohort. Both Co and Cr were significantly higher in the THR cohort in the repeated measurement (Co: 8.3µg/L vs. 12.6µg/L, Cr: 3.15µg/L vs. 3.4µg/L, both P<0.001). WB Co and Cr levels remained below SUL and within their initial values during a mean one-year measurement interval in the majority of patients with bilateral high risk HR device. In contrast to this, 21.1% of patients with THRs had WB Co ion levels exceeding the SUL in the first measurement. WB Co values significantly increased over the measurement interval in the THR group. DISCUSSION: Annual blood metal ion measurement is not useful in patients with bilateral hip resurfacings who have undergone at least one preliminary screening including both metal ion measurement and cross-sectional imaging. It seems, however, to be beneficial in patients with bilateral high risk MoM THR. LEVEL OF EVIDENCE: Level III (retrospective comparative study).

Adverse reaction to metal debris is more common in patients following MoM total hip replacement with a 36 mm femoral head than previously thought: results from a modern MoM follow-up programme.

We conducted a retrospective study to assess the prevalence of adverse reactions to metal debris (ARMD) in patients operated on at our institution with metal-on-metal (MoM) total hip replacements with 36 mm heads using a Pinnacle acetabular shell. A total of 326 patients (150 males, 175 hips; 176 females, 203 hips) with a mean age of 62.7 years (28 to 85) and mean follow-up of 7.5 years (0.1 to 10.8) participating in our in-depth modern MoM follow-up programme were included in the study, which involved recording whole blood cobalt and chromium ion measurements, Oxford hip scores (OHS) and plain radiographs of the hip and targeted cross-sectional imaging. Elevated blood metal ion levels (> 5 parts per billion) were seen in 32 (16.1%) of the 199 patients who underwent unilateral replacement. At 23 months after the start of our modern MoM follow-up programme, 29 new cases of ARMD had been revealed. Hence, the nine-year survival of this cohort declined from 96% (95% CI 95 to 98) with the old surveillance routine to 86% (95% CI 82 to 90) following the new protocol. Although ARMD may not be as common in 36 mm MoM THRs as in those with larger heads, these results support the Medicines and Healthcare Products Regulatory Agency guidelines on regular reviews and further investigations, and emphasise the need for specific a follow-up programme for patients with MoM THRs.