No association between blood count levels and whole-blood cobalt and chromium levels in 1,900 patients with metal-on-metal hip arthroplasty

Background and purpose — The accelerated wear of poorly functioning metal-on-metal (MoM) hip implants may cause elevated whole-blood cobalt (Co) and chromium (Cr) levels. Hematological and endocrinological changes have been described as the most sensitive adverse effects due to Co exposure. We studied whether there is an association between whole-blood Co/Cr levels and leukocyte, hemoglobin, or platelet levels.Patients and methods — We analyzed whole-blood Co and Cr values and complete blood counts (including leukocytes, hemoglobin, platelets) from 1,900 patients with MoM hips. The mean age at the time of whole-blood metal ion measurements was 67 years (SD 10). The mean time from primary surgery to whole-blood metal ion measurement was 8.2 years (SD 3.0). The mean interval between postoperative blood counts and metal ion measurements was 0.2 months (SD 2.7).Results — The median Co value was 1.9 µg/L (0.2–225), Cr 1.6 µg/L (0.2–125), mean leukocyte count 6.7 × 10⁹/L (SD 1.9), hemoglobin value 143 g/L (SD 13), and platelet count 277 × 10⁹/L (SD 70). We did not observe clinically significant correlations between whole-blood Co/Cr and leukocyte, hemoglobin, or platelet counts.Interpretation — Elevated whole-blood Co and Cr values are unlikely to explain abnormal blood counts in patients with MoM hips and the reason for possible abnormal blood counts should be sought elsewhere.

The abnormal wear of poorly functioning MoM implants may cause elevated whole-blood cobalt (Co) and chromium (Cr) levels (Brodner et al. 2003, Cheung et al. 2016). Soft-tissue reactions termed “pseudotumors” related to poorly functioning MoM hip replacements have been widely described (Boardman et al. 2006, Gruber et al. 2007, Pandit et al. 2008). The use of MoM implants has dramatically decreased but due to their previous popularity there are still a large number of patients with MoM hip replacements under follow-up (Silverman et al. 2016).Even though local reactions have been the most discussed, systemic reactions in patients with high-wearing hip implants have been described. Cardiomyopathy, polyneuropathy, hypothyreosis, and polycythemia have been described in some patients with MoM hip implants and in patients with fractured ceramic-on-ceramic implant revised to metal-on-polyethylene, resulting in abrasive wear of the CoCr head by ceramic fragments (Cheung et al. 2016). Systemic adverse events have been linked mostly to Co, and hematological and thyroid effects have been described as the most sensitive responses to Co in humans (Tvermoes et al. 2014). A case report described polycythemia with hemoglobin 190 g/L due to massive abrasive CoCr head wear when a ceramic-on-ceramic implant had been revised to metal-on-polyethylene after fracture of the ceramic liner (Gilbert et al. 2013). Several studies have suggested that blood lymphocyte counts may be affected by implant metals from MoM hip replacements (Hart et al. 2009, Hailer et al. 2011, Penny et al. 2013, Chen et al. 2014, Briggs et al. 2015, Markel et al. 2018). Although thrombocytopenia has not been linked to implant metals, it has been reported that platelets adhere to and are activated by CoCr (Ollivier et al. 2017).Complete blood count including leukocyte count, hemoglobin, and platelets is among the most used blood tests in the world (Horton et al. 2019) and 10–20% of the measurements include abnormal values (Tefferi et al. 2005). Due to wide media attention to MoM hip replacements, patients with MoM hips are sometimes worried whether their abnormal laboratory findings are related to their hip replacement. We sought to find out whether whole-blood metal ion levels are associated with blood count. Our hypothesis was that if Co or Cr affected leukocytes, hemoglobin, or platelets at concentrations noted in our study group, we would observe an upward or downward trend (depending on variable) when blood Co or Cr concentrations are approaching the highest values.