MOM, Metal Ions And Lymphopenia

Main Category: Blood / Hematology
Also Included In: Arthritis / Rheumatology
Article Date: 05 Jun 2009 - 0:00 PDT

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Metal-on-metal hip replacement and resurfacing have become the most commonly used type of procedure in the United Kingdom for patients who are < 60 years of age with osteoarthritis. Therefore, this research consisted of a cross-sectional study with analysis of demographic, clinical and laboratory characteristics of patients who had undergone metal-on-metal hip resurfacing, ceramic-on-ceramic and metal-on-polyethylene hip replacement to assess whether there was a relationship between MOM replacements and circulating metal ions in the blood, and absolute numbers of circulating lymphocytes.

There were 164 patients in the study, of which 106 had MOM hips, all were aged < 65 years and had pre-operative diagnosis of osteoarthritis and no pre-existing immunological disorders. Patients were excluded if their replacement had taken place less than six months previously, thereby avoiding the high-wearing, bedding-in phase. Blood samples were taken using a plastic needle cannula to avoid metal contamination.

The results showed that 'there were significant differences in the levels of metal ions in the whole blood and in the absolute lymphocyte counts'. A group of 10 patients of the 106 from the MOM group had circulating levels of chromium greater than 5 parts per billion. Therefore, the authors conclude that 'patients with MOM hips had reduced peripheral blood counts of T-lymphocytes in particular and B-lymphocytes when compared with control subjects with hip replacements which did not produce metal wear debris'. Although the effect of reduced lymphocytes is unknown, there has been a link between high levels of cobalt and chromium and DNA damage of lymphocytes and the authors recommend that long-term studies need to be conducted to determine whether the moderate lymphopenia associated with MOM hip replacements is detrimental or even beneficial to longevity of the replacement.

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Source
The Journal of Bone and Joint Surgery

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