Cobalt Chromium Toxicity

Correlation between Smoking and Risk of Revision Among Patients with Hip Replacements


Significant Correlation between Smoking and Risk of Revision Among Patients with Metal on metal (MOM) hip replacements

World wide, an estimated one million people are implanted with metal on metal (MOM) hip prostheses. It was originally believed that the MOM prosthesis would have a decrease in implant wear over time. However, recent studies and case reports demonstrate the contrary. MOM total hip arthroplasties indicate a higher failure rate in comparison to other types of hip prostheses. Some prominent effects that result in an elevated failure of the MOM bearings include aseptic loosening (loosening of the total joint replacement) and a hypersensitivity to the metals.

Metal hypersensitivity can cause a myriad of health issues such as osteolysis, severe and chronic pain, infection, and periarticular tissue reactions, which is aptly named an adverse local tissue reaction (ALTR). These all subsequently contribute to the high rate of failure of the MOM prostheses. In addition to the ALTR, there are reported cases of massive bone and tissue necrosis (death) along with the formation of periprosthetic pseudo-tumors. In terms of hip implant revisions, those patients suffering from pseudo-tumors had worse revision rates than those that did not.

Metal hypersensitivity, or metal sensitization and allergy, stems from the release of cobalt and chromium found within the metal bearings. In this study, it is also found that smoking patients with MOM hip prostheses led to poorer results of the hip prostheses than non-smokers. This is due to the association between the traces of cobalt and other metal elements found in cigarette smoke, and the elevated metal ions from the prosthesis. These two sources of metal are potential triggers for an increase in metal hypersensitivity and contribution to a higher risk for revision.

In this study, patients were separated into two groups: never-smokers and ever-smokers. The ever-smokers were further subdivided into current smokers and former smokers. The main concern with the study focused on an all-cause revision, known as any change or removal of a single or multiple prosthetic components. The causes of revision were divided into the following categories: aseptic loosening, infection, dislocation, periprosthetic fracture, impingement, or implant migration. During the revision, findings for ALTR were also recorded. These findings included metallosis, presence of pseudo-tumors, and tissue necrosis (death). In addition to the aforementioned subdivisions, the study was further divided into two sub-cohorts among patients with MOM, cobalt-chromium alloy hip prostheses versus patients with non-metal, ceramic-on-polyethylene (COP) hip prostheses.

The results of the study indicated that ever-smokers in both the MOM and COP cohorts suffered from secondary arthritis as a result of surgery. Among ever-smokers and never-smokers with MOM prostheses, the revision rate was more than tripled for the ever-smokers (8.7 revisions per 1,000 persons) compared to the never-smokers (1.5 revisions per 1,000 persons). The reason for such a discernible difference between never-smokers and ever-smokers with MOM prostheses was an increase in an adverse local tissue reaction (ALTR) among the ever-smokers. In conclusion, there is a strong correlation between smoking and an increase failure rate of MOM hip replacements. This association was not definitively evident among never-smokers and ever-smokers with COP hip arthroplasties.

Source: Strong Association between Smoking and the Risk of Revision in a Cohort Study of Patients with Metal-on-Metal Total Hip Arthroplasty http://onlinelibrary.wiley.com/doi/10.1002/jor.22603/pdf

 

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