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Risk of Infection Secondary to Immunosuppression From Metal on Metal Wear

There is literature and research suggesting a risk of infection from wear products in metal on metal (MOM) hip implants. According to this article, wear products may hinder the immune system via accelerating bacterial growth, possible antibiotic resistance, and a heavy metal reaction. MOM implants were popularized as a result of their supposed longevity. However, metals employed in MOM hip implants degrade from wear, corrosion, and over time. MOM bearings release small amounts of metal ions or particles, and in relatively high numbers results in corrosion. Metal debris in the body prompts an inflammatory response. An inflammatory response stems from various pathological changes in the body. Metal debris can cause adverse local tissue reactions (ALTR), hypersensitivity, and osteolysis (destruction of bone). Recent studies found metal debris presents an ideal environment for bacterial growth.

A major concern for patients is the release of metal into the tissues secondary to wear and corrosion from MOM hip devices. Specifically, rough particles from MOM implants cause local damage, such as ALTR. This results in an increase of metal particles and ions released into the blood stream and surrounding tissues. The article highlights that the nature, size, and amount of particles can determine the effects it has on the body, and subsequently, the body’s reaction to those effects. Metal ions are generated even in MOM implants with corrosion-resistant alloys. Different types of corrosion cause metal particle release. For instance, fretting corrosion causes damage on the surfaces of articulating structures from movement. Cobalt- chromium alloys release metal ions which can produce toxic effects in the body. The article states that cobalt levels were approximately 6 fold higher in patients post MOM implantation compared to pre-implantation. There is a correlation between wear rates and the amount of metal ion levels; the higher the wear rate, the higher the level of metal ions.

Corrosion from MOM implants can influence the immune system and the immune response via different organs and their immune related mechanisms. Metal ions travel in the body through lymph and blood hindering the immune response. The study reveals that simply having a foreign body is enough to require only a small amount of bacteria to cause an infection. Ion release may damage DNA. Cobalt chromium particles can actually damage DNA via its cellular barrier. Metal particles pose the possibility for carcinogenesis. Patients with MOM implants also have a decrease in the immune cells responsible for destroying tumor cells.

The spleen and liver are vital organs regarding immunological mechanisms.  The spleen is vulnerable to corrosion byproducts which alter the number of immunocompetent cells. This illustrates how metal ions reduce the defense against immunocompromising organisms like bacteria. A recent study indicates that chromium ions can collect in the liver. Elevated metal ions in the liver may stimulate hepatocellular necrosis (death of liver cells). Corrosion products from cobalt chromium implants inhibit the release of cells necessary to kill bacteria. The cobalt chromium particles produce toxicity because they create a low pH concentration in the cells that try to destroy bacteria. In addition, bacteria have developed mechanisms to resist metal toxicity, and as a result, are also becoming resistant to antibiotics. This has significant consequences since patients with MOM prostheses are more susceptible to infection at the implant site.

Source: Effects of metal-on-metal wear on the host immune system and infection in hip arthroplasty

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DISCLAIMER:

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