We often encounter consumers of metal on metal ( MoM ) implants such as the Depuy ASR total hip replacement, that complain of pain and swelling long beyond the normal healing time of implant surgery. Some often experience a time of normalcy after the surgery impact has healed only to experience flares of inflammation later. Both partial hip replacement ( resurfacing ) and total hip replacement ( THR ) patients are at risk for complications due to erosion of the surfaces of the implants.

One cause of this can be a phenomenon known as metallosis.  Metallosis is the generally thought of medical condition involving deposition and build-up of metallic debris in the soft tissues of the body. Metallosis has been hypothesized to occur when metallic components in medical implants, specifically joint replacements, abrade against one another. Although this is seen in wrist implants, knee implants and elbow implants, it is most commonly seen in total hip replacement implants and hip resurfacing.
Definition Of Metallosis
Metallosis has also been observed in some patients either sensitive to the implant or for unknown reasons even in the absence of malpositioned prosthesis. Though rare, metallosis has been observed at an estimated incidence of 5% of metal joint implant patients over the last 40 years.  Women may be at slightly higher risk than men. If metallosis occurs, it may involve the hip and knee joints, the shoulder, wrist, or elbow joints.

The abrasion of metal components may cause metal ions to be solubilized. The hypothesis that the immune system identifies the metal ions as foreign bodies and inflames the area around the debris may be because the metal ions may become haptens. (A hapten is a small molecule that can elicit an immune response only when attached to a large carrier such as a protein).
Cobaltism is an established health concern. The involvement of the immune system in this putative condition has also been theorized.  Purported symptoms of metallosis generally include pain around the site of the implant, pseudo-tumors (a mass of inflamed cells that resembles a tumor but is actually collected fluids), and a noticeable rash that indicates necrosis. The damaged and inflamed tissue can also contribute to loosening the implant or medical device. Metallosis can cause dislocation of non-cemented implants as the healthy tissue that would normally hold the implant in place is weakened or destroyed. Metallosis has been demonstrated to cause osteolysis. Osteolysis is the Dissolution or degeneration of bone tissue resulting from disease.

Women who are small in stature and the obese are at greater risk for metallosis because their body structure causes more tension on the implant, quickening the abrasion of the metal components and the subsequent build-up of metallic debris.
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