Metallosis is defined as the body’s reaction to the presence of wear debris in the joint from metallic corrosion. This metallic corrosion occurs as a result of two metal surfaces rubbing against each other. In the case of hip resurfacing, there is a metal implant covering the head of the round femur (thigh bone) that sits inside the hip socket. The material is usually cobalt chromium as titanium and stainless steel are no longer used.
Symptoms of metallosis include hip pain, noises coming from the hip, joint swelling, and elevated metal levels in blood. Noise by itself is not very diagnostic. All joint implants make some noise — most of the noise is vibrational and at a frequency the human ear cannot detect. But with enough friction, the noise may become louder. Squeaking sounds are not as diagnostic of metallosis as clunking sounds that can also be felt as a clunking sensation.
Implant loosening is often a natural consequence of metallosis. When examined, the joint tissues are thickened (fibrotic) and have a grey discoloration. Soft tissue masses called pseudotumors (meaning they are like tumors but aren’t malignant or infected) often develop.
Anyone with metal-on-metal (cobalt) implants will have some increase in cobalt in their hair, blood, urine, and organs. It has even been detected in the placenta of pregnant women with this type of hip implant. The placenta is the organ that connects the developing fetus to the uterine wall. It allows nutrients in and other substances (such as metal debris) in and waste out.
To monitor for metallosis, anyone with metal-on-metal hip resurfacing implants is tested periodically to look for rising levels of cobalt in the blood. The diagnosis of metallosis is made based on patient symptoms, blood testing, and fluid taken from the joint. Early diagnosis is important in effective treatment.
Treatment is usually by surgical means. Sometimes it’s just a matter or repositioning the implant to reduce an uneven wear pattern. In other cases, it becomes necessary to replace the metal-on-metal implant to one that is metal-on-polyethylene (plastic). Advanced or progressive metallosis may only respond by replacing the entire hip joint with an entirely new joint.
Of course, your surgeon will advise you on what to do. The best course of action will be determined based on diagnostic tests including X-rays, blood work, removal and examination of fluid from the joint, and your symptoms. Hopefully this information today will give you a better idea of what to ask your surgeon in making the follow-up decisions about treatment.