The seven points to remember about metal-on-metal implants:
1. There are now FDA guidelines regarding these implants.
2. MoM hip systems should not be implanted in those with kidney failure, metal sensitivity to cobalt, chromium, nickel, immune suppressed patients, those on high dose steroids, and women of childbearing age.
3. Potential risks with with metal-on-metal hip implants according to FDA include:
Bone or device fracture
Elevated metal ion levels in the joint and blood
Transplacental transport of metal ions
Development of local inflammatory reactions and lesions including soft tissue masses and tissue necrosis
Development of potential systemic events related to elevated metal ion levels
Femoral neck fracture (for hip resurfacing)
4. Those patients at risk for problems with metal-on-metal hip implants according to FDA
Patients with bilateral implants
Patients with resurfacing systems with small femoral heads (44mm or smaller)
Patients receiving high doses of corticosteroids
Patients with evidence of renal insufficiency
Patients with suppressed immune systems
Patients with suboptimal alignment of device components
Patients with suspected metal sensitivity (e.g. cobalt, chromium, nickel)
Patients who are severely overweight
Patients with high levels of physical activity.
5. Local symptoms related to MoM implants is as a result of metal particles being released to tissue surrounding the hip implant causing pain, bone and soft tissue damage. As a result patients may develop pain or swelling at or near the hip, a change in walking ability, or a noise from the hip. Other local reaction include:
Hypersensitivity (allergic type reaction)
Osteolysis (bone loss)
Aseptic lymphocytic vasculitis-associated lesions (ALVAL) (histologic reaction in surrounding tissue)
Soft tissue mass (fluid-filled or solid soft tissue mass around the replaced joint that is diagnosed radiologically)
Femoral neck fracture (for resurfacing systems)
6. Systemic reactions to MoM implants has to do with metal ions that were release are moving via blood stream to other organs causing systemic symptoms. These systemic symptoms include:
General hypersensitivity reaction (skin rash)
Neurological changes including sensory changes (auditory, or visual impairments)
Psychological status change (including depression or cognitive impairment)
Renal function impairment
Thyroid dysfunction (including neck discomfort, fatigue, weight gain or feeling cold).
7. Proper patient selection, correct placement, and implantation are most important in order to avoid problems with metal-on-metal implants.
M. Rezaian, MD