MoM hips are hips in which the ball and socket are both made from metal. The metal ball and metal cup slide against each other. Metal wear will cause some tiny metal particles to wear off. MoM implants are more prone to failure, more susceptible to errors in surgical placement and carry additional risk of release of metal particles. These implants were heavily marketed by several manufacturers beginning in the mid-2000s.
Patients were subjected to high failure rates, and exposed to metal particles. These particles have caused implant failure, tissue necrosis, and sometimes bone loss. The effects of metal particles on the long term health of patients is a subject of concern and still largely unknown.
Andrews & Thornton partner John Thornton had personal experience with a defective metal on metal implant which required a surgical replacement and second rehabilitation.
At the request of the FDA the Orthopaedic and Rehabilitation Devices Panel conducted a hearing in June of 2012 about the safety and effectiveness of metal on metal hips. After the hearings the FDA issued a series of cautionary guidelines for doctors and information for patients. The following are excerpts from the FDA patient information:
What symptoms might a metal-on-metal hip implant cause?
Symptoms may include hip/groin pain, local swelling, numbness, or changes in your ability to walk. There are many reasons a patient with a metal-on-metal hip implant may experience such symptoms and it is important that you contact your surgeon to help determine why you are having them.
Are there other medical effects that can occur with my metal-on-metal hip implant?
Metal-on-metal hip implants have the same adverse effects as other types of hip implants, including infection, loosening, bone loss, device or bone fracture, and joint dislocation.
In addition, metal particles from a metal-on-metal implant may cause a reaction around the joint, leading to deterioration of the tissue around the joint, loosening of the implant and failure of the device. Metal ions from a metal-on-metal implant will enter the bloodstream. There are case reports in which patients with metal-on-metal hip implants may have developed an adverse reaction to these metal ions and experienced medical problems that could have been related to their implants. These problems included:
- 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)
Some of the implants such as the DePuy ASR, the Zimmer Durom, and Smith & nephew R3 have been recalled by their manufacturer. Others such as the DePuy Pinnacle Metal on Metal and the Biomet Magnum are still on the market.