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U.S. Department of Health and Human Services

Medical Devices

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Metal-on-Metal Hip Implant Systems

Metal-on-Metal (MoM) hip implants consist of a ball, stem and shell, all made of metal materials. MoM hip implants were designed to offer the following benefits:

  • Less device material wear is generated when the ball and socket rub against each other in comparison to other hip implants
  • Decreased chance of dislocation when the ball of the thighbone (femur) slips out of its socket in the hip bone (pelvis)
  • Decreased chance of device fracture  

There are two types of MoM hip implants:

  • Traditional total hip replacement systems
  • Resurfacing hip systems

Traditional Metal-on-Metal Total Hip Replacement Systems

Metal-on-metal total hip replacement systems consist of a metal ball (femoral head), a metal femoral stem in the thighbone, and a metal cup in the hip bone (acetabular component). The ball attaches to the taper of the stem.

Drawing of a metal-on-metal total hip replacement system. The diseased parts of the hip are removed and replaced with a system comprised of a metal ball, metal stem and a metal

The FDA evaluates total metal-on-metal hip systems through its 510(k) program. Each system has multiple compatible components that must be identified. As of Nov. 30, 2012, the FDA had cleared 190 submissions for metal-on-metal total hip replacement systems, the majority of which were for modifications to previously cleared components. At this time there are five manufacturers of metal-on-metal total hip replacement systems in the U.S.

Metal-on-Metal Resurfacing Hip Systems

Metal-on-metal resurfacing hip systems consist of a trimmed femoral head capped with a metal covering. Any damaged bone and cartilage within the socket are removed and replaced with a metal acetabular component.

Drawing of a metal-on-metal total resurfacing system. A metal cap is placed over the ball portion of the femoral head.

The FDA has approved three metal-on-metal hip resurfacing systems through the pre-market approval (PMA) program. In each approved PMA application, the manufacturer demonstrated the safety and effectiveness of their metal-on-metal hip resurfacing system through non-clinical and clinical performance data. Links to the Summary of Safety and Effectiveness Data (SSEDs) for each of the three approved PMAs are available below: