Each type of implant has its own benefits and risks. Overall, metal-on-metal (MoM) hip implants have been shown to provide high implant survivorship (no need to remove implant and put another in its place) in certain patient populations. In addition, the larger head size of MoM total hip implants is intended to reduce the risk of dislocation, which is a common adverse event associated with total hip replacements. The MoM hip implants that have been identified as having a particularly high public health concern are no longer marketed in the U.S.
Metal-on-Metal Total Hip Replacement Systems
In June 2012, the FDA’s Orthopedic and Rehabilitation Devices Advisory Panel discussed data from Orthopedic device registries and other sources. Data from the Australian1 and United Kingdom2 Orthopedic device registries, both of which contain the largest number of patients and the longest length of follow-up time, indicate that approximately 95 percent of patients with any kind of total hip replacement have not undergone revision surgery (a surgical procedure where your implant is removed and another is put in its place) for seven years after the initial implant.
These Orthopedic device registries note differences in revision rates by primary diagnosis, sex and age. These registries also noted that the use of cement and the type of bearing surfaces had an impact on revision rates. More than 85 percent of patients with MoM total hip replacements from the U.K registry and more than 92 percent of patients with MoM total hip replacements from the Australian registry did not have a revision for seven years after the initial implant.
Registry data shows that MoM hip patients with larger head sizes (36 mm or larger) had more revisions than those with smaller head sizes.
When comparing outcomes of different bearing surfaces, limitations in any registry data make it difficult to draw definitive conclusions. In order to obtain additional data to address safety concerns related to MoM total hip replacement systems, the FDA is requiring manufacturers of MoM total hip replacement systems marketed in the U.S. to conduct postmarket surveillance studies.
Metal-on-Metal Resurfacing Hip Systems
Hip resurfacing is intended to be a bone preserving procedure on the femoral side, since f ailure of a resurfacing implant on the femoral side typically allows for revision to a conventional primary femoral component. Hip resurfacing implants are only available with metal-on-metal (MoM) bearings in the U.S.
At the June 2012 Orthopedic and Rehabilitation Devices Advisory Panel meeting, two of the three hip resurfacing manufacturers in the U.S. discussed the clinical performance of their systems. Manufacturers Smith & Nephew, Inc. and Corin USA Limited said that their resurfacing implants had at least a 90 percent survivorship rate (no revision surgery) with seven years of follow-up. They also reported on survivorship from their PMA post approval studies when considering various risk factors.3 Survivorship of the Wright Medical Technology CONSERVE Plus Total Resurfacing Hip System is available in their PMA Summary of Safety and Effectiveness Data (SSED).4
The manufacturers of MoM resurfacing hip systems are still conducting long-term post-approval studies assessing device survivorship and metal ion levels; the data will be made available after completion of the studies.
3 Smith & Nephew and Corin USA Limited Industry Presentations. Orthopaedic Surgery and Rehabilitation Devices Advisory Panel. June 27, 2012.