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 Australian and United Kingdom Orthopedic device registries, both of which contain the largest number of patients and the longest length of follow‑up time, indicate that approximately 95% 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% of patients with MoM total hip replacements from the U.K registry and more than 92% 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.
Source: FDA Website http://www.fda.gov/MedicalDevices/ProductsandMedicalProcedures/ImplantsandProsthetics/MetalonMetalHipImplants/ucm331960.htm
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