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Metal-on-metal total hip replacement.
Mauricio Silva1, Christian Heisel, Thomas P Schmalzried
1Joint Replacement Institute at Orthopaedic Hospital, Los Angeles, CA 90007, USA.
Clinical Orthopaedics and Related Research
|January 22, 2005
Summary
Metal-on-metal bearings show significantly lower wear rates than traditional polyethylene, but raise concerns about metal ion release and potential hypersensitivity. Long-term studies are crucial to assess the overall risks versus benefits.
Area of Science:
- Biomaterials Science
- Orthopedic Surgery
- Wear Particle Analysis
Background:
- Metal-on-metal (MoM) bearings offer substantially lower wear rates compared to metal-on-polyethylene (MoP) designs.
- MoM wear is influenced by material, geometry, and lubrication, with an initial high-wear run-in period.
Purpose of the Study:
- To review the wear characteristics of MoM bearings.
- To discuss the nature and potential systemic effects of metal wear particles and ions.
- To evaluate the clinical implications and long-term safety concerns associated with MoM bearings.
Main Methods:
- Literature review of wear rates, particle characteristics, and ion levels in MoM bearings.
- Comparison of MoM wear to MoP bearings.
- Analysis of potential risks including hypersensitivity and malignancy.
Main Results:
- MoM bearings exhibit 20-100x lower wear rates than MoP, with nanometer-sized metal particles.
- Elevated serum and urine cobalt (Co) and chromium (Cr) ions are observed, increasing hypersensitivity risk.
- Osteolysis appears rare, but systemic distribution and long-term effects remain largely unknown.
Conclusions:
- While MoM bearings demonstrate favorable wear properties, concerns regarding metal ion release, hypersensitivity, and potential long-term risks necessitate further rigorous investigation.
- Decades of clinical observation are required to definitively ascertain if the benefits of MoM bearings outweigh their associated risks.