Modern metal-on-metal hip implants.

Area of Science:

• Orthopedic Surgery
• Biomaterials Science
• Clinical Epidemiology

Background:

• Metal-on-metal hip implants have been used as an alternative bearing surface in total hip arthroplasty (THA) and hip resurfacing.
• Concerns exist regarding the long-term outcomes and potential adverse effects associated with these devices.

Purpose of the Study:

• To systematically review and summarize the findings on modern metal-on-metal hip implants.
• To identify risk factors associated with revision surgery and adverse tissue reactions.

Main Methods:

• Systematic review of studies published up to July 15, 2011.
• Analysis of data from two joint registries focusing on THA and hip resurfacing outcomes.

Main Results:

• Metal-on-metal THA and hip resurfacing have higher revision rates than other bearing surfaces.
• Larger femoral head components are associated with increased revision risks.
• Older age and suboptimal implant positioning correlate with higher wear, metal debris, and tissue reactions.
• Elevated serum metal ion concentrations were observed, but their clinical significance is undetermined.

Conclusions:

• Metal-on-metal hip implants present a greater risk for revision surgery compared to alternative bearing surfaces.
• Factors such as component size, patient age, and implant positioning influence revision rates and local tissue responses.
• Further research is needed to clarify the clinical implications of elevated metal ion levels.