Metal in Total Hip Arthroplasty: Wear Particles, Biology, and Diagnosis

Area of Science:

• Orthopedics
• Biomaterials Science
• Toxicology

Background:

• Metal-on-metal total hip arthroplasty (THA) was widely used, with over 600,000 procedures between 2006-2012 in the US.
• This bearing type involves articulating metal surfaces, raising concerns about wear debris and ion release.

Purpose of the Study:

• To review the mechanisms of metal wear in metal-on-metal THA.
• To examine the biologic reactions to cobalt and chromium ions released from these implants.
• To discuss the clinical presentation, diagnosis, and management of failing metal-on-metal THA.

Main Methods:

• Literature review focusing on metal wear, ion toxicology, and clinical outcomes of metal-on-metal THA.
• Discussion of diagnostic modalities including inflammatory markers, metal ion levels, imaging (radiographs, MRI with MARS), and ultrasound.

Main Results:

• Metal-on-metal articulations generate wear debris and release cobalt and chromium ions.
• These ions can elicit adverse biologic reactions, leading to implant failure.
• Clinical presentation includes pain, effusion, and pseudotumor formation.

Conclusions:

• The potential benefits of new orthopedic technologies must be weighed against novel failure modes.
• Metal-on-metal bearings exemplify the balance between innovation and clinical outcomes in THA.
• Understanding these failure mechanisms is crucial for orthopedic surgeons.