Cobalt serum levels differ in well functioning Birmingham resurfacing and Birmingham modular THA

Area of Science:

• Orthopedic surgery
• Biomaterials science
• Wear toxicology

Background:

• Metal-on-metal (MoM) bearings in total hip replacements (THP) and hip resurfacings (HR) can release metal ions due to wear and corrosion.
• These ions may lead to local adverse tissue reactions and systemic effects, but patterns differ between MoM THA and HR.

Purpose of the Study:

• To compare metal ion concentrations between MoM THA and HR with identical bearing designs.
• To investigate the longitudinal changes in metal ion levels for both MoM THA and HR.
• To determine the influence of surgical factors (inclination angle, component size) and clinical outcomes on ion levels.

Main Methods:

• A retrospective analysis of 77 Birmingham Hip Resurfacing (HR) and 42 Birmingham MoM Total Hip Replacement (MoM THA) patients.
• Blood samples were collected at a minimum of 13 months post-operation and during annual follow-ups.

Main Results:

• Cobalt levels were significantly higher in MoM THA compared to HR (p < 0.001), while chromium levels showed no significant difference (p = 0.313).
• Cobalt levels increased over time in MoM THA (p = 0.030), but remained stable in HR.
• Acetabular inclination and femoral component size did not affect ion levels in MoM THA. Chromium levels correlated with femoral component size and patient activity/pain scores in HR.

Conclusions:

• Higher cobalt levels in MoM THA, despite using the same bearing design as HR, suggest potential trunnion wear or corrosion.
• Elevated cobalt levels in MoM THA patients should be a significant concern for potential corrosion-related implant failure.