A 72-year-old woman presents 8 years after a cementless total hip replacement with groin pain, elevated ESR, and a serum cobalt level of 12 µg/L (normal <1 µg/L). MRI shows a large pseudotumour around the hip. Which bearing combination is most likely responsible?

• A Metal-on-metal (MoM) ✓
• B Ceramic-on-ceramic (CoC)
• C Metal-on-polyethylene (MoP)
• D Ceramic-on-polyethylene (CoP)

Explanation

Metal-on-metal bearings generate cobalt and chromium ions through tribocorrosion, leading to adverse reaction to metal debris (ARMD) and pseudotumour formation. Elevated serum cobalt (>7 µg/L bilateral, >4 µg/L unilateral) mandates urgent evaluation. CoC and CoP bearings produce ceramic or polyethylene particles that cause far less systemic metal ion release and do not produce pseudotumours of this type.

Reference: Maheshwari Essential Orthopaedics, 6th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.