A 68-year-old woman presents 8 years after right total hip replacement with groin pain and a lytic lesion around the acetabular cup on radiograph. Serum cobalt level is markedly elevated. Aspiration yields a gray-brown fluid. Which bearing couple is most likely responsible?
- A Ceramic-on-ceramic
- B Metal-on-metal ✓
- C Metal-on-polyethylene (conventional)
- D Oxidized zirconium-on-polyethylene
Correct answer: B. Metal-on-metal
Explanation
Metal-on-metal (MoM) bearings release cobalt and chromium ions through tribocorrosion, causing adverse local tissue reactions (ALTR) including pseudotumor formation, metallosis, and osteolysis. Elevated serum cobalt/chromium and gray-brown aspirate (metallosis) are hallmarks. Ceramic-on-ceramic does not produce metallic ions; conventional polyethylene components do not generate sufficient metal debris to cause systemic cobaltemia of this degree.
Reference: Maheshwari Essential Orthopaedics, 6th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.