A 60-year-old woman undergoes total hip replacement with a 36 mm ceramic-on-polyethylene bearing and a titanium stem with a cobalt-chromium modular head. Five years later she develops thigh pain and a periosteal reaction on the femur. Serum cobalt is 5 µg/L. What mechanism best explains this finding?
- A Osteolysis from polyethylene wear debris
- B Adverse reaction to metal debris from trunnion fretting ✓
- C Aseptic loosening from cement mantle failure
- D Stress shielding from the stiff femoral stem
Correct answer: B. Adverse reaction to metal debris from trunnion fretting
Explanation
Modular head-neck junctions in metal-on-polyethylene bearings can generate metal debris through fretting corrosion at the trunnion, producing ARMD, pseudotumors, and periosteal reactions even when polyethylene wear is low. Cobalt elevation with titanium stem and cobalt-chromium head points to trunnion fretting rather than polyethylene-induced osteolysis.
Reference: Campbell's Operative Orthopaedics, 14th ed.
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Written and medically reviewed by the StethoPrep medical team.