Which pathophysiological mechanism primarily drives the catastrophic failure mode known as ‘trunnionosis’ in total hip arthroplasty?

Explanation:
The correct option is b. Trunnionosis specifically refers to the insidious wear and corrosion occurring at the modular head-neck junction (the trunnion) of a femoral stem. The primary mechanism is mechanically assisted crevice corrosion (MACC). Micromotion between the head and the neck continuously disrupts the passivating oxide layer of the metal. Fluid enters the micro-crevices, creating a galvanic cell that drastically lowers local pH and releases free metal ions (like cobalt and chromium). This ultimately triggers a severe adverse local tissue reaction (ALTR) or pseudotumor formation in the surrounding soft tissues. Reference: Pastides PS et al. Trunnionosis: a growing problem. Bone Joint J.