Fig. 1. Explant analysis and tissue responses.

MoM hip components are manufactured from standard, medical-grade CoCr alloy (ASTM-75 or ASTM-1537), which is composed of approximately 65% Co and 30% Cr by weight. Explanted prostheses can be reverse engineered using coordinate measuring machines (CMMs) to quantify the volumetric material loss through wear and corrosion (shown in red in the wear maps below). Serum or whole blood Co and Cr concentrations provide a reliable in-vivo surrogate measure of the rate of this material loss⁸⁰. Panels a,b,c and d relate to the same patient, whose blood Co concentration was elevated at 20.1 µg/l just prior to revision. a The explanted 46 mm diameter Birmingham Hip Resurfacing. b The corresponding CMM generated wear map (volumetric wear rate of 25mm³/year). c and d The synovial tissue sections (hematoxylin and eosin (H&E) stained), (X2 magnification and x15 magnification respectively) showing heavy macrophage infiltration, no lymphocytes. Panels e–h relate to a second patient, whose blood Co concentration was 1.5 µg/l just prior to removal of her ASR XL THR. e The explanted 45 mm diameter prosthesis. f The corresponding CMM generated wear map (volumetric wear rate of 1.5mm³/year). g and h The synovial tissue sections (H&E stained), (x2 magnification and x15 magnification respectively) showing a heavy perivascular lymphocyte infiltrate and extensive synovial necrosis (severe ALVAL).