Background: Gross taper failure (GTF) is a rare but catastrophic failure mode of the head-stem-taper junction of hip prostheses, facilitated by massive material loss. GTF is a two stage process initiated by corrosion leading to head bottoming out, followed by abrasive wear due to the head rotating on the stem. The purpose of this study was to reproduce the clinical failure patterns and to determine the material loss during simulated gait. Methods: Six cobalt-chromium alloy heads (36 mm, 12/14 taper) with three different head lengths (short / medium / extra long) were combined with stem taper replicas made from titanium alloy sized to achieve bottoming out. A hip simulator was used to simulate gait loading after (ISO 14242-1 for 2 million cycles). Results: Wear patterns from in-vitro testing match the clinical failure patterns. Stem taper wear increased linearly with time (p< 0.001). After two million cycles the material loss of short / medium / extra long heads was (M+-STD) 1168±242 mg / 400±23 mg / 94±12 mg on the stem side and 46±36 mg / 46±24 mg / 70±8 mg on the head side. Stem taper wear decreased with increasing head length (p=0.01), whereas clinical failures are mostly seen for long and extra long heads.
