Primary hip replacement stem taper fracture due to corrosion in 3 patients

Wear and corrosion of taper connections in modular hip prostheses have gained much attention due to the serious biological response that can occur due to the metallic debris originating from this articulation (Pivec et al. 2014). This has been observed especially for metal-on-metal (MoM) bearing articulations with large-diameter heads (Gunther et al. 2013). The biological response is attributed to cobalt (Co) and chromium (Cr) ions originating from the female taper interface of the ball head, which is made of CoCr alloy (McGrory et al. 2015, Bishop et al. 2013). No mechanical implant failures (i.e. fractures) have been documented. In contrast, bi-modular primary and revision hip systems with necks and stems made of titanium-aluminium-vanadium alloy (Ti alloy) have shown fracture rates of up to 2.4% due to corrosion without any previous biological responses (Grupp et al. 2010, Norman et al. 2014). Taper fractures of primary Ti alloy THA stems with a modular head taper have not been reported in the literature, but major taper corrosion and material loss have been found for one design in particular (Witt et al. 2014). We present 3 cases of stem taper fracture as the ultimate failure mode of this design.