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Item type:Publication, Access status: without files , The taper corrosion pattern observed for one bi-modular stem design is related to geometry-determined taper mechanics(2017-08); ; ; ; Bi-modular primary hip stems exhibit high revision rates owing to corrosion at the stem-neck taper, and are associated with local adverse tissue reactions. The aim of this study was to relate the wear patterns observed for one bi-modular design to its design-specific stem-neck taper geometry. Wear patterns and initial geometry of the taper junctions were determined for 27 retrieved bi-modular primary hip arthroplasty stems (Rejuvenate, Stryker Orthopaedics) using a tactile coordinate-measuring device. Regions of high-gradient wear patterns were additionally analyzed via optical and electron microscopy. The determined geometry of the taper junction revealed design-related engagement at its opening (angle mismatch), concentrated at the medial and lateral apexes (axes mismatch). A patch of retained topography on the proximal medial neck-piece taper apex was observed, surrounded by regions of high wear. On the patch, a deposit from the opposing female stem taper—containing Ti, Mo, Zr, and O—was observed. High stress concentrations were focused at the taper apexes owing to the specific geometry. A medial canting of the components may have augmented the inhomogeneous stress distributions in vivo. In the regions with high normal loads interfacial slip and consequently fretting was inhibited, which explains the observed pattern of wear.Publicationtype: Journal Article223 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Surface and subsurface changes as a result of tribocorrosion at the stem-neck interface of bi-modular prosthesis(2017-06); ; ; ; This study presents a detailed multi-scale analysis of the degradation processes occurring on both the CoCrMo and TMZF alloy surfaces at different regions across the taper interface. Co-ordinate measurement machine, scanning electron microscopy, transmission electron microscopy and X-ray diffraction methods have been utilised to identify the roles of degradation from the mm to nm scale. Depending on the region of interest, varying topographies and subsurface morphologies were observed across both surfaces. In regions where high pressures are expected, retention of the surface topography was seen on the CoCrMo trunnion. This was complimented by gross shear and plastic deformation of the subsurface material. In regions where maximum penetration was seen, evidence of fretting-corrosion was seen and a loss of the nano-crystalline layer. For the TMZF surface, refinement of the alloy was seen in the top 5 μm, with fatigue cracks within the bulk present. Precipitation and formation of oxide species were observed at depths of 2 μm. The degradation of a bi-modular prosthesis is a complex multifactorial process. It is hypothesised that this formation of oxide species at the interface and within the bulk alloy plays an important role in the degradation through a combined work-hardening and corrosion process.Publicationtype: Journal Article134