The taper corrosion pattern observed for one bi-modular stem design is related to geometry-determined taper mechanics

Abstract

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.

Do SiNx coatings bear the potential to reduce the risk of micromotion in modular taper junctions?

“…23,45 The altered contact mechanics might be one contributor to the slight variances in micromotion of coated tapers found in the present study. However, contact pressures and areas are varying broadly for different taper designs and might come along with nonuniform distributions and stress concentrations, 5,46 especially since the coating performance is based on the coating process and composition. 32,36 Obviously, compensation of geometrical changes due to coating application can be considered during the taper design process ahead of clinical usage.…”

“…[2][3][4] Observed material loss patterns demonstrate the specific contact conditions of the mating surfaces, providing insights in the various mechanical and geometrical facets that affect this kind of failure. 5 Mostly the material loss at the taper interface is negligible and does not result in mechanical implant failure. However, the metal debris 6 leads to clinical implications as the released metal particles can create adverse local soft tissue reactions that foster inflammation, bone resorption, and aseptic loosening.…”

Corrosion of Metallic Biomaterials: A Review

“…Nevertheless, fretting corrosion may occur also at backside contacts in joint prostheses, bone-implant contact regions, overlapping cardiovascular stent contact points and other locations where surface contact and small cyclic motion exist [40]. Hence, fretting corrosion of biomaterials and implants has been studied extensively in the lab as well as on retrieved implants [40,68,142,143,271,329,330,331,332,333,334,335,336,337,338,339,340,341,342,343,344,345,346,347,348]. ASTM F1875 [349] specifies fretting corrosion testing of hip femoral head/bore and cone taper interface in modular implants.…”

How to Proceed with Asymptomatic Modular Dual Taper Hip Stems in the Case of Acetabular Revision

“…A limitation may arise by the fact that the literature review about serum ion levels, radiographic and clinical findings and the retrieval analysis was based in the vast majority on two recalled dual taper stems in the material combination CoCr 29 Mo 6 (neck) and TiMo 12 Zr 6 Fe 2 (stem), and hence a generalization of the findings and transfer to other implant designs and materials of dual taper stems may be limited [64,85,86]. Meftah et al [31] used persistent pain and high cobalt levels as predictors for revision surgery of the dual taper Rejuvenate stem and reported a Kaplan-Meier survivorship of 40% at four years with revision related to neck taper corrosion as the end point.…”