Effects of some technological aspects on the fatigue strength of a cementless hip stem

Abstract

Four prototype cementless hip stems were tested following the ISO 7206 protocol for the assessment of the endurance properties and compared with a cast Cr-Co-Mo (ASTM F75) commercially available stem which was used as reference design. All the tested stems were similar in shape and size, but with some substantial differences. The first was made of forged Ti6A14V alloy (ASTM F136). The second, made of the same material, featured a central hole intended to reduce the bending stiffness of the stem itself. The third was identical to the second but for a small tooling notch in one of the fillets of the hole. The fourth was similar to the first but had a coating of sintered titanium beads in the proximal part. All of these modifications were made to evaluate the effect of fatigue strength of intentional or unintentional features commonly found in commercial stems. The forged Ti6A14V allow was found to be substantially stronger than the cast ASTM F75 Cr-Co-Mo alloy. However, tooling notches or sintered coatings were found to dramatically reduce this strength. Thus, the Ti6A14V alloy calls for an accurate design process, especially when complex shapes or sintered structures are required.

Design and test of hip stem for medullary revascularization

“…Our result for a solid stem (316.7 MPa) is therefore close to their predictions. Viceconti et al investigated the effects of some technological aspects on the fatigue strength of a cementless hip stem [6]. They conducted real fatigue tests following the ISO7206 protocol and estimated the fatigue limit of the hip stem.…”

“…However, if the hollow parameters are appropriately decided, the strength of the hollow stem could be close to that of a solid stem [6]. The purpose of this study is to design and test a hollow hip stem for medullary revascularization, and determine the possible profile of this stem.…”

Abrasive waterjet peening: A new method of surface preparation for metal orthopedic implants

“…17,44,45 Though encouraging, parametric analyses have shown that post-deposition heat treatments have limited effect on the fatigue strength of porous coated Ti6Al4V in relation to the stress concentration. Moreover, Viceconti et al 46 did not find statistically significant changes in the fatigue strength of Ti6Al4V stems with sintered beads after conducting heat Figure 2(b) reveals the significance of notches resulting from plasma-spray coatings and the likelihood of fatigue crack initiation at these sites. The AWJ peened surfaces exhibited much larger profile valley radii than those of the titanium plasma-sprayed surfaces.…”

Failure analysis of two Ti‐alloy total hip arthroplasty femoral stems fractured in vivo

“…Such issues on normative requirements and associated testing of implants for design verification and improvement have indeed been previously recognized and reported. 23,24 …”