Dual-Modular Versus Single-Modular Stems for Primary Total Hip Arthroplasty: A Long-Term Survival Analysis

Background and Objectives: Increased revision rate of dual-modular (DM) femoral stems in primary total hip arthroplasty (THA) because of modular-neck breakage and adverse local tissue reactions (ALTRs) to additional junction damage products is well established and some designs have been recalled from the market. However, some long-term studies of specific DM stems did not confirm the inferiority of these stems compared to standard single-modular (SM) stems, and a head-to-head comparison THA is missing. The objectives of this multicentre study were to determine the survivorship and complication rates of a common DM stem design compared to a similar SM stem. Materials and Methods: In a time frame from January 2012 to November 2015, a cohort of 807 patients (882 hips) consecutively underwent primary cementless THAs at two orthopaedic centres. 377 hips were treated with a Zweimüller-type DM stem THA system and 505 hips with a similar SM stem THA system, both including a modern press-fit acetabulum. Kaplan-Meier survivorship and complication rates were compared between both groups in a median follow-up of 9.0 years (maximum, 9.9 years). Results: The 9-year survivorship of the DM stem THA system (92.6%, 95% CI 89.9-95.3) was significantly lower than that of the SM stem THA system (97.0%, 95% CI 95.2-98.8). There were no differences in revision rates for septic loosening, dislocation, and periprosthetic fractures between the two groups. One ceramic inlay and one Ti-alloy modular neck breakage occurred in the DM stem THA system group, but the main reason for revision in this group was aseptic loosening of components. Conclusions: The survivorship of the DM stem THA system was lower than the similar SM stem THA system in a comparable clinical environment with long-term follow-up. Our results confirmed that no rationale for stem modularity exists in primary THAs.

Long-term survivorship of an exchangeable-neck hip prosthesis with a Ti-alloy/Ti-alloy neck-stem junction

INTRODUCTION

Breakage of exchangeable-neck (EN) and adverse local tissue reactions (ALTRs) to neck-stem junction (NSJ) damage products are responsible for increasing the revision rate of EN hip prostheses. We investigated the survivorship of an EN hip prosthesis including a NSJ with both components made of titanium alloy (Ti-alloy/Ti-alloy) to assess whether, and to what extent, EN breakage and NSJ damage affected implant survivorship.

MATERIALS AND METHODS

Using data from a hip replacement registry, we determined survivorship of 2857 EN prostheses. Long-offset configurations of head and EN were implanted in heavy (> 90 kg) patients only in 23 hips. We investigated under which conditions EN breakages or ALTRs occurred. We also measured titanium (Ti) and vanadium (V) blood concentrations in 24 patients with a unilateral well-working prosthesis.

RESULTS

The 17-year survival rates for any reason and aseptic loosening of any component were 88.9% (95%CI 87.5-90.1; 857 hips at risk) and 96.9% (95%CI 96.0-97.6), respectively. There were two cases of EN breakage and one case of ALTR (metallosis), due to rim-neck impingement, out of 276 revisions. After an average period of 9.8 years (range 7.8-12.8 years), the maximum Ti and V blood concentrations in patients with a well-working prosthesis were 5.0 µg/l and 0.16 µg/l, respectively.

CONCLUSION

The present incidence of EN breakage or ALTR is lower than those reported in other studies evaluating EN hip prosthesis survivorship. This study suggests that (i) the risk of EN breakage is reduced by limiting the use of long-offset configurations in heavy patients and (ii) Ti-alloy/Ti-alloy NSJ damage products do not promote ALTR nor significantly alter the rate of implant loosening. Since design decisions and implant configuration determine the NSJ strength, the NSJ strength in working conditions must be thoroughly investigated to proper define the clinical indications for any EN design.

Investigation on ultrasonic cavitation erosion of TiMo and TiNb alloys in sulfuric acid solution

Two kinds of Ti-alloys, i.e., TiMo and TiNb alloys are manufactured in this paper, and their ultrasonic cavitation erosion behaviors in 0.1 M H₂SO₄ solution are evaluated by the mean depth erosion (MDE), SEM and white light photograph. The results show that MDE of TiMo and TiNb alloys obviously increase with increasing the cavitation erosion time, however, they evidently decrease with the increment of Mo or Nb content at each fixed cavitation erosion time, and even some large blank areas (uneroded areas) still exist on the sample surface after ultrasonic cavitation erosion for 2 h in the case of Ti10Mo and Ti20Nb samples, implying the enhanced anti-cavitation erosion property of Ti-alloy by adding Mo or Nb element. The MDE of Ti10Mo or Ti20Nb sample is lower than that of TC4 sample in the case of each cavitation erosion time, indicating the better cavitation erosion resistance of of Ti10Mo or Ti20Nb sample. The influences of Mo and Nb on the passivity of TiMo and TiNb alloys during the ultrasonic cavitation erosion are detected by potentiodynamic curves. The results display that Ti, TC4, TixMo (x = 1, 5, 10) and TixNb (x = 5, 10, 20) samples are all almost in the passive state within the potential region from 0V_SCE to 1.5V_SCE during ultrasonic cavitation erosion, and the passive current density evidently decreases with increasing Mo or Nb content, indicating the enhanced passive characteristic by adding Mo or Nb alloys during the ultrasonic cavitation erosion.

The influence of temperature during water-quench rapid heat treatment on the microstructure, mechanical properties and biocompatibility of Ti6Al4V ELI alloy

This study investigates the influence of a rapid heat treatment followed by water-quenching on the mechanical properties of Ti6Al4V ELI alloy to improve its strength for use in implants. Prior to the experiment, a dilatometry test was performed to understand the progressive α-to β-phase transformation taking place during heating. The results were then used to carry out heat treatments. Microstructure was analysed using SEM, EBSD, EDX and XRD techniques. Vickers micro-hardness, tensile and high cycle rotating bending tests were used to analyse the influence of the $\alpha'$-phase fraction on the strength of the studied alloy. Results show that this process can provide a Ti6Al4V ELI alloy with a better Yield Strength (YS)/uniform deformation (ε_u) ratio and improved high cycle fatigue strength than those observed in the current microstructure used in medical implants. Lastly, cytotoxicity tests were performed on two types of human cells, namely MG63 osteoblast-like cells and fibroblasts. The results reveal the non-toxicity of the heat-treated Ti6Al4V ELI alloy.