Taper Failure After Large-Diameter Metal-on-Metal Total Hip Arthroplasty

Analytical review on the biocompatibility of surface-treated Ti-alloys for joint replacement applications

INTRODUCTION

With the advancement of joint replacements such as total hip replacement (THR), Titanium (Ti) and its alloys are widely used as implant materials. The bearing surface of Ti improves the longevity of implants. In this perception, researchers design a Ti-alloy that increases the wear and corrosion resistance to enhance osteogenesis and mechanical stability.

AREAS COVERED

: This paper is dedicated to finding the major causes of the failure of THR. Further, this paper provides an overview of the application of metallic alloys and their influencing factors that influence biocompatibility. The most contributing part of this paper focuses on the post-treatment impact on Ti-alloys biocompatibility.

EXPERT OPINION

This paper revealed and discussed that Ti alloys' biocompatibility for orthopedic applications mainly depends on antibacterial activities that decide tissue-implant compatibility. Therefore, performing surface treatment enhances the biocompatibility of Ti alloys. It was also observed that more water contact angle (WCA) induces bacterial growth and enhances cell adhesion. In contrast, the treated surface increases the antibacterial activities at lower WCA. Surface heat treatment with sintering or micro-arc oxidation achieves suitable antibacterial or antimicrobial activities.

Retention of metals in periprosthetic tissues of patients with metal-on-metal total hip arthroplasty is reflected in the synovial fluid to blood cobalt transfer ratio in the presence of a pseudotumour

Background

Modern metal-on-metal (MOM) arthroplasties were performed for over a decade before alarming reports of adverse metal reactions dramatically reduced their use. Failures are seen more often with high-wearing implants, but also well-positioned components with more favourable wear patterns can cause problems. There are no specific clinical indicators that could help us to predict the prognosis of these implants. For this reason, we still need more information on the effect of underlying factors that contribute to this process.

Methods

In this prospective cohort study, we investigated how cup orientation and type of pseudotumour determined by the Hart classification effect the distribution of metals in blood, synovial fluid and tissues surrounding the metal-on-metal hip prosthesis in revision surgery patients. One thousand two hundred twenty-nine metal-on-metal hip patients were screened and of those, 60 patients that had a revision surgery due to adverse metal reaction were included. Whole blood, synovial fluid and synovial/pseudotumour tissue samples were analysed for metal ion concentrations (Co, Cr, Mo and Ti).

Results

The lowest metal concentrations were found when both cup anteversion and inclination were optimal, and the highest when both were suboptimal. Suboptimal anteversion alone raised Cr-ion concentrations more than suboptimal inclination. The concentrations of metals in blood, synovial fluid or synovial soft tissue were the same in patients with and without a pseudotumour, but the relative transfer percentage of cobalt from synovial fluid to blood was higher in patients with a pseudotumour.

Conclusions

The implant orientation alone does not explain the metal concentrations found in tissues or distribution of metals between different tissues. The accumulation of metals in periprosthetic soft tissues increase the total metal load, and in the presence of a pseudotumour this is reflected in the transfer ratio of Co from synovial fluid to the blood. The total metal load of the pseudotumour tissue should be defined in future studies to determine if this will provide new insights for clinical practice.

Gross Stem Taper Failure with Head Dissociation in a Very Active Patient with an Uncemented Femoral Stem

CASE

We report a case of gross taper failure (GTF) in a very active 81-year-old man 14 years after index operation. The patient presented with acute hip pain and shortening of the left leg. X-rays showed the dissociation of the head. The stem had to be revised because of the massive stem taper damage.

CONCLUSION

This case demonstrates that GTF at the head-stem taper junction following mechanically assisted crevice corrosion is not limited to a specific taper design and material. Other risk factors such as high activity level can lead to this failure pattern also in established stem and taper designs.