In Vivo Wear and Corrosion of Titanium Alloy Spinal Implants

A recent article published in Scientific Reports investigated the wear and corrosion of titanium alloy spinal implants in vivo using implants and their surrounding scar tissues removed from 27 patients from May 2019 to April 2021.

In Vivo Wear and Corrosion of Titanium Alloy Spinal Implants

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Background

Pedicle screws and rods are commonly used in spine surgeries. Initially made from stainless steel, these implants exhibited high wear and corrosion in the body, leading to inflammatory reactions from metal particles in adjacent tissues. Titanium alloys have since replaced stainless steel due to their stability.

Despite their benefits, titanium implants can release particles that cause inflammation and allergic reactions. Metal artificial joints may lead to osteolysis, potentially loosening spinal implants and causing complications such as broken screws, nerve damage, and fusion failure.

Therefore, it is crucial to investigate the in vivo performance of titanium implants to evaluate patient rehabilitation. This study aimed to examine the wear and corrosion of titanium implants and the impact of released titanium particles on osteolysis and implant stability.

Methods

The study included 27 patients (18 males and nine females) aged 18 to 75. The group comprised 15 patients with thoracolumbar fractures, 11 with adjacent segment disease, and one with lumbar spondylolisthesis. No infection, loosening, or fracture of the spinal implants was detected preoperatively.

The pedicle screws and rod were removed and confirmed by three surgeons. Soft tissue scars (around 5 mm) of the implants were excised and preserved in 10 % formalin for subsequent testing. Hematoxylin and eosin (H&E) staining was used to evaluate inflammatory cell infiltration, indicating inflammation and foreign body reactions in the tissues.

The morphology of soft tissues was examined using a scanning electron microscope (SEM). Metal particle composition in the soft tissues was analyzed using energy-dispersive X-ray (EDX) spectroscopy to determine whether the spinal plants released metal particles.

The retrieved implants were characterized for wear and corrosion after proper cleaning. Firstly, three researchers observed the retrieved pedicle screws and rods. Implants with surface wear and other abnormal changes were further examined through SEM to detect corrosion, using the Higgs-Goldberg method to identify the degree of corrosion.

The elemental composition of the retrieved spinal implants was determined using EDX spectroscopy. The data was compared to manufacturer data to confirm material consistency and to determine the origin of the metal particles observed in the soft tissue.

Results and Discussion

SEM and EDX observations revealed increasing wear and corrosion of titanium implants over time. However, the precise timing of the wear could not be identified.

Notably, no specific inflammation or foreign body reaction was evident in the tissues around the implant, regardless of the presence of titanium particles. This was attributed to the high tissue compatibility of titanium alloys. Despite producing several wear particles in vivo, they did not initiate inflammatory cell aggregation or mediator release, resulting in no significant increase in osteoclast activity or osteolysis.

The pedicle screws and rods demonstrated varying extents of wear, primarily concentrated at the joint. Corrosion was detected at the screw-rod joint, attributed to slight relative motion. Additionally, mild scratches and wear were evident in the middle of some rods, but these rods showed no signs of corrosion.

The researchers examined the wear and corrosion of uniaxial and polyaxial pedicle screws, with the latter exhibiting greater wear and corrosion in some instances. The wear and corrosion of the pedicle screws were related to their position, with corroded screws mainly located at the ends of the rod. Greater stress at the rod ends was considered responsible for enhancing the wear and corrosion of the screws.

Persistent fretting and stress, rather than the pedicle screw structure, were identified as key reasons behind wear and corrosion. Numerous metal particles were detected in the surrounding soft tissues, but no soft tissue discoloration was observed.

Conclusion

Overall, titanium alloy spinal implants experienced wear and corrosion in vivo, which increased with implantation time. Metal-like particles were found in the soft tissues of seven patients, but no significant inflammatory cell infiltration was observed. These results confirmed the good histocompatibility of titanium alloy particles, which did not trigger inflammation, foreign body reactions, or osteolysis.

Lower wear and corrosion were observed in patients with fractures compared to other patients. Additionally, polyaxial screws exhibited greater wear and corrosion than uniaxial screws, although the reverse was observed in patients with fractures. Thus, screw structure and rod length did not significantly affect wear and corrosion.

Journal Reference

Ji, H., Xie, X., Jiang, Z., Wu, X. (2024). Wear and corrosion of titanium alloy spinal implants in vivo. Scientific Reports. DOI: 10.1038/s41598-024-68057-8

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Nidhi Dhull

Written by

Nidhi Dhull

Nidhi Dhull is a freelance scientific writer, editor, and reviewer with a PhD in Physics. Nidhi has an extensive research experience in material sciences. Her research has been mainly focused on biosensing applications of thin films. During her Ph.D., she developed a noninvasive immunosensor for cortisol hormone and a paper-based biosensor for E. coli bacteria. Her works have been published in reputed journals of publishers like Elsevier and Taylor & Francis. She has also made a significant contribution to some pending patents.  

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