Comparative Analysis of MRI Artifacts Associated with Artificial Spinal Discs

Introduction: Artificial disc replacement (ADR) is a surgical intervention to treat symptomatic disc degeneration by replacing the diseased disc with an artificial disc. A variety of artificial discs with different materials and biomechanical features are available for surgeons to choose. However, most of them contain metallic or composite materials that can cause artifacts on magnetic resonance imaging (MRI), posing challenges to postoperative MRI interpretation. In this study, we compared MRI artifacts produced by two commonly used artificial discs, NuVasive Simplify and Biomet Mobi-C.

Methods: We retrospectively selected patients who have undergone cervical ADRs with either type of artificial discs and had both preoperative and postoperative cervical spine MRI. Patients who have had other cervical spine instrumentation were excluded to ensure that any artifacts observed are attributed to the artificial discs only. T2 turbo spin echo (TSE) axial images were used to measure the artifacts. Areas of artifacts were first measured in two dimensions using either elliptical or polygonal approximation. Volume was then calculated as the summation of the artifact areas multiplied by slice thickness.

Results: The mean artifact volume of Biomet Mobi-C discs and NuVasive Simplify discs was 14.55 cm3 and 2.26 cm3, respectively (p=0.01157). For both types of discs, larger implant size is associated with more artifacts. In addition, Mobi-C causes extensive signal void and susceptibility artifacts in surrounding structures, including the vertebral bodies, intervertebral foramina, and spinal canal. On the other hand, Simplify discs cause only mild signal void in the vertebral bodies without extending to the neural elements.

Conclusion : Biomet Mobi-C discs generate significantly more artifacts on MRI compared to NuVasive Simplify discs. There is a positive correlation between the artifact volume and the size of the implants. Compared to Simplify, Mobi-C also results in more artifacts overlying the foramina and spinal canal, which can interfere with the assessment of critical neural structures on MRI. The larger artifact volume associated with Mobi-C discs is likely attributed to its higher metallic content compared to Simplify discs.