In Vivo Magnetic Resonance Imaging Evaluation of Porous Tantalum Interbody Fusion Devices in a Porcine Spinal Arthrodesis Model

Study Design. Animal experimental study. Objective. To investigate the use of magnetic resonance (MR) imaging in the assessment of lumbar interbody fusion using porous tantalum implants in a porcine spinal fusion model. Summary of Background Data. Porous tantalum has /en used successfully as a spinal interbody fusion device. However, to our knowledge, there has /en no consensus on the optimal technique for evaluating spinal fusion when using porous tantalum implants. Methods. Twelve 12-week-old female Danish Landrace pigs underwent 3 levels of anterior lumbar interbody fusion at L2-3, L4-5 and L6-7. One level was fused using a solid porous tantalum cage with pedicle screw fixation. The other 2 levels were fused using a hollow porous tantalum ring packed with autograft and stabilized anteriorly with staples. Six months postoperatively, T1-weighted, T2-weighted, and gadolinium-DTPA contrast-enhanced MRI were obtained on a GE 1.5-T unit. After sacrifice, conventional radiograph and histological examination were carried out. Results. Eleven pigs went through the experiment without complications. On all the MR sequences, there were significant higher signal intensity bands at the vertebrae-implant interface of nonfused segments compared with that of fused segments and the vertebral bone and implants themselves (P < 0.001). There was an agreement /tween histological findings of fibrous tissues surrounding the implants and the high signal intensity band on T1-and T2-weighted MR images respectively (sensitivity 69.6% and 56.5%, specificity 90.7% and 95.3%), both of which were superior to conventional radiograph images (sensitivity 52.2%, specificity 97.7%), especially the T1-weighted MR images. Conclusion. MR imaging could / an effective and noninvasive way to determine the fusion status of tantalum metal implants. Compared with T2-weighted MR imaging and conventional radiograph, T1-weighted spin-echo MR imaging is more sensitive and specific in detecting nonunion via the lucency /tween the vertebral body and tantalum metal device.