Evaluation of Spinal Interbody Fusion Using Magnetic Resonance Imaging

[Summary.] Study design : Prospective study of magnetic resonance imaging (MRI) in human spinal interbody fusion. Objectives : To determine whether a consistent pattern of bony fusion could be identified on MR images during spinal interbody fusion. Summary of background data : Plain radiography has traditionally been used to monitor changes in bone graft incorporation in patients with spinal interbody fusion. We felt that MRI would provide additional significant information in monitoring the course of bony union in spinal interbody fusion. Methods : Twenty patients underwent spinal interbody fusion via an anterior approach in this study. Beginning immediately after surgery, serial T1-weighted and T2-weighted MR images, as well as post-contrast MRI, were performed. Signal intensity changes were examined in the bone graft, the border between the graft and the adjacent vertebrae, and in the adjacent vertebrae, and were classified into 5 patterns (P1～P5) on each image. Unclassifiable patterns were also defined. Results : On T1-weighted images, the graft exhibited high intensity immediately after surgery. The intensity subsequently decreased with time. On T2-weighted images, the graft was isointense for a period of time after surgery, and then exhibited high intensity. The grafts eventually became isointense on both T1-weighted and T2-weighted images by the time of bony union as determined from plain radiographs. On post-contrast images, an enhancement effect was noted from the upper and lower edges of the graft. This effect gradually increased until the entire graft became enhanced. In the adjacent vertebrae, transient changes were found in the early postoperative period. Post-contrast images revealed contrast enhancement. In cases with a favorable course, there was a tendency to gradually change from P1 to P5 with time. Unfavorable courses were characterized by a mosaic appearance of the graft on the T1-weighted image, widening of the border in the direction of the graft, and continuous changes in the adjacent vertebrae on each image (pattern PU). . Conclusions : A consistent pattern was observed in serial MRI after spinal interbody fusion. This technique would seem useful in evaluating the course of bony fusion.