Modic changes on MR images as studied with provocative diskography: clinical relevance--a retrospective study of 2457 disks

PURPOSE

To assess the value of vertebral body endplate signal intensity (Modic) changes on magnetic resonance (MR) images in predicting a painful disk, with provocative diskography as the reference standard.

MATERIALS AND METHODS

Lumbar spine diskograms and prediskogram MR images of 736 patients (2457 disks) were retrospectively reviewed as part of an institutional review board-approved HIPAA-compliant protocol. Each disk was assigned a Modic subtype: type 0, normal; type 1, nonfatty high signal intensity; type 2, fatty; and type 3, sclerosis. Statistical analysis involved use of a 2 x 2 contingency table of diskogram results for each of the subtypes. The subtype sensitivity, specificity, positive predictive value (PPV), negative predictive value, and confidence intervals (CIs) were calculated. Similar analyses of other MR variables (such as disk herniation, high signal intensity zone, and spondylolisthesis) and type 1 signal intensity changes also were performed.

RESULTS

Type 1 changes (n = 155) had a high PPV (0.81; 95% CI: 0.74, 0.87) for a provocative diskogram. Type 2 changes (n = 126) had a lower PPV (0.64; 95% CI: 0.55, 0.72) for a positive diskogram. Type 3 changes (n = 21) had a PPV (0.57; 95% CI: 0.34, 0.78) that was not significant for a positive diskogram. The PPV of an endplate with a type 1 change (hereafter, type 1 endplate) for a tear in the annulus fibrosis of the disk was also insignificant (0.14; 95% CI: 0.09, 0.20). A similar analysis between a type 1 endplate and the presence of a disk herniation (PPV, 0.26; 95% CI: 0.19, 0.34) and between a type 1 endplate and vertebral body spondylolisthesis (PPV, 0.28; 95% CI: 0.20, 0.35) were significant.

CONCLUSION

Type 1 signal intensity changes on MR images have a high positive predictive value in the identification of a pain generator.

Accuracy of registration methods in frameless stereotaxis

The accuracy of image to patient registration is a critical issue in the intraoperative use of frameless stereotaxic instruments for surgical guidance. This study was performed to assess the accuracy of image to head phantom registration using several standard registration techniques and a clinical frameless stereotaxic instrument. Two types of radioopaque fiducial markers were fixed to a plastic head phantom, and a computed tomography scan of the phantom was performed in the routine fashion. Image to phantom registration was carried out using fiducial markers, fiducial markers plus surface fit, anatomic landmarks, and anatomic landmarks plus surface fit. After each registration, linear inaccuracy measurements were performed for each of 32 markers. Each registration was performed 10 times, and the overall mean error measurements and anterior and posterior error were computed and compared. The overall mean error was smallest for the fiducial registration alone (2.07 mm). The magnitude of error increased significantly for posterior locations for all other registration techniques, but it was not significantly increased for the fiducial registration method. For this hardware configuration, registration with surface-applied fiducial markers is measurably more accurate than registration with surface anatomic landmarks. The addition of surface points to the fiducial registration does not increase the registration accuracy but, in fact, increases the degree of error.