Objective: Signal intensity changes noted on magnetic resonance imaging scans in degenerated disks and adjacent bone marrow have been described and labeled "Modic" changes. Three types are identified, with type 1 being linked to low back pain. This study reports on the reliability of identifying and categorizing Modic marrow changes as would be done in the normal course of clinical practice.
Methods: Fifty-one lumbar spine sagittal magnetic resonance imaging scans of adult male patients older than 40 years were used. Two radiologists independently read each case at 2 different periods; scans were reordered for the second reading. The radiologists recorded the presence or absence of Modic changes anywhere in the lumbar spine for each case and classified each one as type 1, type 2, or type 3, and the level or levels where they were noted. The kappa statistic was used to evaluate inter- and intraexaminer agreement overall and by disk level. Percent agreement was also calculated.
Results: The overall kappa value for the interexaminer agreement of diagnosing the presence/absence of Modic changes for the entire lumbar spine as well as classifying them when present was kappa = 0.52 (moderate) with 71% agreement. At the L4 through 5 level, the kappa value was 0.81 (substantial) with 92% agreement, and at the L5 through S1 level, the kappa value was 0.58 (upper moderate) with 76% agreement. The L3 through L4 level had a kappa value of 0.66 (strong) but was considered "unstable" because of the lack of variability within the cells of the contingency table. The intraexaminer reliability gave a kappa value of 0.71 (strong) (82% agreement) for examiner 1 and a kappa value of 0.87 (almost perfect) (92%) for examiner 2.
Conclusions: The Modic classification system shows moderate to almost perfect inter- and intraexaminer reliability in this study, simulating the methods of diagnosis used in clinical/radiological practice. The results of studies using the Modic system before investigations of its reliability can be viewed with more confidence, and future studies can continue to evaluate the link with patient symptoms and treatment outcomes.