Introduction

In recent years there has been growing interest in Modic changes (MCs), defined as bone marrow lesions adjacent to the vertebral endplate seen on MRI. There are different types of MCs, with different histopathological correlates. However, the natural history of these lesions, which this study aims to examine, is not well established.

Methods

The community-based study sample comprised 110 men (mean age of 48±8 years) from the Twin Spine Study, shown to be highly representative of the corresponding Finnish population, with baseline, 5-year, and 15-year follow-up MRIs. T1- and T2-weighted sagittal lumbar scans were analyzed at the three time points for all participants. Following training and reliability testing, 1320 endplates (T12-S1) were evaluated for MC presence, type (MC1, MC2, or Mixed MC), and dimensions (anteroposterior, transverse and vertical height) at each time point. To better understand the total changes in size of an MC at follow-up, a Sum of Changes variable was used, which was the sum of changes in size of the three dimensions of an MC. Negative values represented a reduction in size, and positive represented an increase in size.

Results

Intra-rater agreement was found to be almost perfect for classification of MCs (k=0.81-0.91). MC2 was the most common type (88% of MCs at baseline, and 89% and 83% at 5- and 15-year follow-up, respectively), with approximately half located at the two lowest disc levels (48-52%). However, MC1s were distributed almost similarly across the lumbar region. The presence of an MC on one endplate, was significantly associated with the presence of an MC on the adjacent endplate (p<0.001).

At baseline, MC1s were present on 16(1%) endplates in 12(10%) participants. Five MC1s persisted at 5-year follow-up, however, all MC1s from baseline had converted to other types by the 15-year follow-up. At 5-year follow-up, there were 8 new MC1s on previously normal endplates (6 in the anterior aspect of the endplate). Out of 16 MC1s in baseline, at 5-year follow-up, one resolved completely and 10 converted to either MC2 or Mixed (all Mixed ones converted to MC2 at 15-year follow-up). There were 40 new MC1s at the 15-year follow-up, with 35(88%) arising from normal endplates and five converting from MC2s. Of the new MC1s at 15-year follow-up, 13(32%) covered the entire endplate and 18(45%) were located anteriorly.

Of the MCs that remained as MC2s throughout the study, the mean Sum of Changes in size over follow-up was 1.05 ± 1.05 (on a -9 to 9 scale), suggesting a modest overall increase, but more than 55% had the same transverse, AP and vertical size. 

Discussion

This longitudinal study confirmed that MC2 is the most common MC type in men, with MC2, but not other types, mainly located at the lower lumbar endplates. Also, MC1 appears to be a transient phase, with no MC1s at baseline persisting to 15-year follow-up. New MCs mostly occurred in the anterior aspect of the endplate, which may provide clues related to pathogenesis. Complete resolution of MCs can occur, but it is very uncommon.