Summary of findings
To our knowledge, this study is the first to investigate the effect of MCs and the herniated disc component on rLDH following PELD. We found that hyaline cartilage is more common in patients with MCs in the intraoperative specimens, and recurrent disc herniation is more common in patients with MCs. Recurrent disc herniation was more common in the hyaline cartilage group. rLDH following PELD preferentially occurs when MCs or the herniated cartilage are present.
Modic changes and herniated cartilage
The variable composition of herniated tissue has been described previously, with various proportions of nucleus pulposus, annulus, hyaline cartilage, and bone being reported.[14, 15] Tanaka et al. suggested that the cartilaginous endplate-osteochondral junction is weak, whereas the cartilaginous endplate-inner annulus fibrosus connection is strong, so herniated tissue usually contains a cartilaginous endplate. Rajasekaran et al. reported that a high proportion of Indian patients had herniations containing cartilage and bone.
MCs, which present as signal alterations in the vertebral endplate and adjacent bone marrow, are found on T1- and T2-weighted MRI. LDH is known to be a strong risk factor for MCs, especially type I.[17, 18] MCs are known to be associated with LDH-containing cartilaginous fragments.[11–13] Schmid et al. reported the presence of a cartilaginous endplate in the extruded disc material in 63% of patients with MCs. Our study confirmed the results; 18/28 (64.3%) of our patients showed evidence of hyaline cartilage in the intraoperative specimens, including 6/9 endplates with type I MCs, and 12/19 endplates with type II. Among 71 endplates without MCs, 14/71 (19.7%) showed evidence of hyaline cartilage in the intraoperative specimens. Hyaline cartilage was more common in patients with MCs.
Effect of Modic changes and herniated cartilage on rLDH
MCs are associated with the herniated cartilage disc component; however, the effect of MCs and the herniated disc component on the rLDH following PELD has received little attention. Our study showed that rLDH preferentially occurs when MCs or the herniated cartilage are present. For the endplates with MCs, the connection between the cartilage endplate and the vertebral body is relatively weak. The cartilage endplate may be separated from the vertebral body and herniated with nucleus pulposus, so the herniated tissue usually contains a cartilage endplate.
For patients with MCs, these conditions usually imply that the endplate structure has been damaged. The herniated cartilaginous endplate is only one part of the damaged endplate, because the connection between the cartilage endplate and the vertebral body is relatively weak, so other parts of the endplate easily separate from the vertebral body and herniate with the nucleus pulposus, and rLHD occurs. Similar to the MCs endplate, if the herniated cartilage is present in the intraoperative specimen, which also reflects damage to the endplate structure, other parts of the endplate easily separate from the vertebral body and herniate with nucleus pulposus, and rLHD preferentially occurs.
Our study has some limitations. Firstly, it was a retrospective study with a small sample size. The relatively small sample size limits the accuracy of correlation between the rate of rLDH and the type of MCs. Secondly, the study focused on the phenotypic association between rLDH and MCs or the herniated disc component, while no correlative mechanism was studied. In particular, we did not confirm the results using biomechanics and histomorphologic methods. Evidently, further study is needed in the future.
Nevertheless, this study suggests that rLDH preferentially occurs after PELD when MCs are present. If we choose PLED for patients with MCs, we need to inform these patients that they have a higher incidence rate of rLHD; fusion may be a better choice, especially for old patients. Meanwhile, if the herniated cartilage is present in the intraoperative specimen, we also should inform these patients that the they have a higher incidence rate of rLHD. Such patients may require a second operation.