Introduction: Schmorl's nodes (SNs) are prevalent endplate abnormalities characterized by the intrusion of intervertebral disc material into the adjacent vertebral body, often attributed to factors like trauma, physical loading, osteoporosis, disc degeneration, ethnicity, genetic factor, and endplate weakness. One of the theories proposed the involvement of the nucleus pulposus extending to the vertebral body's endplate with low bone mineral density (BMD); however, the pathogenesis and clinical significance remains debatable. Furthermore, recognizing the role of sex is crucial in understanding the etiology of SNs because sex-specific insights could lead to more targeted therapies, better diagnostic criteria, and more effective preventive strategies. In addition, sex-type may influence endplate and vertebral body strength. The purpose of this study was to investigate the sex-specific associations between SNs, Modic changes (MC) and osteoporosis (OP) in the thoraco-lumbar and lumbar regions (T10-S1) using magnetic resonance imaging (MRI) in a large population-based study.
Method: 970 participants (317 males, mean age:67.2 years; 653 females, mean age: 66.0 years) with an age range of 21–97 years in the Wakayama Spine Study were assessed. SNs were defined as small well-defined herniation pits with a surrounding wall of hypointense signal. MC were defined as diffuse high-signal changes along either area of the endplate. OP was defined by the Japanese Society for Bone and Mineral Research criteria. Univariate logistic regression analysis was performed for the association between the presence of SN based on age-strata, body mass index (BMI), femoral neck and lumbar OP, and MC in males and females, respectively. Multivariate regression analyses were performed to assess risk factors related to imaging phenotypes.
Results: Overall, there were 390 subjects with SNs (40.2 %; 36.4 % in males; 42.0 % in women) within our population. 20.0 % (n = 194) of SNs subjects had single lumbar disc level involvement (19.6 % in males; 20.2 % in females), whereas 20.2 % (n = 196) had multilevel SN involvement (16.4 % in males; 22.0 % in females). Higher age was significantly associated with increased likelihood of SN (age strata 50-59; OR: 3.25, p<0.005; 60-69, OR: 5.70, p<0.0001; 70-79, OR: 11.34, p<0.0001; ≥80, OR: 13.27, p<0.0001) in females, but age was not associated with SNs in males. In addition, OP and BMI were not significantly associated with SNs in both sexes. Alternatively, MC were significantly associated with SN in females (OR 1.62, p<0.01).
Discussion: This is the first study, to our knowledge, to address in a population the impact of BMD/OP in relation to SN and MC of the thoracic and lumber spines. We noted higher age to be significantly associated with SNs in females but not in males. Contrary to previous reports, reduction of BMD with older age in females was not associated with SNs. Conversely, MC were significantly associated with SNs, independent of sex-type; As such, our study noted that specific drivers or pathomechanisms of endplate abnormalities can exist. Our findings further elaborate upon the understanding of endplate-specific changes of the thoracic and lumbar spinal segments.