Schmorl's nodes: Common, highly heritable, and related to lumbar disc disease

Objective. Schmorl's nodes (SN) are common, but little is known of their relationship with degenerative change and back pain or genetic and environmental factors influencing their expression. We studied healthy female twin volunteers to determine the prevalence and clinical features associated with SN. Methods. Serial sagittal T1- and T2-weighted magnetic resonance images of the lower thoracic and lumbar spine were analyzed in 516 healthy female twins (150 monozygotic and 366 dizygotic). The images were scored for lumbar degenerative change. Presence of SN was noted at cranial and caudal vertebral levels T9 to L5. Data on physical activity and back pain were collected by questionnaire. Heritability of SN was calculated using variance components modeling. Results. SN were found in 30% of subjects. Of the 374 SN, 153 (41%) were in the lumbar spine and 221 (59%) were in the thoracic spine. SN heritability was >70%. There was a positive association between SN and lumbar disc disease (LDD). SN were more frequent in subjects with back pain (for >= 2 SN: odds ratio [OR] 2.68, 95% confidence interval [95% CI] 1.11-6.47, P = 0.03), but this was largely accounted for by the association of SN with LDD (OR 1.97, 95% CI 0.78-5.0, P = 0.15 adjusted for LDD). No independent association of SN with back pain was identified. Conclusion. SN are common in middle-aged women and are strongly genetically determined. They are associated with lumbar degenerative change, which is a risk factor for back pain, but are not themselves an independent risk factor for back pain.