INTRODUCTION: Although the pathophysiology of symptomatic lumbar spinal stenosis (LSS) is not well understood, a narrow central canal or intervertebral foramen is an essential or defining feature. The aim of the present study was to estimate the magnitude of genetic versus environmental influences on anatomical LSS in a general population sample of men. We were also interested in examining disc degeneration and overall skeletal size as possible genetic pathways.
METHODS: We conducted an extended classic twin study using multivariate analyses with consideration of lumbar level. Study participants were 300 male twin pairs (152 monozygotic and 148 dizygotic), from 35‐70 years of age, from a population‐based twin cohort. Subjects' lumbar MRI were evaluated for the primary phenotypes of central canal LSS, as assessed qualitatively by an experienced orthopaedic spine surgeon using a 4‐point grading scheme, and quantitatively measured cross‐sectional area of the dural sac at each spinal level (intra‐rater reliability ICC=0.98). Additional phenotypes for multivariate analyses to examine possible genetic pathways included disc bulging (0‐3 rating) and standing height (cm), as an indicator of overall skeletal size.
RESULTS: The heritability estimate for qualitatively assessed LSS was 66.9%. Similarly, the vast majority of variance in dural sac cross‐sectional area (81.7%) was explained by dominance and additive genetic influences, with similar heritability estimates across lumbar levels. The genetic correlation of quantitatively assessed LSS and disc bulging was 0.38. There were no shared genetic influences between LSS phenotypes and standing height.
DISCUSSION: This is the first study of which we are aware providing an estimate of the heritability of LSS. The study findings revealed central LSS to be highly genetic and support disc degeneration as one pathway through which genes influence anatomical LSS, but not skeletal size as depicted through standing height.