the lumbar spine (1-3). The narrowing factors could be the intervertebral disc herniation, hypertrophy of ligamentum flavum, hypertrophy of facet joint, spondylolisthesis, osteophyte and ectopic fat tissue (Figures 1,2). Epidemiology The exact prevalence of LSS is still unknown. It is estimated that more than 200,000 adults are affected by LSS in the United States (2), and will rise to 64 million elderly adults by the year 2025 (4). The Framingham Study (5) found that congenital relative LSS was 4.7% and absolute LSS was 2.6%, acquired relative and absolute LSS was 22.5% and 7.3%, respectively, for 60-69 years old population, the relative and absolute LSS was 47.2% and 19.4%, respectively. A population-based study in Japan (6) found that the LSS incidence was increased by age, about 1.7-2.2% in 40-49 years old population, and 10.3%-11.2% in 70-79 years old population. Another study reported the incidence of symptomatic LSS is about 10% (7). The LSS is the most common reason for >65 years old patients to undergo the spinal surgery (8). During 2002

Background: To analyse the characteristics of lumbar paraspinal muscle degeneration in individuals with different Roussouly types.Methods: Eighty patients (20 patients for each Roussouly type) with degenerative lumbar disease were retrospectively enrolled from January 2017 to February 2018. The cross-sectional area (CSA) and percentage of fat infiltration (FI) of the paraspinal muscles at the L1-S1 levels were measured using T2-weighted axial MRI and ImageJ software. The measured data were analysed with independent samples t-tests.Results: Degeneration of the paraspinal muscles of the upper lumbar region was significantly severer in Type 1 than in Type 3, the degrees of paraspinal muscle degeneration of Type 2 appeared to be more evenly distributed in all segments than Type 3, and Type 4 showed severer degeneration in L5-S1 than Type 3.Conclusion: The degree of paraspinal muscle degeneration in each segment was different across the four Roussouly types, but the degrees of degeneration were consistent with the characteristics of degenerative disease within each type.