Introduction: Recent advances in imaging technologies have drawn attention to the endplate, a thin mechanical interface rich in blood and neural supply, and its defects as possible culprits in disc degeneration and back pain. However, inconsistent terminology and unreliable measurement methods have hindered research progress, leading to varied prevalence estimates and conflicting findings regarding factors associated with Endplate Structural Defects (EPSD). Recent efforts in standardizing nomenclature and classification have aimed to address these challenges and enhance research consistency. The study aims to determine the prevalence and distribution of EPSD, including specific phenotypes, and associations with age and body mass index (BMI) in an adult male population.
Methods: Previously collected MRI, age and BMI data for 200 Finnish adult males, 61±7.5 years (range: 50 to 79 years) of age and 26.5±3.4 kg/m2 of BMI from the population-based Twin Spine Study were used. The lumbar MRI acquired on a 1.5T scanner were assessed twice using a standardized classification system for EPSD consisting of phenotypes of Schmorl’s nodes, focal defects, corner defects, and erosion. Assessments were repeated and any conflicts between the two readings were reconciled after reviewing the MRI a third time. Descriptive statistics were calculated to determine prevalence and distribution patterns, and associations were investigated with chi-square and logistic regression.
Results: There was a high prevalence of EPSD (45.6%, n=1087), with erosion (17.6%, n=420) and focal defects (16.2%, n=386) being the most common EPSD phenotypes, while corner defects (1%, n=24) were the least often observed. When all EPSD phenotypes were aggregated, EPSD occurred more at the upper lumbar levels (c2= 41.68, p<0.01) and on the caudal endplate relative to the disc (c2= 9.28, p<0.01), and were associated with age (OR: 1.02, 95%CI: 1.01-1.03, p=0.03) but not BMI (OR: 1.00, 95%CI: 0.98-1.03, p=0.72). However, the trends differed by phenotype. While focal defects and Schmorl’s nodes were more prevalent at the upper lumbar levels, erosion and corner defects were more prevalent at the lower lumbar levels. Age was associated with focal defects (OR: 1.02, 95%CI: 1.00 - 1.03, p=0.02) but not Schmorl’s nodes (OR: 1.01, 95%CI: 0.99 - 1.03, p=0.21). Erosion was associated with age (1.03, 95%CI: 1.014, 1.043, p<0.01) but not BMI (OR: 1.02, 95%CI: 0.98 - 1.05, p=0.34). Conversely, corner defects were associated with BMI (OR: 1.15, 95%CI: 1.03 - 1.30, p=0.02) but not age (OR: 1.01, 95%CI: 0.95, 1.08, p=0.68).
Discussion: EPSD are common among older adult males, and the various EPSD phenotypes may have distinct etiologies based on different associations with age, BMI and location. Our findings support a developmental rather than degenerative origin of Schmorl’s nodes, and the association of corner defects with BMI suggests biomechanical influences. Conversely, erosion and focal defects are associated with aging.