Biomechanical Rationale for Varia‐Tions in the Prevalence of Low Back Pain and Schmorl's Nodes Found in Different Patterns of Multi‐Level Disc Gegeneration

Abstract

INTRODUCTION: Previously published re‐ search has shown that contiguous multi‐ level disc degeneration (CMDD) has been noted to significantly increase the likelihood of severe low back pain in comparison to skipped levels of disc degeneration (SLDD). Clinical studies have also shown that Schmorl's nodes are more common in pat‐ terns of SLDD than with CMDD and that such nodes increase the likelihood of disc degeneration. As such, the purpose of this study was to utilize a nonlinear finite ele‐ ment model of the lumbar spine to investi‐ gate various patterns of multi‐level disc degeneration and to investigate correla‐ tions with clinical incidence of low back pain and Schmorl's nodes. METHODS: A previously validated hexahe‐ dral finite element model of a T12‐S1 lum‐ bar spine was adapted to simulate the 13 cases shown in the figure. The degenerated discs were modeled based on published material properties. Biomechanics data for each SLDD and CMDD case were compared against each other, against the single‐level degeneration cases, and against the control (non‐degenerated) case. These results were also compared with data from a large co‐ hort of patients (the Hong Kong Study) re‐ porting low back pain and MRI prevalence of Schmorl’s nodes. RESULTS: The finite element study indicated that CMDD resulted in higher ligament stresses, pedicle stresses, and facet contact forces as compared to the SLDD conditions. Interestingly, comparisons of sequential patterns of disc degeneration (control vs single level degeneration vs contiguous 2 level degeneration vs skipped level 3 level degeneration) showed that the addition of a skipped‐level degenerated disc to a con‐ tiguous level degenerated case actually de‐ creased stresses. Vertebral strain energy was also shown to be a possible predictor in the development of Schmorl’s nodes. DISCUSSION: These results provide insight into the variation in clinical studies of symp‐ tomatic and asymptomatic multi‐level disc degeneration.