Biomechanical effects of partial and full L4-L5 disc nucleotomy: a coupled musculoskeletal finite element modeling study

BACKGROUND: Percutaneous disc nucleotomy effectively reduces intradiscal pressure, thereby alleviating pain caused by disc bulging and herniation. However, the resultant loss of nucleus pressure may disrupt the normal load-sharing among spine structures. In the absence of viable in vivo approaches, advanced computational modeling offers insights into the biomechanical mechanisms underlying recurrent post-nucleotomy pain, disc degeneration, and facet joint arthritis. METHODS: A validated musculoskeletal finite element model of the T1-S1 spine was used to investigate the biomechanical effects of full and partial (1 cc nucleus removal) nucleotomies at the L4-L5 disc during upright standing and forward flexion. RESULTS: Partial nucleotomy caused minor to moderate changes at the treated segment that included reductions in the intradiscal pressure, disc shear load, and total ligament force, whereas peak annular stress-strain, disc bulge, facet joint forces, and local muscle forces increased. In contrast, full nucleotomy eliminated the intradiscal pressure, markedly reduced the disc shear load and unloaded the surrounding ligaments but at the cost of a 1.5- to 4.5-fold increase in the L4-L5 facet joint forces, up to 70% higher annular stresses, up to 0.93 mm greater disc bulging, and up to 25% higher local muscle forces. Load bearing shifted from the depressurized nucleus to the facet joints and surrounding annulus, with minimal impact on adjacent segments. CONCLUSIONS: The unintended increase in post-nucleotomy disc bulging may impinge on nearby nerve roots, offering a biomechanical rationale for pain recurrence. Current findings underscore the biomechanical risks of disc depressurization and reinforce the clinical importance of nucleus-sparing and annulus-sealing techniques in nucleotomy planning.