Dynamic versus rigid lumbar fixation: A multimodal comparison of paraspinal muscle morphology, electromyography, and functional outcomes.

Abstract

This cross-sectional study compared the structural, functional, and neuromuscular outcomes of dynamic versus rigid lumbar fixation. A multimodal framework integrating radiological, morphological, electrophysiological, and patient-reported measures was employed. The primary aim was to determine whether dynamic stabilization systems better preserve paraspinal muscle integrity and neuromuscular function than rigid constructs, while also reducing adjacent segment degeneration (ASD) and disability. Seventy-five participants were allocated to three groups: dynamic rod group (DRG, n = 25), rigid rod group (RRG, n = 25), and healthy controls (CG, n = 25). Paraspinal muscle volumes were assessed via MRI, and ASD was graded using Pfirrmann and Weishaupt classifications. Functional outcomes included Oswestry Disability Index (ODI), Nottingham Health Profile (NHP), McGill torso endurance tests, and surface electromyography (sEMG) normalized to maximum voluntary contraction. The DRG demonstrated significantly greater multifidus and erector spinae volumes (p < 0.001, d ≈ 1.0), superior core endurance (p < 0.001), and lower ODI scores (p = 0.027, d = 0.64) compared to the RRG. sEMG showed higher normalized contraction activity in DRG (p < 0.001, d = 1.10) and elevated resting activity in RRG (p = 0.012, d = 0.73). Radiological findings revealed more severe disc degeneration in RRG (p = 0.018). Time since surgery correlated with progressive degeneration and muscle atrophy, more pronounced in RRG (e.g., r=-0.63, p < 0.001). Dynamic lumbar fixation is associated with better preservation paraspinal muscle morphology, shows better neuromuscular activation profiles, and slows degenerative progression compared with rigid systems. These findings underscore the clinical importance of motion-preserving implants and highlight the role of early rehabilitation in optimizing postoperative recovery and long-term functional outcomes.