Long-Term Radiographic Outcomes of Dynesys Dynamic Stabilization in Lumbar Degenerative Disease: A 5-Year Retrospective Cohort Study

Background Dynamic stabilization systems, such as Dynesys/Dynesys Top Loading (DTL), are developed to preserve segmental motion and mitigate adjacent segment degeneration (ASD) as alternatives to spinal fusion. However, long-term evidence supporting their effectiveness in maintaining a range of motion (ROM) remains limited. Methods In this retrospective study, 44 patients undergoing lumbar dynamic stabilization were evaluated using the Dynesys/DTL system, with ≥ 5 years of follow-up. Radiographic assessments included dynamic flexion–extension radiographs at different postoperative time points. Segmental and whole-spine ROM were measured, while the incidence of ASD was recorded. Results Segmental ROM partially recovered by 6 months (48% of baseline) but progressively declined, preserving only 28% at 2 years and 20% at 5 years (p < 0.05). In contrast, whole-spine ROM remained well preserved throughout the follow-up period, suggesting compensatory motion at nonoperated levels. ASD developed in 17 patients (38.6%), who demonstrated significantly lower segmental ROM preservation at 5 years than those without ASD (9% vs. 27%, p = 0.003). Among the factors analyzed, only sex exhibited a trend toward greater ROM loss, with female patients showing a greater decline. Conclusion Despite achieving early motion preservation, Dynesys/DTL systems do not maintain segmental ROM beyond 5 years and do not consistently prevent ASD. These findings indicate that Dynesys/DTL may function more as a semi-rigid fixation construct than as a truly dynamic stabilization, highlighting the need for improved biomechanical design and further long-term studies.