Sajjad Saghebdoust - Department of Neurosurgery, Razavi Hospital, Mashhad, Iran
Reza Zare - Department of Neurosurgery, Razavi Hospital, Mashhad, Iran
Bipin Chaurasia - Department of Neurosurgery, Neurosurgery Clinic, Birgunj, Nepal
Mohammad Moein Vakilzadeh - Cancer Research Center, Mashhad University of Medical Sciences, Mashhad, Iran
Omid Yousefi - Trauma Research Center, Shiraz University of Medical Sciences, Shiraz, Iran
Mohammad Reza Boustani - Department of Neurosurgery, Golestan Hospital, Tehran, Iran

Objectives: Adjacent segment degeneration (ASDe) and adjacent segment disease (ASDi) are potential long-term complications after lumbar fusion with rigid instrumentation. Dynamic fixation techniques (Topping-off) adjacent to the fused segments have been developed to curtail the risk of ASDe and ASDi. The current study sought to investigate whether the addition of dynamic rod constructs (DRC) in patients with preoperative degeneration in the adjacent disc was effective in reducing the risk of ASDi. Methods: A retrospective analysis was performed on clinical data of ۲۰۷ patients with degenerative lumbar disorders (DLD) from January ۲۰۱۲ to January ۲۰۱۹, who underwent posterior transpedicular lumbar fusion (without Topping-off, NoT/O), and posterior dynamic instrumentation with DRC. Clinical and radiological outcomes were evaluated using Oswestry Disability Index (ODI), Visual Analogue Scale (VAS), and lumbar radiographs one, three, and ۱۲ months postoperatively and annually. ASDe was defined as disc height collapse > ۲۰% and disc wedging > ۵. Patients with confirmed ASDe and aggravation of ODI > ۲۰ or VAS score > ۵ at final follow-up were diagnosed as ASDi. The Kaplan-Meier hazard method was used to estimate the cumulative probability of ASDi within ۶۳ months of surgery. Results: Over three years of follow-up, ۶۵ patients in the NoT/O (۵۹.۶%) and ۵۲ cases (۵۳.۱%) in the DRC groups met the diagnostic criteria for ASDe. Furthermore, ۲۷ (۲۴.۸%) patients in the NoT/O group showed ASDi during the follow-up, compared to ۱۴ (۱۴.۳%) cases in the DRC group (P=۰.۰۵۹). Revision surgery was performed on ۱۹ individuals in the NoT/O and ۸ cases in the DRC groups (P=۰.۰۴۸). The Cox regression model identified a significantly decreased risk of ASDi if DRC was used (Hazard ratio: ۰.۲۹; ۹۵% CI: ۰.۱۳-۰.۶). Conclusion: Dynamic fixation adjacent to the fused segment is an effective strategy for preventing ASDi in carefully selected individuals with preoperative degenerative changes at the adjacent level. Level of evidence: II

Adjacent segment disease, Degenerative lumbar spinal disorders, Dynamic fixation, Lumbar instrumentation, Rigid Fixation