Selahaddin AYDEMİR, Orhan TAŞKIN, Ömer AKÇALI, Ahmet KARAKAŞLI, Emin ALICI
Journal of Turkish Spinal Surgery - 2026;37(EK-1):44-48
The aim of this narrative review is to summarize current evidence regarding the epidemiology, pathophysiological mechanisms, and risk determinants of adjacent segment disc degeneration (ASDD) following adolescent idiopathic scoliosis (AIS) surgery and to emphasize the importance of a balance-centered, rather than level-centered, surgical planning strategy for long-term spinal health. Published data were synthesized within a descriptive framework focusing on selection of fusion levels [upper and lower instrumented vertebra (LIV)], coronal and sagittal alignment parameters, TK restoration, pelvic incidence-lumbar lordosis (PI-LL) harmony, and distal disc geometry. The reported incidence of ASDD following AIS surgery increases with follow-up duration, reaching approximately 25% at 10 years and exceeding 30% after 14 years. The development of ASDD is not solely dependent on the level of the LIV. Local and global alignment characteristics-such as LIV translation, adjacent disc wedging, sagittal vertical axis, insufficient LL, and PI-LL mismatch-have been consistently identified as major risk factors. Fusion extending to L4 or more distal levels has been associated with an increased risk of degeneration, particularly in the presence of sagittal imbalance. ASSD following AIS surgery represents a multifactorial process rather than a purely mechanical consequence of fusion length. Global spinal balance, sagittal alignment, and the quality of surgical correction play pivotal roles in long-term outcomes. Strategies aimed at minimizing the risk of degeneration should prioritize achieving near-neutral sagittal balance, adequate TK, and optimal distal segment geometry, while preserving the shortest feasible fusion.
