Adjacent segment disease (ASD) refers to a clinical spectrum of symptomatic degenerative changes in the segments adjacent to a successfully fused spinal segment(s). Adjacent segment pathology (ASP) is a broader spectrum of constellations, symptomatic and asymptomatic, including adjacent segment degeneration, instability, facet hypertrophy, and stenosis.¹ ASP has also been simplistically classified as radiographic ASP (RASP) and clinical ASP (CASP).

ASD is multifactorial and whether it is the product of natural progression of disk degeneration versus iatrogenic surgery related versus patient specific is highly debatable.², ³, ⁴, ⁵, ⁶, ⁷, ⁸, ⁹, ¹⁰, ¹¹, ¹², ¹³, ¹⁴, ¹⁵, ¹⁶, ¹⁷, ¹⁸, ¹⁹, ²⁰, ²¹, ²², ²³, ²⁴ Although ASD seems to often develop in the first immediate segment,²⁵ an equal incidence of ASD in the first and the second segment has been reported as well.²⁶ Many studies report a wide range of incidence of ASD varying from 5.2% to 100%.²⁷,²⁸ Survival analysis by Sears et al.²⁹ reported a prevalence of 22.2% of further surgery in the adjacent segment after 10 years. Similarly, Ha et al. reported a 72% survival without ASD after 1 year of fusion surgery, 63% after 2 years, and 52% after 4 years.³⁰ Moreover, Ahn et al.³¹ reported that the supraadjacent disk was more prone (79.5% of cases) to ASD when compared to the infraadjacent disk (18.8%), and both disks simultaneously (1.8%).

The surgical treatment for ASD via traditional open surgery often follows the same previous approach that can be complicated by the following elements:

This chapter demonstrates the minimally invasive options in dealing with ASD that very often take different route and approach anatomically and conceptually.