Adjacent Segment Disease¶

Definition¶

Adjacent segment disease (ASD) refers to the development of new degenerative changes at spinal levels immediately above or below a fusion construct. It is the most common long-term complication of spinal fusion, occurring in approximately 25–30% of patients over 10 years.

Pathophysiology¶

Spinal fusion eliminates motion at the fused segment(s), transferring increased mechanical stress to the adjacent mobile segments. This accelerated loading leads to premature disc degeneration, facet hypertrophy, stenosis, and potential instability at the adjacent levels.

Imaging Findings¶

Disc degeneration — Loss of disc height and T2 signal at the level above or below the fusion
Disc herniation — New herniation at the adjacent level
Spinal stenosis — Central or foraminal stenosis at the adjacent level from disc-osteophyte complex, ligamentum flavum hypertrophy, or facet hypertrophy
Spondylolisthesis — New anterolisthesis at the adjacent level from increased stress on the facet joints
Endplate changes — Modic changes at the adjacent level

Location¶

More common above the fusion (cranial adjacent segment) than below (caudal)
Cervical ASD develops faster than lumbar ASD

Clinical Pearl

When evaluating a patient with recurrent symptoms after spinal fusion, always look above and below the construct — adjacent segment disease is more common than hardware failure or pseudarthrosis as a cause of late post-operative symptoms. Motion-preserving alternatives (disc arthroplasty) were developed specifically to reduce ASD, though evidence for this benefit remains debated.

Key Points¶

Most common long-term complication of spinal fusion (25–30% over 10 years)
Results from increased mechanical stress on adjacent mobile segments
More common cranial to the fusion
Disc degeneration, herniation, stenosis, and spondylolisthesis at adjacent levels
MRI evaluates the soft tissues; CT evaluates bony changes
May require extension of the fusion construct

References¶

Gaillard F, et al. Adjacent segment degeneration. Radiopaedia.org. Available from: https://radiopaedia.org/articles/adjacent-segment-degeneration
Saavedra-Pozo FM, Deusdara RAM, Benzel EC. Adjacent segment disease perspective and review of the literature. Ochsner J. 2014;14(1):78-83. PMID: 24688337. Available from: https://pmc.ncbi.nlm.nih.gov/articles/PMC3963057/
Huang X, Cai Y, Chen K, et al. Risk factors and treatment strategies for adjacent segment disease following spinal fusion (Review). Mol Med Rep. 2024;31(2):33. PMID: 39575466. Available from: https://pmc.ncbi.nlm.nih.gov/articles/PMC11605282/
Park P, Garton HJ, Gala VC, Hoff JT, McGillicuddy JE. Adjacent segment disease after lumbar or lumbosacral fusion: review of the literature. Spine (Phila Pa 1976). 2004;29(17):1938-44. PMID: 15534420. Available from: https://pubmed.ncbi.nlm.nih.gov/15534420/
Lee JC, Choi SW. Adjacent segment pathology after lumbar spinal fusion. Asian Spine J. 2015;9(5):807-17. PMID: 26435804. Available from: https://pmc.ncbi.nlm.nih.gov/articles/PMC4591457/
Tobert DG, Antoci V, Patel SP, Saadat E, Bono CM. Adjacent segment disease in the cervical and lumbar spine. Clin Spine Surg. 2017;30(3):94-101. PMID: 27642820. Available from: https://pubmed.ncbi.nlm.nih.gov/27642820/