Adjacent segment degeneration, also referred to as Adjacent Segment Disease (ASD), is the result of chronic instability in the adjacent segment following Spinal fusion.
Pathophysiology
Adjacent segment degeneration usually results from the combined effects of multiple postoperative mechanical factors and the normal aging process of the Spine. Fusion increases the mechanical load on the adjacent spinal segments.
Adjacent segment degeneration after lumbar fusion
Adjacent segment degeneration after lumbar spinal fusion is detectable on imaging in approximately 70 % of patients 10 years postoperatively and is symptomatic in approximately 25 % of patients[^1].
Adjacent segment degeneration after cervical fusion
Following ACDF surgery, the annual risk of developing cervical adjacent segment degeneration is approximately 2.9 % per year[^2]. Cervical adjacent segment degeneration occurs less frequently after multilevel ACDF than after fusion at a single level[^2].