Adjacent Segment Disease (ASD)
The development of pathology at the mobile segment next to a lumbar or lumbosacral spinal fusion has been termed adjacent segment disease. Initially reported to occur rarely, it is now considered a potential late complication of spinal fusion that can necessitate further surgical intervention and adversely affect outcomes. Instrumented lumbar spine surgery is associated with an increased risk of adjacent segment disease (ASD).
- fusion length (especially, three or more levels)
- sagittal malalignment
- facet injury
- advanced age
- prior cephalad degenerative disease
- increased body mass index (BMI)
- preoperative documentation of cephalad degenerative disease (e.g., disc disease, stenosis)
ASD occurred in up to 30% of lumbar instrumented fusions whether performed open or minimally invasively, with or without DS accompanying stenosis. Park et al., however, documented a substantial reduction of ASD 164 months following noninstrumented (5.6% ASD) vs. instrumented lumbar fusions (18.5% ASD). Certainly, in older osteoporotic patients with multiple accompanying comorbid factors (e.g., many requiring prophylactic anti-platelet aggregants including aspirin or anticoagulants), avoidance of instrumentation (e.g., TLIF, PLIF) and alternatively choosing noninstrumented PLF should be strongly considered.
Biomechanical alterations likely play a primary role in causing adjacent segment disease. Radiographically apparent, asymptomatic adjacent segment disease is common but does not correlate with functional outcomes. Potentially modifiable risk factors for the development of adjacent segment disease include fusion without instrumentation, protecting the facet joint of the adjacent segment during placement of pedicle screws,fusion length, and sagittal balance. Surgical management, when indicated, consists of decompression of neural elements and extension of fusion. Outcomes after surgery, however, are modest.