Summary Lumbar adjacent segment degeneration (ASD) is a common condition caused by increased mechanical stress and altered biomechanics at adjacent segments following lumbar fusion surgery, leading to progressive disc degeneration, facet arthropathy, and spinal instability The condition typically presents in adult and elderly patients with progressive low back pain, radicular symptoms, neurogenic claudication, and potential segmental instability Treatment typically follows a conservative course initially with physical therapy, oral medications, and selective nerve root injections. In refractory cases, surgical treatment in the form of spinal fusion with or without revision of prior surgical levels may be indicated Epidemiology Incidence radiographic ASD has an incidence of 36-84% ASD requiring surgery has an incidence of 0-24% bimodal incidence early ASD is likely due to surgical or biomechanical factors late ASD is likely due to the natural course of disease Demographics typically affects patients >50 y/o slight male predominance Location cranial or caudal levels to prior fusion progressive degeneration of the intervertebral disc, spondylosis, and facet arthropathy can lead to lateral recess, neuroforaminal, and spinal canal stenosis Risk factors prior lumbar fusion surgery loss of lumbar lordosis (PI-LL mismatch) login to view 1 more bullet high pelvic incidence poor sagittal balance injury to the adjacent segment facet joint during index surgery host factors age obesity smoking pre-existing disc degeneration at the adjacent level high postoperative demand Etiology Pathophysiology increased stress and strain at the adjacent motion segment lead to advanced degeneration increased facet loading and disc pressure cell biology increased inflammatory mediators lead to accelerated degeneration login to view 3 more bullets Pathoanatomy age-related disc dehydration annular tears facet hypertrophy ligamentum flavum hypertrophy Genetics multifactorial inheritance pattern potential involvement of MMPs, COL9A2, COL11A1 Associated conditions medical osteoarthritis osteoporosis orthopaedic adult spinal deformity neurogenic claudication radiculopathy Classification No formal classification of thoracolumbar adjacent segment disease Classification based on etiology Etiology Degenerative Degenerative disc disease; spondylosis Neurologic Herniated nucleus pulposus; stenosis Instability Spondylolisthesis; rotatory subluxation Deformity Scoliosis; kyphosis Complex Fracture; infection Combined Variable combinations Classification based on symptomatology Asymptomatic vs. Symptomatic Adjacent segment degeneration Radiographic evidence of adjacent segment degeneration without symptoms Adjacent segment disease Radiographic evidence of adjacent segment degeneration with symptoms including axial back pain, radicular symptoms, and/or neurologic symptoms Presentation History History of lumbar arthrodesis procedure New or worsening symptoms at adjacent levels Symptoms common symptoms low back pain radiculopathy neurogenic claudication rare symptoms cauda equina syndrome Physical exam inspection postural imbalance prior approaches range of motion restricted flexion or extension neurologic numbness or weakness diminished reflexes critical to correlate clinical exam with imaging findings Imaging Radiographs recommended views upright scoliosis full-spine series lumbar flexion and extension radiographs findings disc space narrowing osteophytes endplate sclerosis static or dynamic instability on flexion-extension radiographs CT indications determine whether prior lumbar fusion was successful rule out pseudoarthrosis MRI indications progressive or worsening symptoms in the setting of prior lumbar fusion findings spinal stenosis foraminal stenosis ligamentum flavum hypertrophy and/or facet arthropathy facet effusion login to view 1 more bullet Studies Labs ESR/CRP rule out infection if suspected EMG/NCS indicated in patients with unclear neurologic symptoms identify the neurologic level of nerve root compression correlate with imaging findings Differential Adjacent segment degeneration/disease Pseudoarthrosis Proximal junctional kyphosis/acquired adult spinal deformity Treatment Nonoperative observation +/- physical therapy indications login to view 2 more bullets outcomes login to view 2 more bullets Operative extension of lumbar fusion to affected levels indications login to view 3 more bullets techniques login to view 5 more bullets revision of prior lumbar fusion with corrective osteotomy indications login to view 3 more bullets techniques login to view 3 more bullets goals login to view 6 more bullets outcomes login to view 1 more bullet Techniques ALIF approach anterior approach to lumbar spine login to view 2 more bullets anterior longitudinal ligament incised to access the intervertebral disc technique disc is removed and endplates are prepared with removal of cartilage interbody cage is filled with bone graft or bone substitute and impacted, achieving lordotic correction can be performed in isolation or followed by posterior decompression and/or instrumentation outcomes able to achieve a greater lordotic correction than TLIF Lateral interbody fusion approach minimally invasive approach blunt dissection anterior to psoas muscle and posterior to retroperitoneum lumbar plexus at risk (runs along psoas muscle) technique correct level is confirmed, annulotomy performed, and disc is meticulously prepared interbody cage is placed with bone graft or bone substitute TLIF approach posterolateral approach to lumbar spine login to view 2 more bullets access to the intervertebral disc is achieved through Kambin's triangle login to view 4 more bullets technique meticulous disc preparation and removal unilateral or bilateral TLIF cage insertion Corrective osteotomy Smith-Peterson osteotomy (SPO) indications login to view 3 more bullets techniques login to view 2 more bullets pedicle subtraction osteotomy (PSO) indications login to view 3 more bullets technique login to view 2 more bullets complications login to view 3 more bullets vertebral column resection (VCR) indications login to view 1 more bullet required for correction of up to 45° Complications Postoperative anemia, blood loss Infection Nerve injury Pseudoarthrosis Proximal junctional kyphosis Progression of ASD