Adjacent segment disease

 Adjacent segment degeneration

Radiographic change in the intervertebral discs

adjacent to the surgically treated spinal level

hypermobility of the unfused joint


Spinal stenosis, HNP, instability

Adjacent segment Disease

Adjacent segment disease = Symptomatic ASDeg

Transition syndrome


Annual incidence rates 

6% for adjacent segment degeneration

2% for ASD



Biomechanics

Stress on adjacent segment of the fusion

Increase loading on vertebral endplate of proximal segment

Increase of intradisc pressure → Disc degeneration


Malalignment and hypolordosis

increase the load across implants

increase posterior shear and laminar strain at adjacent levels


Damage on posterior stabilizing paraspinous musculature

multifidus


Biomechanics

Risk factors for symptomatic ASD

Meta-analysis of 16 studies involving 3,553 patients

Risk factors

Demographics

body mass index ↑


Preoperative

sagittal plumb line anterior shift

lumbar lordosis(LL)↓

adjacent disc degeneration, adjacent disc height↓


Postoperative

facet joint violation

sagittal plumb line anterior shift

lumbar lordosis(LL)↓

lumbopelvic mismatch(PI-LL)↑, pelvic incidence(PI)↑, pelvic tilt(PT)↑

Operation

Decompression + Fusion

Open posterior laminectomy + fusion extension

PLF, PLIF

Anterior approach

DLIF, OLIF


Decompression alone

Decompressive laminectomy

Minimal invasive approach

LLIF vs PLF for treatment of ASD

47 patients


OP time, blood loss↓ on LLIF group

Lordosis, disc height improvement ↑ on LLIF group

Patient-reported outcome : equivalent

Decompression alone vs Decompression + fusion

Can maintain segmental stability

Cost-effective and less morbid 

Risk of destabilizing the spine


→ Use of decompression alone on ASD without instability


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