Neurosurgery notes/Spine/Deformity/Thoracic and lumbar deformity/Adjacent segment disease

Adjacent segment disease

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Thoracic and lumbar deformity

Definition

  • CASP: Clinical Adjacent Segment Pathology
    • Refers to new degenerative changes at spinal segments adjacent to a previous spinal fusion that cause clinical symptoms (such as pain, neurological deficits, or the need for additional treatment or surgery)
    • Symptomatic adjacent segment disease
  • RASP: Radiological Adjacent Segment Pathology
    • Refers to radiographic evidence of degeneration (such as disc space narrowing, osteophyte formation, or facet degeneration) at adjacent spinal segments after fusion, without any clinical symptoms
    • Patients are asymptomatic.
  • Adjacent segment changes
    • Adjacent segment disease:
      • Adjacent segment changes that required revision surgery
      • Wang 2024: Newly developed or aggravated radiological degeneration adjacent to the fused levels caused recurrent clinical symptoms, such as low back and leg pain, numbness, or intermittent claudication during the follow-up period
    • Adjacent segment degeneration
      • Structural changes identified on imaging, such as disc height reduction, Pfirrmann grade advancement, or herniation
      • No revision surgery has occurred yet
    • Difference bewteen ASDisease vs ASDegeneration
        • Aspect
        ASDis (Adjacent Segment Disease)
        ASDeg (Adjacent Segment Degeneration)
        Definition
        Radiographic changes requiring revision surgery (e.g., disc herniation, collapse, stenosis)
        Radiographic degenerative changes without revision surgery (≥2 criteria: ≥25% disc height loss, >10° lordosis change, vacuum phenomenon, ≥1 Pfirrmann grade progression, new herniation)
        Clinical Impact
        Symptomatic, leading to reoperation (median 63 months post-op)
        Often asymptomatic or conservatively managed
        Incidence
        27.9% (24/86 patients)
        7.0% (6/86 patients)
        PROMs Effect
        ODI 28 (IQR 15-42), EQ5D-5L 70 (IQR 53-83)
        ODI 34 (IQR 14-47), EQ5D-5L 60 (IQR 55-85)
        SPA Association
        No link to global/distal parameters
        No link to global/distal parameters

Adjacent segment degeneration (ASD) 

Numbers

  • Risk of ASD after spinal fusion
  • Asymptomatic (radiological presence) ASD: 46%
  • Symptomatic ASD: 30%
  • ASD requiring surgery: < 3%

Pathophysiology

  • increased motion at the adjacent segment → hypermobility of the facet joint → facetal instability and spondylolisthesis.

Risk factors for ASD

  • Kanna 2025:
    • Highly predictive of need for surgical treatment for ASD
      • Diabetes mellitus
      • Radiculopathy
      • Larger facet angle
      • Three classes of ASD:
        • Disc prolapse
        • Intradiscal instability
        • Anterolisthesis

Distal ASD

  • Development or progression of degenerative changes—such as disc degeneration, facet joint arthrosis, spondylolisthesis, or spinal stenosis—at the spinal segment immediately below (distal to) the lowest instrumented vertebra following lumbar spinal fusion surgery.
  • Risk Factors for Distal ASD: Kasliwal 2012
    • Younger patient age:
      • Possibly due to activity level and biomechanical forces.
    • Preoperative disc degeneration:
      • Pre-existing degeneration at the distal (caudal) segment, most frequently at L5–S1, increases the risk.
    • Longer fusion constructs:
      • Fusions extending over several segments, particularly to the lower lumbar levels
    • Circumferential fusions:
      • 360° constructs increase the biomechanical load on distal segments and accelerate degeneration.
    • Selection of fusion level:
      • Stopping a long fusion at L5 rather than extending to the sacrum/pelvis is associated with a higher risk of symptomatic distal ASD, especially if L5–S1 disc is already degenerated

Classification

  • Type 1: Disc prolapse (protrusion/extrusion/sequestration).
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  • Type 2: Intradiscal instability (Vacuum phenomenon/lateral listhesis).
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  • Type 3: Anterolisthesis and facet instability.
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  • Type 4: Retrolisthesis.
    • Posterior translation of one vertebral body over the inferior one by 3 mm, and or angulation 15 degrees as compared to the adjacent level).
    • Retrolisthesis could represent a compensating mechanism for the loss of lordosis after the fusion procedure
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  • Type 5: Stenosis.
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  • Type 6: Combined.
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Evidence

  • Loggia 2025: Short segment fusion that does not respect (Spinopelvic Alignment (SPA): No significant pre- or postoperative differences in global (PI, SS, PT, LL, PI-LL, LPA) or distal lumbar (DL, LDI, PI-DL, DL-PI, ASL)), does not increase the risk of adjacent segment disease
 

Proximal Junctional Kyphosis (PJK)

  • Definition:
    • PJK is primarily a radiographic finding—an abnormal, increased kyphotic (forward-bending) angle at the upper end of a spinal fusion construct, typically at the spinal segments just above the uppermost instrumented vertebra (UIV)
    • Defined by Glattes: Proximal junctional kyphosis is considered present when the
      • PJK angle is superior to 10° AND
      • PJK is at least 10° greater compared its preoperative value
  • Measurement
    • PJK angle measured by the angle between the lower endplate of the upper instrumented vertebra and the upper endplate of the second supra-adjacent vertebrae.
  • Aetiology
    • High construct rigidity
      • Leading to increased junctional stress at adjacent segments.
    • Wrong selection of the upper instrumented vertebra
    • Inadequate contouring of the rods
    • Soft tissue damage above fused levels
    • Mismatching of the kyphosis correction determined by pelvic incidence
  • Clinical Impact:
      • Often asymptomatic
      • But when severe can be painful and unsightly
      • Many cases are stable and do not require surgical intervention.
      • PJK represents a spectrum: from minor, radiographic changes to cases that may begin to develop symptoms.
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  • Prevention
      • Some studies suggest that gradually reducing stress at the proximal level (Soft landing) of the construct could lower PJK rates.
        • Lange et al. found that cerclage wires at the proximal segment reduced rigidity by about 60% compared to all-pedicle screw constructs.
        • Facchinello et al. and Thawrani et al. reported lower stiffness at the upper instrumented level with proximal hooks, reducing force on anchors.
        • Cahill et al. suggested that a transition rod with a proximal decrease in diameter could reduce disc angulation and implant stress.
        • Ohrt-Nissen et al. showed that double transition rods improved kyphosis restoration in AIS surgery, though its effect on PJK rates is not yet known.

Proximal Junctional Failure (PJF)

  • Definition:
    • PJF is a severe, structural complication that represents the end of the PJK spectrum—it involves actual mechanical failure at the proximal junction456.
  • Aka: “topping off syndrome,” “proximal junctional fracture,” or “proximal junctional collapse.”
  • Features of PJF Include:
    • Structural failure: vertebral body fracture (at UIV or the vertebra above), subluxation/dislocation, implant pullout or breakage, or failure of the posterior ligament complex456.
    • Mechanical instability and/or neurological injury.
    • Typically results in the need for revision surgery due to deformity progression, pain, or neurologic decline.
  • Clinical Impact:
    • PJF is usually symptomatic and associated with significant morbidity—patients may have severe deformity, worsening pain, neurologic deficits, and/or loss of function.
    • Almost always requires further surgical intervention.