Updated: 6/24/2021

Cervical Adjacent Segment Disease

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  • summary
    • Cervical Adjacent Segment Disease is the radiographic degeneration of the disc or facets at the caudal or cephalad segment adjacent to a previous cervical surgical fusion construct.
    • Diagnosis can be made with plain radiographs of the cervical spine.
    • Treatment is observation and medical management for patients with mild symptoms. Surgical management is indicated in patients that have failed conservative treatment.
  • Epidemiology
    • Incidence
      • studies have estimated a 1.6 to 2.4% annual incidence of clinically relevant ASD
      • predicted 25.6% ASD rate at 10 years for patients undergoing ACDF
    • Demographics
      • females have a higher risk factor for the development of adjacent segment disease
      • patients under the age of 60 have an increased risk for the development
    • Anatomic location
      • the lowest three segments of the subaxial spine are the most commonly affected (C4-5,C5-6, and C6-7)
        • C5-6 has the highest risk
          • unclear as to whether this level is more prone to natural progression of spondylosis or sensitive to adjacent segment disease
        • C2-3 has the lowest risk
    • Risk factors
      • smoking is the strongest associated patient factor
      • female sex
      • less than 3 segments included in the fusion construct
        • speculated that fewer motion segments remaining reduces the risk of adjacent segment degeneration
      • C5-6 and C6-7 segments are left adjacent to the fusion construct
        • anatomically the most mobile segments of the cervical spine with the highest rates of degeneration
      • preoperative MRI and myelography demonstrating dura mater indentation and disc protrusion, especially at the C5-6 and C6-7 levels
      • no decrease in risk with fusion vs. nonfusion procedures (i.e. posterior foraminotomy, anterior discectomy)
  • Etiology
    • Forms
      • adjacent segment degeneration
        • radiographic changes of degeneration at levels adjacent to a spinal fusion with or without clinical symptoms
        • adjacent level ossification (ALOD)
          • large anterior marginal osteophyte that forms adjacent to a fused construct
          • unclear whether this leads to adjacent segment disease
      • adjacent segment disease (ASD)
        • development of clinical radiculopathy or myelopathy correlating to a motion segment adjacent to the fusion construct
    • Pathophysiology
      • ASD
        • increased motion at the adjacent disc space to compensate for the rigid fused segment
          • supraphysiologic motion, increased stress, and shear strain leads to accelerated degeneration of the disc space
            • increase intradiscal pressure ensues from the compensatory increase in motion and stress
              • increased disc herniation, loss of disc height, osteophyte formation
              • results in cervical foraminal and central canal stenosis which can lead to clinical radiculopathy and myelopathy
          • clinical data does not entirely support this as cervical disc arthroplasty, which preserves spinal segment motion, does not reduce ASD
        • damage to the anterior longitudinal ligament and longus colli muscle at the time of surgery
        • placement of needle marker into incorrect disc space when localizing the operative level
          • potentially minimize
      • ALOD
        • etiology unclear, but speculated to be an inflammatory reaction that occurs from increased proximity of anterior cervical plate to the adjacent disc space
          • plate place within 5 mm of the adjacent disc increases ossification risk
          • heterotopic bone formation in the anterior longitudinal ligament
  • Classification
    • Park and Associates Classification of Adjacent Level Ossification
      Grade 0
      • No adjacent level ossification
      Grade 1
      • Ossification extending less than 50% of the disc space
      Grade 2
      • Ossification extending greater than 50% of the disc space
      Grade 3
      • Complete bridging of the adjacent disc space
  • Presentation
    • Symptoms
      • radiculopathy
        • pain in dermatome corresponding to adjacent motion segment to previous fusion construct
        • motor weakness corresponding to the root level adjacent to a previous fusion construct
      • myelopathy
        • gait instability
        • hand clumsiness
        • urinary abnormalities
    • Physical exam
      • inspection
        • examine surgical wound
      • motion
        • assess flexion-extension, side bending, and rotational motion
          • document which portion of ROM is painful
      • neurological exam
        • assess fine touch sensation in dermatomal pattern
          • patients with sensory changes should be assessed for peripheral nerve compression (e.g. cubittal tunnel and carpal tunnel syndromes)
        • assess motor strength
        • assess reflexes
          • hyperreflexia may suggest myelopathy
      • provocative tests
        • Hoffman's test - flicking the long finger with positive finding being an involuntary ipsilateral thumb IP joint flexion, which suggests myelopathy
        • Spurling's test - provacative test with compression applied to an extended, rotated, and bent neck to the affected side
          • positive finding suggests radiculopathy
        • should abduction test - lifting the arm above the head reduces or relieves symptoms, suggesting radiculopathy
        • L'hermitte sign - forced neck flexion causes electric sensation down entire body suggesting myelopathy
  • Imaging
    • Radiographs
      • recommended views
        • AP
        • lateral
        • flexion-extension views
      • findings
        • disc space narrowing
        • foraminal stenosis
        • posterior osteophytes
        • facet arthropathy
        • anterior marginal osteophyte extending from adjacent vertebral body
      • degenerative changes on radiographs do not always correlate with clinical symptoms
    • CT
      • indications
        • assess for pseudoarthrosis
        • assess for ossification of posterior longitudinal ligament
      • views
        • sagittal and axial views are most useful
    • MRI
      • indications
        • determine if there is foraminal or central canal stenosis at the adjacent segment
      • views
        • axial and sagittal views are most useful
  • Differential
    • Key differential (top 5)
      • pseudoarthrosis
      • progressive degenerative disc disease
      • indolent infection
      • myelopathy at a segment not adjacent to the fused segment
      • radiculopathy at a segment not adjacent to the fused segment
  • Treatment
    • Nonoperative treatment
      • oral medications, activity modifications, physical therapy, +/- brief period of immobilization
        • indications
          • first line of treatment for radiculopathy and mild myelopathy without impairment
        • modalities
          • oral medications
            • NSAIDs
              • use caution in elderly patients due to risk of gastric bleeding
            • gabapentin
              • commonly used for nerve and associated pain
            • narcotics
              • should be avoided for any chronic condition
          • brief period of immobilization
            • some studies show it is beneficial
        • severe myelopathy should be surgically addressed to avoid stepwise deterioration
    • Operative
      • extension of fusion construct to affected levels
        • indications
          • clinical radiculopathy consistent with the adjacent segment that have not responded well to nonoperative treatment
          • myelopathy
        • inclusion of C5-6 and/or C6-7 into the fusion construct
          • highest liklihood of developing ASD
        • place anterior plate >5 mm from the adjacent level
          • reduces the risk of adjacent level ossification
        • including >3 levels has a reduced risk of developing further ASD
      • cervical total disc replacement
        • indications
          • single level involvement
        • as an index procedure does not appear to have an protective effect on ASD
          • large meta-analyses suggest possible decrease in reoperation rates
        • for the treatment of ASD appears equivalent to ACDF
        • reduced risk of adjacent segment ossification compared to anterior cervical plating
  • Technique
    • Oral medications, activity modifications, and physical therapy
      • techniques:
        • NSAIDs, tramadol, tylenol, and gabapentin
          • should be first-line treatment with symptomatic ASD
        • activity modification
          • avoidance of exacerbating activities
            • can reduce pain by avoiding flare ups
          • avoiding down-gazing activities
          • can avise patients against excessive cell phone use, excess computer use, driving with bad posture, etc.
        • physical therapy
          • strengthening of paraspinal muscles
          • improved posture
          • desensitization
          • hot and cold therapy
          • spinal traction
            • manual or mechanical
            • traction allows for expansion of the neuroforamen and reduces nerve compression temorparily
    • Extension of fusion construct to affected levels
      • approach
        • anterior vs. posterior
          • approach dictated by location of pathology (anterior vs posterior) and clinical symptoms (neck pain, unilateral arm pain, myelopathy)
        • anterior right vs. left
          • unless a ENT study performed to evaluation function of RLN, always assume a deficit if prior anterior surgery and use prior approach to protect contralateral nerve
    • Cervical disc replacement
      • technique
        • single level disease adjacent to previous fusion construct
        • performed through anterior approach
          • critical to align the center of rotation in the both the sagittal and coronal planes
  • Complications
    • Progression of ASD
      • following surgical treatment of ASD by extending fusion construct to affected levels further development of symptomatic degeneration of the newly adjacent segment
      • treatment
        • revision surgery to include affected segment
  • Prognosis
    • Despite a high incidence of clinically relevant ASD, the natural history of cervical spondylosis remains high
      • studies have demonstrated radiographic degenerative findings >80% of asymptomatic unfused patients >60 years of age
      • prevalence of radiographic adjacent segment degneration in arthrodesis patients range from 25% to 91%
    • Increased revision surgery rates
      • overall reoperation rates reported between 6.1 to 25.6%
      • annual reoperation rates reported as high as 0.7 to 3.7%

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