Updated: 3/21/2020

Cervical Adjacent Segment Disease

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Introduction
  • Overview
    • radiographic degeneration of the disc or facets at the caudal or cephalad segment adjacent to a fusion construct
    • treatment is directed at symptomatic patients with conservative measures initially utilized
      • fusion of the affected segments or cervical disc replacement can be performed in patients that have failed conservative treatment
  • Definition
    • 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
  • 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
    • 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
  • 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
  • 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%
Classification
 
 Park and Associates Classification of Adjacent Level Ossification
Grade 0  • No adjacent level ossifcation
Grade 1  • Ossification extending less than 50% of the disc space

Grade 2  • Ossification exending 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 extension 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 psuedoarthrosis
      • 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 degemerative 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
 

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