Instability



Instability


Jeffrey S. Ross, MD









(Left) Wide laminectomy destabilizing spine is shown. Flexion lateral radiograph demonstrates grade 2 anterolisthesis image at L3-4 that improves on extension (see next image). (Right) Lateral radiograph in extension shows grade 2 anterolisthesis, which is mildly reduced image compared to the flexion deformity. Note the widening of the anterior disc space with extension image.






(Left) Sagittal T1WI MR in an adolescent shows severe spondylolisthesis of L5 on S1, with disc degeneration and extensive type I degenerative endplate changes image. (Right) Sagittal T1WI C+ MR shows progressive deformity and retrolisthesis image at operative site following extensive posterior debridement for infection, marked thecal sac compression from the deformity and residual phlegmon image, and extensive dorsal pseudomeningocele image.



TERMINOLOGY


Synonyms



  • Spine instability (SI), segmental instability, abnormal spinal motion, degenerative instability


Definitions



  • Loss of spine motion segment stiffness, when applied force produces greater displacement than normal, with pain/deformity


IMAGING


General Features



  • Best diagnostic clue



    • Deformity that increases with motion and over time


  • Location



    • Any spinal motion segment (composed of 2 adjacent vertebrae, discs, and connecting spinal ligaments)


  • Size



    • Displacement may vary from few mm to width of vertebral body


  • Morphology



    • Displacement of vertebral body with respect to adjacent body


  • Stabilizing anatomic structures



    • Ligaments



      • Anterior longitudinal ligament



        • Resists hyperextension


      • Posterior longitudinal ligament


      • Intertransverse ligaments



        • Connect neighboring transverse processes


      • Interspinous ligaments



        • Resist hyperflexion


      • Facet capsule


      • Ligamentum flavum


    • Intervertebral disc



      • Main stabilizer of lumbar and thoracic spine


    • Muscular attachments



      • Both global (rectus and abdominal muscles) and local paraspinal muscle groups


Radiographic Findings



  • Radiography



    • Various parameters used to measure degenerative instability by plain films



      • Dynamic slip > 3 mm in flexion/extension


      • Static slip ≥ 4.5 mm


      • Angulation > 10-15° suggests need for surgical intervention


    • Traction spurs


    • Vacuum phenomenon


Fluoroscopic Findings



  • Increased motion with flexion/extension or translation


CT Findings



  • NECT



    • Nonspecific findings of degenerative disc disease ± spondylolisthesis


MR Findings



  • T1WI



    • Anterolisthesis, retrolisthesis, lateral translation


    • Nonspecific changes of degenerative disc disease


    • Controversial as to role in defining instability: Type I degenerative endplate changes


  • T2WI



    • Loss of disc signal ± disc space height


  • STIR



    • Type I endplate changes may be more evident on this sequence


  • T1WI C+



    • Nonspecific enhancement of disc due to degenerative disc disease


    • Enhancement of type I degenerative endplate changes


Imaging Recommendations



  • Best imaging tool



    • Flexion-extension plain films


  • Protocol advice



    • MR findings useful as secondary tool for degeneration, endplate changes, stenosis, and herniation


DIFFERENTIAL DIAGNOSIS


Pseudoarthrosis



  • Abnormal low T1 signal extending through disc, posterior elements, and ligaments


Infection



  • Endplate destruction, disc T2 hyperintensity


Tumor



  • Enhancing soft tissue mass


Postoperative



  • Following multilevel laminectomy or facetectomy


PATHOLOGY


General Features

Sep 22, 2016 | Posted by in GENERAL RADIOLOGY | Comments Off on Instability
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