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SAC Radiographic Measurement for Spinal Stenosis

Summary:

SAC stands for "Space Available for the Cord" and is calculated by subtracting the sagittal diameter of the spinal cord from the sagittal diameter of the spinal canal. 

  • The sagittal spinal cord diameter is measure from the posterior wall of the vertebral body (half way down) to the laminar line.
  • The sagittal diameter of the spinal cord usually comes from measurement on an MRI.

SAC Measurements of:

  • > 18 mm = normal
  • 15 to 17 mm = possible abnormality
  • < 14 mm = concerning for spinal cord compression

SAC Measurement

    C3 Vertebrae Image



    • Line (a) = sagittal diameter of the spinal canal
    • Line (b) = sagittal diameter of the vertebral body
    • Gray Dashed Oval = represents the sagittal diameter of the spinal cord that comes from an MRI


    Note:
    The SAC is also commonly used with the Torg ratio to determine the presence or degree of severity of cervical spine stenosis.

    Related Content

    To see related content please select an item below:

     

    Torg Ratio

    References
    1. Herzog RJ et al. Normal cervical spine morphometry and cervical spinal stenosis in asymptomatic professional football players. Plain film radiography, multiplanar computed tomography, and magnetic resonance imaging. Spine 1991;16(6 suppl):S178-86. PubMed
    2. Tiemey RT et al. Head position and football equipment influence cervical spinal cord space during immobilization. J Athl Train 2002;37(2):185-189.  PubMed

     

    Editors & Reviewers

    Editors:  Anthony J. Busti, MD, PharmD, FNLA, FAHA
    Last Updated:  June 2015

Editors:  Anthony J. Busti, MD, PharmD, FNLA, FAHA