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
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- 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
- 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
- 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
C3 Vertebrae Image
Note: The SAC is also commonly used with the Torg ratio to determine
the presence or degree of severity of cervical spine stenosis.
References
Editors: Anthony J. Busti, MD, PharmD, FNLA, FAHA
