Cervical canal stenosis can be acquired (e.g. trauma, discs, and ossification of the posterior longitudinal ligament) or congenital. It refers to narrowing of the spinal canal, nerve root canals, or intervertebral foramina of the cervical spine.
- normal AP diameter is ~17 mm
- relative stenosis 10-13 mm
- absolute stenosis <10 mm
The width of the canal is not, however, constant and progressively decreases as one moves down the cervical spine.
- C1: 23 mm
- C2: 20 mm
- C3-C6: 17 mm
- C7: 15 mm
Canal-to-body ratio of Torg and Pavlov
The standard method of evaluating cervical canal stenosis was historically the sagittal diameter in millimetres, using various cut-offs 1. In two articles published in 1986 and 1987 1,2 Torg and Pavlov et al. introduced the ratio method in order to reduce inter- and intra-observer error caused by variance in magnification and landmarking.
This method uses the ratio of the diameter of cervical canal to the width of the cervical body, with a ratio of <0.8 on the lateral view taken as an indication of cervical stenosis 1.
This ratio is variously referred to as the Torg ratio 3, the Pavlov ratio 3,4, the Torg-Pavlov ratio 5, or the canal-to-body ratio 3.
- 1. Torg JS, Pavlov H, Genuario SE et-al. Neurapraxia of the cervical spinal cord with transient quadriplegia. J Bone Joint Surg Am. 1987;68 (9): 1354-70. Pubmed citation
- 2. Pavlov H, Torg JS, Robie B et-al. Cervical spinal stenosis: determination with vertebral body ratio method. Radiology. 1987;164 (3): 771-5. doi:10.1148/radiology.164.3.3615879 - Pubmed citation
- 3. Blackley HR, Plank LD, Robertson PA. Determining the sagittal dimensions of the canal of the cervical spine. The reliability of ratios of anatomical measurements. J Bone Joint Surg Br. 1999;81 (1): 110-2. Pubmed citation
- 4. Lee MJ, Cassinelli EH, Riew KD. Prevalence of cervical spine stenosis. Anatomic study in cadavers. J Bone Joint Surg Am. 2007;89 (2): 376-80. doi:10.2106/JBJS.F.00437 - Pubmed citation
- 5. Aebli N, Wicki AG, Rüegg TB et-al. The Torg-Pavlov ratio for the prediction of acute spinal cord injury after a minor trauma to the cervical spine. Spine J. 2013;13 (6): 605-12. doi:10.1016/j.spinee.2012.10.039 - Pubmed citation
- 6. Kang Y, Lee JW, Koh YH et-al. New MRI grading system for the cervical canal stenosis. AJR Am J Roentgenol. 2011;197 (1): W134-40. doi:10.2214/AJR.10.5560 - Pubmed citation