Torg-Pavlov Ratio for Cervical Stenosis
Definition and Measurement
What it measures. The Torg-Pavlov ratio, commonly called the Torg ratio, is the sagittal diameter of the cervical canal divided by the sagittal diameter of the vertebral body. Both are taken from a neutral lateral cervical radiograph, so the result is dimensionless.
Torg, Pavlov and colleagues devised it to identify athletes with developmental stenosis at risk of transient cervical neurapraxia. It was described in the 1986 transient-quadriplegia series and the 1987 Pavlov ratio paper.
Taking the measurement. The ratio is measured at each cervical level from C3 to C7, at the mid-height of the vertebral body on a true lateral.
- Landmark
- From the midpoint of the posterior aspect of the vertebral body to the nearest point on the spinolaminar line
- Measurement Method
- Shortest distance on a true lateral at the level of the mid-vertebral body
- Landmark
- Anteroposterior width of the vertebral body at its midpoint
- Measurement Method
- Distance from the anterior cortex to the posterior cortex at the mid-height of the body
- Landmark
- Canal diameter divided by body diameter
- Measurement Method
- Normal is approximately 1.0 or greater; stenosis suggested when less than 0.8
Because numerator and denominator are measured on the same radiograph, magnification error cancels out. That is a genuine strength over absolute canal diameter measurements.
Interpretation and Thresholds
Reading the number. Normal is approximately 1.0 or greater, and a ratio less than 0.8 suggests developmental cervical stenosis. The ratio is a radiographic measurement, not a diagnosis.
- Interpretation
- Normal canal dimensions
- Clinical Significance
- No evidence of developmental stenosis
- Interpretation
- Borderline
- Clinical Significance
- Assess for acquired stenosis (disc osteophyte, ligamentum flavum buckling); correlate clinically
- Interpretation
- Suggests developmental stenosis
- Clinical Significance
- High sensitivity for stenosis but low PPV for neurological injury; proceed to MRI
A low Torg ratio does not mean the athlete cannot play sport. The ratio is a screening trigger, not a disqualification criterion, and it should not be used in isolation: clinical correlation and MRI are required. Multiple large cohort studies in professional American football players have shown that the majority of athletes with ratios below 0.8 are entirely asymptomatic.
Developmental Stenosis versus Spondylotic Stenosis
Why the distinction matters. Developmental and acquired (spondylotic) stenosis have different implications for management and prognosis. The ratio is also used in the work-up of cervical spondylotic myelopathy when developmental stenosis is suspected, and a low ratio across multiple levels with minimal degenerative change favours developmental stenosis.
- Developmental Stenosis
- Congenitally short pedicles and laminae reducing the canal area from birth
- Spondylotic Stenosis
- Acquired narrowing from disc degeneration, osteophytes, ligamentum flavum buckling, and facet hypertrophy
- Developmental Stenosis
- C3 to C5, most commonly C3 to C4 or C4 to C5 (often multiple levels)
- Spondylotic Stenosis
- C5 to C6 and C6 to C7 first (follows disc degeneration)
- Developmental Stenosis
- Low across multiple levels (less than 0.8)
- Spondylotic Stenosis
- May be normal initially; ratio drops as osteophytes narrow the canal
- Developmental Stenosis
- May present young, especially after trauma or in athletes
- Spondylotic Stenosis
- Typically patients over 50 years with progressive myelopathy or radiculopathy
- Developmental Stenosis
- Short pedicles, narrow canal, normal disc heights initially
- Spondylotic Stenosis
- Disc space narrowing, anterior and posterior osteophytes, ligamentum flavum thickening
The Pavlov (Torg) ratio is specifically designed to detect developmental stenosis. In a spondylotic spine, anterior osteophytes enlarge the measured vertebral body diameter, increasing the denominator and artificially lowering the ratio, so the ratio can overestimate the true degree of stenosis. MRI is the gold standard for acquired stenosis.
Transient Cervical Neurapraxia and Cord Injury Risk
What it is. Transient cervical neurapraxia, also called cervical cord neurapraxia (CCN), is a temporary episode of bilateral sensory change (burning, numbness, tingling), motor weakness, or both. It is triggered by hyperextension or hyperflexion of the cervical spine and lasts seconds to minutes, occasionally up to 24 to 48 hours.
Mechanism. In a stenotic canal, hyperextension buckles the ligamentum flavum inward and compresses the cord against the posterior vertebral body or osteophyte complex. The transient nature is thought to reflect a reversible conduction block rather than structural cord damage.
The ratio and neurapraxia. Torg and Pavlov's original work found that athletes who had experienced transient neurapraxia had significantly lower mean Torg ratios than uninjured controls. Subsequent large studies in professional football players, most notably by Herzog et al. and Odor et al., showed that a low ratio is extremely common in asymptomatic players. Younger age and contact sport, in an athlete with developmental stenosis, are risk factors.
Catastrophic injury. Permanent quadriplegia from a cervical cord injury in sport is typically associated with axial loading (spearing), often in combination with flexion or extension. Developmental narrowing in a stable spine does not predispose to it (Torg 1996), and the ratio alone has insufficient predictive value to serve as a screening test for it. MRI-confirmed cord compression or myelomalacia is a far stronger indicator.
Return to play. The decision integrates the full clinical picture: the number of episodes of neurapraxia, the duration of the deficits, and the athlete's sport and position. It also rests on MRI, with the presence or absence of cord signal change, the canal area and the space available for the cord. It is not made on the Torg ratio in isolation.
Grading an episode. Torg's classification describes CCN by its clinical pattern, its distribution and its duration:
- Pattern: plegia (motor), paraesthesia (sensory), or both
- Distribution: all four limbs, upper limbs only, or lower limbs only
- Grade: I under 15 minutes, II 15 minutes to 24 hours, III more than 24 hours
Recurrence. Recurrence after return to play is common, about 56% (Torg 1997). It is inversely related to the canal diameter and the space available for the cord, which is useful for counselling, though the CCN grade itself does not predict recurrence.
Measuring the canal on MRI. The space available for the cord (SAC) is the canal diameter minus the cord diameter, and a reduced SAC predicts neurapraxia better than the bony ratio. Developmental stenosis is defined on MRI by a sagittal canal diameter under about 13 mm, with critical or absolute stenosis under about 10 mm.
Functional stenosis. Cantu's "functional spinal stenosis" is the more relevant modern concept: loss of the protective CSF cushion around the cord, or actual cord deformation, on MRI or CT-myelography, regardless of the bony Torg ratio. No CSF around the cord predicts risk far better than a low ratio, and it is what drives real decisions.
Limitations of the Torg Ratio
Low positive predictive value. The original Torg and Pavlov study reported a high sensitivity for neurapraxia, and Torg's 1996 study put a ratio of 0.8 or less at 93% sensitive but only 0.2% predictive. Subsequent studies of professional football players found that over 30 to 50 percent of asymptomatic players have ratios below 0.8, so the ratio is a poor screening tool for sport restriction.
Big bodies, normal canals. In large athletes the vertebral body diameter (the denominator) may be increased, which reduces the ratio even when the canal itself is of normal absolute diameter. This is one reason the ratio is so low in many asymptomatic football players.
Bone only. The ratio measures bony dimensions and cannot detect disc herniation, ligamentum flavum hypertrophy or ossification of the posterior longitudinal ligament (OPLL), all of which further reduce the effective canal area.
Supplanted by MRI. Modern practice uses MRI to assess the true sagittal canal diameter, the cord cross-sectional area and signal change. The Torg ratio remains useful as an initial screening tool, or in settings where MRI is not immediately available.
Guidelines, Registries and Global Practice
There is no single universal guideline governing the use of the Torg ratio in sport participation screening; practice varies by country and sporting body.
- United States (NCAA and professional sport): The Torg ratio is no longer recommended as a standalone screening tool for cervical stenosis in collegiate or professional athletes. The NCAA Sports Medicine Handbook and team physician consensus statements advise that return-to-play decisions following cervical cord neurapraxia be based on clinical evaluation, MRI findings (cord signal, canal dimensions, space available for the cord), and the number and severity of episodes.
- AO Foundation / international spine practice: The Torg ratio is acknowledged as a historical screening measurement but is considered supplanted by MRI for any clinical decision-making. Developmental stenosis is defined on MRI by a sagittal canal diameter of less than 13 mm (or less than 10 mm by some authors) at any cervical level.
- Global practice variation: In some countries with limited access to MRI, the Torg ratio on lateral radiographs remains a practical initial screening step. In high-resource settings, MRI is obtained directly when cervical stenosis is suspected clinically.
- Key consensus: Across all major sporting bodies and spine societies, the ratio should not be used in isolation to restrict or disqualify athletes from sport. The clinical history, neurological examination, and MRI findings drive management decisions.
- Absolute contraindications to contact sport — a persistent neurological deficit; MRI cord signal change / myelomalacia; cord compression with no functional reserve (no CSF cushion around the cord, or frank cord deformation); ligamentous instability; or symptoms outlasting roughly 36 hours or multiple recurrent episodes with associated MRI changes.
- Relative contraindications / shared decision — a single, brief, fully-resolved episode with a normal MRI and a stable spine may return after counselling, accepting that recurrence is common (~56%) when the canal is narrow; recurrent episodes push firmly toward stopping.
- Prevention, not screening — catastrophic permanent quadriplegia comes from axial loading (head-down "spear" tackling with the neck slightly flexed, straightening the lordosis), which is why spear-tackling is banned — a far more effective intervention than any ratio-based screening.
Viva practice
Canal ÷ BodyHow to measure the Torg ratio
Hook:Both measurements come off the SAME lateral film, so magnification error cancels out — a genuine strength of the ratio.
MUSCLEWhy the Torg ratio is low in athletes (not always stenosis)
Hook:A low ratio in a muscular athlete is often physiological — confirm true stenosis on MRI before restricting play.
Exam Viva
Practise clinical reasoning and management decisions out loud
“A 22-year-old professional rugby player presents after an episode of bilateral arm tingling and weakness lasting 30 seconds following a tackle. He recovered fully within minutes. Lateral cervical radiographs show a Torg ratio of 0.65 at C4. How would you investigate and counsel this player?”
“A 58-year-old woman presents with progressive gait difficulty and clumsy hands over six months. Lateral cervical radiographs show a Torg ratio of 0.6 at C3 to C5 with minimal degenerative change. What is the diagnosis, how would you investigate, and what are the surgical principles?”
Exam cheat sheet
Definition and measurement
- Torg ratio equals sagittal canal diameter divided by vertebral body sagittal diameter on lateral radiograph
- Measured from C3 to C7 at the mid-vertebral body level
- Normal is approximately 1.0 or greater; less than 0.8 suggests developmental stenosis
Clinical significance
- High sensitivity for stenosis but low positive predictive value for neurological injury
- Many asymptomatic elite athletes have ratios below 0.8 due to enlarged vertebral bodies
- Should not be used alone to restrict or disqualify athletes from sport
- MRI is the gold standard for assessing true canal dimensions and cord compression
Transient cervical neurapraxia
- Bilateral sensory or motor changes after hyperextension or hyperflexion, lasting seconds to hours
- Torg classification: Type (sensory, motor, or both) and Grade (I under 15 min, II 15 min to 24 hrs, III over 24 hrs)
- Return-to-play based on clinical grade, MRI findings, and number of episodes
- Cord signal change (myelomalacia) on MRI is an absolute contraindication to contact sport
Developmental versus spondylotic stenosis
- Developmental: congenitally short pedicles, low Torg ratio across multiple levels, C3 to C5
- Spondylotic: acquired from disc degeneration and osteophytes, C5 to C7, ratio may be normal initially
- Developmental stenosis predisposes to earlier myelopathy with even mild degenerative change
Evidence
Neurapraxia of the cervical spinal cord with transient quadriplegia
- Defined transient cervical cord neurapraxia and introduced the canal-to-vertebral-body (ratio) method to detect developmental stenosis.
- In 24 affected athletes the ratio was statistically lower than in 49 controls (~1.0 or more); a ratio under 0.80 indicated significant stenosis (p<0.0001).
- An NCAA survey found ~1.3 per 10,000 football athletes had a history suggestive of cervical cord neurapraxia.
Normal cervical spine morphometry and cervical spinal stenosis in asymptomatic professional football players
- Compared plain radiography, multiplanar CT and MRI of the cervical spine in asymptomatic professional football players.
- The Torg ratio had high sensitivity but poor positive predictive value, generating a large number of false positives.
- Proposed an algorithm using absolute canal dimensions (CT/MRI) rather than the ratio for evaluating stenosis in athletes.
Cervical cord neurapraxia: classification, pathomechanics, morbidity, and management guidelines
- 110 cases of cervical cord neurapraxia (CCN); established a classification system and a computerised MRI measurement technique.
- CCN was NOT associated with permanent neurological injury; the overall recurrence rate after return to play was 56%.
- Recurrence risk was inversely correlated with sagittal canal diameter and the canal/body ratio (p<0.001), useful for counselling — but the CCN grade and MRI/X-ray disease did not predict recurrence.
The ratio and the transient-quadriplegia entity are from Torg et al. 1986 (J Bone Joint Surg Am 1986;68(9):1354-70; PMID 3782207). The high-sensitivity/low-PPV finding is quantified by Herzog et al. 1991 (DOI 10.1097/00007632-199106001-00001) and Torg et al. 1996 (sensitivity 93%, PPV 0.2%; DOI 10.2106/00004623-199609000-00003). The CCN classification and 56% recurrence are from Torg et al. 1997 (DOI 10.3171/jns.1997.87.6.0843), and the 0.7 cutoff for cord injury after minor trauma from Aebli et al. 2013 (DOI 10.1016/j.spinee.2012.10.039).