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Acta Ortopédica Brasileira

Print version ISSN 1413-7852On-line version ISSN 1809-4406

Acta ortop. bras. vol.10 no.4 São Paulo Oct./Dec. 2002 

Morphometry of the spinal canal at cervical region in asymptomatic military young men


Morfometria do canal vertebral no segmento cervical em militares jovens assintomáticos



Augustin MalzacI; Tarcísio Eloy Pessoa de Barros FilhoII

IPost-graduate student
IIAssociate Professor and Director of Spine Surgery Service

Address for correspondence




Spinal canal measurements obtainned from radiographic imaging studies are an integral part of diagnostic evaluation of cervical spine stenosis. Before abnormal spinal morphometry can be determined, it is first necessary to establish normal values for the specific patient population being evaluated. Cervical spinal canal stenosis increase risk of quadriplegia after "minor trauma" in the head or neck, mainly in athletes who participate in contact or collision sports. Prospective and random selection of 500 plain film of the lateral cervical spine in young militaries population in age group 18-20 years old. Those were performed a hundred set of film were for each geographic region, including Manaus, Recife, São Paulo, Porto Alegre and Campo Grande. The first part of this study established normal values for cervical morphometry. The second part determined the most accurate screenning method for detecting cervical spinal stenosis. Normal spinal canal mean value for C3 was 18,27mm, C4 17,98mm, C5 18,33mm and 18,76mm in C6. The TORG ratio was evaluated as a method to detect significant cervical spinal stenosis and was shown to have sensitivity and high positive predictive value. It was observed TORG's ratio of 0,80 or less in 14,4% of the X-rays.

Key Words: Spinal stenosis; cervical vertebrae


A medição do diâmetro sagital do canal vertebral é parte integrante da avaliação diagnóstica de estenose da coluna cervical. Antes de identificar a morfometria anormal é necessário estabelecer valores normais para uma população específica. A estenose do canal cervical pode se converter em fator agravante na vigência de um "trauma menor" na cabeça ou no pescoço, aumentando o risco de dano medular especialmente naqueles que praticam esporte de contato. Foram selecionadas de maneira prospectiva e randomizada quinhentas radiografias em perfil da coluna cervical de militares jovens assintomáticos na faixa etária dos 18 aos 20 anos, agrupados em cem em cada região geográfica, nas cidades de Manaus, Recife, São Paulo, Porto Alegre e Campo Grande. A primeira parte deste estudo estabelece valores normais para a morfometria da coluna cervical. A segunda parte identifica a precisão do índice de TORG para detectar um canal estreito. O valor médio normal encontrado para o diâmetro sagital de C3 foi 18,27mm, C4 17,98mm, C5 18,33mm e 18,76mm em C6. O índice de TORG mostrou ser um método sensível e possui alto valor preditivo positivo, tendo sido observado presença de índice de TORG anormal (menor ou igual a 0,8) em 14,4% das radiografias analisadas.

Descritores: Estenose espinhal; vértebras cervicais




Sports cervical medullary injuries have growing interest from researchers, particularly for involving healthy young people during a variety of physical activities, mostly when involving collision or physical contact, who once have a traumatism present an extremely dramatic clinical picture of transient tetraplegia or medullary neuro-apraxia(43,44,45,47,49,50). In this situation, cervical spine radiograph generally doesn't have any sign of fracture or dislocation(2,3,4,5,6,8,18,19,20,22,24,29, 37,38,42).

In USA the initial concerning was higher because of the growing number of victims during football practice, so leading to the creation of an organization to study the incidence and causes of these injuries. This way it was founded the "Injuries and Fatalities Study American Football Referees Association Committee"(33). Their medical team established new regulations for athlete selection, changes in individual protection equipments, conduct for emergency attention, and early diagnosis. The consequence of these measures was an important reduction in the incidence of this kind of injury.

Later the "National Center for Study of Catastrophic Sports Injuries"(7,39,40,41,54) started to collect data more globally, reaching different sport activities once this problem started to be identified in other sports.

The epidemiological references in USA demonstrate that spinal injuries during physical activity without supervision can reach 10% in activities considered as recreational as surf, diving, and others. Under technical orientation, the incidence is between 0.6 and 1.0% (7,22).

The relationship between the transient tetraplegia clinical picture and the presence of spine canal stenosis was initially established by PENNING (30,31) in the seventies for the relationship it occurs in myelopathies due to spondilosis. The difference resided exactly in that in this case, compressive factors due to degenerated structures such as yellow and posterior longitudinal ligament hypertrophy, articular facets as well as osteophytes while in transient tetraplegia in young the narrowing is due to a congenital vertebral deformity, with a consequent spine canal diameter reduction.

Several authors tried to establish normal measurements of the sagital diameter of the spinal canal at cervical region in plain radiographs in lateral view aiming to define normal values in this segment, ignoring the radiographic enlargement occurring in this kind of test. Due to the distance between the focus-film-individual, there were parameters discrepancy ranging from 13 mm, as defined by WOLF(56), 15 mm (EPSTEIN(13,14) up to 18.5 mm by COUNTEE et al. (apud PAVLOV et al.)(29). This led the authors, starting from the eighties, to investigate radiographic diagnostic methods, which could be easily reproducible by different examiners, without influence of distortion.

TORG et al, in 1986, established a method consisting in a proportion canal-body, by measurement in plain lateral cervical spine radiograph, the sagital diameter of the spine canal by the anterior-posterior length of the body, at its mean point. In this way there is no relevance for the enlarging factor, once the distortion is proportional.

In Brazil, epidemiological considerations for sport cervical spine injuries are still restricted to Sao Paulo State, where there are published cases (3) and a populational study evaluating the incidence of spinal canal stenosis (2).

The aims of this study are:

1. Establish normal values for the sagital diameter of the cervical spine canal, measured in plain radiographs in five hundred young asymptomatic Brazilian military men who regularly practiced sports involving collision and physical contact.

2. Identify the precision of TORG's index for detecting cervical spine narrow canal.

3. To evaluate the Brazilian regions in regard to incidence of spinal stenosis.



A prospective study of 500 plain lateral radiographs of the cervical spine of volunteered male soldiers, born at the region where they were serving the Brazilian Army.

Grouped by one hundred in each geographic region, at the cities of Manaus, Recife, Sao Paulo, Porto Alegre and Campo Grande, random picked Capitals for representing, respectively, North, Northeast, Southeast, South and Middle West, during the year 2000.

A general speech on the research theme was delivered at barracks where exercises usually involve collision or physical contact. The volunteers were randomly identified, and those referring any kind of neurological symptom, disease and/or previous surgery related to cervical spine, were excluded. Those included in the study filled and signed an Informed Consent Form as requested by law.

All volunteers were male, aged between 18 and 20 years, born Brazilian, without skin color or race distinction.

The physical type of the volunteers was between the standards for admission to the Army, according to (Table 1). These standards are used as a reference for selection examinations, respecting the individual biotype and the proportionalities between upper and lower limbs.



The radiographs were taken in Military Hospitals from Manaus, Recife, Sao Paulo, Porto Alegre and Campo Grande. The volunteers were always in standing position, head in neutral position, left shoulder touching the film that was 183 cm (72 inches) from the focus. The film always involved the base of the skull and the cervical-thoracic transition.

The measurement of the sagital diameter of the cervical canal and the anterior-posterior width of the body at third, fourth, fifth and sixth vertebral bodies, was performed three times with a total of twelve thousand measurements in millimeters; from these, were found more than twelve thousand values related to TORG's index, and the sheet had twenty four thousand figures. Minimal and maximal values, as well as the incidence of TORG's index lower or equal to 0.80 at each level were determined.

The instrument used was a digital caliper Mitutoyo code 500-143B, with an approximately 0.02 mm precision.

In the following conditions the film was discharged and replaced: quality was bad, spine rotation, deformity or bone deviation, previous disease as a formation or segmentation defect, cervical lordosis inversion, congenital abnormality of the skull-spine transition and "limbus" vertebra.

In order to avoid any distortion that could interfere in the dimensions of canal and body, it was necessary to randomly calculate an increase of the final sample by 10%.

All measurements were taken three times by the same observer (11) so that, after drawn and measured the lines, they were erased and the procedure was repeated without the reference of the previous drawing, at the four levels of the five hundred radiographs.

The method used for determination of the sagital diameter of the spine canal was measurement of the distance at the mean point between the posterior surface of the body and the closest point of the spino-laminal line. The width of the vertebral body was measured by means of a line that was perpendicular to the mean point of the anterior and posterior faces (Figure 1).



TORG's(42) index was used for identification of how many volunteers from each region had vertebral narrowing, as well as the levels they were found.

TORG's index sensitivity (34) aims to measure its probability of being positive when there is a significant cervical spine stenosis.

The evaluation of the predictive positive value (34) of TORG's index aims to measure the probability of an individual present a significant cervical canal stenosis. It is the proportion of those with abnormal TORG's index and cervical stenosis.

The term abnormal or positive TORG's index, as mentioned in this work, means the relationship canal/body of the evaluated vertebra is equal or less than 0.80.

The relevant results were divided by geographic region and unified.



The sample size was based on the 1996 Brazilian census by the Brazilian Institute, considering young people 14, 15 and 16 years old, male, who are currently in the age range of the study. Were not considered the existing deaths and migrations during this period.

The calculation of the sample size was based on a formula (1), showing the minimal figures for an statistically representative sample would be of 387 people, and this figures were increased in order to balance the series among the regions and to make easier a mathematic comparison, used for a finite population as described by FONSECA (15).


N = sample size

Z = northing of standard normal curve with a 0,045 probability

p = population estimate

q = 1-p

e = sample error.

The probability p < (0.50) and q < (0.50) was adopted because in these conditions variation is maximal for sample calculation thus being safer.

The statistical analysis was performed by means of software from the Technology Nucleus. Correlations between mean data were determined by using a linear regression model. Comparison between mean values of the data was performed by means of variance (ANOVA) with two criteria and TURKEY's (parametric) test.

Variance analysis (ANOVA) according to BANZATTO (1) was adopted aiming comparison of two or more averages, using the double criterion method. The experimental outline used was of random blocks, with three recurrences. Following TURKEY's test at 1% and 5% of probability was performed. The results were considered as statistically significant at p<0.01.

Descriptive statistics was used for analysis of the most relevant data such as average, median, standard deviation, confidence interval, minimal and maximal values.



Data referring to measurements results, radiographs exclusions and statistical data description are reported in (Tables 2 to 8).










Measurements obtained from radiographic images is part of diagnostic evaluation of cervical spine, however for this procedure to be clinically useful it is necessary to establish normal parameters. This study establishes normal values for cervical canal in young Brazilian military males aged between 18 and 20 years, from all geographic regions of the Country.

This study was performed according to the best scientific criteria, ordering the results and comparing to the existing in literature sticking to basic experimentation principles: random, repetition and local control (1).

The interest for cervical canal measures has a particular relationship with medullary compression and/or myelopathy, which can more frequently occur due to spondilosis and/or congenital narrowing of spine bony elements. Clinical manifestations range from a progressively slow incapacity occurring spontaneously, to a sudden tetraplegia after a major or minor trauma.

Acute myelopathy after minor trauma of cervical spine can occur without any fracture or dislocation. This phenomenon is linked to spondilosis, which leads to a gradual canal narrowing, present in elder, whether or not linked to congenital stenosis which occurs in younger people, who practice sports with collision or physical contact.

Cervical canal diameter evaluation started to gain importance by the middle of the past century with the works by BOIJSEN apud WOLF(56) and later by WOLF et al.(56). Starting from there, several other authors(2,3,5,12,16,25,28,42,56) started measuring radiographs aiming to establish the minimal normal values, however the differences between them brought great concert in relation to absolute measurements, due to the enlargement variability. Some of these works did not clearly record if the radiographic measurements were performed at the mean sagital line of the vertebra, essential for cervical stenosis identification (12,16,30,56).

Aiming to eliminate enlargement variability effects, TORG et al. (42) describe a method that ignores the distortion caused by the distance between focus-object-film, consisting in the relationship between two measured values in a plain lateral radiograph, through the mean point of a vertebra, the sagital diameter of the cervical canal starting from the posterior cortical of the vertebral body to the closest point meeting the line linking the spinous process with the laminae, by the length of the anterior-posterior width of the body, according to (Figure 1).

TORG's method proposes that the index, smaller or equal to 0.80 identify a significant narrowing of the cervical canal diameter. In his classic paper, TORG et al.(42) evaluate athletes with transient tetraplegia and demonstrate that many of them had stenosis.

Transient tetraplegia is a temporary medullary dysfunction, characterized by TORG et al. (42) as a distinctive clinical entity involving athletes with cervical trauma in hyperflexion or hyperextension, or head (28,30,33,42,46,54), with a sudden symptom start that may involve upper limbs, lower limbs, the four limbs, or upper and lower limbs at same side, with sensitivity changes as parestesias and eventually reaching anesthesia. Motor deficit consists in weakness or palsy. The typical episode persists for at least 15 minutes (9, 24, 42,48) however in some cases, gradual regression can take 48 hours. There is a complete recovery of motor picture, cervical mobility and remission of the painful picture. However, from the second episode there is less chance of a complete recovery.

In medical literature there is no unanimity in regard of the normal values of spinal canal dimensions. Some authors (8,9,26,36,42,56) tried to determine the stenosis by values below 13 mm. WOLF (56), who repeated the work by BOIJSEN apud WOLF (56) performed two years before, examined 200 asymptomatic adults, changing the distance between the X-Ray source and the film to 183 cm (72 inches), showing that the most frequent value for the normality was 17,00 mm from C3 to C7, and this agrees with the findings in this trial.

The variation coefficient calculated for the values found in this study shows a small difference between the data. This homogeneity translates that these were trustworthy, as observed by statistical analysis for both TORG's index and canal and vertebral body measurements.

The variance analysis of spinal canal sagital diameter measurements, body width and TORG's index, was performed according to the three recurrence criteria. It was shown to have a statistically significant difference (p< 0.01) between vertebras in all regions, following calculated by TURKEY's test at 1% probability, showing similar parameters as shown in Tables 21, 22 and 23.

This research showed, by means of TURKEY's test for variance analysis that the lower values for sagital diameter of the spine canal were in C3 and C4, while the lower anterior-posterior lengths of the body was in C4 and C5. For the relationship canal/body the lowest index were in C3/C4 without statistical difference, followed by C6. These finding are equivalent to other studies (12,13,14,16,25,26,58).

The analysis of the mean variance of all regions together showed that there are statistically significant differences (p<0.01) between cervical spine vertebras, that is, there is no statistical similarity between C3, C4, C5 and C6, proven by TURKEY's test, both for canal and body.

The lowest values for spine canal were found in the levels where TORG's index was lesser or equal to 0.80; these measurements were below 17.00 mm in 47.8% in North region, 91.7% in Northeast; 87.7% in Southeast, 100% in South and 90% in Middle-West regions.

The minimal value for spine canal found in each region were: Northeast: 10.68 mm; Southeast 13.80 mm; West-West 13.94 mm; South 14.37 mm; and North 14.48 mm.

TORG's index in Brazil as a whole, smaller or equal to 0,80 was found in one or more levels in 72 people (14.4%) and 141 levels (7.1%).

Southeast region was the one with higher incidence of spine canal stenosis, with 49 (34.8%) levels, followed by South with 25 (17.7%). Northeast 24 (17.1%); North 23 (16.3%) and Middle West 20 (14.1%). The most frequently affected level was C3 (32.6%), followed by C4 (29.8%), C5 (19.2%) and C6 (18.4%) according to Table 2. Southwest region was also the one with larger number of people with smaller dimensions of cervical canal.

The mean value of sagital diameter of cervical canal in sub-axial segment (C3 to C6) was above 17.00 mm in all levels of all regions.

There is a large series of current researches registering the relationship between cervical canal stenosis and medullary dysfunction secondary to cervical spine trauma (5,7,9,10,16,18,20,22,25,36,49,52,55,56) , particularly during sports practice involving physical contact, mostly because a narrow canal predisposes the athlete to a worse neurological prognosis after a minor spine trauma (7, 53).

Radiographic evaluation in this study had no intrinsic degenerative influence, due to the low age of the series, 18 to 20 years, favoring data homogeneity especially in investigation of cervical canal stenosis incidence.

Observation of data analysis of this study, Southeast region had in 12.3% of the levels a TORG's index lesser or equal to 0.80, while in South it was 6.3%, Northeast 6%, North, 5.8% and Middle West 5%. This incidence in clearly higher in Southeast probably because intensive migration not only from Brazil but also from several nations, in such a cosmopolitan city as Sao Paulo, where the volunteers were selected.

The low incidence of significant cervical spine stenosis in the current study allowed determining the sensitivity and positive predictive value of abnormal TORG's index for detection of narrow canal. For this, the sagital diameter of the canal was compared to the relationship canal/body lesser or equal to 0.80. These tests as used in populational researches to study ill and healthy people, and their results are more relevant for clinical practice.

TORG's index sensitivity (34) evaluates the probability of being abnormal or positive due to cervical canal stenosis; positive predictive value (34) of this index evaluates the probability that a reduced measurements canal result in a below normal TORG's index.

If significant cervical canal stenosis (16) is defined by its sagital diameter lesser than one standard deviation below the average, the sensitivity of TORG's index to detect it is 34.7%. If the parameter considered is to be lesser than two standard deviation below the average, TORG's index sensitivity raises to 80%.

Positive predictive value of abnormal TORG's index was determined in 83% of the levels, that had their sagital cervical canal diameter lesser than one standard deviation below the average, while only 17% had a sagital cervical canal diameter lesser than two standard deviation below the average.

TORG's index lesser or equal to 0.80 was sensitive for cervical stenosis and presented a high positive predictive value in screening asymptomatic young military, from who 14.4% had their ratio canal/body abnormal in one or more levels.

In comparison to HERZOG's et al.(16) study there is a difference in regard of the positive predictive value, particularly because in the current study there was a higher concentration of levels with abnormal TORG's index with the sagital diameter of the cervical canal between one and two standard deviation below the average, while in the first the agreement was higher between the average and one standard deviation below the average.

TORG's index sensitivity to detect a significant cervical canal stenosis was relatively lesser in the current study, because the amount of levels with a sagital diameter lesser than on standard deviation below the average was much higher than those presenting a normal canal/body relationship.

The sensitivity difference and positive predictive value from other studies (16,43,48) can be a feature of Brazilian population, specially because the six measurements of each level were rigorously taken at the mean point of each vertebra.

HERZOG et al. (16) describe in their series that in 41% of the asymptomatic athletes TORG's index was lesser or equal to 0.80 in one or more levels. Concerned about this high percentage, they started studying causes that could be responsible for the results. They understand that it was not the measurement of the canal that determined the significant change in the index, but the difference in the body diameter, judging that TORG et al.(42), in their classical paper, did not value this dimension in the control group, which was not formed by athletes. They suppose the possibility that in an epidemiological study using the ratio canal/body for determine significant stenosis, it may occur that one athlete is rated as having stenosis, being normal; and instruct that in these cases, canal dimensions are investigated by MRI, for evaluating a possible "functional cervical canal stenosis".

The so called "real functional spine canal stenosis" (6) is related to the absence of a "functional reserve" (15) of spine cord, that is a sign seen in T2 weighted images in MRI, myelotomography or myelography, represented by a clear halo involving it, that is, cephalorrhachidian liquid, meaning that there is a space to the adjacent bony spine structure, that also represents protection.

Athletes with TORG's index lesser or equal to 0.80 require an image evaluation by MRI (16,25) for a study of the previous functional reserve before a diagnosis of significant canal stenosis, mostly in those practicing sports with collision and physical contacts due to the natural exposition to spinal trauma. This is extremely important, because there is a higher risk of one of the most dramatic nerve injuries, tetraplegia (7,8,53).

In the current research the biotype of the volunteers was similar, particularly because for a young man to be admitted to Army has to be approved in a health test with rigid criteria particularly for weight and height.

In an editorial paper, TORG et al. (35,51) concluded that there is no relationship between tetraplegia and the physical build of an athlete. The correlation with neck circumference and vertebral size were not proven by HERZOG et al. (16) who, in their work, showed to have no equivalence.

Other studies (12, 56) concluded that cervical spinal canal stenosis increases the risk of medullary damage similarly also in non-athletes (9) when exposed to head and neck traumas, particularly in aged people with important degenerative changes, which additionally reduce the dimensions, due to spondilosis. There is a higher trend to improvement in patients with incomplete nerve injury with a wide canal than in patients with narrowing (12).

Cervical canal stenosis is known as aggravating in "minor trauma" increasing the risk of permanent nerve injury. There is a series of reports backing this statement(3,5,7,9,10,12,16,17,19,22,23,24,26,29,37,42,49) .

Myelopathy associated to cervical canal stenosis, mostly in young athletes, has probably a different medullary injury mechanism than the observed in aged patients (13, 18,27,57). The phatophysiologic bases of transient tetraplegia are not completely understood, even though a growing concerning overcoming academic interest(42).

Cervical stenosis can as well have neurological effects only in brachial plexus once a narrow canal in this case plays a fulcrum by the exit of the root producing stretching at its exit causing a neurological dysfunction with transient symptoms(10,17,20,32,55). Athletes with intervertebral foramen stenosis presented significantly lesser TORG index than the control group(54) who are subject to radicular neuro apraxia in consequence of sport trauma, mostly when involving physical contact(10).

Spine stability was defined by WHITE et al (55) as the ability it has to keep its mobility limits under physiological burdens without causing damage or irritation to medulla or roots.

Cervical instability, spine canal stenosis and exposure to trauma are factors that are part of a current consensus for predisposing an individual to a catastrophic neurological injury(49) during sports practice involving collision or physical contact.

The guideline to exclude an athlete from taking part in physical contact sports is multifactorial(8, 52, 53). It is necessary to evaluate the cervical spine under three different aspects: vertebra congenital abnormality (segmentation defect, odontoid's defect, atlanto-occiput fusion), presence of congenital canal stenosis or post-traumatic sequela (fracture or dislocation). Each condition may present a relative, absolute or no contra-indication, based in the variety of the parameters(50,52).

As it can be noticed by the above mentioned items, the study of cervical spine stability is crucial, so that TORG et al. (49) state that without spine instability there is no increased risk of a permanent neurological damage. This information is vital for decision making that results in stopping or allowing continuity of sports life.

Recently Watkins(52) started analyzing this difficult decision making of allowing a cervical injured athlete to return to sport activity. The decision should be based in three factors: the mechanism causing the injury; objective anatomical injury; and the recovery of the athlete. Due to a potential risk of catastrophic sequela in case of an inappropriate or too early return, the understanding of the natural history of an specific clinical syndrome should be familiar to the specialist.

This research doesn't have as central point to focus on transient tetraplegia, even though all examined people were completely asymptomatic, but to establish normal values for cervical canal morphometry, and identify those with significant stenosis.

The major advantage of this work is, for sure, to draw the attention to the possibility of preventing a medullary injury due to a minor trauma in those who practice sports with collision or physical contact.

The results from this research will contribute for the Major-State of the Army to review their criteria for admission.

The importance of a correct measurement of the cervical canal is much clearer when are considered the clinical consequences of stenosis in this spinal segment, rarely recognized, however potentially tragic.



The study of morphometry of spinal canal at cervical region in young asymptomatic military male, allowed us to conclude that:

1. The incidence of spinal canal stenosis at cervical spine is relevant in young men admitted to the Army.

2. TORG's index has sensitivity and a high positive predictive value.

3. Morphometry of spinal canal at cervical region has a variation according to the geographic region studied.



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Trabalho recebido em 29/07/2002. Aprovado em 31/07/2002
Work performed at Instituto de Ortopedia e Traumatologia da Faculdade de
Medicina da Universidade de São Paulo - São Paulo - SP

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