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Journal of the Anatomical Society of India

A study of inter-pedicular distances of the lumbar vertebrae measured in plain antero-posterior radiograph in Gujaratis

Author(s): Nirvan AB, Pensi CA, Patel JP, Shah GV, Dave RV

Vol. 54, No. 2 (2005-07 - 2005-12)

Nirvan AB, Pensi CA, Patel JP*, Shah GV & Dave RV
B.J. Medical College, Ahmedabad & *NHL MMC, Ahmedabad.

Abstract: Inter-pedicular distances of lumbar vertebral canal at levels L1 to L5 was measured in plain antero-posterior radiographs of the lumbar spine of 202 subjects (101 male, 101 female) from Gujarat of age group 20 to 60 yrs. Mean transverse diameter (Inter-pedicular distance ) is minimum at L1 ( 24.0 mm in male and 23.3 mm in female ) and maximum at L5 ( 30.9 mm in male and 29.8 mm in female ) showing a gradual increase from level L1 to L5. Ratio between transverse diameter of vertebral canal and transverse diameter of the corresponding vertebral body is seen to be constant (0.6) at all lumbar level in both the sexes. The mean inter-pedicular distances of present study are seen to be smaller than the mean inter-pedicular distances of North Indians. The present study confirms that there is ethnic as well as racial variation in the size of the lumbar vertebral canal, thus, emphasizing the need to have normal values and ranges for the transverse diameter of the canal for different populations.

Key words: Inter-pedicular distance, Lumbar vertebrae, Spinal canal.


Various causes have been attributed to low backache, but lumbar spinal canal stenosis as a causative factor is of great interest in "lumber stenosis" especially in the extent to which the cauda equina may be compressed within the lumbar spinal canal by constriction or narrowing of the bony ring of the canal, in contrast to impingement by soft tissues.

Stenosis due to decreased sagittal diameter has been reported in the cervical spine as well as in the lumbar spine. It has been suggested that reduced interpedicular distance is one of the cause of primary narrowing of the spinal canal ( Nelson, 1973 ). Stenosis of the spinal canal due to decreased inter-pedicular distance is to the best of our knowledge, virtually unexplored so we under took this study of interpedicular distance. The present study aims at determining the norms of inter-pedicular distance of the lumbar spinal canal in Gujrati population measured in plain antero-posterior radiographs and also to examine the relationship of the width of the vertebral body with inter-pedicular distance.

Materials and Methods:

Antero-posterior plain radiographs of lumbar spine in 202 subjects aged between 20 to 60 years (101 male and 101 female) belonging to Gujarat were used for the study. The roentgenograms were screened for readability and attempt was made to eliminate subjects with significant anomalies and other problems likely to influence growth and development. The radiographs of both sexes had been taken in the lying down position with an anode film distance of 100 cm. centered on L3 . All measurements were made by using Electronic Digital Vernier Calipers and were recorded to the nearest hundredth of a millimeter. Keeping in view the aims of the study, following observations were made on X-ray:

  1. Transverse diameter of the lumbar spinal canal was measured as the minimum distance between the medial surfaces of the pedicles of a given vertebra (Inter-pedicular distance) (Jones & Thomson, 1968 ).
  2. Transverse diameter of the vertebral body was measured as the minimum distance across the waist of the vertebral body, which is between its upper and lower border.

From the above measurements, mean values and standard deviation were computed for each vertebral level, separately for each sex. Differences between the mean transverse diameter of the spinal canal of male and female at all five lumbar levels were statistically evaluated. The ratio of the transverse diameter of the canal to the width of the vertebral body was also recorded (canal/body ratio) for all lumbar segments. Width of the vertebral body is an index of body size. A definite relation exists between width of the body and the transverse diameter (IPD) of the spinal canal at all lumbar levels, Amonoo Kuofi (1982). By calculating this ratio, it is possible to determine whether an individual's measurements are within normal limits for the respective vertebral body size or not.

Differences between transverse diameters of the spinal canal of adjacent lumbar segments were also calculated for both sexes. These were calculated from available mean transverse diameters. Knowledge of normal values of this parameter could be of importance in detecting isolated segmental changes.


Table – 1 & 2 shows the range and mean transverse diameter of spinal canal in both sexes. The diameter gradually increases from L1 to L5. It is minimum at L1 and maximum at L5. The differences between the mean transverse diameters in male and female at all the five lumbar levels were found to be highly significant. The value of standard deviation is highest at fifth lumbar level, suggesting greater variation in the size of inter-pedicular distance at fifth lumbar level.

The ratio between IPD of spinal canal and width of the vertebral body was calculated for all five lumbar levels (Table-3). The result indicate that although width of the vertebral body and mean IPD of the spinal canal was showing a steady cranio-caudal increase from L1 to L5 but the ratio between two traits is constant at all levels (0.6). It is evident from table-3 that width of vertebral body also increases from L1 to L5, like interpedicular distances. Inter-segmental difference in case of vertebral body is largest at L4 /L5.


In the present study attempt has been made to determine standard normal minimum IPD as a preliminary to clinical investigation of transverse spinal canal stenosis. It has been found that the reduction of coronal diameter of the lumbar spinal canal, caused by reduction in the inter-pedicular distance, is second most common cause of narrowing of the lumbar spinal canal after the reduction in the sagittal diameter, caused by short pedicles. So, we undertook the determination of normal inter-pedicular distance standard to detect spinal canal stenosis. It has been reported that plain antero-posterior radiographs are of considerable value in the recognition of the interpedicular distance. As the age group selected for the present study is very much same as the age group used for earlier such studies, the ethnic differences in the trait could be well compared. Hinck et al.(1966) have shown that before the age of 19 years, the lumbar spinal canal is distinctly narrower than it is in the adult. Inclusion of such young subjects in the sample could result in lowering of the value of mean IPD. So anteroposterior radiographs of normal adults, aged 20 years and above, were included in the study.

95 percent tolerance range is expected to contain 95 percent of the normal population. Any transverse diameter falling outside this range has to be viewed critically. The Mean IPD of the lumbar spinal canal obtained form radiographs in Gujarati male and female, when compared with the data available from previous studies showed a significant difference at all lumbar levels, thus, necessitating separate normal ranges for male and female. There is considerable overlapping of the ranges of male and female. This probably reflects the wide variations of body sizes among the male and female subjects.

Table 4 & 5 show a comparison between the mean inter-pedicular distances of lumbar spinal canal obtained from plain antero-posterior radiographs at levels L1 to L5 in males and females observed in the present study and those reported for other populations of the world. The inter-pedicular distance increased steadily from L1 to L5 in all populations. It is evident from table 4 & 5 that North Indians have greater IPDs at all level from L1 to L5 than that of Gujaratis. It is evident form table-6 that the inter-segmental difference between mean inter-pedicular distances of adjacent lumbar segment is seen to be less in Gujaratis than that reported in North Indians in both sexes, but the canal/body ratio remain same (0.6) in both sexes. It is evident from table-4 & 5 that IPDs of Spanish are higher and of Nigerians are comparatively lower than the IPDs of present study in both sexes. The mean inter-pedicular distances of present study are comparatively lower at upper three lumbar levels and marginally higher at fourth and fifth lumbar level than that of White Americans in male, but in female, the mean IPDs are lower at L1 , & L2 and higher at L3 , L4 & L5 lumbar levels. The mean IPDs of present study are lower at L1 and marginally higher at L2 , L3 & L4 lumbar levels in both sexes, but at L5 equal in male and higher in female than that of Saudis. Graph-1 & 2 showing comparison of mean IPDs of present study with previous studies of both sexes. Table-4 & 5 confirms the findings of ethnical difference in the different races of world and support the statement, "There are no mean values of the vertebral dimensions that are valid for all populations."

The inter segmental difference between mean interpedicular distance is seen to be less in Gujaratis than that reported in North Indians, S.Chhabra (1991) in both sexes. Knowledge of the magnitude of the intersegmental differences between the diameters of adjacent segment could be of value in the detection of isolated segmental changes. The increase of IPDs of Gujarati female is of pattern similar to that of the male but of a slightly smaller magnitude. A comparison between the present data and the data published data on inter-pedicular distance at lumbar levels of other populations also shows that there are marked differences between the mean values reported for the population of different geographic areas. The reasons for these differences are not clear, but interplay of racial, ethnic and environmental factors cannot be ruled out.

Variations can occur in relation to general somatic size within a population. But transverse diameter of the spinal canal at any segmental level Jones & Thomson (1968), Amonoo Kuofi (1982) and Weisz & Lee (1983). This observation has been confirmed by present study of Gujarati population. The observation is significant so that clinicians while assessing the size of the spinal canal from antero-posterior radiographs need not take into consideration variables like built of the individual and X-ray magnification factor. Calculation of canal/body ratio for different segments can also help in specifying whether an individual's measurement on spinal canal are within the normal limits for respective body size or not, thus, helping to identify stenosis or dilatation of the spinal canal.

Table-1: Ranges of inter-pedicular distances (95% tolerance ranges) of each segmental level measured in plain antero-posterior radiographs in adult Gujarati males and females.

Level Ranges of transverse diameter
(IPD in mm.)
Male Female
L1 19.86 to 29.64 20.34 to 26.54
L2 21.94 to 30.28 20.68 to 28.00
L3 22.52 to 32.60 21.68 to 29.80
L4 22.92 to 33.30 22.76 to 32.10
L5 25.00 to 41.00 24.50 to 36.20

Table-2: Mean inter-pedicular distances (IPD in mm.), standard deviation (S.D.) and coefficient of variation (CV %) of the lumbar spinal canal of male and female adult Gujaratis.

Level Mean inter-pedicular distance (mm)
  Male Female
  IPD ± S.D. CV % IPD ± S.D. CV %
L1 24.0 1.72 7.16 23.3 1.54 6.60
L2 25.4 1.67 6.57 24.3 1.70 6.99
L3 26.4 1.92 7.27 25.8 1.92 7.44
L4 27.9 2.19 7.84 27.0 2.07 7.66
L5 30.9 2.43 7.86 29.8 2.36 7.91

?Table-3: Relationship between the width of the vertebral body (W, in mm.) and mean IPD (in mm.) of the lumbar spinal canal (canal/body ratio = C/B) obtained from plain antero-posterior radiograph of both sexes in present study.

Level Male Female
IPD in mm W in mm C/B mm IPD in mm W in mm C/B mm
L1 24.0 39.9 0.6 23.3 38.8 0.6
L2 25.4 42.2 0.6 24.3 40.4 0.6
L3 26.4 44.0 0.6 25.8 42.9 0.6
L4 27.9 46.4 0.6 27.0 45.0 0.6
L5 30.9 51.5 0.6 29.8 49.6 0.6

Table-4: Comparison between mean IPD obtained from radiographs (in mm.) of males between present study and those reported for other populations of the world.

Authors No. of case Vertebral level
L1 L2 L3 L4 L5
Hinck et al (1966) (White Americans) 59 25.9 26.5 26.8 27.6 30.7
Amonoo Koufi (1982)(Nigerians) 150 22.6 22.7 24.5 26.0 28.7
Pierra et al (1988) (Spanish) 110 27.79 28.39 29.44 30.89 34.31
Amonoo Kuofi et al (1990)(Saudis) 160 25.1 25.3 26.3 27.2 30.9
S.Chhabra (1991) (North Indians) 124 26.0 27.7 29.7 32.5 37.4
Present study (Gujarati) (2003) 101 24.0 25.4 26.4 27.9 30.9

Table-5: Comparison between mean IPD obtained from radiographs (in mm.) of females between present study and those reported for other populations of the world.

Authors No. of case Vertebral level
L1 L2 L3 L4 L5
Hinck et al (1966) (White Americans) 59 24.3 24.9 25.4 26.9 29.0
Amonoo Koufi (1982)(Nigerians) 140 21.3 22.5 23.7 25.4 28.4
Pierra et al (1988) (Spanish) 105 25.66 26.25 27.53 29.53 33.39
Amonoo Kuofi et al (1990)(Saudis) 180 23.5 24.0 25.2 26.9 29.0
S.Chhabra (1991) (North Indians) 91 24.1 25.7 27.3 30.1 34.4
Present study (Gujarati) (2003) 101 23.3 24.3 25.8 27.0 29.8

Graph 1: Unavailable

Graph-2: Comparison of Mean IPDs of present study and previous studies of female

Comparison of Mean IPDs


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