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International Journal of Morphology

versão On-line ISSN 0717-9502

Int. J. Morphol. v.25 n.2 Temuco jun. 2007 


Int J. MorphoL, 25(2):393-406, 2007.


Morphometry of Vertebral Pedicles: a Comprehensive Anatomical Study in the Lumbar Region

Morfometría de los Pedículos Vertebrales: Un Exhautivo Estudio Anatómico en la Región Lumbar


*Prakash; *Latha V. Prabhu; *Rajanigandha Vadgaonkar; *Mángala M. Pai; *Anu V. Ranade & **Gajendra Singh

* Department of Anatomy, Centre for Basic Sciences, Kasturba Medical College, Bejai, Mangalore, Karnataka,Pin: 575004. India.
** Department of Anatomy, Institute of Medical Sciences, Bañaras Hindu University, Varanasi, U. P. Pin: 221005. India.

Dirección para correspondencia

SUMMARY: This comprehensive anatomical study on bones and X-rays regarding pedicles of lumbar vertebrae was performed in two parts. In the first part of the present work direct gross measurements of 3 different diameters (v, d, and 1) of both the pedicles of LI to L5 vertebrae (200 male and 200 female) were recorded through sliding vernier caliper. In the second part plain anteroposterior radiographs of the lumbar spine from 500 individuals (250 males and 250 females) were collected, and divided in 6 age groups and 2 different diameters (t and h) were recorded. The minimum horizontal diameter (d) of both the pedicles increased from LI to L5. Whereas, the vertical height (v) of both the pedicles increased from LI to L2, decreased from L2 to L3 and increased from L3 to L5. The anteroposterior length (1) increased bilaterally from LI to L2 and decreased from L2 to L5. All the aforementioned parameters were greater in male than corresponding vertebrae of female. Same trends were confirmed by the radiological study. The maximum horizontal diameter (t) of pedicles on both sides of vertebrae was significantly greater in females in less than 20 years of subjects, due to early pubertal growth spurt, whereas it was significantly greater in males in rest of all the age groups at all segments of vertebral spine. The maximum vertical height (h) of both the pedicles was significantly greater in males of age groups greater than 30 years from LI to L5.

KEY WORDS: Pedicle; Vertebra lumbar; Spine; Morphometry.

RESUMEN: Este estudio sobre huesos y radiografías del pedículo de las vértebras lumbares fue realizado en dos partes. En la primera se midieron directamente con un caliper, 3 parámetros (v, d, y 1) en los pedículos de Ll a L5 (200 casos de sexo femenino y 200 de sexo masculino). En la segunda parte, se recolectaron 500 radiografías anteroposteriores (250 de hombres y 250 de mujeres) y se dividieron en 6 grupos etarios, registrándose dos diferentes diámetros (t y h). El diámetro horizontal menor se incrementó de Ll a L5 mientras que la altura vertical (v) de ambos pedículos de Ll a L2, decreció de L2 a L3 y se incrementó de L3 a L5. La longitud anteroposterior (1) se incrementó bilateralmente de Ll a L2 y decreció de L2 a L5. Todos los parámetros mencionados fueron mayores en el hombre que en la mujer. Los mismos se confirmaron en el estudio radiográfico. El diámetro horizontal máximo (t) de los pedículos de ambos lados fue significativamente mayor en mujeres con menos de 20 años debido a un temprano crecimiento acelerado en la pubertad mientras que, fue significativamente mayor en los hombres en todos los grupos etarios, en la totalidad de las vértebras. La altura vertical máxima de ambos pedículos fue significativamente mayor en los hombres del grupo mayor de 30 años desde Ll a L5.

PALABRAS CLAVE: Pedículo; Vértebra lumbar; Columna vetebral; Morfometria.


Pedicle screw fixation is the most common fixation technique employed in the posterolateral type of spinal fusion. This method of fixation of lumbar spine for different diseases has progressively being more used in the last decades. Zindrick (1991) in his study described it as the method of choice for stabilization of the lumbosacral spine. Various pedicle screw systems involve insertion of screws through the pedicle into the vertebral body from the posterior aspect. In all types of spinal fusion whether it is transpedicular screw fixation or some other method, the primary aim is to immobilize a particular spine level (Lorenz etal., 1993; Stefee 1986; Zindrick). Wires and plates might be secured to pedicle screws. Zindrick et al. (1986) opined that the success of the transpedicular screw fixation technique depends upon the ability of the screw to obtain and maintain purchase within the vertebral body. Factors like the size of the pedicle, its quality of bone, and whether associated with osteoporosis or any other demineralising diseases, and finally the choice of the screw determine the prognosis associated with the success of the pedicle screw fixation. A pedicle is the strongest part of a lumbar vertebra, which is made up of entirely cortical bone with a small core of cancellous bone Roy-Camiller et al. (1986). Strong and large pedicles of lumbar vertebra as compared with the thoracic and cervical ones make them ideal for screw instrumentation.

Like any other procedure, this technique also has some serious drawbacks. Amonoo-Kuofi (1995) reported complications arising due to oversized screws resulting in displacement of screws, dural tears, leakage of cerebrospinal fluid and injuries to nerve roots with neurological deficits (Esses & Sachs 1992; Kag et al. 1986;Matuokae et al. 2002; Weinstein et al. 1992; Zindrick et al 1986). Detailed knowledge of the anatomy of the spine, with the clear understanding of the pedicle screw systems implementation, can reduce the risks of complication (Weinstein et al. ).

Regarding the size of the screw, Zindrick et al. (1986) reported that larger diameter screws were stronger and gave better results, hence majority of surgeons continue preferring as large a screw as possible for any given pedicle. The screw performance is also influenced by the geometric variables of the design; improvements in the pullout strength can be achieved by an increase in the major diameter of the screw Skinner (1990). The choice of the screw diameter is determined by the minimum (horizontal) diameter of the pedicle, whereas the pathway of the screw is decided by the transverse (width) and vertical (height) parameters of the pedicle (Amonoo-Kuofi; Krag et al. 1986; Singel et al. 2004; Weinstein et al; Zindrick et al. 1987).

Chaynes et al. (2001) in their cadaveric study concluded that of the pedicular measurements only width limits the diameter of fixation screws. Goel et al. (2005) opined that the strength of the bone-screw interface, for a given screw size (or fill within the pedicle cross section) increases with depth of screw penetration. Weinstein et al. described that approximately 60% of fixation strength of the thoracic and lumbar pedicles lies in the pedicle, whereas 20-25% of fixation strength is derived from the anterior cortex and the rest 15-20%o of strength comes from the cancellous bone. Brantly et al (1994) reported that besides the screw diameter the strength of the interface is also determined by the degree of fill of the screw with respect to the pedicle cross-section. Increased percent fill increases vertebral fixation strength in linear manner, especially if the depth of the screw penetration was at least 80%o. Zdeblick et al. (1993) found an inverse relationship between the pedicle width and cycles to failure, for given screw size. McKinley et al. (1997) reported the effect of pedicle morphometry on pedicle screw loading in a synthetic model and suggested that screw bending moments within the pedicle increased incrementally with increasing pedicle length, rising 30%> as length increased from 8.0 mm to 12.0 mm, whereas changes in pedicle width did not affect screw loads within the pedicle. They concluded that in situ pedicle screw loads increased significantly as pedicle length increased and as pedicle height decreased (McKinley etal). These biomechanical studies recommend that a surgeon should select a screw that has a diameter close to the inner pedicle diameter in order to achieve a good bone screw interface (Goel et al.). In terms of the screw itself, the biomechanical data supports the use of a screw that will fill the cancellous bone region of the pedicle and will penetrate up to eighty percent of the vertebral body along the pedicle axis. These recommendations are valid for vertebral bodies with normal bone quality (nonosteoporotic) (Goel et al.)

Rosol et al. (1996) reported vertebral morphometry derived from digital images using clinical radiographs measured with vernier calipers and a film phantom, and claimed it to be accurate, reproducible, and convenient. The morphometry of the vertebral pedicle has been studied by various authors (Hasegawa et al., 1996; Kim et al., 1994; Krag et al. 1988;Matuoka&Basile; Olsewskieía/., 1990; Zindrick et al. 1987) both in cadavers and imagery examinations. Pedicle screw designing based on pedicle morphology was the most important indication of all the aforementioned studies. Majority of pedicle morphometry studies were based on white population in different parts of the world (Amonoo-Kuofi; Berry et al. 1987; Coles et al. 1988; Krag et al.; Olsewski etal; Roy-Camille etal, 1984; Saillant 1976; Zindrick 1987).

Weinstein et al. reported anatomical variations regarding the size, shape and angulations of pedicle even within the same populations. Amonoo-Kuofi, reported in his study the horizontal and vertical diameters of the pedicles of the lumbar vertebrae, which were measured from plane anteroposterior radiographs of the lumbar spines of male and female subjects aged from 10 to 65 years. He concluded with significant age related variations along with the significant differences between the pedicle diameters of male and females.

Indian population forms the one-fifth of the total population of the world and the non-resident Indians are also distributed widely in many countries whereas only few studies are available on this population. Secondly there are very limited literature reported comparing the direct gross morphometry of lumbar vertebra with the X-rays studies. Hence, the present study was undertaken. The present work included gross three dimensional measurements of the minimum horizontal diameter (d), the vertical height (v), and the anteroposterior length (1) of the lumbar pedicles, from bones of Indian population. Further horizontal and vertical diameters of the pedicles were measured from the plain anteroposterior radiographs obtained from disease or deformity free individuals from the same place. Final conclusion was made by comparing the observations of the two separate studies in a scientific manner.


The study was divided in two parts. In the first part of the present work fully ossified 200 male and 200 female lumbar vertebrae greater than 20 years of age were used for direct gross morphometry of the pedicles. They were collected from preserved sets of bones obtained from individual cadavers received at Department of Anatomy, KMC, Mangalore. Only the normal and completely ossified vertebrae were included in the study. Lumbar vertebrae for osteometric study were kept on the table and different measurements were taken directly on the bones. Sliding vernier caliper was used to measure the different parameters. The Vernier caliper is an extremely precise measuring instrument; the reading error is 1/20 mm = 0.05 mm. To ensure that the full diameters were measured, the different axes of the pedicles were kept perpendicular to the caliper. The jaws were closed lightly on the vertebral pedicles. Each parameter was measured twice and then recorded. The methodology followed was as described in Hrdlicka's Practical Anthropometry (1952). Following measurements were performed on both sides and were recorded in mm.

a. The deepest points on lateral and medial aspects, at right angles to the long axis of the pedicles were considered for the measurement of minimum horizontal diameter (d) (Fig. 1A).
b.  On the upper and lower margins of the pedicle in the vertical plane two points just opposite to each other from the lateral aspect were considered for the measurement of the vertical height (v) (Fig. 1B).
c.  The anteroposterior length (1) of the pedicle was measured along the long axis of the pedicle from its superior aspect on both the sides of the pedicle separately (Fig. 1C).

  Fig. 1. A.The deepest points on lateral and medial aspects, at right angles to the long axis of the pedicles were considered for the measurement of minimum horizontal diameter (d). Fig. 1 B. On the upper and lower margins of the pedicle in the vertical plane two points just opposite to each other from the lateral aspect were considered for the measurement of the vertical height (v). Fig. 1C. The anteroposterior length (1) of the pedicle was measured along the long axis of the pedicle from its superior aspect on both the sides of the pedicle separately.

In the second part of the present work, plain anteroposterior radiographs of the lumbar spine of 500 individuals (250 males and 250 females) from different age groups (age span of 10 years) ranging from 10-70 years were studied. No individuals were exposed to X-rays; rather radiographs were collected from patient records of different emergency hospitals in Mangalore. Only easily readable x-ray films, certified as normal spine radiographs by a radiology expert were used in the study. Radiographs from male and female individuals were categorized separately into six age groups, each with age span of 10 years. Distribution of samples according to sex and different age groups are shown in Table I.

Two different diameters of the pedicles seen as extremes of their outline in the x-ray films were measured bilaterally in two planes perpendicular to each other (Fig. 2). The maximum dimension of the pedicle in the sagittal plane was recorded as vertical diameter (h) in mm. The maximum diameter of the pedicle in horizontal plane at right angles to the vertical diameter was recorded as (t) in mm. Terminal points of the pedicle were labeled by a fine marker. Radiographs were scanned and then computer was used to measure the diameters of the right and left pedicles of all the lumbar vertebrae and values were recorded in mm.

  Fig. 2. Plain X-ray anteroposterior view of the lumbar spine: illustrating the landmarks used for measuring the various diameters of the pedicles. The (h) is maximum vertical diameter and (t) the maximum horizontal diameter.

Statistical Analysis. All the results have been expressed as mean ± SEM. 'Z' test was employed for all the statistical comparisons. Any value of PO.05 or Z (Normal deviate) > 1.96 was regarded as significant.


Observations have been reported in two parts. First part incorporates direct gross three dimensional measurements, while the second part presents findings from plane anteroposterior radiographs.

1. Results were recorded in both male and female vertebrae separately. Mean values with standard deviation of height, width and length of left and right pedicles of LI to L5 vertebrae of both the sexes are shown in Fig. 3 and Fig. 4, respectively.

Important observations were as follows, a) Side variations were evident in majority of bones. Though there were different mean ± SEM values for right and left pedicles in large number of the vertebrae, the difference was not statistically significant. Maximum difference was observed between mean values of right (14.5mm) and left (15.1mm) pedicles in the vertical height (v) of the L3 vertebrae.

b) Mean values for all the diameters from LI to L5 for both the pedicles were significantly (p < 0.05) greater in males than females, except for (d) value at L3 and (v) value at L5 in the left pedicles and (d) value at L3 in the right pedicles, these differences were not significant.
c)  The minimum horizontal diameter (d) increased from LI to L5. LI showed the minimum value (mean: 8.2 ±0.43mm), while L5 the maximum (mean: 16.2 ±0.55mm).
d) The vertical height (v) was minimum (mean: 14.6 ±0.39mm) at LI and maximum (mean: 17.4 ±0.39mm) at L5. Values increased from LI to L2, decreased from L2 to L3, increased from L3 to L4 and markedly increased from L4 to L5.
e) The anteroposterior length (1) was maximum (mean: 8.3 ±0.33mm) at L2 and minimum (mean: 6.1 ±0.23mm) at L5. Values increased from LI to L2, and decreased from L2 to L5.
f)  In this part of study all the means of measured parameters ranged from minimum (7.7±0.38mm) to maximum (17.9±0.43mm).

The second part presents X-ray findings. Figures (5 to 14) depict the mean horizontal (t) and vertical (h) diameters of pedicles in males and females from 1 st to 5th lumbar vertebrae. Important radiological observations were as follows.

a). Difference in right and left pedicles values were evident in majority of the radiographs and values of both the sides were not just the repetition of each other, though the difference of the values were not found statistically significant in all the study groups.
b) The maximum horizontal diameters (t) of the pedicles were greater in females of the 10 to 20 years age group, in all (L1 to L5) vertebrae studied from the radiographs. In rest of all the age groups (> 20 years) afore mentioned diameter of the pedicles were greater and statistically significant in males at all levels of vertebral segments studied. This diameter (t) increased from LI to L5 in all the age groups studied.
c) The maximum vertical height (h) of the pedicles was significantly greater in males of all age group (>30 years) from LI to L5. The (h) value was not significantly greater in males of 20.1- to 30 years' age group from LI to L2, while in the age group 10-20 years it was again not significantly greater in males from L2 to L5. The vertical height (h) of both right and left pedicles from the radiographs of both sexes increased from LI to L2, decreased from L2 to L3, increased from L3 to L5. Thus, L2 was the transition vertebra from this measuring parameter.
d) In this part of the study means of all the measured parameters ranged from minimum (7.9±0.21mm) to maximum (18.4±0.30mm).


Chaynes et al. reported a cadaveric study on vertebral pedicle anatomy in relation to pedicle screw fixation. They reported that the pedicular height in spine gradually increases from T1 to L5. On the contrary in the present study the vertical height (v) in bone specimens increased from LI to L2, decreased from L2 to L3, increased from L3 to L4 and markedly increased from L4 to L5. In the present work, the minimum horizontal diameter (d) in lumbar spine increased from LI to L5, whereas in the study reported by Chaynes et al. (2001), the pedicular width was greatest at the three junctional regions of the spine. Linear measurements of both vertebral pedicles were made in ten complete lumbar cadaveric spines using calipers in study reported by Chaynes et al. , whereas our study report the same was based on measurements of bone specimens of fully ossified 200 male and 200 female lumbar vertebrae greater than 20 years of age; hence the aforementioned differences may be one of the factors responsible for the different observations.

Analyses of the observations with prior works by other authors reveal many interesting facts. In previous reports by Amonoo- Koufi and Singel et al. , values for left and right pedicles of the lumbar vertebra were nearly the same, on the contrary in our study the results were different and hence presented separately. Singel et al. reported that nearly all the measurements were greater in females than the males, whereas in our report all the mean values of the parameters observed in male subjects scored significantly higher and this can be justified as they have to support greater upper body weight. The anteroposterior length from body of the vertebra to the transverse process along the long axis was not included in majority of the previous works, although it is important for screw fixation techniques. These values were maximum at L2 level and minimum at L5 level in both left and right pedicle in both the sexes. Short stature of average Indian population compared to the western world can be correlated for the decreased value of all the parameters bilaterally from LI to L5 in both the sexes. Greater vertical height (v) values of L2 vertebra than LI and L3 is due to the closer location of the first lumbar pedicle to the transitional junction of thoracolumbar spine, and is again the site of complex zygapophyseal joint. The brunt of this force transmission should then be on L2 vertebra which has adapted itself resulting in increased pedicle vertical height. This stable position makes the L2 vertebra less prone to dislocate as compared to LI transition vertebra. All the explanations given by previous authors (Amonoo-Kuofi; Coles et al. 1998; Fidler, 1988; Krenz & Troup, 1973; Postachini & Cinotti, 1992; Singel et al) regarding the greater vertical height of LI pedicle will finally apply to the L2 pedicle. The uniform increase in minimum horizontal diameter from L1 to L5 bilaterally in both males and females is similar to observations and explanations given by the earlier authors and is primarily related to the role of weight transmission.

Age related variations observed from X-rays concluded some facts which could not be assessed from direct gross measurements. The maximum horizontal diameter (t) of both right and left pedicles from radiographs of female subjects were significantly greater than male counterpart at all vertebral segments from LI to L5 in adolescent age group (10-20 years), this finding was contrary to the rest of all the age groups (>20 years), where it was significantly greater in males. Aforementioned observations can best be correlated with early pubertal growth spurts in females than males, which reflected as different trend in 10-20 years age group. Same explanation applies to the maximum vertical height (h), though the differences were not statistically significant, inferring that this parameter was relatively less affected by pubertal changes in both the sexes. Similar observations were reported by Amonoo- Kuofi, though his study was different as there were no differences between right and left pedicles measurement and the gender difference were not significant in majority of elder (> 50 years) age groups. He related the larger vertical diameter of the pedicle of the 1 st lumbar vertebra (in both males and females) as compared with the vertical diameters of 2nd and 3rd lumbar pedicles by the weight bearing functions and concluded that vertical diameter with its larger dimension and wider variations with age, contributes more to weight- bearing function than the horizontal diameter. He opined that after the 5th decade of life the horizontal and vertical diameters of pedicles in females showed a tendency to increase, while male diameters decreased (1995). On the contrary in the present study the aforementioned diameters in elder (>50 years) age group showed a tendency to decrease in both the sexes. Hence it can be hypothesized that age related osteoporosis along with wear and tear processes is responsible for decreasing diameters in the X-rays.

What are the factors contributing to the measured differences between specimens and the X-rays in the present study? Following possibilities can be hypothesized:

1. Partial volume effects are responsible for this phenomenon which resulted in greater values in the radiological study than the direct specimen observations.
2. In plain radiographs, magnification factor can only be roughly estimated, besides X-rays measurements had the common limitation of the two dimensional structures.
3. Bone specimen observations had the usual benefit of three dimensional structures; on the other hand, the fact that some dry bone properties differ from the in vivo bones was the main limitation.


Analysis of both parts of the present study reflects similar trends regarding age, gender, and side variations. Although, the measured value of different parameters was slightly greater in the radiological study than the direct observations, which were measured through sliding calipers. Finally, to conclude, the direct gross study of the pedicles, although has some limitations, is still the more appropriate anthropometry tool to apply for adequate screw placement in spinal fusion. We recommend further studies in this direction to consider the impact of anatomical variation in the thoracolumbar and lumbosacral transition zones from which still some more clinical relevant conclusions may be drawn.



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Received: 02-02-2007 Accepted: 06-03-2007

Correspondence to:

Dr. Prakash
Assistant Professor, Dept. of Anatomy,
Centre for Basic Sciences, Kasturba Medical College,
Pin: 575004
Bejai, Mangalore, Karnataka

Phone No: 919342321730, 918242211746 (Off.) Fax No.: 918242428183



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