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Journal of the Anatomical Society of India

A study of Width and Height of Lumbar Pedicles in Saurashtra Region

Author(s): Singel TC, Patel MM, Gohil DV

Vol. 53, No. 1 (2004-01 - 2004-06)

Department of Anatomy, M.P. Shah Medical College, Jamnagar.

Abstract:

Lumbar Pedicles from an important part of lumbar spine. They also have the quality of playing an important role in transmission of weight in lumbar spine. The Present study was conducted on 60 adult lumbar vertebrae in dept. of Anatomy, M.P. Shah Medical College, Jamnagar. Out of 60 vertebrae studied, 45 were of males & 15 were of females. The Height and Width of Lumbar pedicles were measured with the help of Sliding Vernier Caliper. The observations showed that there is always an increase in width of lumbar pedicles proceeding from L1 to L5 levels and the width being maximum at L5 level to enable in weight transmission. The observations also showed that the height of lumbar pedicles decreases as we move from L3 to L5 levels i.e. at the lower lumbar levels to enable the transmission of weight through thoracolumbar region.

Key words: Lumbar Pedicles, Height, Width and Sliding Vernier Caliper.

Introduction:

The pedicle of lumbar vertebra is strong and large. This helps in placement of screws through them. Transpedicular screw fixation of spine has developed as a very successful method of spinal fixation. The fixation of lumbar spine is needed for various spinal problems like fracture in lumbar spine, resection of tumours in vertebral bodies, gross spondylolisthesis and lumbar instabilities.

In addition to above mentioned advantages pedicle screw fixation can also be used in patients who have been laminectomized (Krag et al, 1986). However, the success of technique depends on ability of screw to obtain and maintain purchase of bone within body of vertebra (Zindrick, 1986). This is based on the factors like choice of size of screw for a particular pedicle size, and a presence or absence of osteoporosis in pedicle.

However, the pedicle screw has its own disadvantages also. Because of mismatched size of screw and pedicle the instrumentation may fail. This may result in cortex perforation of pedicle or fracture of pedicle. Sometimes pedicle screw may loosen. The complications associated with oversized pedicle screw are dural tears, leakage of cerebrospinal fluid and injuries to nerve roots (Amonoo-Kuofi, 1995).

As seen above the pedicle screw fixation has its own advantages and disadvantages. The horizontal diameter of pedicle decides the screw diameter. The transverse (width) and vertical (height) parameters of pedicle decides the screw path.

For this reason, the detail of pedicle morphometry becomes important as it helps in the selection of most suited pedicle screw.

Almost all the previous workers have reported the data on morphometry of the pedicle based on a common pool of vertebrae (male and female vertebrae were pooled together) (Saillant, 1976, Roy-Camille, 1984, Zindrick et al, 1987, Berry et al, 1987 & Krag, 1988). However, recently Scoles (1988), Olsewski (1990) & Amonoo-Kuofi (1995) have reported statistically significant sex differences in pedicle morphometry.

Most of previous studies of the morphometry of pedicle are based on white populations (Saillant, 1976, Roy-Camille, 1984, Zindrick et al, 1987, Berry et al, 1987, Scoles et al, 1988, Krag et al, 1988, Olsewski et al, 1990 & Amonoo-Kuofi, 1995).

Thus according to Krogman (1978); as the racial variations in skeleton are well known, hence the morphometry of the pedicle may vary from population to population. Even within the same population the anatomical variations have been reported on the pedicle shape, size and angulation (Weinstein et al, 1992).

Therefore, the present study was conducted in the Saurashtra region of Gujarat state to measure the height and width of lumbar pedicles.

The pedicles of lumbar vertebrae are short, thick, dorsal projections, from the superior part of body at the junction of its lateral and dorsal surfaces (Williams et al, 1995). The pedicle is strongest part of a lumbar vertebra. They are made of entirely cortical bone with a small core of cancellous bone (Roy-Camille et al, 1986). The upper margins form the superior vertebral notch, and lower margins form the inferior vertebral notch, and both contribute to corresponding intervertebral foramen (Williams et al, 1995).

As pedicle is the strongest part of lumbar vertebrae, it acts as a strut to transmit forces between the body and neural arch. Pal and Routal (1986 & 1987) using the morphometric methods studied the role of neural arch in weight transmission. According to them, the load in thoracic and lumbar regions is transmitted through two vertical running columns, anterior of which is formed by vertebral bodies and intervertebral discs while posterior column is formed by successive articulations of neural arch elements (facet joints, laminae, and ligamentous complex). Both these columns are involved in load transmission. Their studies have also shown that the relative magnitude of compressive force passing through the body and neural arch alters with the change of curvature at cervicothoracic and thoracolumbar junction. The transfer of compressive forces between the body and neural arch takes place through the pedicle, which acts as a beam connecting the two columns. Due to anterior curvature in thoracic region, the weight in thoracic region is transmitted from neural arch to body through the inclined pedicles. In lumbar region, where the curvature is posterior a part of compressive force of the body (anterior column) is transmitted to the neural arch (posterior column) through the pedicles. This transfer of load between body and neural arch (i.e. between anterior and posterior columns) tends to approach the line of gravity.

According to Schneck (1989) the characteristic morphology of lumbar pedicles decides and hence dictates its importance. The size of lower lumbar pedicle, particularly L5, helps in preventing forward slide of L5 over S1. Schneck adds to this, the tripod system of vertebra is made more stable, by the diverging alignment of pedicles in antero-posterior plane, thus bringing the superior articular facet anteriorly. The interpedicular distance is maximum in its posterior part, effecting this tripod system for support. Schneck has another fact added to above one, that the lower lumbar pedicle have their medial aspects going obliquely away from canal as the pedicles go inferiorly which altogether helps in sacro iliac load transmission.

Bogduk and Twomey (1992), mention that all forces sustained by any of the posterior elements are ultimately channelled to the pedicles, which then go to body of vertebra. Bogduk and Twomey have found that the pedicles transmit both tension and bending forces.

Schneck (1989), opines that pedicles transmit both gravitational loads and muscular movements.

Amonoo-Kuofi (1995) has reported on his study of horizontal and vertical diameters of pedicle of lumbar vertebrae. This study was done on plain radiographs of male and female, with age range from 10-65 years. He has measured pedicle diameters and has reported for significant differences and variations in different age groups of both sexes.

Materials and Methods:

Forty-five male and fifteen female lumbar vertebrae were considered for the present study of pedicle morphometry. The vertebral columns were obtained from preserved sets of bones of individual dead bodies received at Anatomy Department, M. P. Shah Medical College, Jamnagar. The bones were preserved since its collection by considering and keeping in mind various affection by external environments, and other factors destroying preserved bones. However, all vertebrae and other bones were fully ossified. All sets of vertebra included in the study were normal. The following parameters were taken as mentioned.

(1) Vertical Height of pedicle (h) in mm: This was noted by a sliding vernier caliper. The closest points just opposite each other on the upper and lower margins of pedicles, in the vertical plane on its lateral aspect were considered and their distance measured in mm. First, record was taken on right pedicle and then on left. The method adopted for measuring the height was according to HRDLICKA'S Practical Anthropometry.

(2) Pedicle width (w) in mm: The deepest points on the lateral and medial aspect of each pedicle were chosen. The thickness was measured at these points, at right angles to the long axis of pedicle. It was recorded by a sliding caliper in mm as described be HRDLICKA'S Practical Anthropometry. First reading was taken for right pedicle and then for left.

All these measurements were taken in millimeters and degrees. The mean and standard deviations for each side was calculated and student 't' test was used to determine the difference between right and left sides. As there was no significant statistical difference between the parameters for right and left sides; hence the data were pooled together.

Observations and Results:

Observations were recorded separately for both males and females.

Table-1 shows the range, mean, standard deviation and 't' value of height and width of pedicles of male and female lumbar vertebrae. Thus according to the above table, we can observe that the height of pedicles decreases from L1 to L5; but the width for pedicles increases from L1 to L5. As seen in the table, the mean vertical height of pedicle for males was maximum at L2 level (15mm). The minimum mean width of pedicle for males was recorded at L1 level (8.2mm). The maximum mean width for males recorded was at L5 level (18.2mm).

The mean height of the pedicle for females was found to be maximum at L1 level (15.5mm). The minimum mean height for females was found at L5 level (13.25mm). The maximum mean width for females was found at the L5 level (19.25mm). The 't' test was applied for seeing statistical significant difference between males and females.

The mean width of female pedicles at L5 was 19.25mm; and mean width of male pedicles at L5 was 18.2mm. But the range of width of pedicles at L5 in males was 15 to 23mm; and the range of female pedicular width at L5 was 16 to 21mm.

Discussion:

The pedicle is the strongest part of lumbar vertebra. It acts as a strut to transmit forces between the body and neural arch. According to Pal and Routal (1986 & 1987), it is a highly loaded element of neural arch along with facets and laminae. They have reported that the pedicles in lumbar vertebrae are close to the horizontal position, and hence the weight transmission in lumbar spine is from body to neural arch towards the line of gravity. They have also suggested that the pedicle connects the anterior column (body) and posterior column (neural arch). The fifth lumbar pedicle helps in preventing the forward slide of L5 over S1 (Schneck, 1989). Schneck views that the pedicle, as a part of tripod support system of vertebra, makes the system more strong, by its alignment in anteroposterior plane. According to Steffee (1986), the force nucleus is the site of concentration and gathering of all vertebral forces. According to Bogduk and Twomey (1992) all forces sustained by any of the posterior elements are channelled to pedicle and then they go to vertebral body. They add to this that the pedicle transmits both tension and bending forces. According to Schneck (1989) the forces acting on superior articular facet, inferior articular facet, lamina, body and transverse processes all gather on pedicle and they transmit all the gravitational loads and muscular movements.

Amonoo-Kuofi (1995) has studied horizontal and vertical diameters of pedicles on radiographs of 270 males and 270 females. He has observed variations in different age groups and at different levels of lumbar spine. According to table-2; Amonoo-Kuofi's readings of 40-49.9 years age group reveals that the width of pedicles in males & females is maximum at L5 with 14.2mm & 12.5mm respectively and similarly, the width of pedicles in males & females, according to the present study, shows that it is maximum at L5 with 18.2mm & 19.5mm respectively. Thus it shows that the width of pedicles goes on increasing from L1-L5 according to Amonoo-Kuofi & present study.

The study by Amonoo-Kuofi depicted in table-2 also reflects that the height of pedicles in males & females are maximum at L5 with 20.7mm & 17.5mm respectively, but, on the contrary, the present study reveals that the height of pedicles is maximum at L1, L2 & L3 levels & after which it goes on decreasing at L4 & L5 levels for both males & females. 0.27

Amonoo-Kuofi showed that there was a cephalocaudal gradient of increase (from L1-L5) of the horizontal diameters (width) of male & female pedicles in all age groups except the males of the 5th decade. He has also shown that there was a cephalocaudal increase of the vertical diameters (height) of pedicles from L1-L5 in males & females of all age group except the 20-29.9 years female age group.

Table 1

  Males(n=45) Females(n=15) 't' value height
width(w) height(h) width(w) height(h) width(w) height(h)
L1 Mean 14.7mm 8.2mm 15.5mm 8.5mm 0.63 0.2
S.D. 4.3 6.7 2 2
Range 13-17mm 6-11mm 14-17mm 6-11mm
L2 Mean 15mm 8.5mm 14.5mm 8.75mm 0.5 0.27
S.D. 4.6 6.5 1 1.87
Range 13-17mm 6-13mm 14-15mm 7-12mm
L3 Mean 14.7mm 10.4mm 14.8mm 10.6mm 0.14 0.12
S.D. 3.5 7 0.72 2.5
Range 13-17mm 8-14mm 14-15mm 9-13mm
L4 Mean 14mm 13.5mm 14mm 13.8mm 0 0.14
S.D. 4 7 1.78 4.1
Range 11-17mm 11-17mm 13-15mm 11-17mm
L5 Mean 13.4mm 18.2mm 13.25mm 19.25mm 0.1 0.44
S.D. 6 9.7 2.5 3.25
Range 11-17mm 15-23mm 12-15mm 16-21mm

Table 2

  Amonoo-Kuofi Present study
Level male female   male female
L1 Height(h) 19.4 16.3 Height(h) 14.7 15.5
Width(w) 10.3 8.7 Width(w) 8.2 8.5
L2 Height(h) 18.9 15.3 Height(h) 15 14.5
Width(w) 10.7 9 Width(w) 8.5 8.75
L3 Height(h) 19.3 15.9 Height(h) 14.7 14.8
Width(w) 12.1 10.5 Width(w) 10.4 10.6
L4 Height(h) 19.9 16.1 Height(h) 14 14
Width(w) 13 11.1 Width(w) 13.5 13.8
L5 Height(h) 20.7 17.5 Height(h) 13.4 13.25
Width(w) 14.2 12.5 Width(w) 18.2 19.25

The present study showed that the width (horizontal) of pedicles increased from L1-L5 in both sexes but the height (vertical) of pedicles decreased from L3-L5 in both sexes. i.e.: in the lower lumbar pedicles.

Thus Amonoo-Kuofi observed that there was increase in vertical height of pedicles (male & female) from L1-L5. But it is quite intriguing that, the present study showed a decrease in height (vertical) of pedicles (male & female) from L3-L5. i.e.: at the lower lumbar levels.

This contrast can be because of the difference in methods adopted by Amonoo-Kuofi and the present study. Amonoo-Kuofi studied the plain radiographs of lumbar spine whereas the present study was based on measurement of lumbar pedicles on the lumbar vertebrae with the help of vernier caliper.

Also another feature for this contrast can be that of racial variation. Amonoo-Kuofi had studied different population of particular race in Saudi Arabia; whereas the present study was conducted on Indian population of Gujarat state, Saurashtra region.

Clearly, weight-bearing and mechanical factors appear to play important roles in morphological and functional adaptation of the vertebral column to the changing demands associated with growth. Corroborative evidence brought by Porter et al (1989) established that in individuals aged 18yrs and over, increasing levels of physical activity were associated with increasing strength of the vertebral column. The posterior elements of the vertebral bodies, in particular, have a marked ability to undergo regrowth and remodeling (Krenz & Troup, 1973, Fidler, 1988 & Postacchini& Cinotti, 1992). It would seem, therefore, that if the pedicles were subjected to changing mechanical stresses, they would probably show appropriate variations in strength (or diameters). The 1st lumbar pedicle is located at the thoracolumbar transitional junction. A report by Davis (1955) demonstrated that this junction was the site of a complex zygapophyseal joint (the thoracolumbar mortice joint), which was adapted to withstand marked compressive forces transmitted from the relatively immobile thoracic segment to the highly mobile lumbar segment of the vertebral column. He showed that the vertebrae and pedicles at this junction were reinforced to withstand the forces that had to be transmitted across this junction. Considering the above, Present study shows that the height of pedicles at L1 level is maximum as compared to other lumbar levels.

According to Amonoo-Kuofi, the studies reported by Pal & Routal (1987) suggested that, in the lumbar region the pedicles play an important part in the transfer of weight from the neural arch to the anterior part of the vertebral column. But actually, according to the studies of transmission of weight through the lower thoracic and lumbar regions of the vertebral column by Pal & Routal (1987), they have suggested that in the thoracic region, where the curvature is concave anteriorly, the load is transmitted from the posterior to the anterior column and in the lumbar region where the curvature is concave posteriorly the load is transmitted from anterior to posterior; i.e.: from the anterior part of the vertebral column to the neural arch. This shifting of load is in accordance with the position of the line of gravity. According to Pal & Routal (1987), at the level L5, where transfer of weight from the anterior to the posterior column is suspected, load through the pedicles has to pass in an antigravity direction, i.e.: opposite to the direction of inclination of the pedicles. Thus the transfer of load from the body to the laminae in L5 (and to certain extent in L4) will be upwards against gravity through the strong pedicles, Pal & Routal (1987). Therefore considering the above facts, the pedicles of L5 vertebrae will always have maximum width. Thus the Present study shows that the width of pedicles is maximum at L5 levels for transmission of weight as discussed above.

Conclusion:

Thus, according to the above discussion, the present study concludes that there is always an increase in width of lumbar pedicles proceeding from L1 to L5 levels and the width being maximum at L5 level to enable in weight transmission.

Referring to the above discussion, the present study concludes that the height of lumbar pedicles decreases as we move from L3 to L5 levels i.e.: at the lower lumbar levels and the height being maximum at L1 and L2 levels to enable the transmission of weight through thoraco-lumbar region.

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