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SPINE Table of Contents   
Year : 2005  |  Volume : 39  |  Issue : 3  |  Page : 145-147
Morphometry of lumbar intervertebral foramen


1 Department of Anatomy, St. John's Medical College, Bangalore, India
2 Department of Orthopedics, St. John's Medical College, Bangalore, India

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   Abstract 

Background: The spinal nerve roots exit through the intervertebral foramina and the proportion between the size of the foramen and the relative space occupied by the root determines the chance of root compression in the intervertebral foramen. Not much data exists regarding the variations in the dimensions of the intervertebral foramen in Indian subjects.
Methods: Twenty one sets of lumbar vertebrae dissected out from the cadavers in the Department of Anatomy, was used for the study. The vertical and transverse diameters of the intervertebral foramina were measured. The vertebral foramen index was then calculated by taking the ratio between the vertical diameter and the transverse diameter.
Result: It was seen that the vertical diameter was more than the transverse diameter at all levels except at the L5-S1 foramen where it was the other way round. Even though there was a difference in the foramen size between the right and the left sides, it was not statistically significant. There was decrease in the transverse diameter from L 1 (mean 9.89 mm) to L 3 levels (mean 9.78 mm) and thereafter an increase at L 4 (mean 11.15 mm). The vertical diameter showed an increase from L 1 (mean 14.83 mm) to L 2 levels (mean15.52mm) and thereafter a decrease from L 3 (mean 15.29 mm) to L 5 (mean 12.48 mm) which was not statistically significant. The antero-posterior dimension of the superior notch was less than that of the inferior notch at all levels. The vertebral foramen index showed a gradual increase from L 1 (mean 1.47) to L 3 (1.58) and thereafter a decrease at L 5 level (0.94).
Conclusion: The foramen dimensions are critical in determining the foraminal constrictions of the lumbar spine. The transverse and vertical dimensions do not have a bearing on each other, as indicated by the vertebral foramen index.

Keywords: Intervertebral foramen; Lumbar canal stenosis; Vertebral foramen index; Lumbar vertebrae; Sciatica.

How to cite this article:
Devi R, Rajagopalan N. Morphometry of lumbar intervertebral foramen. Indian J Orthop 2005;39:145-7

How to cite this URL:
Devi R, Rajagopalan N. Morphometry of lumbar intervertebral foramen. Indian J Orthop [serial online] 2005 [cited 2019 Sep 18];39:145-7. Available from: http://www.ijoonline.com/text.asp?2005/39/3/145/36687

   Introduction Top


Lumbar spinal stenosis is one manifestation of the general process of spinal degeneration that occurs with aging. The symptoms of lumbar stenosis can either be a neurogenic claudication due to central canal narrowing or radicular symptoms due to narrowing of the inter-vertebral foramen (IVF). Although the diagnosis can be strongly suspected from the history and physical findings alone in many cases or by MRI scans, knowledge of the spinal anatomy is a pre­requisite for proper diagnosis and management of canal stenosis.

The spinal nerve root exits through the intervertebral foramen and the proportion between the size of the foramen and the relative space occupied by the root determines the chance of root compression in the intervertebral foramen. The inter-vertebral foramen has, as part of its boundaries, two movable joints - inter-vertebral joint anteriorly and zygapophyseal joint posteriorly. The compact bone of the deep arches of the inferior vertebral notch of the vertebra above and the shallow superior vertebral notch of the vertebra below form the superior and inferior boundaries respectively. Each foramen contains a segmental mixed spinal nerve and its sheath, two to four recurrent meningeal nerves, spinal arteries and plexiform venous connections between internal and external vertebral venous plexuses.

Narrowing of the intervertebral foramen can be due to several mechanisms. Normal spinal movements can change the size of the foramen i.e. foramen undergoes narrowing or widening, depending on the movements performed. The dimensions of the intervertebral foramen are influenced by dynamic and postural factors. For example, when a person rises from recumbency to standing, the resulting axial load on the intervertebral disc causes further bulging of the annulus, which in turn compromises the foramen. There can also be overriding of the bony processes that make up the degenerated facet joint, which can impinge on the nerve in the foramen. Finally, excessive lumbar curvature to compensate for thoracic, pelvic or leg length discrepancies can influence foramenal dimensions. Pathological bulging of the annulus fibrosis or new bone spurs can encroach on the nerves anteriorly. Hypertrophy of the facet joint limits the foramen posteriorly. A scoliotic curvature of the spine or collapse of the IV disc can reduce the vertical height of the IVF [1] .

Anatomical narrowing of the lumbar vertebral canal and inter-vertebral foramina have been reported as the cause of compression of the cauda equina and the emerging nerve roots [2],[3] . Low backache radiating to the legs, weakness and paraesthesia along the distribution of the affected nerve roots were the main presenting symptoms in whom the studies were attempted.

The inter-vertebral foramen is described as being at cross-roads between peripheral nerves and movable skeletal support; transmitting nerves, blood vessels and lymphatics. As joints bound the IVF anteriorly and posteriorly, normal spinal movements cause changes in foramen size. Thereby, based on movements performed, the foramen undergoes narrowing or widening [4],[5],[6].

Study of the IVF is essential for the evaluation of their role in nerve root canal stenosis. A normal morphometric database of the IVF is difficult in view of very little published data available in this aspect. There was not any published data with regard to studies on intervertebral foramina in Indian subjects.


   Material and methods Top


Twenty one sets of lumbar vertebrae dissected from the cadavers in the Department of Anatomy, was taken for the study. It was not possible to assess the age of the cadavers, but all the selected ones belonged to the middle age group of 25-60 years. Those specimens which had gross anomalies, IV disc collapse or osteophytes were excluded. The specimens were dissected out carefully, removing all the soft tissues, with the exception of ligamenta flava and the intervertebral disc. The shape of the intervertebral foramen was noted and the vertical and transverse diameters of the intervertebral foramina were measured using a sliding Vernier Caliper and recorded to the nearest tenth of a millimeter. A single observer did all the measurements at two different sittings, and the mean of the two values corrected to the nearest millimeter was taken to confirm the intra-observer reliability. Differences between the first and second readings ranged from 0 to .15mm with a median of 0.04 mm.

Vertical diameter of the IVF was taken at its rim from the root of the transverse process of the vertebra above to the root of the transverse process of the vertebra below. The transverse diameter of the IVF was taken at the level of the upper border of the IV disc. The mean value and the standard deviation were calculated at each vertebral level for both the transverse and vertical diameters. The variation of the different measurements in the cephalo-caudal direction was analyzed for statistical significance by using the 'One way Anova with post Hoc test (Scheffe).

The vertebral foramen index was calculated by taking the ratio between the vertical diameter and the transverse diameter, at all levels, on both sides.


   Results Top


The upper part of the foramen had a larger antero­posterior diameter than the lower part giving a key hole appearance for the foramen at all levels. In other words, the inferior vertebral notch was broader than the superior vertebral notch at all levels.

Morphological study of the specimen showed that the vertical diameter was more than the transverse diameter at all levels except at the L 5 -S 1 foramen level, where a reverse pattern was found [Table - 1]. The difference in the transverse and vertical diameters noticed bilaterally was not statistically significant.

There was decrease in the transverse diameter from L 1 to L 3 levels and thereafter an increase at L 4 . The increase at L 4 level was statistically significant bilaterally when compared with the values at the upper vertebral levels. The vertical diameter showed an increase from L 1 to L 2 levels and thereafter a decrease from L 3 to L 5 which was not statistically significant.

Looking at the vertebral foramen index, the values on each side showed a gradual increase from L 1 to L 3 and thereafter a decrease indicating that the transverse and vertical dimensions do not have a bearing on each other (Table 2).


   Discussion Top


The key hole appearance of the intervertebral foramen found in the present study was in accordance with the findings of Schneck [7], who had described it as 'pear' or 'light bulb' shaped. The formation of the osseous intervertebral canal has a bearing on its shape. The anterior wall of the intervertebral foramen is formed by the lower aspect of the body of the upper vertebra above, the intervertebral disc in the middle and lower part and by the small upper portion of the back of the body of the lower vertebra at the lowest level. The posterior wall, on the other hand, is formed by the lower portion of the pars interarticularis of the lamina of the higher vertebra superiorly and the superior articular process of the lower vertebra inferiorly. As the anterior posterior dimension of the superior margin of the pedicle is lesser than its inferior margin, the superior articular process is located well anterior of its articulating inferior articular process. This anterior positioning of the superior articular facet narrows the IVF in the lower part giving it the 'key hole' or 'light bulb' appearance. The IVF shape has also been described as an inverted 'tear drop' [8] .

At the lower lumbar vertebral levels, the deep gutter on the back of the vertebral body causes a further widening of the IVF on the anterior aspect. The posterior positioning of the inferior articular process widens the transverse diameter posteriorly as well. The lamina slopes further posteriorly lower down. These factors account for the increasing transverse diameter of the IVF. The antero-posterior dimension of the pedicle as well as the gradually increasing medio­lateraldimension is important in determining the transverse diameter of the IVF in the superior as well as inferior aspects [7] .

Quite contrary to the present study, that done on Nigerians showed a slight, but steady decrease in the transverse diameter in both sexes with a high degree of variation [9] [Table - 3]. Yet another study, showed a decrease in the transverse diameter upto L4 and thereafter an increase at L5 [10] [Table - 3].

The integrity of the IV disc has a bearing on the vertical diameter of the IVF, considering the fact that the IV disc constitutes 40-50% of middle part of its anterior wall. Studies have demonstrated that removal of the IV disc can reduce the foramen height on an average by 6.5mm [11].

Studies done correlating nerve root compression with posterior disc height, IVF height, and the foraminal cross sectional area revealed that nerve root compression was evident in cases where the foraminal height was fifteen millimeters or less suggesting that these critical dimensions may be indicators of foraminal stenosis in the lumbar spine. Not necessarily a nerve root compression causes sciatica [12] .

 
   References Top

1.Alexander JT Lumbar spinal stenosis: Diagnosis and treatment op­tions. Jacksonville Medicine / June, 1999 ( / as on September, 2004).  Back to cited text no. 1    
2.Schlesinger EB, Taveras JM. Factors in the production of "cauda equina" syndromes in lumbar discs. Trans Am Neurol Assoc. 1953; 78, 263-68.  Back to cited text no. 2    
3.Verbiest H. A radicular syndrome from developmental narrowing of the lumbar vertebral canal. J Bone Joint Surg(Br). 1954; 36, 230-237.  Back to cited text no. 3    
4.Sunderland S. The anatomy of the intervertebral foramen and mechanisms of compression and stretch of nerve roots. In: Modern Develop­ment in Principles and Practice of Chiropractice. Ed. Haldeman S. New York: Appleton-Century-Croft. 1980; 45-64.  Back to cited text no. 4    
5.Herkowitz HN et al. Lumbar disc disease. In: The Spine-Volume I. 4 th Edn. Phildelphia: WB Saunders. 1982; 508-585.  Back to cited text no. 5    
6.Crelin. Functional anatomy of lumbosacral spine. In: Syposium on Idiopathic Low back Pain. St.Louis: CV Mosby and Co, 1982; 59-77.  Back to cited text no. 6    
7.Schneck CD. The anatomy of lumbar spondylosis. Clin Orthop. 1985.14;193.  Back to cited text no. 7    
8.Hsu Ken, Zucherman James The X-stop interspinous process distrac­tion for treatment of lumbar spinal stenosis under local anesthesia (Spine. Dr.com as on September, 2004)  Back to cited text no. 8    
9.Amonoo-Koufi H S The sagittal diameter of the lumbar vertebral canal in normal adult Nigerians J Anat. 1985. 140 (1); 69-78.  Back to cited text no. 9    
10.Cramer GD, Howe J, Glenn WV, Greenstein J, and Potvin W Mor­phometric comparison of Computed tomography to Magnetic resonance imaging in the evaluation of the lumbar intervertebral foramina Clin Anat. 1994. 7; 173 -180.  Back to cited text no. 10    
11.Cinnoti G, De Santio P, Nofroni I, Postacchini F Stenosis of lumbar intervertebral foramen: anatomic study on predisposing factors Spine, 2002.  Back to cited text no. 11    
12.Hasegawa T, HS, Haughton VM, Nowicki BH. Lumbar foraminal stenosis: Critical heights of the intervertebral discs and foramina: A  Back to cited text no. 12    

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Correspondence Address:
N Rajagopalan
Department of Orthopedics, St. John's Medical College, Bangalore 560 034
India
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/0019-5413.36687

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    Tables

  [Table - 1], [Table - 2], [Table - 3]



 

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    Abstract
    Introduction
    Material and methods
    Results
    Discussion
    References
    Article Tables
 

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