Child’s Nerv Syst (2001) 17:275–282 © Springer-Verlag 2001

Hun K. Park Satish Rudrappa Manuel Dujovny Fernando G. Diaz

Received: 23 December 1999

H.K. Park (✉) · S. Rudrappa M. Dujovny · F.G. Diaz Department of Neurosurgery, Wayne State University, School of Medicine, 550 East Canfield Avenue, Room 38, Detroit, MI 48201, USA Tel.: +1-313-5770966 Fax: +1-313-5770973

JOURNAL CLUB

Intervertebral foraminal ligaments of the lumbar spine: anatomy and biomechanics

Abstract The anatomical existence of the transforaminal ligaments has been studied extensively. However, there are very few studies examining how the transforaminal ligaments could be involved in the causation of nerve root compression and the low back pain syndrome. In this article, the authors review earlier studies in an attempt to find anatomical and biomechanical correspondence be-

Introduction Numerous studies have indicated that back pain is the one of the leading causes of absenteeism in the workforce. Even though it is well established that episodes of back pain are self-limiting, the prevalence and the duration of the disease are increasing in industrialized societies. Thus, health care professionals are concerned that the rate of disability attributable to back pain is increasing at a faster rate than population growth. A study on the lifetime prevalence of sciatica shows that 40% of the adult population have had sciatica at some time during their lifetime. The same study indicates that low back pain with sciatica is a common problem, and various causes have been mentioned. The definitions of sciatica used differ in the various epidemiological studies available. It is, in general, regarded as pain radiating along the course of the sciatic nerve to below the knee. The most common cause of sciatica is a herniated nucleus pulposus of the disc, but this is not the only explanation for sciatica. Spondylolysis, spondylolisthesis, facet joint hypertrophy and lateral canal stenosis can cause sciatica with back problems in about 25% of cases. Sciatica is usually treated nonoperatively, but a minority of patients may require hospitalization and surgical care. Operation

tween the intervertebral foraminal ligaments of the lumbar spine and the low back pain syndrome. Keywords Intervertebral foramen · Transforaminal ligaments · Nerve root · Lumbar foraminal stenosis

rates vary, but it is estimated that there are over 450 cases per 100,000 in the United States. No cause can be determined in some patients, since back pain is a multifactorial disorder with many possible etiologies. Therefore, various surgerical operations, including fusion techniques, are done on these patients, with variable results. One hypothesis is that the cause of lateral canal stenosis is compression of the nerve root by the transforaminal ligaments. Very few reports in the literature include anatomical and biomechanical descriptions of these ligaments or any discussion of their role in nerve root entrapment. The articles reviewed in this paper describe studies of the anatomical, biomechanical and clinical aspects of the lumbar transforaminal ligaments.

Transforaminal ligaments of the lumbar spine [8] Presentation In this paper the authors report on an anatomical study of ten lumbar spines. Each specimen was collected at autopsy, from a fresh cadaver with intact ligament structure. The average age of the subjects at death was 68.3

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Fig. 1 Corporotransverse superior (1) and inferior (2) ligament

Fig. 4 Inferior transforaminal (5) ligament

Fig. 2 Superior transforaminal (3) ligament

Fig. 5 Posterior transforaminal (6) ligament

Fig. 3 Mid-transforaminal (4) ligament

or corporotransverse ligament in frequency. The superior corporotransverse ligament was seen in 27 intervertebral foramina, and the inferior corporotransverse ligament appeared in 12 intervertebral foramina. The superior, middle and inferior transforaminal ligaments were seen at only 2 to 4 levels. In general, these were most frequently located between L-1 and L-2 and between L-3 and L-4. They ligaments were seen neither at all levels nor on both sides of the spine in any one specimen. In one specimen the authors noted complete ossification of superior corporotransverse ligaments on the right side at level L5–S1 level and the nerve root was found to be emerging below it.

years, and the pathological causes of death were not related to musculoskeletal disease or spine disease. The detailed configuration of each of 47 anomalous transforaminal ligaments was described. These ligaments are strong, unyielding structures varying in width and thickness between 2 mm and 5mm. Five types of foraminal ligaments were found; these are anatomically designated as the superior and inferior corporotransverse ligaments, and the superior, middle and inferior transforaminal ligaments. The superior corporotransverse ligament is the most frequently seen in the spine, followed by the inferi-

Interpretation Earlier anatomical studies have already revealed variations in the lumbosacral ligament and the radiating ligament in the lumbar area, and it was rare for them to have a configuration such that they could cause nerve root pressure. In this early article about intervertebral structure, the authors describe the anatomy and nature of transforaminal ligaments. The normal intervertebral foramen and five transforaminal ligaments are clearly illustrated in geometrical line drawings (Figs. 1, 2, 3, 4, 5).

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However, the precise nature and origin of these ligaments are not clear, and in most instances they appear to be a condensation of the fascia overlying the foraminal exit, which grossly diminishes the space available for the emerging nerve root. The authors, in fact, were not able to reach any conclusion on the clinical significance of these ligaments. However, this article provides some insight into the facts about the transforaminal ligaments. The authors collected data in specimens taken from subjects whose average age at death was over 65 years and who had died with various pathologies including different types of malignant disease. It is difficult to predict whether old age or pathology contribute to the variation in the results. Additional limited geometric data shortened the biomechanical analysis of weight-bearing and of range of movement in lumbar spine.

Ligaments associated with lumbar intervertebral foramina at L1–L4 level [1]

compartment between the posterior of the pedicle and transverse process, transmits the large branch of the segmental artery. The midtransforaminal ligament is a strong, horizontally placed, ligament, which forms the bed for the exiting spinal nerve. External ligaments radiate forward from the root of the transverse process toward the vertebral body with superior, transverse and inferior orientations. These ligaments with the internal and intraforaminal ligaments divide the intervertebral foramen into smaller compartments. The central large compartment transmits the ventral root of the spinal nerve. Anterior to this compartment, there are small compartments transmitting spinal, recurrent meningeal and segmental arteries and veins. Posterior to the central compartment, there are two neurovascular tunnels. The superior tunnel transmits the medial division of the posterior primary ramus and branches of the lumbar arteries. The inferior tunnel transmits the lateral division of the posterior ramus and to branches of segmental vessels. All these ligaments were demonstrable in the fetal spinal column.

Presentation Intervertebral foramina were first described by Hadley [9], who defined such a foramen as a crossroads at which the spinal nerve, vessels and lymphatics were transferred between skeletal support and the peripheral nervous system. It has been found since that the size of the foramen is constantly changing owing to body movement. However, it is not clear whether the foraminal contents move relative to each other during normal spinal movement. It appears that foraminal changes in size and the security of foraminal structure may be involved in low back pain and sciatica. The authors studied 12 lumbosacral spines, including one from a 24-week fetus, to find whether these intervertebral foraminal ligaments are true ligaments and are linked to neighboring structures traversing the intervertebral foramina. The fetus was studied to establish the developmental origin. The ligaments associated with the intervertebral foramen were classified in three types – internal, intraforaminal and external foraminal ligaments. The internal ligaments are oblique inferior transforaminal ligaments, located in the lower part of the intervertebral foramen and extending from the posterolateral surface of the intervertebral disc to the anterior surface of the superior articular facet. The internal ligament makes a separate compartment in the lower part of the intervertebral foramen to transmit the veins. Intraforaminal ligaments are attached to the three different margins in the foramen. The anterior one runs from the root of the pedicle to the inferior border of the same vertebral body above the level of the disc, which is known to transmit the small branch of the spinal artery and the recurrent meningeal nerve. The oblique superior transforaminal ligament, which forms the anterosuperior

Interpretation The observations recorded in the present study differed from those of the earlier studies regarding the incidence and geography of the ligaments. The earlier observations published [3, 8, 11, 12, 13] indicated that the ligaments occur in a random pattern and were distributed arbitrarily in nonsymmetrical patterns. In this study, the authors claimed that these ligaments were not anomalous and were probably developmental in origin. Further, it is suggested that they are normal features of the intervertebral foramen. It seems unlikely that they could be the source of encroachment of the foramen. Crelin [7] supported the idea that the ligament is compatible with normal functions of the lumbar spine, because changes in foraminal dimension did not put its contents at risk during movement. Thus, the likelihood of nerve impingement would depend on the status of the ligament and narrowing of the foramen, or on pathologic changes to structures in the foramen as the biomechanical reason for it. There is no indication of fetal development; rather, it is suggested that the ligament gradually develops from the muscle, to reach maturation with advancing age in response to localized strain and stress. However, no case histories corresponding to the specimens examined in this study were available, even though it is noted that a spine in which previous trauma or bone disease was suspected was excluded. Additional information could be useful to elucidate vertebral status, such as the history of sciatica and pattern of pain. The relationship between the hypertrophic degenerative changes in the surrounding facet joints and what happens to these ligaments in the degenerative status should be discussed.

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Ligaments associated with lumbar intervertebral foramina. The fifth lumbar level [2] Presentation The present study attempted to examine the fifth lumbar intervertebral foramen to find whether any ligaments could support the normal function of the lumbosacral junction. Twelve embalmed adult cadavers and two formalin-fixed fetuses (fetal ages 21 and 24 weeks), were dissected by the authors. The study included the ligaments related to the 5th lumbar spinal nerve. What they found were four types of ligaments traversing the space just outside the intervertebral foramen. The ligaments were named lumbosacral ligament, lumbosacral hood, corporotransverse ligament and mamillotransverse accessory ligaments. The corporotransverse and mamillotransverse ligaments were the only ones noted in all their specimens. The authors make it clear in the study that the lumbosacral ligament is a separate ligament and not a subdivision of the iliolumbar ligament as reported in earlier papers [15]. The medial border of this ligament is found to be free and crescentic and to form the lateral boundary of the opening for the ventral primary ramus. Fibers from the free border run from the transverse process of L-5 to the sacrum. The upper part of the ligament formed a thickened and round cord toward the transverse process. The features were depicted in both the adult and the fetal spine. The lumbosacral hood is described as a flat fibrous band that forms a canopy over the ventral ramus. The lower border of this ligament arches over the ventral ramus and the branches of the iliolumbar vessels. The lower border attaches to the sacrum by means of two slips, which are medial and lateral to the neural complex. The corporotransverse ligament is noted in all their specimens, including the fetal specimen. The attachment of this ligament is found to be similar to the inferior corporotransverse ligaments of the upper four lumbar levels. This ligament divides the anterior intervertebral foraminal opening into smaller superomedial and larger inferolateral compartments. The inferolateral opening transmits the ventral root of the spinal nerve along with the spinal branch of the iliolumbar artery and the plexus of veins. The authors have also mentioned that owing to its attachment to the lateral surface of the intervertebral disc, the ligament could help to prevent the anterior displacement of the intervertebral disc. A mamillotransverso-accessory ligament was also seen in all adult and fetal spines. It is a Y-shaped strong, flattened band-like ligament. The lateral division of the dorsal primary ramus is found passing between this ligament and the posterior thickened part of lumbosacral ligament, whereas the medial division of the dorsal ramus passes between the anterior and posterior limb of the mamillotransverse ligament.

Interpretation From the early biomechanical study by Bell [5], it was found that L-4 takes higher compression force than L-5. However, the L5 segment makes higher flexion and extension mobility and axial rotation but has less movement in lateral bending than the L1–4 segment. When the L-5 vertebra combines with the immobile sacrum, it became a major load-bearing portion of the pelvic girdle. This character limits motion of the segment but provides stability for the entire structure. This study of the L5 level extends that of the lumbar intervertebral ligament at the level of L1–4 conducted by the authors. The previous article found that the intervertebral foraminal ligaments in the L1–4 segment were classified in three types: internal, intraforaminal and external. Each ligament contributed to the makeup of a separate compartment in the intervertebral foramen and it provides a passage for neural and vascular structures. However, L-5 is in the transitional region of the vertebra column, so that its morphological character was emphasized to determine the extraspinal relationship. The direction of facets of the zygapophyseal joint is important because it forms the anterior and posterior boundary of the foramen. The transverse process of L-5 is important because it makes the ventral margin of the intervertebral foramen. The authors noted four ligaments traverse the intervertebral foramen. The lumbosacral ligament links the transverse process and sacrum. The lumbosacral hood forms a canopy of the ventral ramus. It is attached to the transverse process and lateral body of the fifth lumbar vertebra. Only two ligaments were observed in both fetal and adult spine. The first, the mamillo-transverso-accessory ligament, is located between the accessory and articular process of L-5. The second ligament is the corporotransverse ligament, which runs laterally to the intervertebral foramen. It is attached to the accessory process of L-5 and the lumbosacral ligament. Authors put forward biomechanical explanations for how those ligaments protect the nerve root and get around from the sympathetic ramus infringement and other vessels. Comparison of this and previous studies made a mechanism conceivable for changes to the transforaminal ligament causing disc resorption or degeneration at the L-5/S-1 level. The terms used for the ligaments do not illustrate a clear consensus on nomenclature. However, details of these ligaments and their biomechanical status are well described. There is obviously a need for their importance in the clinical settings to be delineated.

Neural foraminal ligaments of the lumbar spine: appearance at CT and MR imaging [14] Presentation In this article the authors studied cadavers from seven women and six men (mean age: 62 years old) within

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48 h after death. Frozen spinal columns (T-11 to S-2) were prepared and then imaged by a CT scanner in consecutive 1.5-mm-thick sections. The sledge freezing microtome was sectioned in an exactly corresponding plane with the CT scanner at 20-µm intervals. Then the sectioned surface at 1.0-mm intervals was photographed by a macrophotography system. CT images and the corresponding sections from the microtome were compared. The ligaments in the neural foramen were identified. The authors studied 114 neural foramina at 57 spinal levels from T-12 to L-5 to S-1 levels. MR study was done in fresh cadavers of three women and two men, obtained within 48 h of death. In order to run MR, spinal columns were thawed at room temperature, and then imaged by means of a 1.5-T MR unit. The thickness selected for sections used for the MR scanning was 1 mm. The spine was frozen again and the freezing microtome was used to section in the same plane as used in the MR examination. Twenty-seven neural foramens at 17 spinal levels (from L-1 to S-1) were studied in axial and parasaggital planes. From 84.2% of the neural foramina (total 96 foramina) in parasagittal sections, fibrous bands were identified near the intervertebral disc. It originated from the intervertebral disc and extended to the pedicle and adjacent portions of the superior articular process and the ligamentum flavum. The most frequent type was the fanshaped (39.5%) structure at L-3 to S-1. The single or multiple fibrous bands (34.2%) were common at high lumbar levels (L1–3). On CT images these bands were identified in the inferior ventral portion of neural foramen and appeared as linear or curvilinear structures. The apex was located usually at the upper posterolateral margin of the intervertebral disc. The attachment to the pedicle was also seen clearly. The ligament was evident in the corresponding CT scan images if it was identified in the parasagittal anatomical section. On axial sections, more linear structures were seen spanning the neural foramen and attaching to the intervertebral disc margin and superior articular process. These ligaments are found 1 mm caudal to fascicles of spinal nerves in parasagittal sections and 1 mm medial to the spinal nerves in the axial sections. It may suggest a possible significant role of the compression by these ligaments on nerve root inducing sciatica. These findings were noted in the neural foramina on both sides. In the parasagittal MR images, the ligaments showed lower signal intensity than that of the adjacent fat tissue. The origin of the ligament was usually identified at the upper margin of the intervertebral disc. Anatomical findings demonstrated on CT data were noted similarly with MR images.

Interpretation There is an increasing demand to find the possibility of whether ligaments in the lumbar neural foramina may restrict the spinal nerves. Since the dimensions of the foraminal ligament is extremely small and it is not easily defined in gross anatomy, using advanced modern imaging technology is encouraged. This study utilized the advanced CT and MR technique with the anatomical study. The study was well carried out and found good anatomical-radiological correspondence. The advantage in this study was the use of fresh unfixed specimens, which always gives the detailed anatomical findings an edge over thoserecorded in formalin-preserved cadavers. The authors have shown the consistency of transforaminal ligaments in the specimens. They have also shown that relative positions with as little as 1 mm between the ligament and the nerve roots suggest the chance of entrapment of the nerve root by the ligaments. The same study can be extended to patients with low back pain to disclose the relation between the ligaments and nerve root compression. Kinetic study of neural foramen during flexion, extension and rotation can clarify the question of whether the ligament can contribute to nerve root compression. The pathologic changes between the ligament and the surrounding intervertebral structure should be evaluated to determine whether degenerative changes contribute to this condition.

The effects of transforaminal ligaments on the sizes of T-11 to L-5 human intervertebral foramina [4] Presentation In this article the authors have studied four lumbosacral spines and examined 49 intervertebral foramina (IVF). None of the spines exhibited pathologic or minor degenerative changes. They measured the superior to inferior (SI) and anterior to posterior (AP) dimensions of the intervertebral foramen by using calipers. The spines were bisected at the midsagittal plane. The ventral roots of the lumbar spines and lower thoracic spinal nerves were identified. The relative positions of the intervertebral foraminal content were examined with reference to any ligamentous material identified in the foramen. Superior and inferior dimensions were measured in a plane perpendicular to the plane of the disc connected with that intervertebral foramen. The smallest dimension of the entire depth of intervertebral foramen was measured by the probe. In the same manner, AP dimensions parallel to the disc were measured. All the measurements by two observers were repeated three times and averaged. The SI and AP size of foramen and any compartment developed by ligaments were compared using one-way analysis of variance in the different levels of the spine.

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Only 35 of 49 IVF contained at least one transforaminal ligament. Almost 50% of IVF contained more than one ligamentous structure, and the inferior transforaminal ligament is the one most commonly found (40%), followed by the superior transforaminal ligament, which was found in 23% of all IVF. The superior corporotransverse ligament was found in 18% of the IVF. The oblique superior transforaminal ligament, described previously by Amonoo-Kuofi et al. [1, 2] was found to be 13% at this time. The least frequently found was the inferior corporotransverse ligament (4%). The AP of IVF and compartment for the ventral ramus was measured. From the SI dimension of this compartment and IVF, it was found that the transforaminal ligament decreased in functional area in 92% of the samples. The AP dimensions of the compartmentformed by the ventral ramus andthe IVF were not significantly decreased in the presence of the transforaminal ligament. Only 5 of 11 cases were found in which the presence of transforaminal ligament decrease the functional area occupied by the ventral ramus. Interpretation This study provides strong evidence that the transforaminal ligament is not an anomaly, but rather a typical structure in the spine. The dimensions of the intervertebral foramen were measured accurately in the superior-interior and the anterior-posterior direction for each vertebra from T-11 to L-5. The data compared were observed in IVF without a ligament and IVF with a ligament. The superoinferior dimensions of T-12 through L-4 generally had no difference. Statistically, only L-5 has a significantly smaller SI than the rest of the vertebra. The AP dimension was similar in all IVF. The authors have hypothesized that if transforaminal ligaments are present within the IVF, the ventral ramus of the spinal nerve could reduce the space within the foramen. In this article, it was proved that the transforaminal ligament could lead to more space occupation. However, there is no evidence that the size of IVF may be connected with unexplained low back pain. Such lesions as disc prolapse or facet joint hypertrophy obviously lead to diminished spaces, but gradual pathologic changes in patients can also cause such diminished spaces. It is not possible to scrutinize this point in this study, because the spines used in the study were not affected by any visible pathology, and there were neither clinical data nor any clues to pathology. It is well known that the size of the ventral nerve root seems to vary from person to person and from one spinal level to another. The authors made no mention of interpersonal difference of the ventral ramus.

Lumbar foraminal stenosis: critical heights of the intervertebral discs and foramina [10] Presentation Eighteen cadavers (5 men and 13 women) provided 100 lumbar intervertebral foramina for this article. The average age of the subjects was 60 years at the time of death, and specimens with pathologic changes (compression deformity or spondylolisthesis in lumbar vertebrae) were not included in the study. The lumbar spines were frozen into rectangular blocks of ice, and the sections were prepared by using a heavy-duty sledge freezing microtome. The sectioned surfaces were 1 mm apart and were saved as photographs. Of the ten different measurement of the sectioned photographs, the focus was placed on disc heights, foraminal heights, foraminal widths, AP width of the ligamentum flavum, posterior bulging of the intervertebral disc and the width of the posterior osteophyte. In addition, the cross sections of the foraminal area and nerve root were determined using a computerized digitizer system. The anatomical measurement at the different intervertebral levels did not show a significant difference except at the mid-point AP disc height. The lumbosacral level revealed least disc height was at the AP midpoint. The cross-sectional areas of the foramina and nerve root correlated positively. There were significant correlations between the posterior disc heights and the heights of the foramina at the intervertebral space between L-2 and the sacral conjunction. Nerve root compression was found in 21 foramina and their foraminal cross-sectional areas decreased significantly between L3 and S-1. Disc heights and the height of the foraminal cross-sectional area in the nerve root compression groups were significantly smaller than those in the normal group except L-4 and L-5. Posterior disc heights and foraminal heights were especially associated with entrapment and compression of the nerve root. Interpretation In order to study biomechanical deformation of nerve roots, all the tissue components of the neural structure must be understood. The authors limited the geography of stenosis within the intervertebral foramen. The boundary of the intervertebral foramina in lumbar spine is composed of pedicle, pars interarticularis, articular process and ligamentum flavum. Within the intervertebral foramina, the dorsal root ganglion is the largest and most frequent structure. It was found that the observed shape of the foramen changed by narrowing of the disk space. The ratio between the nerve root and cross-sectional area of foramina may indicate the risk of nerve root compression. However, the dorsal root ganglion may compress the nerve root in the inferior lumbar spine because the

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lower portion of the lumbar spine permits a greater range of x-axis rotation. The increased range of motion and greater axial compression load to the inferior spine accelerate the critical chance of low back pain. Intraforaminal ligaments were shortly described in this study. At the upper intervertebral space (L-1 to L-3), the ligaments were attached to the part between the superior margin of the disc and the superior articular process. At the lower intervertebral space (L-3 to S-1), it was attached on the surface of the intervertebral disc and inferior surface of the pedicle. The article did not include the full range of the transforaminal ligament and its biomechanical contribution to the structure. Therefore, it is difficult to understand how many cases of the nerve root compress were affected by the existence of the transforaminal ligament. The answers for correlation between disk height, nerve compression, foramina and its ligament were not cleared in the study either. Even if we know the disc height, it is still not known in which direction the foramen is getting smaller during the dynamic condition. This explains why post disc height cannot be a strong grounds for critical nerve entrapment especially in a neural position. Clinically, the prevalence of nerve root compression increased in the inferior lumbar spine owing to the larger nerve roots in the inferior level. Thus, any reason increasing the ratio between the nerve root sectional area and intraforaminal cross-sectional area may explain the high risk of nerve root entrapment.

Discussion The relationship between the lumbosacral nerve root, the surrounding tissue and transforaminal ligaments is rarely observed. The origin of symptoms of sciatica and reasons for the intermittent entrapment of the sciatic nerve are not usually investigated. The existence of ligamentous elements related to the intervertebral foramen was hardly ever described in anatomical studies conducted before 1969. It was presented as nonexistent in most lumbosacral spines or as an anomalous structure of the vertebra, and it was claimed that the ligaments appeared in a random pattern. Since 1988, Amonoo-Kuofi et al. [1, 2] and other researchers have suggested that lumbar foraminal ligaments may contribute to the normal function of the lumbosacral spine. Most anatomical studies reported since then clearly show the existence of the lumbar intervertebral foraminal ligaments. These studies used modern technologies such as CT, MRI and digitized imaging. It was found that the foraminal ligaments were present in all specimens and at all levels of the lumbar spine. Church et al. [6] explored the pattern of ligament distribution in 94% of the foraminal space. Based on the transverse diameter of the neural compartment, 35% of the foramen area is occupied by the nerve root. The existence of the ligament significantly reduced the space available in the fo-

ramen. Nevertheless, there was no evidence that those ligaments exerted any pressure on the vessels transversing the foramen. It is hypothesized that these ligaments diminish the space available for the nerve roots within the foramina. The exact clinical significance of the ligaments in causing nerve root compression and the low back pain has yet to be established. On the other hand, there is no clear consensus on terminology, the same terms being used to describe different transforaminal ligaments. It needs to be standardized before any real understanding of the osseous extraspinal relationships of the ligaments becomes possible. Degenerative arthritis of the posterior facet is known to be the most common sequential change to result from lumbar disc space narrowing. In such cases there is a biomechanical disturbance in the vertebral body. When the intervertebral distance decreases, it results in anterior or posterior displacement rather than a smooth sliding movement of the vertebral body. The increased movement creates the destructive effect on the disc and the articular process. Significant positive correlations were demonstrated between posterior disk height and foraminal cross-sectional area. Nerve root compression was found in all groups that had a decreased foraminal cross-sectional area. With degeneration of the disc and the narrowing of the disc space in turn, there is a possibility that the intervertebral foramen will become narrowed. The associated ligaments can increase hypertrophy along the adjacent articular surfaces as a part of the degenerative mechanism, which may effect compression on the exiting nerve roots. It is also postulated that when the thecal tube shifts forward during the straight leg raising test the nerve root could be compressed by the thickened degenerated corporotransverse ligaments. The presence of foraminal ligaments in the lumbosacral spine is clinically important. There are numerous reports of failures of surgical decompression. It is of critical importance that a diagnostic method is available to detect whether the foramen is compressed or not. CAT scan and MR studies can visualize close relationships between these ligaments and the nerve roots. What needs to be done in the future is to correlate the role of transforaminal ligaments in nerve root entrapment and radiological appearances in patients with low back pain. Thin (1 mm) sections through the intervertebral foramen in both the sagittal and the axial planes with 3-D reconstruction should be routinely used in those patients with back pain without obvious compressive elements explaining the pain. Functional MRI might be useful to detect the effect of these ligaments on the nerve roots in the axial loading. The use of an operating microscope and demonstration of the relief of nerve root compression when the ligaments are sectioned can be used as a substitute to confirm the hypothesis. In the future, the question of whether the movement of ligaments results in nerve root compression under dynamic conditions needs to be answered.

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