Intervertebral foraminal ligaments of the lumbar spine: anatomy and biomechanics

A comparative study of the anatomy and MRI images of the lumbar foraminal ligaments at the L1-L5 levels

PURPOSE

The purpose of this study was to evaluate the ability of MRI images to reveal foraminal ligaments at levels L1-L5 by comparing the results with those of anatomical studies.

METHODS

Eighty lumbar foramina were studied. First, the best MRI scanning parameters were selected, and the transverse and sagittal axes of each lumbar foramina were scanned to identify and record the ligament-like structures in each lumbar foramen. Then, the cadaveric specimens were anatomically studied, and all ligament structures in the lumbar foramina were retained. The number, morphology and distribution of ligaments under anatomical and MRI scanning were observed. Histological staining of the dissected ligament structures was performed to confirm that they were ligamentous tissues. Finally, the accuracy of ligament recognition in MRI images was statistically analyzed.

RESULTS

A total of 233 foraminal ligaments were identified in 80 lumbar intervertebral foramina through cadaveric anatomy. The radiating ligaments (176, 75.5%) were found to be attached from the nerve root to the surrounding osseous structures, while the transforaminal ligaments (57, 24.5%) traversed the intervertebral foramina without any connection to the nerve roots. A total of 42 transforaminal ligament signals and 100 radiating ligament signals were detected in the MRI images of the 80 intervertebral foramina.

CONCLUSION

The MRI can identify the lumbar foraminal ligament, and the recognition rate of the transforaminal ligament is higher than that of the radiating ligament. This study provides a new method for the clinical diagnosis of the relationship between the lumbar foraminal ligament and radicular pain.

In vivo detection of the lumbar intraforaminal ligaments by MRI

PURPOSE

Intraforaminal ligaments (IFL) are of great interest to anatomists and clinicians to fully understand the detailed anatomy of the neuroforamina and to diagnose unclear radicular symptoms. Studies published until now have described radiological imaging of the IFLs using magnetic resonance imaging (MRI) on donor bodies. In the present study, we investigated the detectability of lumbar IFLs in vivo in adults using the high spatial resolution of the constructive interference in steady state (CISS) sequence.

METHODS

A total of 14 patients were studied using a 1.5 T MRI scanner. The lumbar spine was imaged using the parasagittal CISS sequence, and the detectability of the IFLs was assessed for each lumbar level. All image datasets were analyzed by a radiologist, an orthopedic surgeon, and an anatomist. Interrater reliability was expressed as Fleiss' Kappa. Using a single data set, a three-dimensional (3D) model was created to map the location of the IFLs within the intervertebral foramen (IF) and the immediate surrounding vessels.

RESULTS

Overall, the radiologist was able to detect IFLs in 60% of all imaged IFs, the orthopedic surgeon in 62%, and the anatomist in 66%. Fleiss' Kappa for the various segments varies from 0.71 for L4/5 up to 0.90 for L3/4.

CONCLUSION

Lumbar IFLs were successfully detected in vivo in every patient. The detection frequency varied from 42-86% per IF. We demonstrated reproducible imaging of the IFLs on MRI, with good interrater reliability. The present study was a launching point for further clinical studies investigating the potential impact of altered IFLs on radicular pain.

Structure of Lumbar Intervertebral Foraminal Ligaments Based on 3-Dimensional Reconstruction Through Ultrathin Cryomilling of a Human Cadaver

BACKGROUND

This study aimed to assess the feasibility of using the 3-dimensional (3-D) reconstruction technique based on ultrathin cryomilling to show the lumbar intervertebral foraminal ligaments in situ.

METHODS

Cryomilling was performed on an embalmed human cadaver to acquire successive cross-sectional images. In each of the images, the boundaries of lumbar intervertebral foraminal ligaments and their adjacent structures were outlined, labeled, and reconstructed for 3-D modeling. The morphology, attachments, and spatial orientation of ligaments were described.

RESULTS

A total of 9 ligaments in 10 lumbar intervertebral foramina (IVFs) were identified and reconstructed. These ligaments can be divided into 5 types. The IVFs were divided into 2 or 3 main portions by the first 4 types of ligaments (transforaminal ligaments, corporotransverse ligaments, "reticular" ligaments, and "Y-shaped" ligaments). The radiating ligaments (the fifth type of ligaments) attached to the surrounding structures of the IVF and were connected directly to the nerve root sleeves. Although there was no indication of neurovascular compromise in this normal specimen, these ligaments limit the space within the bony IVF such that under certain pathologic conditions (e.g., inflammation), their presence would make neurovascular compression more likely than if they were absent.

CONCLUSIONS

The 3-D reconstruction technique based on ultrathin cryomilling can effectively show the lumbar intervertebral foraminal ligaments and their anatomical characteristics in situ, providing a new way to clarify the relationships between these ligaments and their adjacent structures.

Clinical Outcome of Minimally Invasive Decompression Without Discectomy in Contained Foraminal Disc Herniation: A Single-Center Study

BACKGROUND

Foraminal disc herniation is rare. When conservative treatment fails, it is often treated with discectomy via a paraspinal or Wiltse approach. In contained foraminal disc herniation, more symptoms arise from the foraminal compression of the exiting nerve root, including the dorsal root ganglion, than from the herniation itself. We aimed to evaluate the benefits of stand-alone decompression without discectomy for patients with contained foraminal disc herniation.

METHODS

This study included 17 patients with unilateral single-level foraminal disc herniation (14 women and 3 men; mean age, 62.8 ± 14.6 years, range, 37-86 years). Disc herniation was confirmed as contained by preoperative magnetic resonance imaging and/or computed tomography and by intraoperative exploration. All patients underwent thorough decompression without discectomy, via a paraspinal approach. Pain was evaluated preoperatively and at 3 and 12 months postoperatively using a visual analog scale (VAS). The Oswestry Disability Index (ODI) and Macnab criteria were used to evaluate final outcomes.

RESULTS

The most commonly affected level was L5-S1. All 17 patients showed significant improvements in VAS and ODI scores at 3 and 12 months postoperatively. According to the Macnab criteria, outcome results were excellent in 13 patients and good in 4. The mean duration of follow-up was 18.4 ± 2.4 months, with no recurrences or lumbar instability at the final follow-up.

CONCLUSIONS

Stand-alone decompression without discectomy is an effective method for relieving symptoms and preserving the disc in contained foraminal disc herniation. A minimally invasive approach with thorough decompression techniques yields good results.

Effectiveness of Percutaneous Lumbar Extraforaminotomy in Patients with Lumbar Foraminal Spinal Stenosis: A Prospective, Single-Armed, Observational Pilot Study

Objective

In lumbar foraminal spinal stenosis (LFSS), numerous ligaments may play an important role in causing radiculopathy by narrowing the exit of the nerve root. In order to achieve effective decompression of lumbar foraminal ligaments, a specially designed instrument for percutaneous lumbar extraforaminotomy (PLEF) was invented. The purpose of this study was to evaluate the effectiveness of PLEF in patients with intractable radiculopathy from LFSS.

Design

A prospective, single-armed, observational pilot study.

Setting

A pain center in a tertiary university-based hospital.

Methods

The PLEF was performed in patients who suffered from radiculopathy with concordant imaging evidence of a mild to severe degree of LFSS. For each patient, an 11-point numerical rating scale (NRS) pain score, the Oswestry Disability Index (ODI), the Roland Morris Disability Questionnaire (RMDQ) score, and any adverse events were evaluated at three-month follow-ups. Successful responder percentage defined as 40% or greater reduction from baseline NRS score with no increase in ODI, and the RMDQ score was assessed at three months.

Results

Among 26 patients who underwent PLEF, 20 patients completed the study protocol. PLEF was successful in 12 patients (60%). The overall mean pain reduction at three months was 36.3%. Patients who responded well also showed improvement in the ODI (-20%) and RMDQ score (-8.4) at their three-month follow-up. No serious complications were reported in the study.

Conclusions

The PLEF can be an effective and safe treatment option, as well as a minimally invasive procedure, for the management of patients suffering from refractory radiculopathy caused by LFSS.

The morphology and clinical significance of the intraforaminal ligaments at the L5-S1 levels

BACKGROUND CONTEXT

The extraforaminal ligaments between the L5 and S1 lumbar spinal nerves and the tissues surrounding the intervertebral foramina have been well studied. However, little research has been undertaken to describe the local anatomy of the intraforaminal portion of the L5-S1 spine and detailed anatomical studies of the intraforaminal ligaments (IFLs) of the L5-S1 have not been performed.

PURPOSE

The objective of this study was to identify and describe the IFLs in relation to the L5-S1 intervertebral foramen (IVF) and to determine their clinical significance.

STUDY DESIGN

A dissection-based study of five embalmed and five fresh-frozen human cadavers was carried out.

METHODS

Twenty L5-S1 intervertebral foramina from five embalmed cadavers and five fresh cadavers were studied, and the IFLs were identified. The quantity, morphology, origin, insertion, and spatial orientation of the IFLs in the L5-S1 region were observed. The length, width, diameter, and thickness of the ligaments were measured with a vernier caliper. This study has been supported by grants from the National Natural Science Foundation of China (Grant No. 31271286) without potential conflict of interest-associated biases in the text of the paper.

RESULTS

The IFLs could be found from the entrance zone (inside) to the exit zone (outside) of the L5-S1 IVF. These ligaments were found to be of two types: a radiating ligament, which connected the nerve root sleeves that radiated to the transverse processes and wall of the IVF, and a transforaminal ligament, which connected the structures around the IVF. In our study, the radiating ligaments were found more often than the transforaminal ligaments.

CONCLUSIONS

The results demonstrate that IFLs are common structures in the IVF and that there are two types of IFLs: the transforaminal ligaments and the radiating ligaments. Transforaminal ligaments may be the potential cause of back pain. The radiating ligaments may contribute to dura laceration and epidural hemorrhage during endoscopic spinal adhesiolysis through the sacral hiatus, and an appreciation of this relationship might help reduce the risk of such complications.

2015 Young Investigator Award Winner: Cervical Nerve Root Displacement and Strain During Upper Limb Neural Tension Testing: Part 2: Role of Foraminal Ligaments in the Cervical Spine

STUDY DESIGN

A cross-sectional cadaveric examination of the mechanical effect of foraminal ligaments on cervical nerve root displacement and strain.

OBJECTIVE

To determine the role of foraminal ligaments by examining differences in cervical nerve root displacement and strain during upper limb neural tension testing (ULNTT) before and after selective cutting of foraminal ligaments.

SUMMARY OF BACKGROUND DATA

Although investigators have determined that lumbar spine foraminal ligaments limit displacement and strain of lumbosacral nerve roots, similar studies have not been conducted to prove that it is true for the cervical region. Because the size, shape, and orientation of cervical spine foraminal ligaments are similar to those in the lumbar spine, it is hypothesized that foraminal ligaments in the cervical spine will function in a similar fashion.

METHODS

Radiolucent markers were implanted into cervical nerve roots C5-C8 of 9 unembalmed cadavers. Posteroanterior fluoroscopic images were captured at resting and upper limb neural tension testing positioning before and after selective cutting of foraminal ligaments.

RESULTS

Selective cutting of foraminal ligaments resulted in significant increases in inferolateral displacement (average, 2.94 mm [ligaments intact]-3.87 mm [ligaments cut], P < 0.05) and strain (average, 9.33% [ligaments intact]-16.31% [ligaments cut], P < 0.03) of cervical nerve roots C5-C8 during upper limb neural tension testing.

CONCLUSION

Foraminal ligaments in the cervical spine limited cervical nerve root displacement and strain during upper limb neural tension testing. Foraminal ligaments seem to have a protective role, reducing displacement and strain to cervical nerve roots during tension events.

LEVEL OF EVIDENCE

2.

The morphology and clinical significance of the extraforaminal ligaments at the cervical level

STUDY DESIGN

A dissection-based study of 6 embalmed cadavers.

OBJECTIVE

To identify and describe the extraforaminal ligaments (EFLs) in relation to the area of the cervical intervertebral foramina and to evaluate their clinical significance.

SUMMARY OF BACKGROUND DATA

EFLs between the lumbar spinal nerves and the tissues surrounding the intervertebral foramens have been well established. However, research work has been undertaken to describe the local anatomy of the extraforaminal part of the cervical spine; detailed anatomic studies of the EFLs of cervical nerves have not been performed.

METHODS

One hundred ninety-six cervical intervertebral foramina from 6 adult embalmed cadavers were studied, and the existence and type of the EFLs were identified. The morphology, quantity, origin, insertion, and the spatial orientation of the EFLs in the cervical region were observed, and the length, width, or diameter and thickness of the ligaments were measured with a vernier caliper.

RESULTS

The EFLs could be found from the second cervical to the first thoracic spinal nerve. These ligaments could be divided into 2 types: radiating ligaments, which connected the nerve root sleeves that radiated to the transverse processes, the wall of the intervertebral foramina, and even the adjacent nerve root through the small transverse foramen; transforaminal ligaments, which originated from the anteroinferior margin of cranial transverse process and inserts in the superior margin of the anterior tubercle of caudal transverse process crossing the spinal nerve ventrally.

CONCLUSION

Between the cervical spinal nerves and nearby structures, there are 2 types of the EFLs. The radiating ligaments may serve as a protective mechanism against traction and play an important role in the positioning of the nerves in the intervertebral foramen. However, in all probability, the transforaminal ligaments may be the underlying cause of the cervical radiculopathy.

Thoracic and lumbar intraforaminal ligaments

OBJECT

The author conducted a study to investigate the anatomy of the intraforaminal ligaments of the thoracic and lumbar nerve roots and describe their anatomical relationships and functional properties. This anatomical study performed on the intervertebral foramina, intraforaminal ligaments, transforaminal ligaments, and nerve roots of the thoracic and lumbar spine was performed in human cadavers.

METHODS

The foraminal anatomy was studied in 11 whole cadavers (5 females, 6 males) previously prepared with formaldehyde, whose ages at the time of death ranged from 16 to 71 years. The thoracic and lumbar spinal columns were separated from the cervical and sacral segments en bloc using an electric band saw. The paraspinal muscles and their attachments were removed by sharp and meticulous dissection, and the thoracic and lumbar intervertebral foramina were examined under a surgical microscope. The intervertebral foraminal ligaments and nerve roots were exposed. The foraminal contents were identified and studied in detail. The intraforaminal ligaments were stained using H & E to determine ligamentous fiber.

RESULTS

Intraforaminal ligaments connect the periosteum and transforaminal ligaments to the nerve root sleeves and vessels within the fatty areolar tissue. Histologically, the ligamentous attachment of the nerve roots within the foramina consists of adipose and connective tissue.

CONCLUSIONS

The nerve roots are surrounded by intraforaminal ligaments, which may act in conjunction with the dura and periosteum to protect the nerve roots mechanically.

Extraforaminal lumbar interbody fusion for the treatment of isthmic spondylolisthesis

STUDY DESIGN

A preliminary study about extraforaminal lumbar interbody fusion (ELIF) technique for the treatment of isthmic spondylolisthesis.

OBJECTIVE

To introduce a new surgical fusion technique for isthmic spondylolisthesis with minimally invasive procedure.

SUMMARY OF BACKGROUND DATA

Posterolateral fusion, posterior lumbar interbody fusion, and anterior lumbar interbody fusion with posterior fixation are the options of the surgical treatment for isthmic spondylolisthesis. Still, complications can be related to these approaches. The authors tried to approach directly to lesion-the exiting nerve root, to decompress and to stabilize with minimally invasive procedure. Through extraforaminal approach, we can expose the exiting nerve root only to perform interbody fusion without intra-abdominal dissection or exposing central dura and traversing nerve root.

METHODS

Five patients with isthmic spondylolisthesis underwent ELIF with percutaneous pedicle screw fixation (PPF) between August 2005 and April 2007. In all subjects, the 3-cm-long posterior skin incisions were made bilaterally about 6 to 8 cm lateral from the midline. The multifidus muscle was separated with blunt dissection from the longissimus muscles. We identified the isthmus and neural foramen, removed fibrocartilage and the lateral border of ligamentum flavum covering the exiting nerve root, separated the soft tissue attached to the root and the transverse process, and retracted the root to perform discectomy. We prepared the endplates, cages with allograft, inserted them under C-arm fluoroscopic guidance, and performed the procedures on the contralateral side. After the arthrodesis, posterior instrumentation was augmented with PPF.

RESULTS

Five patients underwent ELIF+PPF; despite a small number of cases, the outcomes were satisfactory.

CONCLUSIONS

ELIF technique makes exposing only the exiting nerve root easy to perform interbody fusion without violating either the abdominal cavity or the posterior musculoligamentous and the bony stabilizers of the spine. This may be considered as one of the minimally invasive surgical options for isthmic spondylolisthesis.

Anatomic Analysis of the Transforaminal Ligament in the Lumbar Intervertebral Foramen

OBJECTIVE:

The objective of this study was to evaluate the clinical significance of the transforaminal ligaments (TFLs) in relation to the area of the lumbar intervertebral foramen (IVF) by analyzing cadaveric spines.

METHODS:

One hundred ninety-eight cadaveric lumbar IVFs were studied, and the existence and type of TFLs were identified. All IVFs were photographed, and the images were saved. The areas of the IVFs and TFLs were measured with the Scion Image for Windows image analysis program.

RESULTS:

TFLs were found in 82.8% of the IVFs. The oblique inferior transforaminal ligament was the most common. The mean area of the IVFs was 155.8 ± 51.1 mm2, and the mean area occupied by the TFLs was 46.3 ± 37.6 mm2. The mean percentage of the IVF area occupied by the TFLs was 28.5 ± 18.8%.

CONCLUSION:

TFLs are common structures in the IVF and may reduce the space available for the spinal nerve root within the IVF. In this circumstance, any compromise of the IVF may impinge on the nerve root.

Extraforaminal ligament attachments of human lumbar nerves

STUDY DESIGN

An anatomic study of the extraforaminal attachments of the lumbar spinal nerves was performed using human lumbar spinal columns.

OBJECTIVES

To identify and describe the existence of ligamentous structures at each lumbar level that attach lumbar spinal nerves to structures at the level of the extraforaminal region.

SUMMARY OF BACKGROUND DATA

During the last 120 years, several mechanisms to protect the spinal nerve against traction have been described. All these structures involved are located in the spinal canal, proximal to the intervertebral foramen.

METHODS

Five embalmed human lumbar spines (T12-S1) were used. Bilaterally, the extraforaminal region was dissected to describe and measure anatomic structures and their relationships. Histology was performed with staining on the sites of attachment and along the ligament.

RESULTS

The levels T12-L2 show bilaterally 2 ligaments, a superior extraforaminal ligament and an inferior extraforaminal ligament. The superior extraforaminal ligament emerges from the joint capsule of the facet joints and inserts in both, the intervertebral disc and the ventral crista of the intervertebral foramen, passing the spinal nerve laterally. In one specimen on level L2-L3, the superior extraforaminal ligament is not attached to the spinal nerve. The inferior extraforaminal ligament emerges from the intervertebral disc, passing the nerve medially and attaching the spinal nerve. At the levels L2-L5, the inferior extraforaminal ligaments are only attached to the intervertebral disc, not to the joint capsule. Histologically, the ligaments consisted of mainly collagenous structures.

CONCLUSION

Ligamentous connections exist between lumbar extraforaminal spinal nerves and nearby structures.