The denticulate ligament: anatomical properties, functional and clinical significance

Neural canal ridges: A novel osteological correlate of postcranial neuroanatomy in dinosaurs

In this article, we document the widespread presence of bony ridges in the neural canals of non-avian dinosaurs, including a wide diversity of sauropods, two theropods, a thyreophoran, and a hadrosaur. These structures are present only in the caudal vertebrae. They are anteroposteriorly elongate, found on the lateral walls of the canal, and vary in size and position both taxonomically and serially. Similar bony projections into the neural canal have been identified in extant teleosts, dipnoans, and urodelans, in which they are recognized as bony spinal cord supports. In most non-mammals, the dura mater that surrounds the spinal cord is fused to the periosteum of the neural canal, and the denticulate ligaments that support the spinal cord can pass through the dura and periosteum to anchor directly to bone. The function of these structures in dinosaurs remains uncertain, but in sauropods they might have stabilized the spinal cord during bilateral movement of the tail and use of the tail as a weapon. Of broader significance, this study emphasizes that important new discoveries at the gross anatomical level can continue to be made in part by closely examining previously overlooked features of known specimens.

Straight leg raise versus knee extension angle: which structure limits the test in asymptomatic subjects?

OBJECTIVES

This study aimed to determine if the first onset of symptoms (discomfort) during the straight leg raise (SLR) (hip flexion with an extended knee) and the Knee Extension Angle (KEA) tests (knee extension with 90°of hip flexion) results from nervous or muscular structures in asymptomatic individuals. The secondary objective was to investigate if the gender influences the structure related to the discomfort.

METHODS

This cross-sectional study consisted of a single assessment session during which the structure related to participants' discomfort during the KEA and SLR was identified. For this identification, a structural differentiation (SD) was conducted during both tests using passive mobilization of the cervicothoracic spine in flexion and extension. Changes in participants' discomfort were monitored during the SD to determine whether a change or lack of change was consistent with variations in the load applied to the suspected structures either muscular or neural. If the structure related to the participants' discomfort could not be identified, two additional tests were conducted: the lateral SLR and the Slump test.

RESULTS

One hundred and seventy-eight individuals were included. Median [IQR] age was 21 years [20;23], and 57.3% were female. The structure related to participants' discomfort was similar for the SLR and the KEA (p = 0.451): neural for 72.5% of participants in the SLR and 75.8% in the KEA. Gender only influenced the structure identified in the KEA test, with a significantly higher rate of nerve-related discomfort in females than males and a significantly higher rate of muscle-related discomfort in males (p = 0.002).

CONCLUSION

In asymptomatic individuals, the discomfort induced by the SLR and the KEA tests could be related to either muscular or neural structures. Therefore, structural differentiation is necessary to identify the structure causing the discomfort in both research and clinical practice.

Exploring the effect of displacement rate on the mechanical properties of denticulate ligaments through uniaxial tensile testing

Denticulate ligaments play a key role in stabilizing the spinal cord (SC). Accurate representation of these structures in finite element modelling, whether in quasi-static or dynamic conditions, is essential for providing biofidelic responses. Therefore, understanding, characterizing and comparing the tensile mechanical properties of denticulate ligaments at different loading velocities is crucial. A total of 38 denticulate ligament samples at different cervical levels (anatomical levels from C1 to C7) were obtained from 3 fresh porcine SCs and 86 uniaxial tensile tests were performed immediately after dissection using an electro-mechanical testing system equipped with a 22 N loadcell. The mechanical tests included 10 cycles of preconditioning and a ramp with displacement rates of 0.1 mm s-1, 1 mm s-1 and 10 mm s-1. Bilinear piecewise fitting and trilinear piecewise fitting were performed to determine the elastic modulus and maximum stress and strainof the samples. While no significant differences in the mechanical behavior of the denticulate ligaments were found across the different displacement rates, notable variations were found between spinal levels, with a significantly higher elastic modulus at the lower cervical levels.

Atlas orthogonal chiropractic management of trigeminal neuralgia: A series of case reports

CONTEXT

Trigeminal neuralgia is a debilitating facial pain condition. Upper cervical chiropractic care has been mentioned as a possible solution OBJECTIVE: To determine the effects of Atlas Orthogonal upper cervical chiropractic technique adjustments on trigeminal neuralgia sufferers DESIGN: Case series SETTING: A private chiropractic practice PARTICIPANTS: Five persons with chronic, severe, daily trigeminal neuralgia pain, radiological findings of significant head tilt, pain upon upper cervical palpation, and supine leg length inequality INTERVENTIONS: Up to two consultations and/or Atlas Orthogonal adjustments a week for eight weeks OUTCOME MEASURES: Self-reported reduction in trigeminal neuralgia pain and changes in radiological findings, sensitivity to upper cervical palpation, and leg length inequality RESULTS: Four participants reported reduced trigeminal neuralgia pain, including two with complete cessation of pain. Three participants reduced medication dosages. One reported no change.

Mechanical differences of anterior and posterior spinal nerve roots revealed by tensile testing

Cervical spondylotic myelopathy can damage the nerves and structures of the subarachnoidal canal. The spinal cord is attached to the subarachnoidal canal via structures such as nerve roots (NR), which play an important role in its positioning and can be affected by cervical spondylotic myelopathy Understanding the tensile mechanical properties of nerve roots is therefore crucial. A total of 37 swine nerve samples (15 bundles, 12 posterior roots, and 10 anterior roots) were mechanically tested within 12 h of sacrifice by a tensile test on a Mach 1 system (Biomomentum, Montreal, Canada) equipped with a 17 N load cell. Bi-linear piecewise fitting was performed to determine the elastic modulus, maximal strain and stress at failure, as well as the coefficients of the 1st- and 3rd-order Ogden models. Additionally, a sensitivity analysis on the Ogden coefficients was performed. The elastic modulus for the bundles, posterior roots, and anterior roots were 3.7 ± 3.1 MPa, 0.23 ± 0.18 MPa, and 0.31 ± 0.27 MPa, respectively. Significant differences (P < 0.05) were found between the bundles and the anterior/posterior roots. Coefficients for the 1st-, 2nd- and 3rd-order Ogden models were provided for each type of sample. Nerve roots have different properties depending on their types. The 1st-order Ogden model may be used to model the mechanical properties of NR using constitutive laws.

Comparison of biomechanical parameters of two Chinese cervical spine rotation manipulations based on motion capture and finite element analysis

Objective: The purpose of this study was to obtain the stress-strain of the cervical spine structure during the simulated manipulation of the oblique pulling manipulation and the cervical rotation-traction manipulation in order to compare the mechanical mechanism of the two manipulations. Methods: A motion capture system was used to record the key kinematic parameters of operating the two manipulations. At the same time, a three-dimensional finite element model of the C0-T1 full healthy cervical spine was established, and the key kinematic parameters were loaded onto the finite element model in steps to analyze and simulate the detailed process of the operation of the two manipulations. Results: A detailed finite element model of the whole cervical spine including spinal nerve roots was established, and the validity of this 3D finite element model was verified. During the stepwise simulation of the two cervical spine rotation manipulations to the right, the disc (including the annulus fibrosus and nucleus pulposus) and facet joints stresses and displacements were greater in the oblique pulling manipulation group than in the cervical rotation-traction manipulation group, while the spinal cord and nerve root stresses were greater in the cervical rotation-traction manipulation group than in the oblique pulling manipulation group. The spinal cord and nerve root stresses in the cervical rotation-traction manipulation group were mainly concentrated in the C4/5 and C5/6 segments. Conclusion: The oblique pulling manipulation may be more appropriate for the treatment of cervical spondylotic radiculopathy, while cervical rotation-traction manipulation is more appropriate for the treatment of cervical spondylosis of cervical type. Clinicians should select cervical rotation manipulations for different types of cervical spondylosis according to the patient's symptoms and needs.

Epidural and Intrathecal Drug Delivery in Rats and Mice for Experimental Research: Fundamental Concepts, Techniques, Precaution, and Application

Epidural and intrathecal routes are the most effective drug administration methods for pain management in clinical and experimental medicine to achieve quick results, reduce required drug dosages, and overcome the adverse effects associated with the oral and parenteral routes. Beyond pain management with analgesics, the intrathecal route is more widely used for stem cell therapy, gene therapy, insulin delivery, protein therapy, and drug therapy with agonist, antagonist, or antibiotic drugs in experimental medicine. However, clear information regarding intrathecal and epidural drug delivery in rats and mice is lacking, despite differences from human medicine in terms of anatomical space and proximity to the route of entry. In this study, we discussed and compared the anatomical locations of the epidural and intrathecal spaces, cerebrospinal fluid volume, dorsal root ganglion, techniques and challenges of epidural and intrathecal injections, dosage and volume of drugs, needle and catheter sizes, and the purpose and applications of these two routes in different disease models in rats and mice. We also described intrathecal injection in relation to the dorsal root ganglion. The accumulated information about the epidural and intrathecal delivery routes could contribute to better safety, quality, and reliability in experimental research.

Spinal Cord Boundary Conditions Affect Brain Tissue Strains in Impact Simulations

Brain and spinal cord injuries have devastating consequences on quality of life but are challenging to assess experimentally due to the traumatic nature of such injuries. Finite element human body models (HBM) have been developed to investigate injury but are limited by a lack of biofidelic spinal cord implementation. In many HBM, brain models terminate with a fixed boundary condition at the brain stem. The goals of this study were to implement a comprehensive representation of the spinal cord into a contemporary head and neck HBM, and quantify the effect of the spinal cord on brain deformation during simulated impacts. Spinal cord tissue geometries were developed, based on 3D medical imaging and literature data, meshed, and implemented into the GHBMC 50th percentile male model. The model was evaluated in frontal, lateral, rear, and oblique impact conditions, and the resulting maximum principal strains in the brain tissue were compared, with and without the spinal cord. A new cumulative strain curve metric was proposed to quantify brain strain distribution. Presence of the spinal cord increased brain tissue strains in all simulated cases, owing to a more compliant boundary condition, highlighting the importance of the spinal cord to assess brain response during impact.

Cervical Transdural Discectomy with Laminoplasty for the Treatment of Multi-segment Cervical Spinal Stenosis Accompanied with Cervical Disc Herniation: Technical Note and Clinical Outcome

Objective

To describe the surgical technique of cervical transdural discectomy with laminoplasty (CTDL) for the treatment of multi‐segment cervical spinal stenosis (CSS) accompanied with cervical disc herniation (CDH) and investigate its surgical outcomes and complications.

Methods

This was a clinical study. Between 2012 and 2018, 31 patients (13 males and 18 females) with multi‐segment CSS (over two cervical segments) accompanied with huge CDH and underwent CTDL were enrolled in this study. The details of CTDL technique with general anesthesia was described by the authors. The average follow‐up period of patients was 65.03 months (range from 24 to 126 months). Perioperative parameters such as age, sex, operative level, operative time, estimated blood loss, ambulation time, and operative complications were recorded. The results of clinical metrics such as the visual analog scale (VAS) and Japanese Orthopaedic Association (JOA) scores in the preoperative and during the follow‐up period were obtained and used to evaluate clinical outcomes. Radiographic improvement was evaluated by the compression ratio, sagittal maximum spinal cord compression (SMSCC), and cervical range of motion (ROM). The preoperative and postoperative follow‐up parameters (VAS, JOA, Compression ratio, SMSCC, and ROM) were assessed with paired t test. A P‐value <0.05 was considered statistically significant.

Results

In the study, the mean age of the 31 patients was 55.23 ± 10.97 years. The mean operative time was 192.45 ± 24.17 min (ranging from 150 to 245 min), and intraoperative blood loss was 322.58 ± 129.00 mL (ranging from 150 to 600 mL). The VAS neck pain was improved significantly over the follow‐up period (P < 0.05, respectively). The VAS arm pain improved significantly from 6.26 ± 0.93 preoperatively to 1.74 ± 0.63 at 24 months postoperatively (P < 0.001). There was no significant difference in improvement of VAS arm pain between 24 months postoperatively and final follow‐up (P = 0.180). Compared with preoperative JOA score, JOA score was significantly improved at 24 months postoperatively (14.79 ± 1.84 vs 9.66 ± 2.81, P < 0.001). Meanwhile, there were no statistically significant differences between the final follow‐up and the postoperative JOA scores (15.08 ± 1.71 vs 14.79 ± 1.84, P = 0.051). Postoperative patients showed significantly higher index of compression ratio (58.30 ± 8.51 vs 27.17 ± 3.89, P < 0.001) and lower SMSCC (25.12 ± 5.67 vs 33.66 ± 5.38, P < 0.001). In addition, there was no significant difference between preoperative and postoperative cervical ROM (P = 0.740). One patient observed postoperative symptom of C₆ nerve root injury, which was resolved within 24 months after the surgery; meanwhile, the neurological monitoring also reflected the intraoperative stretching of the C₆ nerve root. Two cases involved postoperative cerebrospinal fluid (CSF) leakage which may have been related to laceration of dura mater.

Conclusions

This study suggested that CTDL technique could acquire satisfactory surgical outcomes for patients with multi‐segment CSS accompanied with CDH, but the surgical indications of the patients need to be selected strictly.

Anterior approach to remove a pre-medullary meningioma in the cervical spine: Technical case report

BACKGROUND

Regarding their relation to the spinal cord (SC), resection of pre-medullary meningiomas may be technically challenging. Anterior approach via corpectomy represents a nice option reducing the need for mobilization of the SC.

CASE DESCRIPTION

We describe the case of a patient presenting with a cervical meningioma, located anterior to the SC and operated on through an anterior approach. Surgery consisted of a 2-levels discectomy and C7 corpectomy, midline opening of the dura and then microsurgical resection of the tumor. After coagulation of the implantation base, the dura was then closed in a watertight fashion. Finally, the anterior column was reconstructed using a titanium mesh-cage and anterior plating.

CONCLUSION

In the case of cervical meningioma located anterior to the SC, anterior approach may be considered as an alternative option to remove the tumor.

Arachnoid and dural reflections

The dura mater is the major gateway for accessing most extra-axial lesions and all intra-axial lesions of the central nervous system. It provides a protective barrier against external trauma, infections, and the spread of malignant cells. Knowledge of the anatomical details of dural reflections around various corners of the skull bases provides the neurosurgeon with confidence during transdural approaches. Such knowledge is indispensable for protection of neurovascular structures in the vicinity of these dural reflections. The same concept is applicable to arachnoid folds and reflections during intradural excursions to expose intra- and extra-axial lesions of the brain. Without a detailed understanding of arachnoid membranes and cisterns, the neurosurgeon cannot confidently navigate the deep corridors of the skull base while safely protecting neurovascular structures. This chapter covers the surgical anatomy of dural and arachnoid reflections applicable to microneurosurgical approaches to various regions of the skull base.

A spinal organ of proprioception for integrated motor action feedback

Proprioception is essential for behavior and provides a sense of our body movements in physical space. Proprioceptor organs are thought to be only in the periphery. Whether the central nervous system can intrinsically sense its own movement remains unclear. Here we identify a segmental organ of proprioception in the adult zebrafish spinal cord, which is embedded by intraspinal mechanosensory neurons expressing Piezo2 channels. These cells are late-born, inhibitory, commissural neurons with unique molecular and physiological profiles reflecting a dual sensory and motor function. The central proprioceptive organ locally detects lateral body movements during locomotion and provides direct inhibitory feedback onto rhythm-generating interneurons responsible for the central motor program. This dynamically aligns central pattern generation with movement outcome for efficient locomotion. Our results demonstrate that a central proprioceptive organ monitors self-movement using hybrid neurons that merge sensory and motor entities into a unified network.

The Restless Spinal Cord in Degenerative Cervical Myelopathy

BACKGROUND AND PURPOSE

The spinal cord is subject to a periodic, cardiac-related movement, which is increased at the level of a cervical stenosis. Increased oscillations may exert mechanical stress on spinal cord tissue causing intramedullary damage. Motion analysis thus holds promise as a biomarker related to disease progression in degenerative cervical myelopathy. Our aim was characterization of the cervical spinal cord motion in patients with degenerative cervical myelopathy.

MATERIALS AND METHODS

Phase-contrast MR imaging data were analyzed in 55 patients (37 men; mean age, 56.2 [SD,12.0] years; 36 multisegmental stenoses) and 18 controls (9 men, P = .368; mean age, 62.2 [SD, 6.5] years; P = .024). Parameters of interest included the displacement and motion pattern. Motion data were pooled on the segmental level for comparison between groups.

RESULTS

In patients, mean craniocaudal oscillations were increased manifold at any level of a cervical stenosis (eg, C5 displacement: controls [n = 18], 0.54 [SD, 0.16] mm; patients [n = 29], monosegmental stenosis [n = 10], 1.86 [SD, 0.92] mm; P < .001) and even in segments remote from the level of the stenosis (eg, C2 displacement: controls [n = 18], 0.36 [SD, 0.09] mm; patients [n = 52]; stenosis: C3, n = 21; C4, n = 11; C5, n = 18; C6, n = 2; 0.85 [SD, 0.46] mm; P < .001). Motion at C2 differed with the distance to the next stenotic segment and the number of stenotic segments. The motion pattern in most patients showed continuous spinal cord motion throughout the cardiac cycle.

CONCLUSIONS

Patients with degenerative cervical myelopathy show altered spinal cord motion with increased and ongoing oscillations at and also beyond the focal level of stenosis. Phase-contrast MR imaging has promise as a biomarker to reveal mechanical stress to the cord and may be applicable to predict disease progression and the impact of surgical interventions.

The Cranial Bowl in the New Millennium and Sutherland's Legacy for Osteopathic Medicine: Part 2

Cranial osteopathic medicine is practiced all over the world, respecting the dictates of the creator, Dr Sutherland. Despite the current manual approach faithfully follows the theoretical and practical bases that make up the cranial model of the last century, there are many scientific evidences that highlight the criticalities of the same model. In the first part we reviewed the role of the meninges and cerebrospinal fluid (CSF), as well as we discussed some rhythms present in the central nervous system; these latter elements are the pillars to support the theoretical idea of the movement of the skull evaluated and palpated by the osteopath. In this second part we will review the mechanical characteristics of other structures that make up the cranial system, highlighting new perspectives for clinical practice, thanks to the most recent data derived from scientific research.

Cervical Canal Morphology: Effects of Neck Flexion in Normal Condition: New Elements for Biomechanical Simulations and Surgical Management

STUDY DESIGN

Continuous measurements and computation of absolute metrics of cervical subarachnoid space (CSS) and spinal cord (SC) geometries proposed are based on in vivo magnetic resonance imaging and 3D reconstruction.

OBJECTIVE

The aim of the study is to offer a new methodology to continuously characterize and to quantify the detailed morphology of the CSS and the cervical SC in 3D for healthy subjects in both neutral supine and flexion.

SUMMARY OF BACKGROUND DATA

To the best of our knowledge, no study provides a morphological quantification by absolute indices based on the 3D reconstruction of SC and CSS thanks to in vivo magnetic resonance imaging. Moreover, no study provides a continuous description of the geometries.

METHODS

Absolute indices of SC (cross-sectional area, compression ratio, position in the canal, length) and of CSS (cross-sectional area, occupational ratio, lengths) were computed by measures from 3D semi-automatic reconstructions of high resolution in vivo magnetic resonance images (3D T2-SPACE sequence) on healthy subjects (N = 11) for two postures: supine neutral and flexion neck positions. The variability induced by the semi-automatic reconstruction and by the landmarks positioning were investigated by preliminary sensitivity analyses. Inter and intra-variability were also quantified on a randomly chosen part of our population (N = 5).

RESULTS

The length and cross-sectional area of SC are significantly different (P < 0.05) in flexion compared with neutral neck position. Spinal cord stays centered in the canal for both postures. However, the cross-sectional area of CSS is submitted to low variation after C3 vertebra for both postures. Occupational ratio (OR) and compression ratio (CR) after C3 are significantly lower in flexion.

CONCLUSION

This study presented interpretations of morphological measures: (1) left-right stability (described by the Left-Right eccentricity index) ensured by the denticulate ligaments and the nerve roots attached to the dural sheaths, (2) a Poisson effect of the SC was partially notified through its axial (antero-posterior [AP] diameter, OR, CR) and its longitudinal geometrical descriptions (length of spinal cord [LSC]). Such morphological data can be useful for geometrical finite element modeling and could now be used to compare with injured or symptomatic subjects.

LEVEL OF EVIDENCE

3.

The anatomical features of denticulate ligament in human fetuses

PURPOSE

To determine the morphological features of the denticulate ligament in fetal period.

METHODS

Twelve formalin-fixed fetuses (six females and six males) with a mean gestational age of 27.0 ± 2.04 weeks (range between 25 and 32 weeks) were dissected to reveal morphological properties of the denticulate ligaments.

RESULTS

Denticulate ligament was observed as a continuous ligament extending throughout the length of spinal cord in all fetuses. It separated the vertebral canal into two as anterior and posterior parts and was anchored to the dura mater on either side of the spinal cord with mostly triangular processes as well as thin band-like extensions. The first denticulate ligament process was always a large and prominent fibrous band and was arising from the spinal cord surface, extending in an oblique direction upward to the anterolateral rim of foramen magnum, below and posterior to the hypoglossal canal. The last denticulate ligament process was observed either in the T11-12 (2 sides, 8%), T12-L1 (15 sides, 62%) or L1-2 (7 sides, 30%) and all were band-like processes. At certain spinal cord levels, denticulate ligament had no processes to attach duramater while in some other fetuses double denticulate ligament processes were detected within the same interval. The distance between the denticulate ligament process and the superior spinal nerve root and the distance between the denticulate ligament process and the inferior spinal nerve root were measured at each spinal level. This distance was found to be increased from upper to lower levels of the spine.

CONCLUSION

Detailed morphological data about fetal denticulate ligament presented in this study provide significant information which may be essential during several surgical interventions performed in early postnatal period and childhood focusing on the spinal cord, spinal nerve roots and meningeal structures.

Syringosubarachnoid shunt: insertion technique

Background: Syringomyelia is a rare disorder but its impact on patients' quality of life can be devastating. The exact pathophysiology remains unknown; the syrinx can either be idiopathic or associated with conditions such as Chiari malformation, scoliosis, malignancy, infection and trauma. Several techniques have been described to decompress syringomyelia with distal drainage to the subarachnoid space, pleura or peritoneum.Method: We present a modification of the syringosubarachnoid shunt insertion technique with minimal myelotomy and the use of a T shaped shunt which does not require suturing to the pia matter to prevent shunt migration.Conclusion: This technique for syringosubarachnoid shunt insertion is likely to prevent shunt migration and scarring whilst minimizing suturing and optimising syrinx decompression.

Biomechanical Effects on Cervical Spinal Cord and Nerve Root Following Laminoplasty for Ossification of the Posterior Longitudinal Ligament in the Cervical Spine: A Comparison Between Open-Door and Double-Door Laminoplasty Using Finite Element Analysis

Many clinical case series have reported the predisposing factors for C5 palsy and have presented comparisons of the two types of laminoplasty. However, there have been no biomechanical studies focusing on cervical spinal cord and nerve root following laminoplasty. The purpose of this study is to investigate biomechanical changes in the spinal cord and nerve roots following the two most common types of laminoplasty, open-door and double-door laminoplasty, for cervical ossification of the posterior longitudinal ligament (OPLL). A finite element (FE) model of the cervical spine and spinal cord with nerve root complex structures was developed. Stress changes in the spinal cord and nerve roots, posterior shift of the spinal cord, and displacement of the cervical nerve roots were analyzed with two types of cervical laminoplasty models for variations in the degree of canal occupying ratio and shape of the OPLL. The shape and degree of spinal cord compression caused by the OPLL had more influence on the changes in stress, posterior shift of the spinal cord, and displacement of the nerve root than the type of laminoplasty. The lateral-type OPLL resulted in imbalanced stress on the nerve roots and the highest nerve root displacement. Type of laminoplasty and shape and degree of spinal cord compression caused by OPLL were found to influence the changes in stress and posterior displacement of the cervical spinal cord and nerve roots. Lateral-type OPLL might contribute to the development of C5 palsy due to the imbalanced stress and tension on the nerve roots after laminoplasty.

The denticulate ligament - Tensile characterisation and finite element micro-scale model of the structure stabilising spinal cord

BACKGROUND

Damage to the spinal cord is one of the most debilitating pathologies with considerable health, economic and social impact. Improved prevention, treatment and rehabilitation after spinal cord injury (SCI) requires the complex biomechanics of the spinal cord with all its structural elements and the injury mechanism to be understood. This comprehensive understanding will also allow development of models and tools enabling better diagnosis, surgical treatment with increased safety and efficacy and possible development of regenerative therapies. The denticulate ligaments play an important role in stabilising spinal cord within the spinal canal. They participate in spinal cord movements and play a role in determining the stress distribution during physiological but also traumatic loading. We present detailed tensile characterisation of the denticulate ligaments and a Finite Element micro-scale model of the ligament relating its structure with the distribution of stress under physiological loading.

METHOD

Denticulate ligaments were dissected from cervical spinal levels from 6 porcine cervical specimens with fragments of the pia and dura mater and characterised in terms of their geometry and response to uniaxial tensile loading. The stress-strain characteristics were recorded until rupture of the ligament, ultimate parameters and Young's moduli were determined. The parametric micro-structural Finite Element model was constructed based on literature microscope and histological images of a denticulate ligament as a phenomenological representation of the complex microstructure of a soft tissue. The model was validated against the experimental data.

RESULTS

Stress-strain characteristics obtained in tensile test were typical for a soft tissue behaviour. No statistically relevant differences in ultimate strength, strain and Young's moduli were observed between the ligaments harvested from different vertebral levels. Average ultimate tensile stress was 1.26 ± 0.20 MPa at strain 0.51 ± 0.00, rupturing force (1.01 ± 0.21 N) was in agreement with results obtained previously. The Finite Element model accurately predicted the extension-load behaviour of the denticulate ligament in elastic regime. The micro-scale structural representation enabled capturing deformation modes representative of the experimentally observed behaviour.

CONCLUSIONS

The presented stress-strain characteristics of the denticulate ligaments add valuable data to the understanding of the biomechanics of the spinal cord and enable development of more accurate models. The developed micro-scale model was capable of capturing biomechanical response of collagenous tissue under tensile loading, it can be applied for the prediction of other soft tissues behaviours. The denticulate ligament model should be included into future spinal cord models to fully represent the complex system's biomechanics and enable development of surgical aid tools to improve patient outcomes and future regenerative therapies.

Assessment of the cervical spine denticulate ligament using MRI volumetric sequence: Comparison between 1.5 Tesla and 3.0 Tesla

BACKGROUND

Denticulate ligaments (DLs) are pial extensions on each side of the spinal cord, comprising about 20 to 21 pairs of fibrous structures connecting the dura mater to the spinal cord. These ligaments are significant anatomical landmarks in the surgical approach to intradural structures. To our knowledge, there is no previous study on the detection of DLs using MRI.

METHODS

After IRB approval, we retrospectively evaluated 116 consecutive MRI scans of the cervical spine, using the volumetric sequence 3D COSMIC, 65 and 51 studies with 1.5T and 3.0T respectively. We did not include trauma and tumor cases. Two independent radiologists assessed the detection of cervical spine DLs independently and blinded for each cervical vertebral level. We compared the frequency of detection of these ligaments in 1.5 Tesla and 3.0 Tesla MRI using Fisher exact test considering P<0.05 as significant. We evaluated interobserver agreement with Kappa coefficient.

RESULTS

We observed high detection frequency of the cervical spine DLs using both 1.5T (70 to 91%) and 3.0T (68 to 98%). We found no statistically significant difference in the detection frequency of ligaments between the 1.5T and 3.0T MRI in all vertebral levels. Using 3.0T, radiologists identified ligaments better in higher vertebral levels than for lower cervical levels (P=0.0003). Interobserver agreement on the identification of DL was poor both for 1.5T (k=0.3744; CI 95% 0.28-0.46) and 3.0T (k=0.3044; CI 95% 0.18-0.42) MRI.

CONCLUSIONS

Radiologists identified most of the cervical DLs using volumetric MRI acquisition. Our results suggest 1.5T and 3.0T MRI performed similarly in the detection of DLs.

Increased stress and strain on the spinal cord due to ossification of the posterior longitudinal ligament in the cervical spine under flexion after laminectomy

Myelopathy in the cervical spine due to cervical ossification of the posterior longitudinal ligament could be induced by static compression and/or dynamic factors. It has been suggested that dynamic factors need to be considered when planning and performing the decompression surgery on patients with the ossification of the posterior longitudinal ligament. A finite element model of the C2-C7 cervical spine in the neutral position was developed and used to generate flexion and extension of the cervical spine. The segmental ossification of the posterior longitudinal ligament on the C5 was assumed, and laminectomy was performed on C4-C6 according to a conventional surgical technique. For various occupying ratios of the ossified ligament between 20% and 60%, von-Mises stresses, maximum principal strains in the spinal cord, and cross-sectional area of the cord were investigated in the pre-operative and laminectomy models under flexion, neutral position, and extension. The results were consistent with previous experimental and computational studies in terms of stress, strain, and cross-sectional area. Flexion leads to higher stresses and strains in the cord than the neutral position and extension, even after decompression surgery. These higher stresses and strains might be generated by residual compression occurring at the segment with the ossification of the posterior longitudinal ligament. This study provides fundamental information under different neck positions regarding biomechanical characteristics of the spinal cord in cervical ossification of the posterior longitudinal ligament.

Spinal subdural abscess following repeat lumbar microdiscectomy: A case report of imaging findings for a rare infection

Spinal subdural abscess is a rare central nervous system infection with just over a hundred cases reported. It is much less common than spinal epidural abscess. While most case reports have focused on route of infection and treatment options, there have not been any reports that focused on the unique MRI findings of spinal subdural abscess. We describe a case of spinal subdural abscess diagnosed by MRI in a 33-year-old male who presented with headaches after undergoing a microdiscectomy procedure, and review the underlying anatomic features of the spinal meninges which produce the appearance of a spinal subdural abscess.

Effect of posterior decompression extent on biomechanical parameters of the spinal cord in cervical ossification of the posterior longitudinal ligament

Ossification of the posterior longitudinal ligament is a common cause of the cervical myelopathy due to compression of the spinal cord. Patients with ossification of the posterior longitudinal ligament usually require the decompression surgery, and there is a need to better understand the optimal surgical extent with which sufficient decompression without excessive posterior shifting can be achieved. However, few quantitative studies have clarified this optimal extent for decompression of cervical ossification of the posterior longitudinal ligament. We used finite element modeling of the cervical spine and spinal cord to investigate the effect of posterior decompression extent for continuous-type cervical ossification of the posterior longitudinal ligament on changes in stress, strain, and posterior shifting that occur with three different surgical methods (laminectomy, laminoplasty, and hemilaminectomy). As posterior decompression extended, stress and strain in the spinal cord decreased and posterior shifting of the cord increased. The location of the decompression extent also influenced shifting. Laminectomy and laminoplasty were very similar in terms of decompression results, and both were superior to hemilaminectomy in all parameters tested. Decompression to the extents of C3-C6 and C3-C7 of laminectomy and laminoplasty could be considered sufficient with respect to decompression itself. Our findings provide fundamental information regarding the treatment of cervical ossification of the posterior longitudinal ligament and can be applied to patient-specific surgical planning.

Anatomy and biomechanics of the craniovertebral junction

The craniovertebral junction (CVJ) has unique anatomical structures that separate it from the subaxial cervical spine. In addition to housing vital neural and vascular structures, the majority of cranial flexion, extension, and axial rotation is accomplished at the CVJ. A complex combination of osseous and ligamentous supports allow for stability despite a large degree of motion. An understanding of anatomy and biomechanics is essential to effectively evaluate and address the various pathological processes that may affect this region. Therefore, the authors present an up-to-date narrative review of CVJ anatomy, normal and pathological biomechanics, and fixation techniques.

Biomechanical characteristics of the porcine denticulate ligament in different vertebral levels of the cervical spine-preliminary results of an experimental study

BACKGROUND

Few studies exist on the mechanical properties of denticulate ligaments and none report the variation in these properties at different levels of the spine. The aim of this study was to perform an experimental determination of load-extension and stress-strain characteristics of the denticulate ligament and to establish if their properties change at different vertebral levels of the cervical spine.

METHOD

The study was carried out on a total of 98 porcine denticulate ligament samples dissected from seven fresh porcine cervical spinal cord specimens. All of the samples were subjected to an uniaxial tensile test at a speed of 2mm/min, during which the load-extension characteristics were registered.

RESULTS

The analysis revealed a decrease of the failure force in the caudal orientation indicated by significant differences between the C1 (1.04±0.41N) and C7 (0.55±0.12N) vertebral levels (P=0.037). The average ultimate force that broke the denticulate ligaments was 0.88N. The mean value of Young׳s modulus was 2.06MPa with a minimum of 1.31MPa for C7 and maximum of 2.46MPa for C5.

CONCLUSIONS

The values of the denticulate ligament failure force in samples from different cervical vertebrae levels differ significantly. The presented data should be taken into consideration during numerical modelling of the human cervical spinal cord.