Comparison of Cervical Spine Anatomy in Calves, Pigs and Humans

Quantification of porcine lower thoracic spinal cord morphology with intact dura mater using high-resolution μCT

BACKGROUND AND PURPOSE

Spinal cord stimulation (SCS) is approved by the Food and Drug Administration for treating chronic intractable pain in the back, trunk, or limbs through stimulation of the dorsal column. Numerous studies have used swine as an analog of the human spinal cord to better understand SCS and further improve its efficacy. We performed high-resolution imaging of the porcine spinal cord with intact dura mater using micro-computed tomography (μCT) to construct detailed 3-dimensional (3D) visualizations of the spinal cord and characterize the morphology of the dorsal and ventral rootlets.

METHODS

We obtained spinal cords from Yorkshire/Landrace crossbred swine (N = 7), stained samples with osmium tetroxide, and performed μCT imaging of the T12-T15 levels at isotropic voxel resolutions ranging from 3.3 to 50 μm. We measured the anatomical morphology using the 3D volumes and compared our results to measurements previously collected from swine and human spinal cords via microdissection techniques in prior literature.

RESULTS

While the porcine thoracic-lumbar spinal cord is a popular model for SCS, we highlight multiple notable differences compared to previously published T8-T12 human measurements including rootlet counts (porcine dorsal/ventral: 12.2 ± 2.6, 26.6 ± 3.4; human dorsal/ventral: 5.3 ± 1.3, 4.4 ± 2.4), rootlet angles (porcine ventral-rostral: 161 ± 1°, ventral-caudal: 155 ± 6°, dorsal-rostral: 148 ± 9°, dorsal-caudal: 142 ± 6°; human ventral-rostral: 170 ± 3°, ventral-caudal: 22 ± 10°, dorsal-rostral: 171 ± 3°, dorsal-caudal: 15 ± 7°), and the presence and count of dorsal rootlet bundles.

CONCLUSIONS

Detailed measurements and highlighted differences between human and porcine spinal cords can inform variations in modeling and electrophysiological experiments between the two species. In contrast to other approaches for measuring the spinal cord and rootlet morphology, our method keeps the dura intact, reducing potential artifacts from dissection.

How Static and Cyclic Loading Affect the Mechanical Properties of the Porcine Annulus Fibrosus

This study sought to evaluate the effects of prolonged cyclic loading on the tissue-level mechanical properties of the spinal annulus fibrosus. Functional spinal units (FSUs) were obtained from porcine cervical spines at the C3-C4 and C5-C6 levels. Following a 15-min preload of 300 N of axial compression, the FSUs were split into three groups: the cyclic loading group cycled between 0.35 MPa and 0.95 MPa for 2 h (n = 8); the static loading group was compressed at 0.65 MPa for 2 h (n = 10); and a control group which only underwent the 300 N preload (n = 11). Following loading, samples of the annulus were excised to perform intralamellar tensile testing and interlamellar 180 deg peel tests. Variables analyzed from the intralamellar test were stress and strain at the end of the toe region, stress and strain at initial failure (yield point), Young's modulus, ultimate stress, and strain at ultimate stress. Variables evaluated from the interlamellar tests were lamellar adhesion strength, adhesion strength variability, and stiffness. The analysis showed no significant differences between conditions on any measured variable; however, there was a trend (p = 0.059) that cyclically loaded tissues had increased adhesion strength variability compared to the static and control conditions. The main finding of this study is that long-duration axial loading did not impact the intra- or interlamellar mechanical properties of the porcine annulus. A trend of increased adhesion strength variability in cyclically loaded samples could indicate a potential predisposition of the annulus to delamination.

Experimentally Validated Finite Element Analysis of Thoracic Spine Compression Fractures in a Porcine Model

Vertebral compression fractures (VCFs) occur in 1 to 1.5 million patients in the US each year and are associated with pain, disability, altered pulmonary function, secondary vertebral fracture, and increased mortality risk. A better understanding of VCFs and their management requires preclinical models that are both biomechanically analogous and accessible. We conducted a study using twelve spinal vertebrae (T12-T14) from porcine specimens. We created mathematical simulations of vertebral compression fractures (VCFs) using CT scans for reconstructing native anatomy and validated the results by conducting physical axial compression experiments. The simulations accurately predicted the behavior of the physical compressions. The coefficient of determination for stiffness was 0.71, the strength correlation was 0.88, and the failure of the vertebral bodies included vertical splitting on the lateral sides or horizontal separation in the anterior wall. This finite element method has important implications for the preventative, prognostic, and therapeutic management of VCFs. This study also supports the use of porcine specimens in orthopedic biomechanical research.

Finite element modeling to predict the influence of anatomic variation and implant placement on performance of biological intervertebral disc implants

Background

Tissue-engineered intervertebral disc (TE-IVD) constructs are an attractive therapy for treating degenerative disc disease and have previously been investigated in vivo in both large and small animal models. The mechanical environment of the spine is notably challenging, in part due to its complex anatomy, and implants may require additional mechanical support to avoid failure in the early stages of implantation. As such, the design of suitable support implants requires rigorous validation.

Methods

We created a FE model to simulate the behavior of the IVD cages under compression specific to the anatomy of the porcine cervical spine, validated the FE model using an animal model, and predicted the effects of implant location and vertebral angle of the motion segment on implant behavior. Specifically, we tested anatomical positioning of the superior vertebra and placement of the implant. We analyzed corresponding stress and strain distributions.

Results

Results demonstrated that the anatomical geometry of the porcine cervical spine led to concentrated stress and strain on the posterior side of the cage. This stress concentration was associated with the location of failure of the cages reported in vivo, despite superior mechanical properties of the implant. Furthermore, placement of the cage was found to have profound effects on migration, while the angle of the superior vertebra affected stress concentration of the cage.

Conclusions

This model can be utilized both to inform surgical procedures and provide insight on future cage designs and can be adopted to models without the use of in vivo animal models.

Morphometric analysis of cervical vertebrae in some marine and land mammals

Bones or skeletal remains can be used to answer a number of questions related to species, sex, age or cause of death. However, studies involving vertebrae have been limited as most were performed on skulls or long bones. Here, we have stated the hypothesis that the morphometry of cervical vertebrae can be used for species identification and body size estimation among marine and land mammals. The cervical vertebrae from eight and 14 species of marine and land mammals were used to collect morphometric data. Cluster dendrogram, principal component analysis, discriminant analysis and linear regression were used to analyse the data. The results indicate that, based on an index of C4 to C7, there were 13 out of 22 species for which identity could be correctly predicted in 100% of the cases. The correlations between cervical vertebrae parameters (height, width and length of centrum) in marine (average R^2 =  0.87, p < .01) and land (average R^2 =  0.51, p < .01) mammals were observed. These results indicate that vertebral morphometrics could be used for species prediction and verification of body weight in both marine and land mammals.

Neuropathological and Motor Impairments after Incomplete Cervical Spinal Cord Injury in Pigs

Humans, primates, and rodents with cervical spinal cord injury (SCI) show permanent sensorimotor dysfunction of the upper/forelimb as consequence of axonal damage and local neuronal death. This work aimed at characterizing a model of cervical SCI in domestic pigs in which hemisection with excision of 1 cm of spinal cord was performed to reproduce the loss of neural tissue observed in human neuropathology. Posture and motor control were assessed over 3 months by scales and kinematics of treadmill locomotion. Histological measurements included lesion length, atrophy of the adjacent spinal cord segments, and neuronal death. In some animals, the retrograde neural tracer aminostilbamidine was injected in segments caudal to the lesion to visualize propriospinal projection neurons. Neuronal loss extended for 4-6 mm from the lesion borders and was more severe in the ipsilateral, caudal spinal cord stump. Axonal Wallerian degeneration was observed caudally and rostrally, associated with marked atrophy of the white matter in the spinal cord segments adjacent to the lesion. The pigs showed chronic monoplegia or severe monoparesis of the foreleg ipsilateral to the lesion, whereas the trunk and the other legs had postural and motor impairments that substantially improved during the first month post-lesion. Adaptations of the walking cycle such as those reported for rats and humans ameliorated the negative impact of focal neurological deficits on locomotor performance. These results provide a baseline of behavior and histology in a porcine model of cervical spinal cord hemisection that can be used for translational research in SCI therapeutics.

Multiphoton imaging and Raman spectroscopy of the bovine vertebral endplate

The interface between the intervertebral disc and the vertebral body is important to the discs' biomechanics and physiology, and is widely implicated in its pathology. This study aimed to explore biochemically and structurally the bony endplate, cartilage endplate and intervertebral disc, below the nucleus and below the annulus in healthy bovine tails. Multiphoton imaging and spontaneous Raman spectroscopy were employed. Raman spectroscopy provided relative quantification of mineral and matrix components across the vertebral endplate and its adjacent areas with microscopic spatial resolution. Microscopy utilising second-harmonic generation (SHG) and two-photon fluorescence (TPF) allowed for the structural identification of distinct endplate regions. The cartilage endplate was revealed as structurally distinct from both the bone and disc, supporting its biomechanical function as a transition zone between the soft and hard tissue components. The collagen fibres were continuous across the tidemark which defines the interface between the mineralised and non-mineralised regions of the endplate. Raman spectroscopy revealed gradients in phosphate and carbonate content through the depth of the endplate and also differences beneath the nucleus and annulus consistent with a higher rate of remodelling under the annulus.

Combined Percutaneous Kyphoplasty/Pediculoplasty by Posterolateral Transpedicular Approach for Painful Cervical Spine Metastases: A Single-Center Prospective Study

Purpose

In patients requiring percutaneous kyphoplasty (PKP) for painful cervical spine metastases (PCSMs), the surgical approach is of utmost importance. Anterolateral and transoral routes are generally used at present, whereas PKP as well as percutaneous pediculoplasty (PPP) via posterolateral transpedicular approach (PTPA) has yet to be pursued in the treatment of PCSMs. The study was designed to evaluate safety and efficacy of PKP procedures combined with PPP via PTPA as treatment of PCSMs.

Patients and Methods

The patients with PCSMs were enrolled and housed in a database. The pain intensity of enrolled patients was gauged by Visual Analog Scale (VAS), ranging from 0 (none) to 10 (extreme). After preprocedural imaging assessment, combined PKP/PPP via PTPA was performed under the guidance of CT and fluoroscopic monitoring. Postprocedural VAS scores, complications, cement dosage, and hospitalization were recorded in the database for analysis. All cases were followed up for 6 months.

Results

Adult enrollees (7 women, 4 men) with PCSMs successfully underwent PKP/PPP via PTPA between February 2019 and January 2020, injected with 3.7±0.7 mL (range, 2.5-4.8 mL) of cement on average. Other than a single instance of asymptomatic cement leakage into paravertebral soft tissues, no complications ensued. Significant analgesic effects observed 24 hours after procedures were sustained for up to 6 months in follow-up surveys. Postprocedural hospitalizations were as brief as 2.2±0.8 days.

Conclusion

Combined PKP/PPP via PTPA is safe and effective as treatment of PCSMs, enabling quick pain relief and patient recovery.

Comparison of the anatomical morphology of cervical vertebrae between humans and macaques: related to a spinal cord injury model

Non-human primates are most suitable for generating cervical experimental models, and it is necessary to study the anatomy of the cervical spine in non-human primates when generating the models. The purpose of this study was to provide the anatomical parameters of the cervical spine and spinal cord in long-tailed macaques (Macaca fascicularis) as a basis for cervical spine-related experimental studies. Cervical spine specimens from 8 male adult subjects were scanned by micro-computed tomography, and an additional 10 live male subjects were scanned by magnetic resonance imaging. The measurements and parameters from them were compared to those of 12 male adult human subjects. Additionally, 10 live male subjects were scanned by magnetic resonance imaging, and the width and depth of the spinal cord and spinal canal and the thickness of the anterior and posterior cerebrospinal fluid were measured and compared to the relevant parameters of 10 male adult human subjects. The tendency of cervical parameters to change with segmental changes was similar between species. The vertebral body, spinal canal, and spinal cord were significantly flatter in the human subjects than in the long-tailed macaques. The cerebrospinal fluid space in the long-tailed macaques was smaller than that in the human subjects. The anatomical features of the cervical vertebrae of long-tailed macaques provide a reference for establishing a preclinical model of cervical spinal cord injury.

Morphometry of the kangaroo spine and its comparison with human spinal data

The upright posture of the kangaroo suggests that the spine of the kangaroo could be a possible substitute model for biomechanical studies of the human spine. A prerequisite for this should be the agreement of anatomy in humans and kangaroos. The purpose of this study was to investigate the anatomical parameters of the kangaroo spine from C4 to S4 and compare them with existing anatomical data of the human spine. Eight complete spines of the red giant kangaroo were obtained and 21 anatomical parameters were measured from the vertebral bodies, spinal canal, endplate, pedicles, intervertebral discs, transverse, and spinous processes. Most similarities between kangaroo and human spines were found for the vertebral bodies in the cervical and the lumbar spine. The largest differences were evident for the spinous processes. Although both species are somehow upright, these differences may be explained by the way how they move. Jumping probably requires more muscle strength than walking on two legs.

Experimental Model for Interlaminar Endoscopic Spine Procedures

BACKGROUND

Endoscopic spinal surgery is becoming quite popular, and the pursuit of a training model to improve surgeons' skills is imperative to overcome the limited availability of human cadavers. Our goal was to determine whether the porcine spine could be a representative model for learning and practicing interlaminar percutaneous endoscopic lumbar procedures (IL-PELPs).

METHODS

Lumbar and cervical segments of the porcine cadaver spine were used for the IL-PELP. We have described the technical notes on the difficulties of the procedure and the relevant anatomical features. To endorse the porcine cadaver for this procedure, 5 neurosurgeons underwent 1 day of training and completed a survey.

RESULTS

The porcine lumbar spine has small interlaminar windows, and laminectomy is necessary, mimicking the translaminar approaches for higher human lumbar spine levels. The porcine cervical spine has wide and high interlaminar windows and mimics the human L5-S1 interlaminar approach. Entering the spinal canal with the working sheath and endoscope and training the rotation maneuver to access the disc space is only possible in the lumbar segment. It was possible to perform flavectomy and to identify and dissect the dural sac and nerve root in both the lumbar and cervical spine. The neurosurgeons considered the porcine model of good operability and, although different, possible to apply in humans.

CONCLUSIONS

The porcine spine is an effective and representative model for learning and practicing IL-PELPs. Although the described anatomical differences should be known, they did not interfere in performing the main surgical steps and maneuvers for IL-PELPs in the porcine model.

Ex vivo computed tomography evaluation of loading position on morphometry of the caudal cervical intervertebral disk spaces of dogs

OBJECTIVE To provide an objective, quantitative morphometric description of the caudal cervical intervertebral disk (IVD) spaces of dogs. SAMPLE Vertebral specimens consisting of C4 through C7 from 5 medium-sized dogs. PROCEDURES CT images were obtained with the specimens positioned in neutral, flexion, extension, and lateral bending positions. Size and shape of the cranial and caudal end plates, angle between the end plates (IVD wedge angle), and craniocaudal distance (IVD width) between end plates for the 4 loading positions were measured and compared for the 3 segments (C4-5, C5-6, and C6-7). RESULTS End plate size and shape, IVD wedge angle, and IVD width were not significantly different among the 3 segments. Caudal cervical end plates were consistently larger than cranial cervical end plates. The IVD wedge angle ranged from -4.8° to 15.2°. Flexion induced a reduction in IVD width in the ventral portion of the IVD, whereas extension induced a decrease in width in the dorsal portion of the IVD. Central IVD width remained unchanged among the loading positions. CONCLUSIONS AND CLINICAL RELEVANCE Unique morphometric and dynamic characteristics of the caudal cervical IVD space of dogs were detected. These findings may help investigators when designing IVD prostheses for dogs with cervical spondylomyelopathy.

Comparative Morphometry of the Wisconsin Miniature SwineTM Thoracic Spine for Modeling Human Spine in Translational Spinal Cord Injury Research

Background/Aims

Spine and spinal cord pathologies and associated neuropathic pain are among the most complex medical disorders to treat. While rodent models are widely used in spine and spinal cord research and have provided valuable insight into pathophysiological mechanisms, these models offer limited translatability. Thus, studies in rodent models have not led to the development of clinically effective therapies. More recently, swine has become a favored model for spine research because of the high congruency of the species to humans with respect to spine and spinal cord anatomy, vasculature, and immune responses. However, conventional breeds of swine commonly used in these studies present practical and translational hurdles due to their rapid growth toward weights well above those of humans.

Methods

In the current study, we evaluated the suitability of a human-sized breed of swine developed at the University of Wisconsin-Madison, the Wisconsin Miniature Swine^TM (WMS^TM), in the context of thoracic spine morphometry for use in research to overcome limitations of conventional swine breeds. The morphometry of thoracic vertebrae (T1-T15) of 5-6 months-old WMS was analyzed and compared to published values of human and conventional swine spines.

Results

The key finding of this study is that WMS spine more closely models the human spine for many of the measured vertebrae parameters, while being similar to conventional swine in respect to the other parameters.

Conclusion

WMS provides an improvement over conventional swine for use in translational spinal cord injury studies, particularly long-term ones, because of its slower rate of growth and its maximum growth being limited to human weight and size.

[Research progress on mechanical performance evaluation of artificial intervertebral disc]

The mechanical properties of artificial intervertebral disc (AID) are related to long-term reliability of prosthesis. There are three testing methods involved in the mechanical performance evaluation of AID based on different tools: the testing method using mechanical simulator, in vitro specimen testing method and finite element analysis method. In this study, the testing standard, testing equipment and materials of AID were firstly introduced. Then, the present status of AID static mechanical properties test (static axial compression, static axial compression-shear), dynamic mechanical properties test (dynamic axial compression, dynamic axial compression-shear), creep and stress relaxation test, device pushout test, core pushout test, subsidence test, etc. were focused on. The experimental techniques using in vitro specimen testing method and testing results of available artificial discs were summarized. The experimental methods and research status of finite element analysis were also summarized. Finally, the research trends of AID mechanical performance evaluation were forecasted. The simulator, load, dynamic cycle, motion mode, specimen and test standard would be important research fields in the future.

The Role of Functional Neuroanatomy of the Lumbar Spinal Cord in Effect of Epidural Stimulation

In this study, the neuroanatomy of the swine lumbar spinal cord, particularly the spatial orientation of dorsal roots was correlated to the anatomical landmarks of the lumbar spine and to the magnitude of motor evoked potentials during epidural electrical stimulation (EES). We found that the proximity of the stimulating electrode to the dorsal roots entry zone across spinal segments was a critical factor to evoke higher peak-to-peak motor responses. Positioning the electrode close to the dorsal roots produced a significantly higher impact on motor evoked responses than rostro-caudal shift of electrode from segment to segment. Based on anatomical measurements of the lumbar spine and spinal cord, significant differences were found between L1-L4 to L5-L6 segments in terms of spinal cord gross anatomy, dorsal roots and spine landmarks. Linear regression analysis between intersegmental landmarks was performed and L2 intervertebral spinous process length was selected as the anatomical reference in order to correlate vertebral landmarks and the spinal cord structures. These findings present for the first time, the influence of spinal cord anatomy on the effects of epidural stimulation and the role of specific orientation of electrodes on the dorsal surface of the dura mater in relation to the dorsal roots. These results are critical to consider as spinal cord neuromodulation strategies continue to evolve and novel spinal interfaces translate into clinical practice.

Use of Pig as a Model for Mesenchymal Stem Cell Therapies for Bone Regeneration

Bone is a plastic tissue with a large healing capability. However, extensive bone loss due to disease or trauma requires extreme therapy such as bone grafting or tissue-engineering applications. Presently, bone grafting is the gold standard for bone repair, but presents serious limitations including donor site morbidity, rejection, and limited tissue regeneration. The use of stem cells appears to be a means to overcome such limitations. Bone marrow mesenchymal stem cells (BMSC) have been the choice thus far for stem cell therapy for bone regeneration. However, adipose-derived stem cells (ASC) have similar immunophenotype, morphology, multilineage potential, and transcriptome compared to BMSC, and both types have demonstrated extensive osteogenic capacity both in vitro and in vivo in several species. The use of scaffolds in combination with stem cells and growth factors provides a valuable tool for guided bone regeneration, especially for complex anatomic defects. Before translation to human medicine, regenerative strategies must be developed in animal models to improve effectiveness and efficiency. The pig presents as a useful model due to similar macro- and microanatomy and favorable logistics of use. This review examines data that provides strong support for the clinical translation of the pig model for bone regeneration.