Comparative finite element analysis of the first thoracic vertebra in artiodactyls.

Artiodactyls exhibit a striking diversity of the cervical vertebral column in terms of length and overall mobility. Using finite element analysis, this study explores the morphology at the cervico-thoracic boundary and its performance under loads in artiodactyls with different habitual neck postures and body sizes. The first thoracic vertebra of 36 species was loaded with (i) a compressive load on the vertebral body to model the weight of the head and neck exerted onto the trunk; and (ii) a tensile load at the spinous process to model the pull via the nuchal ligament. Additional focus was laid on the peculiar shape of the first thoracic vertebra in giraffes. We hypothesized that a habitually upright neck posture should be reflected in the greater ability to withstand compressive loads compared to tensile loads, whereas for species with a habitually suspended posture it should be the opposite. In comparison to species with a suspended posture, species with an upright posture exhibited lower stress (except Giraffidae). For compressive loads in larger species, stress surprisingly increased. Tensile loads in larger species resulted in decreased stress only in species with an intermediate or suspensory neck posture. High stress under tensile loads was mainly reflecting the relative length of the spinous process, while high stress under compressive loads was common in more "bell"-shaped vertebral bodies. The data supports a stability-mobility trade-off at the cervico-thoracic transition in giraffes. Performance under load at the cervico-thoracic boundary is indicative of habitual neck posture and is influenced by body size.

Vertebral heart size and vertebral left atrial size reference ranges in healthy Miniature Schnauzers.

OBJECTIVE: The inclusion of vertebral heart score (VHS) and, more recently, the inclusion of the vertebral left atrial size (VLAS) in radiographic evaluation have become important screening tools for identifying dogs with occult cardiac disease. Several recent papers have shown there are interbreed variations in the VHS reference range. Our hypothesis is that the Miniature Schnauzer would also have a higher reference range for its VHS. ANIMALS: The electronic medical records of IDEXX Telemedicine Consultants were searched for Miniature Schnauzers undergoing thoracic radiographs between March 1, 2022, and February 28, 2023. METHODS: Dogs were included if they had 3 view thoracic radiographs performed and no evidence of cardiopulmonary disease was detected. Dogs with incomplete radiographic studies or cardiac or extracardiac disease were excluded. The VHS and VLAS measurements were performed by 2 board-certified cardiologists independent of one another. RESULTS: A total of 1,000 radiographs were obtained of which 272 were included for the study. The overall range for the VHS in this cohort was 9.68 to 12.07 with a median of 10.9. For VLAS measurements, a range of 1.71 to 2.4 was documented with a median of 2.0. CLINICAL RELEVANCE: The VHS for Miniature Schnauzers without cardiac disease was confirmed to be higher than the canine reference range.

Assessment of a fully-parametric thoraco-lumbar spine model generator with articulated ribcage.

The present paper describes a novel user-friendly fully-parametric thoraco-lumbar spine CAD model generator including the ribcage, based on 22 independent parameters (1 posterior vertebral body height per vertebra + 4 sagittal alignment parameters, namely pelvic incidence, sacral slope, L1-L5 lumbar lordosis, and T1-T12 thoracic kyphosis). Reliable third-order polynomial regression equations were implemented in Solidworks to analytically calculate 56 morphological dependent parameters and to automatically generate the spine CAD model based on primitive geometrical features. A standard spine CAD model, representing the case-study of an average healthy adult, was then created and positively assessed in terms of spinal anatomy, ribcage morphology, and sagittal profile. The immediate translation from CAD to FEM for relevant biomechanical analyses was successfully demonstrated, first, importing the CAD model into Abaqus, and then, iteratively calibrating the constitutive parameters of one lumbar and three thoracic FSUs, with particular interest on the hyperelastic material properties of the IVD, and the spinal and costo-vertebral ligaments. The credibility of the resulting lumbo-sacral and thoracic spine FEM with/without ribcage were assessed and validated throughout comparison with extensive in vitro and in vivo data both in terms of kinematics (range of motion) and dynamics (intradiscal pressure) either collected under pure bending moments and complex loading conditions (bending moments + axial compressive force).

Implantation Corridors in Canine Thoracic Vertebrae: A Morphometric Study in Dogs of Varying Sizes.

OBJECTIVE: Surgical stabilization to treat fractures, luxations, and congenital malformations in the thoracic spine can be difficult due to its unique anatomy and surrounding structures. Our objective was to document the morphometrics of the thoracic vertebrae relating to an ideal trajectory for dorsolateral implant placement in a variety of dog sizes and to assess proximity to important adjacent critical anatomical structures using computed tomography (CT) studies. STUDY DESIGN: Medical records for 30 dogs with thoracic CT were evaluated. Implantation corridor parameters for thoracic vertebrae (T1-T13) were measured, including the length, width, angle from midline, and allowable deviation angle for corridors simulated using an ideal implant trajectory. The distances from each vertebra to the trachea, lungs, aorta, subclavian artery, and azygos vein were also measured. RESULTS: Implantation corridor widths were often very narrow, particularly in the mid-thoracic region, and allowable deviation angles were frequently small. Distances to critical anatomical structures were often less than 1 mm, even in larger dogs. CONCLUSION: Thoracic implantation requires substantial precision to avoid breaching the canal, ineffective implant placement, and potential life-threatening complications resulting from invasion of surrounding anatomical structures.

Correlation Analysis Between Computed Tomography and Magnetic Resonance Imaging for Assessing Thoracic Pedicle Morphology.

OBJECTIVE: This study aimed to determine the accuracy and reliability of using magnetic resonance imaging (MRI) to characterize thoracic pedicle morphology in the normal population. METHODS: Computed tomography (CT) and MRI datasets of 63 surgically treated patients were included in the study. Bilateral T3, T6, T9, and T12 vertebral levels were evaluated for the type of pedicle, pedicle chord length, and pedicle isthmic diameter on both MRI and CT scans. Pedicles were classified according to Sarwahi et al. into type A (normal pedicle), >4 mm cancellous channel; type B, 2-4 mm channel; type C, completely cortical channels >2 mm; and type D, <2 mm cortical bone channel. RESULTS: Of 504 pedicles, 294 were classified as type A, 173 as type B, 24 as type C, and 13 as type D based on a CT scan. MRI had an overall accuracy rate of 92.86% for detecting type A, 96.53% for type B, and 100% for type C and type D compared with CT scans. Regarding the thoracic levels, MRI had an overall concordance of 97.98% at T3 level, 94.43% at T6 level, 98.11% at T9 level, and 99.3% at T12 level with CT readings. Comparing measurements between MRI and CT studies for pedicle isthmic diameter and pedicle chord length showed moderate to good reliability at all measured levels. CONCLUSIONS: Pedicle measurements obtained by MRI may be used to estimate pedicle dimensions, allowing surgeons to preoperatively determine pedicle screw sizes based on MRI scans alone.

Thoracolumbar transitional vertebrae: Quantitative differentiation and associated numeric variation in the vertebral column using skeletal remains.

Transitional vertebrae at the thoracolumbar region are called thoracolumbar transitional vertebrae (TLTV) and retain physical features from the thoracic and lumbar regions. Since TLTV were first classified 40 years ago, there has been much discrepancy regarding its features, identification and clinical relevance. Vertebral body levels are used in the medical field as a frame of reference to locate specific organs, vessels, nerves or landmarks. Any numeric variation or deviation in the vertebral column may lead to clinical errors. Previous findings have suggested a high association between numeric variation and the presence of TLTV. Therefore, the aim of this study was to identify the types of TLTV observed and to identify any possible associated numeric variation in the vertebral column. This study also aimed to validate the established technique to quantitatively differentiate TLTV from T12 and L1 at the thoracolumbar junction using skeletal remains from a South African population group. Skeletal remains (n = 187) remains from the Pretoria bone collection were assessed. Measurements were taken of the angle of the superior zygapophyseal processes of the last thoracic vertebra (T12), the first lumbar (L1), and identified TLTV. The results indicate a TLTV prevalence of 35% (n = 66/187). The results show that each vertebral type (T12, L1, TLTV) fall into independent confidence intervals: T12 is 188° ± 9.22 (CI: 187° < µ < 189.6°), 110° ± 7.52 (CI: 109.2° < µ < 111.3°) in L1, and 135° ± 24.51 (CI: 130.4° < µ < 139.1°) in the TLTV. This study observed that 70% of cases with TLTV was associated with numeric variation in the spine, both homeotic and meristic and that TLTV has a 35% prevalence. The results clearly show that quantitative morphometric analysis can effectively differentiate TLTV from other vertebral types at the thoracolumbar junction in skeletal remains.

Statistical shape modelling of the thoracic spine for the development of pedicle screw insertion guides.

Spinal fixation and fusion are surgical procedures undertaken to restore stability in the spine and restrict painful or degenerative motion. Malpositioning of pedicle screws during these procedures can result in major neurological and vascular damage. Patient-specific surgical guides offer clear benefits, reducing malposition rates by up to 25%. However, they suffer from long lead times and the manufacturing process is dependent on third-party specialists. The development of a standard set of surgical guides may eliminate the issues with the manufacturing process. To evaluate the feasibility of this option, a statistical shape model (SSM) was created and used to analyse the morphological variations of the T4-T6 vertebrae in a population of 90 specimens from the Visible Korean Human dataset (50 females and 40 males). The first three principal components, representing 39.7% of the variance within the population, were analysed. The model showed high variability in the transverse process (~ 4 mm) and spinous process (~ 4 mm) and relatively low variation (< 1 mm) in the vertebral lamina. For a Korean population, a standardised set of surgical guides would likely need to align with the lamina where the variance in the population is lower. It is recommended that this standard set of surgical guides should accommodate pedicle screw diameters of 3.5-6 mm and transverse pedicle screw angles of 3.5°-12.4°.

Evaluation of thoracic vertebrae in healthy White New Zealand rabbit (Oryctolagus Cuniculus): Computed tomographic and morphometric study.

BACKGROUND: Computed tomography currently has a prominent role in diagnosis and evaluation of vertebral column. On the other hand, a thorough knowledge about vertebral column property in normal state is prerequisite an accurate diagnosis of different abnormalities in this region. OBJECTIVE: The purpose of this study was to present a complete and exact descriptive and morphometric evaluation of thoracic vertebrae in rabbits with computed tomography. In images which were constructed by CT, several structures and different parts of the thoracic vertebrae have been named. METHODS: Ten healthy, mature, White New Zealand rabbits were evaluated. The morphologic and morphometric parameters of the thoracic vertebrae were studied. In this study, several parameters of thoracic vertebrae, such as vertebral body height, spinous process height, transverse process length, transverse process width, etc., were measured by computed tomography. RESULTS: Some parameters, such as spinal canal height, spinal canal width, pedicle length, pedicle width, end plate width, and endplate height, had no significant difference through thoracic vertebrae but other parameters, such as vertebral body height, transverse process length, transverse process width, spinous process angle, transverse process angle, and vertebral body length, had a significant difference. CONCLUSIONS: In this study, a comprehensive anatomic atlas of CT anatomy of the thoracic vertebrae was produced for use by veterinary radiologists, clinicians, and surgeons. Finally, we must mention these two important points: (1) Many of the differences observed between rabbits and humans are based on the way the trunks of these two creatures are located on the ground and the differences in the way their bodies move. (2) In studies that are done by modelling humans on animals, it should be noted that the terms used in animal anatomy are different and the names are used using the principles of veterinary anatomy.

Axial skeletal morphological studies on the helmeted Guinea fowl (Numida meleagridis).

This study on the morphological features of bones of the helmeted guinea fowl (Numidia meleagridis) specifically the axial skeleton was conducted for documentation and valuable information on differences when compared with other species of the same order. Ten (10) Helmeted guinea fowls (5 females and 5 males) with an average weight of 3.0 kg were euthanized via jugular vein severance with bone preparation achieved via the use of insect larvae. The skull presented an elongated structure made up of paired and unpaired flat, short and long bones with distinctive features. The frontal bone projected caudodorsally to form a horn like structure, the frontal process at its middle while the vomer was absent. The cervical vertebrae were 14 in number starting from the first (Atlas) to the last vertebra without a rib. Specific distinguishing features were evident in the Atlas, Axis, 3rd to 5th, 6th to 11th and 12th to 14th cervical vertebrae. The thoracic vertebrae presented 7 bones comprising the 1st single free vertebra; notarium (fused 2nd to 5th), 6th single free vertebra and the last 7th vertebrae that fused with the synsacrum which was an ankylosis of the lumbar and sacral vertebrae. The caudal vertebrae were 7 with the last; the pygostyle being distinct in appearance. The ribs were 7 pairs, of which the first two were asternal while the remaining five were sternal and consisted of proximal vertebral and distal sternal portions. The curved uncinate process articulated to the caudal border of the 2nd and vertebral portions of the 3rd to 5th ribs. The guinea fowl proved to be a carinate by presenting a single sternum with dorsolateral processes and a ventral carina. In conclusion, this study revealed that except for the skull, the axial skeleton of the Helmeted Guinea fowl presented similarities to that of the domestic fowl (Gallus domesticus).

Review of morphology, development, and evolution of the notarium in birds.

The notarium is a rigid bony structure, which resulted from the fusion of thoracic vertebrae of some pterosaurs and birds. It is high variable, ranging from two to six fused thoracic vertebrae. In this study, we reviewed and analyzed approximately 270 specimens of neornithine birds (representing 80% of the living orders) and some fossils in order to identify the number of fused vertebrae, degree and sites of vertebral fusion, occurrence of sutures, and other structures of potential phylogenetic and functional significance. These data were analyzed using a recent time-calibrated molecular phylogenetic tree and principal component analyses analysis evaluating the relationship with long bones in order to reconstruct macroevolutionary trends related to the evolution of the notarium. The occurrence of this structure shows a mosaic distribution over neornithine phylogeny, originating several times independently, especially during the Paleogene, in predominantly ground-dwelling forms. The notarium of these groups is characterized by: neural spines fused into single structure, intervertebral openings small to absent, large ventral keels forming ventral plates, and fused transverse processes. Derived neornithines, such as aquatic forms and long-legged birds, have a tendency to display a decreased degree of fusion between the vertebrae, which may indicate a reduction or disappearance of the notarium.

Morphometric description of thoracic vertebral pedicles in adult Malawian cadavers and implications for transpedicula spine fixation / Descripción morfometrica de los pedículos vertebrales torácicos en cadáveres de Malawi adultos e implicaciones para la fijación transpedicular de la columna

SUMMARY: Thoracic pedicles are important during the surgical repair of the thoracic spine deformities. Individuals show considerable differences in the asymmetric dimensions of the thoracic pedicles across populations. The purpose of this study was to determine the thoracic pedicle size and angle in adult Malawian cadavers and to suggest the clinical implications associated particularly the transpedicular fixation of spinal deformities. Adult thoracic vertebra from undetermined sex specimens (n=227) from the skeletal collection in the Anatomy Division, Biomedical Sciences Department, College of Medicine, University of Malawi were measured to assess the pedicle width, pedicle height, chord length, transverse diameter, interpedicular distance, transverse and sagittal pedicle angles. The mean pedicle width was 4.71 ± 1.83 mm (left side) and 4.82 ± 1.77 mm (right side) and the mean pedicle height was 12.63 ± 2.61 mm (left side) and 12.60 ± 2.54 mm (right side). The mean transverse pedicle angle was 12.22 ± 2.30 degrees (left side) and 12.46 ± 2.34 degrees (right side). The mean sagittal pedicle angle was 9.24 ± 2.67 degrees (left side) and 9.40 ± 2.76 degrees (right side). The mean interpedicular distance was 16.67 ± 2.23 mm. Our sample population generally showed smaller thoracic pedicle dimensions than those reported in other populations. Prior knowledge of the variations regarding the thoracic pedicle dimensions is vital for the determination of the pedicle screw size and design. Most importantly the information helps surgeons during preoperative planning of the transpedicular thoracic spine fixation and radiological interpretation.

RESUMEN: Los pedículos de las vértebras torácicas son importantes durante la reparación quirúrgica de las deformidades de la columna torácica. Los individuos muestran diferencias considerables en las dimensiones asimétricas de las vértebras torácicas entre poblaciones. El propósito de este estudio fue determinar el tamaño y el ángulo los pedículos de las vértebras torácicas en cadáveres de Malawi adultos y sugerir las implicaciones clínicas asociadas a la fijación transpedicular de las deformidades espinales. Se midieron 227 vértebras torácicas de muestras de individuos de sexo indeterminado de la colección esquelética en la División de Anatomía, Departamento de Ciencias Biomédicas, Facultad de Medicina, Universidad de Malawi para evaluar el ancho del pedículo, la altura del pedículo, la longitud, el diámetro transversal, distancia interpedicular y ángulos pediculares transversales y sagitales. El ancho medio del pedículo fue de 4,71 ± 1,83 mm (lado izquierdo) y 4,82 ± 1,77 mm (lado derecho) y la altura media del pedículo fue de 12,63 ± 2,61 mm (lado izquierdo) y 12,60 ± 2,54 mm (lado derecho). El ángulo pedicular transverso medio fue de 12,22 ± 2,3 grados (lado izquierdo) y 12,46 ± 2,34 grados (lado derecho). El ángulo pedicular sagital medio fue de 9,24 ± 2,67 grados (lado izquierdo) y 9,40 ± 2,76 grados (lado derecho). La distancia interpedicular media fue de 16,67 ± 2,23 mm. La población de esta muestra mostró dimensiones de los pedículos de las vértebras torácicas generalmente más pequeñas que las informadas en otras poblaciones. El conocimiento previo de las variaciones con respecto a las dimensiones de los pedículos de las vértebras torácicas es vital para la determinación del tamaño y diseño del tornillo pedicular. Lo más importante es que la información ayuda a los cirujanos durante la planificación preoperatoria para la fijación transpedicular de la columna torácica y su interpretación radiológica.

Thoracolumbar Spine Trauma.

Thoracolumbar spine trauma can result in potentially life-threatening consequences and requires careful management to ensure good outcomes. The purpose of this chapter is to discuss the anatomy, diagnostic tools, non-operative, and operative treatments important when addressing thoracolumbar trauma.

Morphometric study on the 12th thoracic vertebrae which is most frequently exposed to trauma and the closest vertebra to thoracic aorta.

BACKGROUND: To describe gender-related differences in the length of the left chord and pedicle at the level of 12th thoracic vertebrae and appropriate length of the screw to be applied so as to decrease the perforation risk of anterior cortex of the corpus and preventable injury of major vascular vessels. METHODS: Axial bone window computed tomography images of T12 vertebral pedicles of 60 patients (30 males and 30 females, age >25 years) without any sign of spinal trauma were obtained and morphometric data were analyzed. RESULTS: Mean ages of the female (n=30) and male (n=30) patients were 32.17±4.24 and 31.70±3.60 years, respectively. The left chord lengths of T12 of the male (38.17±2.54 mm) and female (36.62±2.27 mm) patients were compared and a statistically significant difference was found between these two measurements (p=0.016). A statistically significant difference between the length of the left chord (37.40±2.51) (range, 32-44 mm) and age (31.93±3.91) (range, 25-40 years) and also a moderate degree of correlation were observed (p=0.002), (r=0.401). A statistically significant difference and a moderate degree of correlation were found between the lengths of the left chords (37.40±2.51; range, 32-44 mm) and the left pedicles (12.12±1.34; range, 10.0-15.80 mm) (p=0.001), (r=0.577). CONCLUSION: Significant differences and correlations exist between the left pedicle and the left chord in male and female patients and patients with different ages. The data obtained can be used as a guide to determine the implant size and intraoperative management of T12 vertebral pedicle.

Combined, Rib-Sparing, Bilateral Approach to the Ventral Mid and Low Thoracic Spine: Study on Comparative Anatomy and Surgical Feasibility.

BACKGROUND: Pathologies of the ventral thoracic spine represent a challenge, igniting arguments about which should be the ideal surgical approach to access this area. Anterior transthoracic thoracotomy and a number of posterolateral routes have been developed. Among the latter, costotransversectomy has demonstrated to provide good ventral exposure with a lower, but not negligible, morbidity. The optimal approach should be the one minimizing surgical morbidity on both neural and extraneural structures while optimizing exposure. METHODS: The authors described the combined, rib-sparing, bilateral approach (CRBA) to the ventral mid/low-thoracic spine. The technique combines a transfacet pedicle partially sparing approach on one side and a transpedicular with transverse process resection on the contralateral one. A laboratory investigation was conducted. The technique was applied in a surgical setting, and a case was reported. RESULTS: CRBA is rib-sparing, completely extracavitary, and does not require pleural exposure and paraspinal muscle splitting, thus minimizing potential morbidity. The combination of 2 corridors ensures the greatest exposure compared with standard posterolateral approaches. The only blind corner is limited to a small area just in front of the dural sac. A bimanual approach optimizes control during surgical manipulation, even if the area of maneuverability and cross-section areas of surgical corridors are slightly limited compared to traditional costotransversectomy due to the minimally invasive nature of the procedure. CONCLUSIONS: CRBA represents a safe and effective option to access the ventral mid/low thoracic spine. It provides great exposure and bimanual manipulation of the surgical target, minimizes potential morbidity, and avoids entrance into the thoracic cavity and paraspinal muscle splitting.

Trunk Injuries in Athletes.

ABSTRACT: Trunk pain is a common cause of performance limitation and time away from sport in athletes. However, atraumatic trunk injuries are underrepresented in medical literature and underrecognized clinically. Delays in diagnosis and initiation of appropriate treatment can increase injury morbidity and return-to-play time. Currently, evidence-based guidelines for diagnosis and treatment of trunk pain in athletes are limited. Thus, we provide an overview of atraumatic sport-related injuries to the thoracic spine (disc herniation, scoliosis, kyphosis), ribcage (bone stress injury, costochondritis, Tietze syndrome, slipping rib syndrome, costovertebral or costotransverse joint dysfunction), and chest and abdominal wall musculature (intercostal, serratus anterior, oblique strains, regional myofascial pain), highlighting sport-specific biomechanical considerations. We aim to increase awareness of these causes of trunk pain among sports medicine providers in an effort to guide diagnostic and treatment recommendations that will ultimately improve overall musculoskeletal health in athletes.

Thoracic and lumbar spine pedicle morphology in Japanese patients.

PURPOSE: Pedicle morphology is important for intraoperative surgical anatomy and to define pedicle screw design and parameters. However, differences of pedicle size according to ethnicity and gender are not well studied. The purpose of this study is to investigate morphological characteristics of the pedicle in Japanese patients for determining adequate screw size and optimal surgical planning. METHODS: We investigated thoracic and lumbar pedicle morphology in Japanese patients using computed tomography (CT) measurements and analyzed the standard size of pedicles on upper thoracic to lumbar spine CT images in 227 Japanese patients. RESULTS: Gender had a larger impact on the shape and size of pedicles than racial differences. In the distribution of pedicle width, we calculated the ratio of values less than 4.5 mm, that in females resulted to be over 30% for the Th3-Th9 segment, and particularly high, above 60% at Th4 and Th5. CONCLUSION: Our measurement analysis showed that pedicle morphological parameters in Japanese patients showed tendency to be smaller to those found in other studies, and particularly in female patients, they were statistically significantly smaller. Adequate transpedicular instrumentation for Japanese patients will require smaller size pedicle-related devices that will match our anatomical findings to achieve safe device placement. In addition, serving ethnically non-homogenous patient population can require further to spinal morphometric for precise device selection.

Pushing the boundary? Testing the "functional elongation hypothesis" of the giraffe's neck.

Although giraffes maintain the usual mammalian cervical number of seven vertebrae, their first thoracic vertebra (T1) exhibits aberrant anatomy and has been hypothesized to functionally elongate the neck. We test this "functional elongation hypothesis" by combining phylogenetically informed analyses of neck length, three-dimensional (3D) vertebral shape, and of the functional significance of shape differences across a broad sample of ruminants and camelids. Digital bone models of the cervicothoracic transition were subjected to 3D geometric morphometric analysis revealing how the shape of the seventh cervical (C7) has converged in several long-necked species. However, we find a unique "cervicalization" of the giraffe's T1. In contrast, we demonstrate a "thoracalization" of C7 for the European bison. Other giraffids (okapi and extinct Sivatherium) did not exhibit "cervicalized" T1 morphology. Quantitative range of motion (ROM) analysis at the cervicothoracic transition in ruminants and camelids confirms the "functional elongation hypothesis" for the giraffe in terms of increased mobility, especially with regard to dorsoventral flexion/extension. Additionally, other factors related to the unique morphology of the giraffe's cervicothoracic transition such as neck posture and intervertebral stability are discussed and should be considered in future studies of giraffe neck evolution.

Accuracy and technical limits of percutaneous pedicle screw placement in the thoracolumbar spine.

PURPOSE: The two-dimensional fluoroscopic method of percutaneous pedicle screw instrumentation has been clinically described as reliable method in the caudal thoracic and lumbosacral spine. Its accuracy has not been clearly reported in the cranial thoracic spine. The aim of this in vitro study was to investigate percutaneous pedicle screw placement accuracy according to pedicle dimensions and vertebral levels. METHODS: Six fresh-frozen human specimens were instrumented with 216 screws from T1 to S1. Pedicle isthmus widths, heights, transversal pedicles and screws were measured on computed tomography. Pedicle cortex violation ≥ 2 mm was defined as screw malposition. RESULTS: The narrowest pedicles were at T3-T5. A large variability between transversal pedicle axes and percutaneous pedicle screw was present, depending on the spinal level. Screw malposition rates were 36.1% in the cranial thoracic spine (T1-T6), 16.7% in the caudal thoracic spine (T7-T12), and 6.9% in the lumbosacral spine (L1-S1). The risk for screw malposition was significantly higher at cranial thoracic levels compared to caudal thoracic (p = 0.006) and lumbosacral (p < 0.0001) levels. Cortex violation ≥ 2 mm was constantly present if the pedicle width was < 4.8 mm. CONCLUSION: Percutaneous pedicle screw placement appears safe in the caudal thoracic and lumbosacral spine. The two-dimensional fluoroscopic method has a limited reliability above T7 because of smaller pedicle dimensions, difficulties in visualizing radiographic pedicle landmarks and kyphosis.

Vertebral pneumaticity is correlated with serial variation in vertebral shape in storks.

Birds and their ornithodiran ancestors are unique among vertebrates in exhibiting air-filled sinuses in their postcranial bones, a phenomenon called postcranial skeletal pneumaticity. The factors that account for serial and interspecific variation in postcranial skeletal pneumaticity are poorly understood, although body size, ecology, and bone biomechanics have all been implicated as influencing the extent to which pneumatizing epithelia invade the skeleton and induce bone resorption. Here, I use high-resolution computed-tomography to holistically quantify vertebral pneumaticity in members of the neognath family Ciconiidae (storks), with pneumaticity measured as the relative volume of internal air space. These data are used to describe serial variation in extent of pneumaticity and to assess whether and how pneumaticity varies with the size and shape of a vertebra. Pneumaticity increases dramatically from the middle of the neck onwards, contrary to previous predictions that cervical pneumaticity should decrease toward the thorax to maintain structural integrity as the mass and bending moments of the neck increase. Although the largest vertebrae sampled are also the most pneumatic, vertebral size cannot on its own account for serial or interspecific variation in extent of pneumaticity. Vertebral shape, as quantified by three-dimensional geometric morphometrics, is found to be significantly correlated with extent of pneumaticity, with elongate vertebrae being less pneumatic than craniocaudally short and dorsoventrally tall vertebrae. Considered together, the results of this study are consistent with the hypothesis that shape- and position-specific biomechanics influence the amount of bone loss that can be safely tolerated. These results have potentially important implications for the evolution of vertebral morphology in birds and their extinct relatives.

Regional differences in zygapophysial joint cavities: A histological study of human fetuses.

Human zygapophysial joints (ZJ) have regional differences in shape and orientation during prenatal growth. However, there is limited knowledge of the synovial recess during fetal development. We examined sagittal and horizontal histological sections of the vertebral columns of 30 human fetuses at gestational ages of 8-37 weeks. Fetuses of all gestational ages had subaxial cervical articular processes that were thicker than in the thoracolumbar regions, and as large as the corresponding vertebral bodies. A small or large synovial recess extending beyond the articular cartilage was evident at most regions. The cervical ZJ had large or deep recesses that extended inferiorly in midterm fetuses and posteromedially along the vertebral pedicle and lamina in near-term fetuses. Likewise, the thoracic ZJ had small recesses that extended superiorly in midterm fetuses and medially in near-term fetuses. The lumbar recesses extended laterally beyond the medially shifted articular cartilage of the upper adjacent vertebrae in near-term fetuses and the lumbar articular surface was smallest in the three regions at all stages. At any region, a deep recess appeared before an area expansion of the ZJ cartilage. A drastic change in direction and size of the prenatal recess seemed to occur depending on a possible minute dislocation of the ZJ. In particular, a deep posteromedial recess of the cervical ZJ, which extended far beyond the articular cartilage, might be necessary to maintain high flexibility suitable for the strong flexion posture in utero.