Sagittal wedging of intervertebral discs and vertebral bodies in the cervical spine and their associations with age, sex and cervical lordosis: A large-scale morphological study.

Many recent studies have focused on the functional and clinical importance of cervical lordosis. However, there is little accurate knowledge of the anatomical parameters that constitute cervical lordosis (i.e., the sagittal wedging angles of intervertebral discs and vertebral bodies) and their associations with age and sex. Standing lateral cervical radiographs of 1020 subjects (424 males, 596 females) with a mean age of 36.6 ± 17.0 years (range 7-95 years) were evaluated retrospectively. Cervical lordosis, the sum of intervertebral disc wedging angles from C2/C3 to C6/C7 and the sum of vertebral body wedging angles from C3 to C7 were measured. The sum of intervertebral disc wedging and the sum of vertebral body wedging were 20.6° ± 14.7° and -12.8° ± 10.3°, respectively. The sum of intervertebral disc wedging increased significantly with age and was significantly greater in males than females, whereas there was no sex-related difference in the sum of vertebral body wedging. The sum of intervertebral disc wedging was negatively correlated with sum of vertebral body wedging. Wedging of discs contributed to C2-C7 cervical lordosis more significantly than wedging of vertebral bodies. There were moderate positive correlations between cervical lordosis and intervertebral disc wedging angles at C3/C4, C4/C5 and C5/C6; weak correlations were observed at C2/C3 and C6/C7. This study constitutes the largest currently available analysis comprehensively documenting the anatomical characteristics of sagittal wedging of intervertebral discs and vertebral bodies in the cervical spine. The findings could improve understanding of the internal architecture of cervical lordosis among clinicians.

Trabecular Architecture and Mechanical Heterogeneity Effects on Vertebral Body Strength.

PURPOSE OF REVIEW: We aimed to synthesize the recent work on the intra-vertebral heterogeneity in density, trabecular architecture and mechanical properties, its implications for fracture risk, its association with degeneration of the intervertebral discs, and its implications for implant design. RECENT FINDINGS: As compared to the peripheral regions of the centrum, the central region of the vertebral body exhibits lower density and more sparse microstructure. As compared to the anterior region, the posterior region shows higher density. These variations are more pronounced in vertebrae from older persons and in those adjacent to degenerated discs. Mixed results have been reported in regard to variation along the superior-inferior axis and to relationships between the heterogeneity in density and vertebral strength and fracture risk. These discrepancies highlight that, first, despite the large amount of study of the intra-vertebral heterogeneity in microstructure, direct study of that in mechanical properties has lagged, and second, more measurements of vertebral loading are needed to understand how the heterogeneity affects distributions of stress and strain in the vertebra. These future areas of study are relevant not only to the question of spine fractures but also to the design and selection of implants for spine fusion and disc replacement. The intra-vertebral heterogeneity in microstructure and mechanical properties may be a product of mechanical adaptation as well as a key determinant of the ability of the vertebral body to withstand a given type of loading.

Accuracy and Reliability of Computer-aided Anatomical Measurements for Vertebral Body and Disc Based on Computed Tomography Scans.

OBJECTIVE: To assess whether the computed tomography (CT)-based method of three-dimensional (3D) analysis (Mimics) was accurate and reliable for spine surgical anatomical measurements. METHODS: A total of 40 lumbar segments and 32 inter-vertebral discs from eigth adult male cadavers without fractures or deformities fixed with the classical formaldehyde method were included in this research on 5 June 2017. CT scans including seven dimensions: anterior height of the vertebral body (VBHa), middle height of the vertebral body (VBHm), posterior height of the vertebral body (VBHp), width of the upper endplate (EPWu), depth of the upper endplate (EPDu), anterior height of the inter-vertebral disc in the median sagittal plane (IDHa), and posterior height of the inter-vertebral disc in the median sagittal plane (IDHp). They were performed based on uniform conditions (slice thickness: 0.625 mm) using a CT scanner on 8 June 2017. Afterwards, the surgical anatomical measurements were conducted with a Vernier caliper on 12 June 2017. The computer-aided anatomical measurements were conducted by three investigators using Mimics 16.0 to perform 3D reconstructions of CT bone on 16 June 2017. Finally, the length and angle were measured with associated measurement tools, yielding a verified accuracy of 0.01 mm and 0.01°, respectively. Each measurement was repeated three times, and all anatomical data was analyzed using the statistical software and P-value < 0.05 was considered statistically significant. RESULTS: The results showed no statistically significant difference was observed between the surgical anatomical and computer-aided anatomical measurements (P > 0.05) for lumbar vertebra measurements, and the absolute difference between surgical and computer-aided data were all less than 1.0 mm (for the VBHa, VBHm, VBHp, EPWu, and EPDu were 0.12, 0.03, 0.03, 0.31, and 0.03 mm, respectively). Moreover, although the absolute differences of discs was larger than those of lumbar vertebras, no significant differences were detected between the computer-aided and surgical anatomical measurements for the IDHa, as well as IDHp in the vast majority of measurements (P = 0.543, 0.079 or 0.052 for IDHa, and P = 0.212, 0.133 or 0.042 for IDHp). In addition, excellent reliability correlation was observed between the measurements of each investigator, and the reliability coefficients in the intra-groups were all greater than 0.9 except for IDHp (reliability coefficient = 0.892). Additionally, the reliability coefficients were greater than 0.9 for the all between-group correlations, and a significant correlation was also observed. Furthermore, no statistically significant difference for three anatomical values was found in the computer-assisted measurements of the lumbar bone structure (P > 0.05). Similarly, we did not observe a statistical difference in the anatomical data of the lumbar discs from the three measures (P > 0.05). CONCLUSIONS: Computer-aided anatomical measurement for spine based on CT scans presents the high accuracy and reliability for improving spinal surgical procedures.

Characterization of progressive changes in pedicle morphometry and neurovascular anatomy during growth in adolescent idiopathic scoliosis versus adolescents without scoliosis.

STUDY DESIGN: Prospective cohort study. OBJECTIVES: Investigate the progressive changes in pedicle morphometry and the spatial relationship between the pedicles and neurovascular structures in patients with AIS during growth. Adolescent idiopathic scoliosis (AIS) is a complex three-dimensional spine deformity. AIS pedicles are known to be asymmetrical when compared to adolescents without scoliosis. Defining the anatomical changes occurring progressively in scoliosis as it increases with time and growth is essential for understanding the pathophysiology of scoliosis and for treatment planning. MRI is the ideal method to study the growing spine without ionising radiation. METHODS: 24 females with AIS (mean 12.6 years, right sided main thoracic curves) and 20 non-scoliotic females (mean 11.5 years) were selected from an ongoing database. Participants underwent two 3D MRI scans (3 T scanner, T1, 0.5 mm isotropic voxels) approximately 1 year apart (AIS: mean 1.3 ± 0.05 years, control: mean 1.0 ± 0.1 years). The pedicle width, chord length, pedicle height, transverse pedicle angle, sagittal pedicle angle, distance from vertebrae to aorta and distance from pedicle to dural sac were measured from T5 to T12. Inter- and intra-observer variability was assessed. RESULTS: From scans 1-2 in the AIS group, the dural sac became closer to the left pedicle (p < 0.05, T6, T8-T10 and T12) while the distance from the vertebrae to the aorta increased (p < 0.05, T6-T10). No significant changes in these measurements were observed in the non-scoliotic group. Between scans, the AIS chord length and transverse pedicle angle increased on the left side around the apex (p < 0.05) creating asymmetries not seen in the non-scoliotic cohort. The mean pedicle height increased symmetrically in the non-scoliosis cohort (p < 0.05) and asymmetrically in the AIS group with the right side growing faster than the left at T6-T7 (p < 0.05). CONCLUSION: Asymmetrical growth patterns occur in the vertebral posterior elements of AIS patients compared to the symmetrical growth patterns found in the non-scoliotic participants. LEVEL OF EVIDENCE: Level II prospective comparative study.

Augmented reality-based navigation increases precision of pedicle screw insertion.

BACKGROUND: Precise insertion of pedicle screws is important to avoid injury to closely adjacent neurovascular structures. The standard method for the insertion of pedicle screws is based on anatomical landmarks (free-hand technique). Head-mounted augmented reality (AR) devices can be used to guide instrumentation and implant placement in spinal surgery. This study evaluates the feasibility and precision of AR technology to improve precision of pedicle screw insertion compared to the current standard technique. METHODS: Two board-certified orthopedic surgeons specialized in spine surgery and two novice surgeons were each instructed to drill pilot holes for 40 pedicle screws in eighty lumbar vertebra sawbones models in an agar-based gel. One hundred and sixty pedicles were randomized into two groups: the standard free-hand technique (FH) and augmented reality technique (AR). A 3D model of the vertebral body was superimposed over the AR headset. Half of the pedicles were drilled using the FH method, and the other half using the AR method. RESULTS: The average minimal distance of the drill axis to the pedicle wall (MAPW) was similar in both groups for expert surgeons (FH 4.8 ± 1.0 mm vs. AR 5.0 ± 1.4 mm, p = 0.389) but for novice surgeons (FH 3.4 mm ± 1.8 mm, AR 4.2 ± 1.8 mm, p = 0.044). Expert surgeons showed 0 primary drill pedicle perforations (PDPP) in both the FH and AR groups. Novices showed 3 (7.5%) PDPP in the FH group and one perforation (2.5%) in the AR group, respectively (p > 0.005). Experts showed no statistically significant difference in average secondary screw pedicle perforations (SSPP) between the AR and the FH set 6-, 7-, and 8-mm screws (p > 0.05). Novices showed significant differences of SSPP between most groups: 6-mm screws, 18 (45%) vs. 7 (17.5%), p = 0.006; 7-mm screws, 20 (50%) vs. 10 (25%), p = 0.013; and 8-mm screws, 22 (55%) vs. 15 (37.5%), p = 0.053, in the FH and AR group, respectively. In novices, the average optimal medio-lateral convergent angle (oMLCA) was 3.23° (STD 4.90) and 0.62° (STD 4.56) for the FH and AR set screws (p = 0.017), respectively. Novices drilled with a higher precision with respect to the cranio-caudal inclination angle (CCIA) category (p = 0.04) with AR. CONCLUSION: In this study, the additional anatomical information provided by the AR headset superimposed to real-world anatomy improved the precision of drilling pilot holes for pedicle screws in a laboratory setting and decreases the effect of surgeon's experience. Further technical development and validations studies are currently being performed to investigate potential clinical benefits of the herein described AR-based navigation approach.

The effect of vertebral body stapling on spine biomechanics and structure using a bovine model.

BACKGROUND: Adolescent idiopathic scoliosis is a common condition affecting 2.5% of the general population. Vertebral body stapling was introduced as a method of fusionless growth modulation for the correction of moderate idiopathic scoliosis (Cobb angles of 20-40°), and was claimed to be more effective than bracing and less invasive than fusion. The aim of this study was to assess the effect of vertebral body stapling on the stiffness of a thoracic motion segment unit under moment controlled load, and to assess the vertebral structural damage caused by the staples. METHODS: Thoracic spine motion segments from 6 to 8 week old calves (n=14) were tested in flexion/extension, lateral bending, and axial rotation. The segments were tested un-instrumented, then a left anterolateral intervertebral Shape Memory Alloy (SMA) staple was inserted and the test was repeated. Data were collected from the tenth load cycle of each sequence and stiffness was calculated. The staples were carefully removed and the segments were studied with micro-computed tomography to assess physical damage to the bony structure. Visual assessment of the vertebral bone structure on micro-CT was performed. FINDINGS: There was no change in motion segment stiffness in flexion/extension nor in axial rotation. There was a reduction in stiffness in lateral bending with 30% reduction bending away from the staple and 12% reduction bending towards the staple. Micro-CT showed physeal damage in all the specimens. INTERPRETATION: Intervertebral stapling using SMA staples cause a reduction in spine stiffness in lateral bending. They also cause damage to the endplate epiphyses.

Anatomía morfométrica de importancia clínica del atlas en relación a la estabilización del complejo atlantoaxial y occipitocervical / Morphometric anatomy of clinical importance of the atlas in relation to the stabilization of the atlantoaxial and occipitocervical complex

RESUMEN: Evaluar de manera integral los parámetros morfométricos de la vértebra atlas (C1) en la población mexicana de relevancia en la realización de procedimientos quirúrgicos de la unión craneocervical con el fin de proveer datos cuantitativos indispensables para su realización. Para este estudio se utilizaron un total de 576 vértebras C1 secas de población mexicana contemporánea. Se realizaron 11 mediciones respecto a la morfología de C1. Las mediciones se efectuaron bilateralmente utilizando un vernier digital milimétrico con una precisión de 0,01 milímetros y se aplicó un análisis estadístico. Un total de 576 vértebras atlas (C1), fueron medidas de manera bilateral, todas nuestras mediciones se reportaron en milímetros. El promedio del ancho de las masas lateral fue de 14,87 mm ± 1,38 mm. El promedio de la altura de las masas laterales fue de 4,05 mm ± 0,93 mm. El promedio del ancho del foramen transverso fue de 5,93 mm ± 0,98 mm. El promedio del largo del foramen transverso fue de 6,96 mm ± 0,98 mm. El promedio de la altura del foramen transverso fue de 5,76 mm ± 1,31 mm. El promedio del ancho del surco de la arteria vertebral fue de 18,87 mm ± 1,3 mm. El promedio de la distancia entre la línea media y el margen medial del surco de la arteria vertebral sobre la superficie anterior del arco posterior de C1 en su cara superior fue de 12,47 mm ± 3,14 mm. El promedio de la distancia entre la línea media y el margen medial del surco de la arteria vertebral sobre la superficie posterior del arco posterior de C1 en su cara superior fue de 18,75 mm ± 3,94 mm. El promedio de la distancia entre la línea media y el margen lateral del surco de la arteria vertebral sobre la superficie anterior del arco posterior de C1 en su cara superior fue de 19,7 mm ± 2,52 mm. El promedio de la distancia entre la línea media y el margen lateral del surco de la arteria vertebral sobre la superficie posterior del arco posterior de C1 en su cara superior fue de 29,52 mm ± 3,23. Nuestro estudio demuestra que las mediciones realizadas en nuestra población presentan diferencias significativas respecto a lo reportado actualmente en la literatura. Es necesario contar con un conocimiento de la morfología vertebral en nuestra población para disminuir la ventana de error al realizar procedimientos quirúrgicos que involucren este segmento.

SUMMARY: To evaluate in an integral way the morphometric parameters of the atlas (C1) vertebra in the Mexican population of relevance in performing surgical procedures of the craniocervical junction in order to provide quantitative and essential data for its realization. For this study, a total of 576 dry C1 vertebrae of contemporary Mexican population were used. Eleven measurements were carried out regarding the morphology of C1. The measurements were made bilaterally using a millimeter digital vernier with an accuracy of 0.01 millimeters and a statistical analysis was applied. A total of 576 atlas vertebrae (C1) were measured bilaterally, all our measurements were reported in millimeters. The average width of the lateral masses was 14.87 mm ± 1.38 mm. The average height of the lateral masses was 4.05 mm ± 0.93 mm. The average width of the transverse foramen was 5.93 mm ± 0.98 mm. The average length of the transverse foramen was 6.96 mm ± 0.98 mm. The average height of the transverse foramen was 5.76 mm ± 1.31 mm. The average width of the groove of the vertebral artery was 18.87 mm ± 1.3 mm. The average distance between the midline and the medial edge of the vertebral artery groove on the anterior surface of the posterior arch of C1 on its superior surface was 12.47 mm ± 3.14 mm. The average distance between the midline and the medial border of the vertebral artery groove on the posterior surface of the posterior arch of C1 on its upper face was 18.75 mm ± 3.94 mm. The average distance between the midline and the lateral border of the vertebral artery groove on the anterior surface of the posterior arch of C1 on its superior surface was 19.7 mm ± 2.52 mm. The average distance between the midline and the lateral border of the vertebral artery groove on the posterior surface of the posterior arch of C1 on its superior surface was 29.52 mm ± 3.23. Our study shows that the measurements made in our population present differences with respect to what is currently reported in the literature. It is necessary to have knowledge of vertebral morphology in our population to reduce the error window when performing surgical procedures involving this segment.

Morphometric Study of Cervical Vertebrae C3-C7 in a Population from Northeastern Mexico / Estudio Morfométrico de las Vértebras Cervicales C3-C7 en una Población del Noreste de México

Knowing the dimensions of the vertebral elements is very important for the development of instrumentation related to the cervical spine. Ethnic variations have been reported in these dimensions and, to date, there have been no morphometric studies of this area performed on the Mexican population. We conducted a morphometric study of 150 cervical vertebrae (C3-C7) obtained from a northeastern Mexican population to determine the dimensions of the bodies, pedicles, laminae, spinous processes, and superior and inferior articular processes. We did not find significant differences (p<0.05) in measurements taken of the left and right sides. The dimensions of the vertebral bodies were larger at lower levels. The pedicles of the C3 vertebra were larger in all dimensions compared to the other vertebrae. The largest height of the laminae was observed at C7 and the largest transverse length was observed at C5. The dimensions of the bodies, spinous processes, and laminae increased from C3-C7, whereas the dimensions of the pedicles and superior and inferior articular process height decreased toward the lower cervical levels.

Las mediciones de los elementos vertebrales son importantes para la instrumentación de columna cervical. Se han reportado variaciones étnicas en estas medidas y en la actualidad no existen estudios morfométricos en la población mexicana. Se realizó un estudio morfométrico en 150 vértebras cervicales (C3-C7) para determinar las medidas de los cuerpos, pedículos, láminas, procesos espinosos y articulares superiores e inferiores. No se encontraron diferencias significativas (p<0.05) en las medidas tomadas entre ambos lados. Las dimensiones de los cuerpos vertebrales se incrementan en niveles más bajos. Los pedículos de la vértebra C3 son mayores en todas sus dimensiones. La mayor altura de las láminas se observó en C7 y la mayor longitud transversal en C5. Las dimensiones del cuerpo, procesos espinosos y láminas se incrementan de C3-C7, mientras las dimensiones de los pedículos, altura de procesos articulares superiores e inferiores disminuyen en los niveles cervicales más bajos.