Automatic generation of subject-specific finite element models of the spine from magnetic resonance images

The generation of subject-specific finite element models of the spine is generally a time-consuming process based on computed tomography (CT) images, where scanning exposes subjects to harmful radiation. In this study, a method is presented for the automatic generation of spine finite element models using images from a single magnetic resonance (MR) sequence. The thoracic and lumbar spine of eight adult volunteers was imaged using a 3D multi-echo-gradient-echo sagittal MR sequence. A deep-learning method was used to generate synthetic CT images from the MR images. A pre-trained deep-learning network was used for the automatic segmentation of vertebrae from the synthetic CT images. Another deep-learning network was trained for the automatic segmentation of intervertebral discs from the MR images. The automatic segmentations were validated against manual segmentations for two subjects, one with scoliosis, and another with a spine implant. A template mesh of the spine was registered to the segmentations in three steps using a Bayesian coherent point drift algorithm. First, rigid registration was applied on the complete spine. Second, non-rigid registration was used for the individual discs and vertebrae. Third, the complete spine was non-rigidly registered to the individually registered discs and vertebrae. Comparison of the automatic and manual segmentations led to dice-scores of 0.93–0.96 for all vertebrae and discs. The lowest dice-score was in the disc at the height of the implant where artifacts led to under-segmentation. The mean distance between the morphed meshes and the segmentations was below 1 mm. In conclusion, the presented method can be used to automatically generate accurate subject-specific spine models

Etiology and pathogenesis of adolescent idiopathic scoliosis

Despite many years of dedicated research into the etio-pathogenesis, not one single cause for adolescent idiopathic scoliosis has been identified. The purpose of this review is to give a comprehensive overview of the current evidence and main etiological theories. Intrinsic causal mechanisms are found in the alignment of the upright human spino-pelvic complex and growth patterns of the immature spine. Studies on potential extrinsic mechanisms are mainly focused on neuromuscular, metabolic, and genetic etiological pathways. We can conclude that scoliosis is the spine's preconditioned response to a multitude of offenses that lead to a disturbance of the delicate human rotational spino-pelvic balance during growth

Reply to Weiss, H.-R. Comment on “Costa et al. The Effectiveness of Different Concepts of Bracing in Adolescent Idiopathic Scoliosis (AIS): A Systematic Review and Meta-Analysis. J. Clin. Med. 2021, 10, 2145”

We would like to thank you for the opportunity to reply to the comments in regard of the letter by Dr. Weiss [...

Complete Remodeling after Conservative Treatment of a Severely Angulated Odontoid Fracture in a Patient with Osteogenesis Imperfecta : A Case Report

Study Design. Case report. Objective. This is the first case report describing successful healing and remodeling of a traumatic odontoid fracture that was dislocated and severely angulated in a patient with osteogenesis imperfecta who was treated conservatively. Summary of Background Data. Osteogenesis imperfecta (OI) is a rare genetic disorder resulting in a low bone mass and bone fragility, predisposing these patients to fractures that often occur at a young age. Although any bone in the body may be involved, odontoid fractures are uncommon in this population. Because of a very high fusion rate, conservative management is accepted as a safe and efficient treatment of fractures of the odontoid in children. Several authors, however, recommend surgical treatment of patients who have failure of conservative treatment and have severe angulation or displacement of the odontoid.  Methods. A 5-year-old female, diagnosed with OI type I, presented with neck pain without any neurological deficits after falling out of a rocking chair backward, with her head landing first on the ground. Computed tomography confirmed a type III odontoid fracture without dislocation and she was initially treated with a rigid cervical orthosis. At 1 and 2 months of follow-up, progressive severe angulation of the odontoid was observed but conservative treatment was maintained as the space available for the spinal cord was sufficient and also considering the patient's history of OI.  Results.  Eight months postinjury, she had no clinical symptoms and there was osseous healing of the fracture with remodeling of the odontoid to normal morphology.  Conclusion.  Even in patients with OI, severely angulated odontoid fractures might have the capacity for osseous healing and complete remodeling under conservative treatment

Three-dimensional pelvic incidence is much higher in (thoraco)lumbar scoliosis than in controls

Purpose The pelvic incidence (PI) is used to describe the sagittal spino-pelvic alignment. In previous studies, radiographs were used, leading to less accuracy in establishing the three-dimensional (3D) spino-pelvic parameters. The purpose of this study is to analyze the differences in the 3D sagittal spino-pelvic alignment in adolescent idiopathic scoliosis (AIS) subjects and non-scoliotic controls. Methods Thirty-seven female AIS patients that underwent preoperative supine low-dose computed tomography imaging of the spine, hips and pelvis as part of their general workup were included and compared to 44 non-scoliotic age-matched female controls. A previously validated computerized method was used to measure the PI in 3D, as the angle between the line orthogonal to the inclination of the sacral endplate and the line connecting the center of the sacral endplate with the hip axis. Results The PI was on average 46.8° ± 12.4° in AIS patients and 41.3° ± 11.4° in controls (p = 0.025), with a higher PI in Lenke type 5 curves (50.6° ± 16.2°) as compared to controls (p = 0.042), whereas the Lenke type 1 curves (45.9° ± 12.2°) did not differ from controls (p = 0.141). Conclusion Lenke type 5 curves show a significantly higher PI than controls, whereas the Lenke type 1 curves did not differ from controls. This suggests a role of pelvic morphology and spino-pelvic alignment in the pathogenesis of idiopathic scoliosis. Further longitudinal studies should explore the exact role of the PI in the initiation and progression of different AIS types.Funding agencies: K2M; Alexandre Suerman Md/PhD grant; Swedish Society of Spinal surgeons</p

What is the Actual 3D Representation of the Rib Vertebra Angle Difference (Mehta Angle)?

STUDY DESIGN: Cross-sectional study. OBJECTIVE: To establish the relevance of the conventional two-dimensional (2D) RVAD and the relationship with the complex three-dimensional (3D) apical morphology in scoliosis. SUMMARY OF BACKGROUND DATA: The rib vertebra angle difference (RVAD, also known as Mehta's angle) describes apical rib asymmetry on conventional radiographs and was introduced as a prognostic factor for curve severity in early onset scoliosis, and later applied to other types of scoliosis as well. METHODS: An existing idiopathic scoliosis database of high-resolution CT scans used in previous work, acquired for spinal navigation, was used. Eighty-eight patients (Cobb angle 46-109°) were included. Cobb angle and 2D RVAD, as described by Mehta, were measured on the conventional radiographs and coronal digitally reconstructed radiographs (DRR) of the prone CT scans. A previously validated, semi-automatic image processing technique was used to acquire complete 3D spinal reconstructions for measurement of the 3D RVAD in a reconstructed true coronal plane, axial rotation and sagittal morphology. RESULTS: The 2D RVAD on the X-ray was on average 25.3 ± 11.0° and 25.6 ± 12.8° on the DRR (P = 0.990), but in the true 3D coronal view of the apex, hardly any asymmetry remained (3D RVAD: 3.1 ± 12.5°; 2D RVAD on X-ray and DRR versus 3D RVAD: P < 0.001). 2D apical rib asymmetry in the anatomical coronal plane did not correlate with the same RVAD measurements in the 3D reconstructed coronal plane of the rotated apex (r = 0.155; P = 0.149). A larger 2D RVAD was found to correlate linearly with increased axial rotation (r = 0.542; P < 0.001) and apical lordosis (r = 0.522; P < 0.001). CONCLUSIONS: The 2D RVAD represents a projection-based composite radiographic index reflecting the severity of the complex 3D apical morphology including axial rotation and apical lordosis. It indicates a difference in severity of the apical deformation. LEVEL OF EVIDENCE: 4

Anterior Spinal Overgrowth is the Result of the Scoliotic Mechanism and is Located in the Disc

STUDY DESIGN: Cross-sectional. OBJECTIVE: To investigate the presence and magnitude of anterior spinal overgrowth in neuromuscular scoliosis and compare this to the same measurements in idiopathic scoliosis and healthy spines. SUMMARY OF BACKGROUND DATA: Anterior spinal overgrowth has been described as a potential driver for the onset and progression of adolescent idiopathic scoliosis (AIS). Whether this anterior overgrowth is specific for AIS or also present in non-idiopathic scoliosis has not been reported. METHODS: Supine CT scans of thirty AIS patients (thoracic Cobb 21-81°), thirty neuromuscular (NM) scoliotic patients (thoracic Cobb 19-101°) and thirty non-scoliotic controls were used. The difference in length in per cents between the anterior and posterior side (((ΔA-P)/P)*100%, abbreviated to A-P%) of each vertebral body and intervertebral disc, and between the anterior side of the spine and the spinal canal (A-C%) were determined. RESULTS: The A-P% of the thoracic curves did not differ between the AIS (+1.2 ± 2.2%) and NM patients (+0.9 ± 4.1%, P = 0.663), both did differ, however, from the same measurements in controls (-3.0 ± 1.6%; P < 0.001) and correlated linearly with the Cobb angle (AIS r = 0.678, NM r = 0.687). Additional anterior length was caused by anterior elongation of the discs (AIS: A-P% disc +17.5 ± 12.7% versus A-P% body -2.5 ± 2.6%; P < 0.001, NM: A-P% disc +19.1 ± 18.0% versus A-P% body -3.5 ± 5.1%; P < 0.001). The A-C% T1-S1 in AIS and NM patients were similar (+7.9 ± 1.8% and +8.7 ± 4.0%, P = 0.273), but differed from the controls (+4.2 ± 3.3%; P < 0.001). CONCLUSIONS: So called anterior overgrowth has been postulated as a possible cause for idiopathic scoliosis, but apparently it occurs in scoliosis with a known origin as well. This suggests that it is part of a more generalized scoliotic mechanism, rather than its cause. The fact that the intervertebral discs contribute more to this increased anterior length than the vertebral bodies suggests an adaptation to altered loading, rather than a primary growth disturbance

Anterior Spinal Overgrowth is the Result of the Scoliotic Mechanism and is Located in the Disc

STUDY DESIGN: Cross-sectional. OBJECTIVE: To investigate the presence and magnitude of anterior spinal overgrowth in neuromuscular scoliosis and compare this to the same measurements in idiopathic scoliosis and healthy spines. SUMMARY OF BACKGROUND DATA: Anterior spinal overgrowth has been described as a potential driver for the onset and progression of adolescent idiopathic scoliosis (AIS). Whether this anterior overgrowth is specific for AIS or also present in non-idiopathic scoliosis has not been reported. METHODS: Supine CT scans of thirty AIS patients (thoracic Cobb 21-81°), thirty neuromuscular (NM) scoliotic patients (thoracic Cobb 19-101°) and thirty non-scoliotic controls were used. The difference in length in per cents between the anterior and posterior side (((ΔA-P)/P)*100%, abbreviated to A-P%) of each vertebral body and intervertebral disc, and between the anterior side of the spine and the spinal canal (A-C%) were determined. RESULTS: The A-P% of the thoracic curves did not differ between the AIS (+1.2 ± 2.2%) and NM patients (+0.9 ± 4.1%, P = 0.663), both did differ, however, from the same measurements in controls (-3.0 ± 1.6%; P < 0.001) and correlated linearly with the Cobb angle (AIS r = 0.678, NM r = 0.687). Additional anterior length was caused by anterior elongation of the discs (AIS: A-P% disc +17.5 ± 12.7% versus A-P% body -2.5 ± 2.6%; P < 0.001, NM: A-P% disc +19.1 ± 18.0% versus A-P% body -3.5 ± 5.1%; P < 0.001). The A-C% T1-S1 in AIS and NM patients were similar (+7.9 ± 1.8% and +8.7 ± 4.0%, P = 0.273), but differed from the controls (+4.2 ± 3.3%; P < 0.001). CONCLUSIONS: So called anterior overgrowth has been postulated as a possible cause for idiopathic scoliosis, but apparently it occurs in scoliosis with a known origin as well. This suggests that it is part of a more generalized scoliotic mechanism, rather than its cause. The fact that the intervertebral discs contribute more to this increased anterior length than the vertebral bodies suggests an adaptation to altered loading, rather than a primary growth disturbance