Influence of cervical spine sagittal alignment on range of motion after corpectomy: a finite element study.

BACKGROUND: Sagittal alignment of the cervical spine might influence the development of radiological adjacent segment pathology (RASP) after central corpectomy (CC). Range of motion (ROM) of the adjacent segments is closely linked to the development of RASP. METHODS: To investigate the ROM of the adjacent segments after CC, we developed a C2-T1 finite element (FE) model. The model with a lordotic sagittal alignment served as the baseline model. Models with straight and kyphotic alignment were generated using mesh morphing methods. Single-level corpectomy at C5 was done on these models. Segmental ROMs of intact and corpectomized spines were compared for physiologic flexion-extension loads. RESULTS: The flexion ROM decreased by an average of 13% with the change in sagittal alignment from lordosis to kyphosis; however, a consistent decrease was not observed in extension. After CC, the ROM increased by an average of 95% and 31% in the superior and inferior adjacent segments. With kyphotic change in the sagittal alignment, the postoperative increase in flexion ROM exhibited a decreasing trend, while this was not seen in extension. CONCLUSIONS: Kyphotic changes of the intact spine resulted in segmental stiffening, and after corpectomy, it resulted in inconsistent variations of segmental extension ROMs.

Rear-Impact Neck Whiplash: Role of Head Inertial Properties and Spine Morphological Variations on Segmental Rotations.

Whiplash injuries continue to be a concern in low-speed rear impact. This study was designed to investigate the role of variations in spine morphology and head inertia properties on cervical spine segmental rotation in rear-impact whiplash loading. Vertebral morphology is rarely considered as an input parameter in spine finite element (FE) models. A methodology toward considering morphological variations as input parameters and identifying the influential variations is presented in this paper. A cervical spine FE model, with its morphology parametrized using mesh morphing, was used to study the influence of disk height, anteroposterior vertebral depth, and segmental size, as well as variations in head mass, moment of inertia, and center of mass locations. The influence of these variations on the characteristic S-curve formation in whiplash response was evaluated using the peak C2-C3 flexion marking the maximum S-curve formation and time taken for the formation of maximum S-curve. The peak C2-C3 flexion in the S-curve formation was most influenced by disk height and vertebral depth, followed by anteroposterior head center of mass location. The time to maximum S-curve was most influenced by the anteroposterior location of head center of mass. The influence of gender-dependent variations, such as the vertebral depth, suggests that they contribute to the greater segmental rotations observed in females resulting in different S-curve formation from men. These results suggest that both spine morphology and head inertia properties should be considered to describe rear-impact responses.

Cervical spine morphology and ligament property variations: A finite element study of their influence on sagittal bending characteristics.

Cervical spine finite element models reported in biomechanical literature usually represent a static morphology. Not considering morphology as a model parameter limits the predictive capabilities for applications in personalized medicine, a growing trend in modern clinical practice. The objective of the study was to investigate the influence of variations in spinal morphology on the flexion-extension responses, utilizing mesh-morphing-based parametrization and metamodel-based sensitivity analysis. A C5-C6 segment was used as the baseline model. Variations of intervertebral disc height, facet joint slope, facet joint articular processes height, vertebral body anterior-posterior depth, and segment size were parametrized. In addition, material property variations of ligaments were considered for sensitivity analysis. The influence of these variations on vertebral rotation and forces in the ligaments were analyzed. The disc height, segmental size, and body depth were found to be the most influential (in the cited order) morphology variations; while among the ligament material property variations, capsular ligament and ligamentum flavum influenced vertebral rotation the most. Changes in disc height influenced forces in the posterior ligaments, indicating that changes in the anterior load-bearing column of the spine could have consequences on the posterior column. A method to identify influential morphology variations is presented in this work, which will help automation efforts in modeling to focus on variations that matter. This study underscores the importance of incorporating influential morphology parameters, easily obtained through computed tomography/magnetic resonance images, to better predict subject-specific biomechanical responses for applications in personalized medicine.

Influence of morphological variations on cervical spine segmental responses from inertial loading.

OBJECTIVES: The objective of this study was to investigate the influence of morphological variations in osteoligamentous lower cervical spinal segment responses under postero-anterior inertial loading. METHODS: A parametric finite element model of the C5-C6 spinal segment was used to generate models. Variations in the vertebral body and facet depth (anteroposterior), posterior process length, intervertebral disc height, facet articular process height and slope, segment orientation ranging from lordotic to straight, and segment size were parameterized. These variations included male-female differences. A Latin hypercube sampling method was used to select parameter values for model generation. Forces and moments associated with the inertial loading were applied to the generated model segments. The 7 parameters were grouped as local or global depending on the number of spinal components involved in the shape variation. Four output responses representing overall segmental and soft tissue responses were analyzed for each model variation: response angle of the segment, anterior longitudinal ligament stretch, anterior capsular ligament stretch, and facet joint compression in the posterior region. Pearson's correlation coefficient was used to compute the correlations of these output responses with morphological variations. RESULTS: Fifty models were generated from the parameterized model using a Latin hypercube sampling technique. Variation in response angle among the models was 4° and was most influenced by change in the combined dimension of vertebral body and facet depth, followed by size of the segment. The maximum anterior longitudinal ligament stretch varied between 0.1 and 0.3 and was strongly influenced by the change in the segment orientation. The anterior facet joint region sustained tension, whereas the posterior region sustained compression. For the anterior capsular ligament stretch, the most influential global variation was segment orientation, whereas the most influential local variations were the facet height and facet angle parameters. In the case of posterior facet joint compression, segment orientation was again most influential, whereas among the local variations, the facet angle had the most influence. CONCLUSION: Shape variations in the intervertebral disc influenced segmental rotation and ligament responses; however, the influence of shape variations in the facet joint was confined to capsular ligament responses. Response angle was most influenced by the vertebral body depth variations, explaining greater segmental rotations in female spines. Straighter spine segments sustained greater posterior facet joint compression, which may offer an explanation for the higher incidence of whiplash-associated disorders among females, who exhibit a straighter cervical spine. The anterior longitudinal ligament stretch was also greater in straighter segments. These findings indicate that the morphological features specific to the anatomy of the female cervical spine may predispose it to injury under inertial loading.

[Diagnostic and predictive importance of the blast transformation test and basophil activation test in retinal vasculitis]. / Intérêt diagnostique et prédictif du test de transformation blastique et du test d'activation des basophiles au cours des vascularites rétiniennes.

22 patients suffering from Birdshot retinochoroidopathy (10), idiopathic vasculitis (6) and Behcet disease (6) and treated by cyclosporine were tested at regular intervals during 11 to 38 months by the lymphocyte stimulation test (LST) and basophil degranulation test (HBDT) with S retinal antigen. These two tests were found frequently positive especially during acute inflammation for the LST. However HBDT was positive in all the patients before relapse of acute inflammation which is in favor of its predictive value and its involvement in the triggering of inflammation at the basophiles or at the local mast cell level.

[Intravenous immunoglobulins and anti-idiotypic suppression of auto-immunity]. / Immunoglobulines intraveineuses (IVIg) et suppression anti-idiotypique de l'auto-immunité.

This review summarizes the clinical use of intravenous immunoglobulins (IVIg) in autoimmune diseases and focuses on the mechanisms by which IVIg suppress autoimmune responses. Evidence is presented of a role of IVIg in modulating the regulatory function of the idiotypic network on the expression of the natural and pathological autoimmune repertoires.

[Syphilitic uveitis and human immunodeficiency virus infection]. / Uvéite syphilitique et infection par le virus de i'immunodéficience humaine.

Ocular syphilis is rare in human immunodeficiency virus infected individuals. We think that syphilis should be considered in evaluating such patients presenting with uveitis. Most often, ocular syphilis includes retinitis associated with anterior or posterior uveitis, sometimes with optic neuritis. Concurrent neurosyphilis is frequent and may be more aggressive; it may progress more rapidly and cause more atypical signs than in patients without human immunodeficiency virus infection. This suggests the need for lumbar puncture in the evaluation of coinfected patients. The standard serological tests for syphilis (in blood and cerebrospinal fluid) may be nonreactive in human immunodeficiency virus seropositive patients. It may be because of the alteration of immunologic response of such patients. All coinfected patients with human immunodeficiency virus and syphilis should be treated with high-dose intravenous penicillin G sodium as recommended for neurosyphilis. We describe two human immunodeficiency virus infected patients with ocular syphilis and neurosyphilis.

[Keratoplasty in children. Analysis of 127 surgically treated eyes over 10 years]. / Kératoplasties chez l'enfant. Analyse sur 10 ans de 127 yeux opérés.

One hundred and twenty-seven eyes of children less than 15 years of age underwent keratoplasty with one to ten years follow-up. The cases were divided into three groups of age, and the results are compared. Graft transparency has a direct correlation with the age of patient and type of corneal disease. Penetrating keratoplasty carries a better surgical and visual prognosis when carried out late in childhood. This is not only the fact of the particular etiologies found in this subgroup of age. When adjusting the results to the both factors age and etiology, we have demonstrated their independent. The visual benefits of corneal transplantation in selected cases in children appear to outweigh the difficulties and problems engendred by this procedure.

Severe retinochoroidopathy: variations of humoral and cellular immunity to S-antigen in a longitudinal study.

Ten patients with birdshot retinochoroidopathy, six with isolated retinal vasculitis and eight with Behçet's disease were treated with cyclosporine for one to three years. Autoantibodies to several retinal proteins, circulating lymphocyte subsets and cellular reactivity to S-antigen were evaluated repeatedly during this period. Autoantibody titers were similar in patients and in controls. However the serum content of antibodies to IRBP or S-antigen was lessened during inflammatory periods in some patients. In some sera, antibodies reacted with enzyme digested S-antigen preparations by immunoblot, whereas the same sera were negative for the native protein. A decrease of the CD4+ subpopulation of peripheral blood lymphocytes was associated with relapses of ocular inflammation in birdshot retinochoroidopathy. In this disease and in idiopathic retinal vasculitis, the positive lymphocyte stimulation test and basophil degranulation test with S-antigen were significantly most frequent in the period preceding a relapse of ocular inflammation. These tests could therefore be of predictive value for relapses occurring within the next few months.

[Results of myopic keratomileusis. A retrospective clinical study apropos of 40 cases]. / Résultats du kératomileusis myopique. Etude clinique rétrospective à propos de 40 cas.

The authors report in a retrospective study, the results of myopic keratomileusis. 40 eyes were operated on at the department of ophthalmology of Hotel-Dieu Hospital in Paris, with a range follow-up of 6 to 24 months. The mean pre-operative spherical equivalent was - 15.08 +/- 3.32 D., and the mean post-operative spherical equivalent was - 5.02 +/- 3.75 D. relative to preoperative conditions, best corrected visual acuity were unchanged in 6 cases, improved in 16 cases and diminished in 18 cases. The predictability of results was better for patients with myopia in the range of - 9 to - 16 D. During the first post-operative year, a mean regressive tendency of 3 diopters was noted. Complications are reported and analysed. Myopic keratomileusis is indicated for myopia between - 10 and - 16 D., when correction by contact lenses has failed. Candidates for surgery must be informed and consent about possibilities, limits and risks of the procedure.