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Congenital spine deformities may be influenced by movements in utero, but the effects of foetal immobility on spine and rib development remain unclear. The purpose of the present study was to determine (1) critical time-periods when rigid paralysis caused the most severe disruption in spine and rib development and (2) how the effects of an early, short-term immobilisation were propagated to the different features of spine and rib development. Chick embryos were immobilised once per single embryonic day (E) between E3 and E6 and harvested at E9. To assess the ontogenetic effects following single-day immobilisation, other embryos were immobilised at E4 and harvested daily between E5 and E9. Spinal curvature, vertebral shape and segmentation and rib development were analysed by optical projection tomography and histology. The results demonstrated that periods critical for movement varied for different aspects of spine and rib development. Single-day immobilisation at E3 or E4 resulted in the most pronounced spinal curvature abnormalities, multiple wedged vertebrae and segmentation defects, while single-day immobilisation at E5 led to the most severe rib abnormalities. Assessment of ontogenetic effects following single-day immobilisation at E4 revealed that vertebral segmentation defects were subsequent to earlier vertebral body shape and spinal curvature abnormalities, while rib formation (although delayed) was independent from thoracic vertebral shape or curvature changes. A day-long immobilisation in chicks severely affected spine and rib development, highlighting the importance of abnormal foetal movements at specific time-points and motivating targeted prenatal monitoring for early diagnosis of congenital scoliosis.

The incidence of congenital spine deformities, including congenital scoliosis, kyphosis and lordosis, may be influenced by the in utero mechanical environment, and particularly by fetal movements at critical time-points. There is a limited understanding of the influence of fetal movements on spinal development, despite the fact that mechanical forces have been shown to play an essential role in skeletal development of the limb. This study investigates the effects of muscle forces on spinal curvature, vertebral segmentation and vertebral shape by inducing rigid or flaccid paralysis in the embryonic chick. The critical time-points for the influence of fetal movements on spinal development were identified by varying the time of onset of paralysis. Prolonged rigid paralysis induced severe defects in the spine, including curvature abnormalities, posterior and anterior vertebral fusions and altered vertebral shape, while flaccid paralysis did not affect spinal curvature or vertebral segmentation. Early rigid paralysis resulted in more severe abnormalities in the spine than later rigid paralysis. The findings of this study support the hypothesis that the timing and nature of fetal muscle activity are critical influences on the normal development of the spine, with implications for the understanding of congenital spine deformities. This article is protected by copyright. All rights reserved.

International audience; Study Design. In a retrospective study, we report on 16 patients with congenital kyphosis due to progressively ossifying anterior unsegmented bars. Objective. To specify the therapeutic strategy in such malformation. Summary of Background Data. Congenital kyphosis due to progressively ossifying anterior unsegmented bars is a particular and uncommon entity of congenital kyphosis. Progressive anterior vertebral bars result in slowly progressive kyphosis, which rarely lead to neurological compromise. Sagittal equilibrium of the spine is maintained by compensatory curves adjacent to the primary curve. Methods. All patients had clinical assessment and successive measurements of segmental angle made on a standing lateral radiograph of the spine. Magnetic resonance imaging was obtained in four patients. Six patients were just observed. A brace was used in three. And seven were treated surgically. Results. The compensatory capacity of the spine is reduced in lumbar area where there are few discs spaces below the bar. Presentation therefore tends to be at an earlier age and pain is more common. Magnetic resonance imaging enables definition of the structures immediately posterior to the bar and provides information regarding the integrity of the intervertebral disc. Conclusion. There is usually no need for surgery in thoracic and thoracolumbar localization. In lumbar localization, if the diagnosis is done early in childhood and if magnetic resonance imaging shows beyond the anterior ossification a normal T2-weighted magnetic resonance imaging disc space signal, desepiphysiodesis bar resection and cement interposition is mandatory. If the disc magnetic resonance imaging signal is abnormal or if the disc space is totally ossified, we propose a surgical correction of the kyphosis. For such cases a posterior wedge osteotomy seems to be the more suitable procedure.