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The personal experience of a general practitioner who sustained a fracture-dislocation of the atlanto-axial joint is recorded. The inefficient application of an unyielding (non-inertial) lap and diagonal seat belt permitted this injury, although one does not know what other injuries might have occurred had the belt not been worn.
Measurements of joint angles during motion analysis are subject to error caused by kinematic crosstalk, that is, one joint rotation (e. g., flexion) being interpreted as another (e.g., abduction). Kinematic crosstalk results from the chosen joint coordinate system being misaligned with the axes about which rotations are assumed to occur. The aim of this paper is to demonstrate that measurement of the so-called "screw-home" motion of the human knee, in which axial rotation and extension are coupled, is especially prone to errors due to crosstalk. The motions of two different two-segment mechanical linkages were examined to study the effects of crosstalk. The segments of the first linkage (NSH) were connected by a revolute joint, but the second linkage (SH) incorporated gearing that caused 15 degrees of screw-home rotation to occur with 90 degrees knee flexion. It was found that rotating the flexion axis (inducing crosstalk) could make linkage NSH appear to exhibit a screw-home motion and that a different rotation of the flexion axis could make linkage SH apparently exhibit pure flexion. These findings suggest that the measurement of screw-home rotation may be strongly influenced by errors in the location of the flexion axis. The magnitudes of these displacements of the flexion axis were consistent with the inter-observer variability seen when five experienced observers defined the flexion axis by palpating the medial and lateral femoral epicondyles. Care should be taken when interpreting small internal-external rotations and abduction-adduction angles to ensure that they are not the products of kinematic crosstalk.
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If one excludes trauma, problems of the neck and shoulder in children are relatively uncommon. Still, the pediatrician or family practitioner should have sufficient familiarity to provide the family with appropriate counseling and referral. This article emphasizes the common problems, but also notes less common conditions that, if unrecognized, may have serious impact on the health and well-being of the child.
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Xenopus laevis embryos injected with follistatin developed abnormally with enlarged anterior structures and defective tails. Histological sections reveal that these follistatin treated embryos contain large amount of notochordal tissue that fails to elongate. Embryonic responses to follistatin are dose and stage specific. These results suggested that follistatin contributes to body axis formation, with its most visible effect on notochord formation.
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The cross-table lateral view is essential in the initial workup of a trauma patient with a suspected cervical-spine injury. The identification of the radiographic "ring" of C2 on the cross-table lateral view is discussed. When a type III odontoid fracture is present, the ring of C2 is disrupted. We propose that "identification of the ring of C2" should be added to the emergency physicians' systematic checklist when clearing a cross-table lateral view of the cervical spine.
We report the case of a 33-year-old man who presented to the emergency department the morning after a motor vehicle accident with physical findings consistent with central cord syndrome. Radiographs of the cervical spine revealed os odontoideum. This abnormality of the odontoid process has not previously been described in association with central cord syndrome.
The clinical findings of rotatory subluxation of the atlas are subtle and x-ray films involving the upper cervical segment are difficult to interpret. Nevertheless, patients with rotatory subluxation must be separated from those with "stiff necks," for they require hospital admission for cervical traction if complications are to be avoided. A case is reported and management and diagnosis are reviewed.
The atlas and axis ossification centers of 106 human fetal and neonate skeletons were measured. The skeletons belong to the collection in the Department of Forensic Medicine of the Albert Szent-Györgyi Medical University, Szeged, Hungary. The age of the skeletons ranged from 4 to 10 lunar months. Nine linear measurements on the atlas, seven on the axis neural arches ossification centers and three on each one of the axis centra ossification centers were taken. We did simple and multiple linear regression analysis to estimate the age of fetuses. The results show that it is possible to use regression equations to estimate the fetal body length and age from atlas and axis ossification centers measurements during the whole period of development studied. The study of size and shape of the ossification centers using factorial analysis (principal component analysis) shows that the shape of the dens of the axis might be useful to estimate fetal viability.
We performed some experiments to investigate the temporal and spatial details of the dorsal induction exerted by dorsal vegetal cells in Xenopus embryo. Two dorsal vegetal cells (D1 cells) were transplanted into the ventral vegetal region of a recipient at the 32-cell stage. At various times after transplantation, the ventral animal-equatorial part was explanted and cultured. The explants isolated 5.5 h after transplantation (time 5.5) elongated and formed somites. In RT-PCR analysis, the expression of dorsal gene, chordin was activated in the explants isolated after time 4.0 (about the 4000-cell stage which corresponds to the mid blastula transition (MBT)) at control stage 10. In another series of experiments, ventral animal-equatorial and dorsal vegetal parts were isolated from the 4000-cell stage embryos and they were combined for 2.0-2.5 h. These ventral animal-equatorial explants elongated and formed somites. The chordin expression was also observed in the explants. But the 32- and 256-cell stage dorsal vegetal cells failed to exert the dorsalizing activity within the 2.0-2.5 h of the conjugation. These results suggest that 2 h contact after MBT is necessary and sufficient for the dorsal induction from the dorsal vegetal cells and it occurs as a result of the zygotic gene expression. Consistent with this idea, the zygotic dorsal genes, siamois and chordin were expressed on the upper regions of the transplanted D1 descendants at stage 10. Furthermore, this region began to gastrulate when the D1 cell was transplanted with upside-down orientation. Our data indicate that the upper region of the D1 descendants by itself act as the Spemann organizer rather than the Nieuwkoop center.
During gastrulation in Xenopus convergence and extension movements, mediated by mediolateral intercalations, are the driving force for early neural plate morphogenesis. Here we show that the winged helix transcriptional regulator, Xfd-12' is dynamically expressed in medial neural plate precursors that undergo convergence and extension movements. These medial neuraxial progenitors are specified in and beyond the Spemann organizer prior to specification of the basal anlage of the neural plate. The initiation of Xfd-12' expression coincides with the induction of mesendoderm by Nodal-related growth factors at the late blastula stage. Comparative expression analysis suggests that cellular rearrangements at the pre-gastrulation stage account for regionalization of the Spemann organizer into head and trunk organizer compartments, the latter in which medial neural plate progenitors reside. While the maintenance of Xfd-12' expression in the dorsal non-involuting marginal zone requires FGF signalling, its subsequent positioning along the medial aspect of the neuraxis depends on signalling by Wnt and Nodal-related family members. Based on these findings we propose that XFD-12' is a trunk organizer component that might control convergence and extension movements of medial neural plate precursors during gastrulation.