Mandibular distraction osteogenesis: at what age to proceed.

OBJECTIVE: To evaluate if there is a difference in mandibular distraction osteogenesis (MDO) treatment success rates and adverse outcomes in newborns, early infants, and older pediatric patients. DESIGN: Retrospective medical review spanning a nine-year period. Ten newborn (≤ 35 days old), five early infant (36 days-5 months) and eight older pediatric (> 5 months) patients underwent MDO for treatment of micrognathia with a severe tongue-based obstruction. Success was defined as avoidance of tracheostomy or CPAP, and decannulation of patients with tracheotomies. Postoperative complications were grouped into minor and major. RESULTS: MDO successfully treated 90% of newborns, 100% of early infants and 100% of older pediatric patients. There was no difference in the rates of success (p=0.48), minor (p=1.00) and major (p=1.00) postoperative complications between newborns and early infants. Older pediatric patients had no treatment failures, tended to have fewer minor (p=0.18) and significantly fewer major (p= 0.04) postoperative complications compared to younger patients. The distractor pin mobility (9%) and scar revisions (13%) were uncommon. CONCLUSIONS: Mandibular distraction osteogenesis is a reliable method for relieving severe tongue-based obstructions in pediatric patients. When comparing newborns and early infant patients, treatment success rates and the occurrence of complications were not found to be different. Older pediatric patients had no treatment failures, and tended to have fewer postoperative complications compared to younger patients.

Rupture of thin liquid films: generalization of weakly nonlinear theory.

In this paper, we investigate the rupture dynamics of thin liquid films driven by intermolecular forces via weakly nonlinear bifurcation analysis. The dynamic equations governing slow dynamics of the perturbation amplitude of the near-critical mode corresponding to several models describing the evolution of thin liquid films in different physical situations appear to have the same structure. When antagonistic (attractive and repulsive) molecular forces are considered, nonlinear saturation of the instability becomes possible, while the boundary of this supercritical bifurcation is determined solely by the form of the intermolecular potential. The rupture time estimate obtained in closed form shows an excellent agreement with the results of the previously reported numerical simulations of the strongly nonlinear coupled evolution equations upon fitting the amplitude of the small initial perturbation. We further extend the weakly nonlinear analysis of the film dynamics and apply the Galerkin approximation to derive the amplitude equation(s) governing the dynamics of the fastest growing linear mode far from the instability threshold. The comparison of the rupture time derived from this theory with the results of numerical simulations of the original nonlinear evolution equations shows a very good agreement without any adjustable parameters.

Actin disassembly 'clock' and membrane tension determine cell shape and turning: a mathematical model.

Motile cells regulate their shape and movements largely by remodeling the actin cytoskeleton. Principles of this regulation are becoming clear for simple-shaped steadily crawling cells, such as fish keratocytes. In particular, the shape of the leading edge and sides of the lamellipodium-cell motile appendage-is determined by graded actin distribution at the cell boundary, so that the denser actin network at the front grows, while sparser actin filaments at the sides are stalled by membrane tension. Shaping of the cell rear is less understood. Here we theoretically examine the hypothesis that the cell rear is shaped by the disassembly clock: the front-to-rear lamellipodial width is defined by the time needed for the actin-adhesion network to disassemble to the point at which the membrane tension can crush this network. We demonstrate that the theory predicts the observed cell shapes. Furthermore, turning of the cells can be explained by biases in the actin distribution. We discuss experimental implications of this hypothesis.

The elasticity of motor-microtubule bundles and shape of the mitotic spindle.

In the process of cell division, chromosomes are segregated by mitotic spindles -- bipolar microtubule arrays that have a characteristic fusiform shape. Mitotic spindle function is based on motor-generated forces of hundreds of piconewtons. These forces have to deform the spindle, yet the role of microtubule elastic deformations in the spindle remains unclear. Here we solve equations of elasticity theory for spindle microtubules, compare the solutions with shapes of early Drosophila embryo spindles and discuss the biophysical and cell biological implications of this analysis. The model suggests that microtubule bundles in the spindle behave like effective compressed springs with stiffness of the order of tens of piconewtons per micron, that microtubule elasticity limits the motors' power, and that clamping and cross-linking of microtubules are needed to transduce the motors' forces in the spindle. Some data are hard to reconcile with the model predictions, suggesting that cytoskeletal structures laterally reinforce the spindle and/or that rapid microtubule turnover relieves the elastic stresses.

Stability of localized solutions in a subcritically unstable pattern-forming system under a global delayed control.

The formation of spatially localized patterns in a system with subcritical instability under feedback control with delay is investigated within the framework of globally controlled Ginzburg-Landau equation. It is shown that feedback control can stabilize spatially localized solutions. With the increase of delay, these solutions undergo oscillatory instability that, for large enough control strength, results in the formation of localized oscillating pulses. With further increase of the delay the solution blows up.

The physics of filopodial protrusion.

Filopodium, a spike-like actin protrusion at the leading edge of migrating cells, functions as a sensor of the local environment and has a mechanical role in protrusion. We use modeling to examine mechanics and spatial-temporal dynamics of filopodia. We find that >10 actin filaments have to be bundled to overcome the membrane resistance and that the filopodial length is limited by buckling for 10-30 filaments and by G-actin diffusion for >30 filaments. There is an optimal number of bundled filaments, approximately 30, at which the filopodial length can reach a few microns. The model explains characteristic interfilopodial distance of a few microns as a balance of initiation, lateral drift, and merging of the filopodia. The theory suggests that F-actin barbed ends have to be focused and protected from capping (the capping rate has to decrease one order of magnitude) once every hundred seconds per micron of the leading edge to initiate the observed number of filopodia. The model generates testable predictions about how filopodial length, rate of growth, and interfilopodial distance should depend on the number of bundled filaments, membrane resistance, lamellipodial protrusion rate, and G-actin diffusion coefficient.

Nonlinear rupture of thin liquid films on solid surfaces.

In this letter we investigate the rupture instability of thin liquid films by means of a bifurcation analysis in the vicinity of the short-scale instability threshold. The rupture time estimate obtained in closed form as a function of the relevant dimensionless groups is in striking agreement with the results of the numerical simulations of the original nonlinear evolution equations. This suggests that the weakly nonlinear theory adequately captures the underlying physics of the instability. When antagonistic (attractive/repulsive) molecular forces are considered, nonlinear saturation of the instability becomes possible. We show that the stability boundaries are determined by the van der Waals potential alone.

MULTISCALE TWO-DIMENSIONAL MODELING OF A MOTILE SIMPLE-SHAPED CELL.

Cell crawling is an important biological phenomenon underlying coordinated cell movement in morphogenesis, cancer, and wound healing. In recent decades the process of cell crawling has been experimentally and theoretically dissected into further subprocesses: protrusion of the cell at its leading edge, retraction of the cell body, and graded adhesion. A number of one-dimensional (1-D) models explain successfully a proximal-distal organization and movement of the motile cell. However, more adequate two-dimensional (2-D) models are lacking. We propose a multiscale 2-D computational model of the lamellipodium (motile appendage) of a simply shaped, rapidly crawling fish keratocyte cell. We couple submodels of (i) protrusion and adhesion at the leading edge, (ii) the elastic 2-D lamellipodial actin network, (iii) the actin-myosin contractile bundle at the rear edge, and (iv) the convection-reaction-diffusion actin transport on the free boundary lamellipodial domain. We simulate the combined model numerically using a finite element approach. The simulations reproduce observed cell shapes, forces, and movements and explain some experimental results on perturbations of the actin machinery. This novel 2-D model of the crawling cell makes testable predictions and posits questions to be answered by future modeling.

Pathologic analysis of routine tonsillectomy and adenoidectomy specimens.

OBJECTIVES: Recent literature has suggested that histopathologic analysis of routine tonsillectomy and adenoidectomy (T&A) specimens may be unnecessary. This study investigates T&A specimen handling practices in the United States between 1989 and 1999. METHODS: Surveys were sent to 4715 members of the American Academy of Otolaryngology. Surveys assessed practice type, pathologic processing practices (full, gross, no pathology), and reasons for change. The authors also performed a retrospective analysis of 1583 pediatric T&A specimens for evidence of occult malignancy. RESULTS: Practice types were 80% private, 12% academic, 6% salaried, and 2% military. Chi squared analysis revealed a significant increase (P < 0.001) in respondents ordering "gross only" and "no pathology." The retrospective analysis found no occult malignancies. CONCLUSIONS: There is a statistically significant increase in the number of otolaryngologists sending routine T&A specimens for "gross only" and "no pathology." There was no correlation between the type of practice and changes in pathologic analysis performed.

Management of nasal fractures.

The nasal bones are the most commonly fractured bones in the body. Accurate diagnosis and appropriate surgical intervention are key in the management of nasal fractures. While these injuries are not life-threatening, mismanagement of nasal fractures can lead to both aesthetic and functional deformities. A thorough history and careful physical examination are adequate for the diagnosis of nasal fractures. Literature in the field does not support the use of x-ray films to aid in the diagnosis. The majority of injuries are seen after significant edema becomes present and cannot be accurately reduced at that time. Therefore, with the exception of grossly displaced fractures, open fractures, and septal hematomas, most nasal fractures should be definitively treated after 3 to 10 days once swelling has resolved. This article will review pertinent nasal anatomic structure, pathophysiological characteristics of nasal fractures, diagnostic techniques, treatment modalities, and common controversies associated with nasal fractures.

Regulation of cell death in flower petals.

The often rapid and synchronous programmed death of petal cells provides a model system to study molecular aspects of organ senescence. The death of petal cells is preceded by a loss of membrane permeability, due in part to increases in reactive oxygen species that are in turn related to up-regulation of oxidative enzymes and to a decrease in activity of certain protective enzymes. The senescence process also consists of a loss of proteins caused by activation of various proteinases, a loss of nucleic acids as nucleases are activated, and enzyme-mediated alterations of carbohydrate polymers. Many of the genes for these senescence-associated enzymes have been cloned. In some flowers, the degradative changes of petal cells are initiated by ethylene; in others, abscisic acid may play a role. External factors such as pollination, drought and temperature stress also affect senescence, perhaps by interacting with hormones normally produced by the flowers. Signal transduction may involve G-proteins, calcium activity changes and the regulation of protein phosphorylation and dephosphorylation. The efficacy of the floral system as well as the research tools now available make it likely that important information will soon be added to our knowledge of the molecular mechanisms involved in petal cell death.

Identification of senescence-associated genes from daylily petals.

The petals of daylily (Hemerocallis hybrid) have a genetically based program that leads to senescence and cell death ca. 24 h after the flower opens. In order to determine the components of this program, six cDNAs, whose levels increase during petal senescence, were isolated and sequenced and designated DSA3, 4, 5, 6, 12 and 15. All six DSAs are members of gene families and all but DSA5 and DSA6 have one to three other very similar genes. GenBank database homology searches indicate that DSA3 is most similar at the amino acid level to an in-chain fatty acid hydroxylase which is bound to cytochrome P450, DSA4 may be an aspartic proteinase, DSA5 is as yet unidentified, DSA6 is a putative S1-type nuclease, DSA12 is very similar to a cytochrome P450-containing allene oxide synthase, and DSA15 may be a fatty acid elongase. Except for DSA12, the genes are expressed at low levels in daylily roots. Levels of the DSA mRNAs in leaves are less than 4% of the maximum detected in petals, and there are no clear differences between younger and older leaves. With the exception of DSA4, accumulation of the DSA mRNAs is increased 3.2 to 43 times by a concentration of abscisic acid that causes premature senescence of the petals. The relationship of the putative DSA gene products to senescence and cell death of daylily petals is discussed.

Ripening of surface phases coupled with oscillatory dynamics and self-induced spatial chaos through surface roughening.

Some pattern formation processes on single-crystal catalytic surfaces involve transitions between alternative surface phases coupled with oscillatory reaction dynamics. We describe a two-tier symmetry-breaking model of this process, based on nanoscale boundary dynamics interacting with oscillations of adsorbate coverage on microscale. The surface phase distribution oscillates together with adsorbate coverage, and, in addition, undergoes a slow coarsening process due to the curvature dependence of the drift velocity of interphase boundaries. The coarsening is studied both statistically, assuming a circular shape of islands of the minority phase, and through detailed Lagrangian modeling of boundary dynamics. Direct simulation of boundary dynamics allows us to take into account processes of surface reconstruction, leading to self-induced surface roughening. As a result, the surface becomes inhomogeneous, and the coarsening process is arrested way before the thermodynamic limit is reached, leaving a chaotic distribution of surface phases. (c) 1999 American Institute of Physics.