Craniofacial distraction osteogenesis: a review of 3278 cases

The nascent field of craniofacial distraction osteogenesis has not yet been subjected to a rigorous evaluation of techniques and outcomes. Consequently, many of the standard approaches to distraction have been borrowed from the experience with long bones in orthopedic surgery. The ideal "latency period" of neutral fixation, rate and rhythm of distraction, and consolidation period have not yet been determined for the human facial skeleton. In addition, because the individual craniofacial surgeon's experience with distraction has generally been small, outcomes and meaningful complication rates have not yet been published.In this study, a four-page questionnaire was sent to 2476 craniofacial and oral/maxillofacial surgeons throughout the world, asking about their experiences with distraction osteogenesis. Information about the types of cases, indications for surgery, surgical techniques, postoperative management, outcomes, and complications were tabulated. Of 274 respondents (response rate, 11.4 percent), 148 indicated that they used distraction in their surgical practice. One hundred forty-five completed surveys were entered into a database that provided information about 3278 craniofacial distraction cases. Statistical analyses were performed comparing the rates of premature consolidation, fibrous nonunion, and nerve injury, on the basis of the use of a latency period and different rates and rhythms of distraction. In addition, the rates of all complications were determined and compared on the basis of the number of distraction cases performed per surgeon.The results of the study clearly show a wide variation in the surgical practice of craniofacial distraction osteogenesis. Although the cumulative complication rate was found to be 35.6 percent, there is a pronounced learning curve, with far fewer complications occurring among more experienced surgeons (p < 0.001). The presence of inferior alveolar nerve injury as a result of mandibular distraction was much lower for respondents whose distraction regimens consisted of no more than 1 mm of distraction per day (19.5 percent versus 2.4 percent; p < 0.001). No evidence was found to support the use of a latency period or to divide the daily distraction regimen into more than one session per day. Conclusions could not be drawn from this study regarding the length of the consolidation period. Overall, the surgeon-reported outcomes are comparable with those published for other craniofacial procedures, despite the higher incidence of complications.Although conclusions made on the basis of a subjective questionnaire need to be interpreted cautiously, this study has strength in the large numbers of cases reviewed. Because of the anonymity of responses, it has been assumed that surgeons who responded to the survey reported accurate numbers of complications and successful outcomes. Finally, additional clinical and animal studies that will be of benefit in advancing the field of craniofacial distraction osteogenesis are outlined.     

Simulating uterine contraction by using an electro-chemo-mechanical model

Contractions of uterine smooth muscle cells consist of a chain of physiological processes. These contractions provide the required force to expel the fetus from the uterus. The inclusion of these physiological processes is, therefore, imperative when studying uterine contractions. In this study, an electro-chemo-mechanical model to replicate the excitation, activation, and contraction of uterine smooth muscle cells is developed. The presented modeling strategy enables efficient integration of knowledge about physiological processes at the cellular level to the organ level. The model is implemented in a three-dimensional finite element setting to simulate uterus contraction during labor in response to electrical discharges generated by pacemaker cells and propagated within the myometrium via gap junctions. Important clinical factors, such as uterine electrical activity and intrauterine pressure, are predicted using this simulation. The predictions are in agreement with clinically measured data reported in the literature. A parameter study is also carried out to investigate the impact of physiologically related parameters on the uterine contractility.     

Virus-neuron interaction: an experimental model

Conclusion These examples demonstrate the usefulness of embryonic neurons for investigation ofneurotropic virus pathogenesis studies. The different steps of viral interactions of neurotropicviruses with the brain necessitate studies of the intrinsic neural properties of the infected cells:1) entry of virus into the intra-cellular compartment, 2) transport of virus from one brainstructure to another brain area, 3) replication of virus in the host-cells, 4) altered brainfunctions. Understanding the mechanisms of neural pathogenesis is a prerequisite for theelaboration of antiviral strategies based upon recovery of the brain from functional alterationsusing drugs active on brain functions.     

Cell locomotion forces versus cell contraction forces for collagen lattice contraction: an in vitro model of wound contraction

Cultured human dermal fibroblasts suspended in a rapidly polymerizing collagen matrix produce a fibroblast-populated collagen lattice. With time, this lattice will undergo a reduction in size referred to as lattice contraction. During this process, two distinct cell populations develop. At the periphery of the lattice, highly oriented sheets of cells, morphologically identifiable as myofibroblasts, show cell-to-cell contacts and thick, actin-rich staining cytoplasmic stress fibers. It is proposed that these cells undergoing cell contraction produce a multicellular contractile unit which reorients the collagen fibrils associated with them. The cells in the central region, referred to as fibroblasts, are randomly oriented, with few cell-to-cell contacts and faintly staining actin cytoplasmic filaments. In contrast it is proposed that cells working as single units use cell locomotion forces to reorient the collagen fibrils associated with them. Using this model, we sought to determine which of these two mechanisms, cell contraction or cell locomotion, is responsible for the force that contracts collagen lattices. Our experiments showed that fibroblasts produce this contractile force, and that the mechanism for lattice contraction appears to be related to cell locomotion. This is in contrast to a myofibroblast; where the mechanism for contraction is based upon cell contractions. Fibroblasts attempting to move within the collagen matrix reorganize the surrounding collagen fibrils; when these collagen fibrils can be organized no further and cell-to-cell contacts develop, which occurs at the periphery of the lattice first, these cells can no longer participate in the dynamic aspects of lattice contraction.     

Muscle contraction history: modified Hill versus an exponential decay model

In recent years, it has been recognised that improvements to classic models of muscle mechanical behaviour are often necessary for properly modelling co-ordinated multi-joint actions. In this respect, the purpose of the present study was to improve on modelling stretch-induced force enhancement and shortening-induced force depression of muscle contraction. For this purpose, two models were used: a modified Hill model and a model based loosely on mechano-chemistry of the cross-bridge cycle (exponential decay model). The models were compared with a classic Hill model and experimental data. Parameter values were based, as much as possible, on experimental findings in the literature, and tested with new experiments on the gastrocnemius of the rat. Both models describe many features of slow-ramp movements well during short contractions (300–500 ms), but long-duration behaviour is described only partly. The exponential decay model does not incorporate a force–velocity curve. Therefore, its good performance indicates that the status of the classic force–velocity characteristic may have to be reconsidered. Like movement-induced force depression and enhancement, it seems a particular manifestation of time-dependent force behaviour of muscle, rather than a fundamental property of muscle (like the length–tension curve). It is argued that a combination of the exponential decay model (or other models based on the mechano-chemistry of contraction) and structurally based models may be fruitful in explaining this time-dependent contraction behaviour. Furthermore, not in the least because of its relative simplicity, the exponential decay model may prove more suitable for modelling multi-joint movements than the Hill model. Received: 19 March 1999 / Accepted in revised form: 9 June 2000     

Effects of mandibular distraction osteogenesis on the inferior alveolar nerve: an experimental study in monkeys

A series of experimental studies were performed in monkeys to study the effect of mandibular distraction osteogenesis on the inferior alveolar nerve at different times before and after distraction. A mandible osteotomy was performed and distraction was carried out unilaterally in 10 young rhesus monkeys and bilaterally in six. The intact nerves on the contralateral side of the 10 monkeys were used for the control. Care was taken to avoid destroying the integrity of the inferior alveolar nerve during the surgical procedure. After a 5-day latency period, the distraction device was activated at a rate of 0.5 mm twice each day for 15 days. Sensory nerve action potential testing was applied before and 1 day after the operation, at completion of distraction, and at 2, 4, 6, 9, and 12 weeks of fixation. Necropsy was performed at the completion of distraction and 2, 4, 6, and 12 weeks of fixation. The mental nerves were taken, sectioned, and stained with lead citrate and uranyl acetate, and examined with a transmission electron microscope. The inferior alveolar nerves in the distraction gap were obtained, and paraffin slides were made and stained with hematoxylin and eosin, Luxol fast blue, and Bodian methods. The authors found that immediately after the mandible osteotomy, most nerves showed signs of slight acute injury; the latency was increased by 5.553 percent, and the amplitude was decreased to 1808 microV. This might be caused by the surgical procedure or by compressions produced by swelling tissues around the nerves. When distraction was completed, the latency was prolonged for an average of 22.18 percent, and the amplitude average had attenuated to 28.54 percent (804 microV) of the preoperative value on the distracted side. Most nerve fibers exhibited signs of degeneration, such as myelin disruption, swelling of cell organs greatly increased in axoplasm, axon tearing, and myelin fragments engulfed by macrophages. These were nerve reactions to the tensions produced by mandible lengthening. As time elapsed, the nerve's action potential recovered gradually because of its repairing ability, the latency shortened, amplitude increased, Schwann cells proliferated and formed new myelin sheaths, and the tearing axons reconnected. After 12 weeks of consolidation, there was still a latency of 12.384 percent prolongation because of the prolonged conduction distance, and the average amplitude was restored to 2786 microV, the approximate preoperative value. The nerve seemed to be repaired completely; its myelin thickness, axon diameter, and ultrastructure were all similar to those of the control. It was concluded that mandibular distraction osteogenesis can produce some degree of harmful effects on the function and structure of inferior alveolar nerves, but it is reversible and relatively slight. Along with the regeneration of the nerve's myelin and axon, the nerve function can gradually rehabilitate to a normal level.     

Element concentrations and cataract: an experimental animal model

The determination of inorganic ions in cataractous human lenses has been the subject of several investigations; nevertheless, few studies have been concerned with trace element contents in lenses, and data are sometimes contradictory. An animal experimental model of induced cataract is here proposed with the aim of evaluating the changes of Ca, Na, K, Cu and Zn concentrations. The cataract was produced by an Nd: YAG Laser treatment of the right eye of sexteen male rabbits. The determination of the elements was performed by atomic absorption spectrometry (both flame and flameless methods) after an acid digestion of samples. Compared with the results obtained in left lenses used as a control (Ca 14.4±5.7 mg/kg d.w.; Na 1.3±0.5 g/kg d.w.; K 9.9±1.1 g/kg d.w.; Cu 0.24±0.09 mg/kg d.w.; Zn 24.8±2.3 mg/kg d.w.), the mean concentration values of opaque lenses showed some significant changes for Ca, Na, and Cu (Ca 123.7±106.6 mg/kg d.w.; Na 4.5±4.3 g/kg d.w; Cu 0.43±0.21 mg/kg d.w.). Potassium showed a tendency to decrease, and zinc to increase. Positive correlations were found between calcium and sodium both in controls (r=0.73, p<0.001) and in treated lenses (r=0.87, p< 0.0001). An inverse correlation between Ca and K confirmed the tendency of potassium to decrease.     

Neuropathy in experimental diabetes: an animal model.

A morphometric study of the common peroneal nerve in early experimental diabetes in rats showed that fibre size was diminished. The reduction in the size of the axon was twice that of the myelin sheath. This may contribute to the understanding of the impaired motor conduction velocity found in diabetics shortly after the onset of their disease.     

Fasciocutaneous flaps: an experimental model in the pig

No experimental studies have substantiated the claim that fasciocutaneous flaps are superior to skin flaps. Using fasciocutaneous flaps designed in the pig, both flap survival and blood flow were assessed. The forelimb and hindlimb fasciocutaneous flaps survived to 8.2 +/- 0.3 cm and 7.9 +/- 0.3 cm, respectively, compared with 7.3 +/- 0.3 cm and 6.7 +/- 0.3 cm for the comparable cutaneous flaps, a statistically significant finding (p less than 0.01). Random fasciocutaneous flaps survive 12 to 18 percent longer than skin flaps. Using the radioactive microsphere technique, blood flow was measured after flap elevation, and flap survival was estimated using fluorescein. Again, a significant difference in flap survival was found, but there was no significant difference in measured blood flow. This can be explained by the relatively large interval between blood flow measurements (2 cm) compared with the observed difference in survival length (1.0 +/- 0.3 cm).     

Ca2+-dependent facilitated shortening in isotonic contraction of trachealis muscle

We compared isotonic shortening with isometric force generation as a function of external Ca2+ in 166 tracheal smooth muscle (TSM) strips from 27 mongrel dogs in vitro. Concentration-response curves were generated with muscarinic stimulation (acetylcholine, ACh), alpha-adrenergic receptor activation (norepinephrine after beta-adrenoceptor blockade, NE), serotonin (5-HT), and KCl-substituted Krebs-Henseleit solution. The concentrations of 5-HT causing half-maximal shortening (ECS50, 1.54 +/- 0.14 X 10(-7) M) and half-maximal active isometric tension (ECT50, 1.72 +/- 0.30 X 10(-7) M) were similar (P = NS). Likewise, ECS50 (21.9 +/- 0.7 mM) and ECT50, (22.0 +/- 0.9 mM) were similar for KCl. In contrast, facilitated isotonic shortening (i.e., greater isotonic shortening for comparable degrees of force generation) was elicited with ACh and NE for all levels of force generation between 15 and 85% of maximum and for all concentrations of ACh from 3 X 10(-8) to 3 X 10(-5) M (P less than 0.05 for all points). Facilitated isotonic shortening also was elicited for all concentrations of NE from 10(-8) to 10(-6) M (P less than 0.05 for all points). Removal of Ca2+ from the perfusate substantially reduced the potency of ACh (P less than 0.001) and abolished differences between ECS50 (2.23 +/- 0.28 X 10(-5) M) and ECT50 (2.50 +/- 0.46 X 10(-5) M, P = NS). We demonstrate that for comparable degrees of force generation, muscarinic and alpha-adrenergic receptor activation cause greater isotonic shortening than KCl or 5-HT and that this facilitated shortening is associated with the concentration of external Ca2+.     

Estimation of hepatic volume by SPECT during liver regeneration: an experimental study in an animal model

To calculate hepatic volume in the dog by single photon emission computerized tomography (SPECT), we determined the limits of the organ by choosing an isocontour on each section. This choice entailed prior calculation of an overestimated pseudovolume. The accuracy of the measurement in the animal then approached that of measurements in vitro. We used the method to monitor hepatic regeneration in the dog after 65% hepatectomy and detected oedema and postoperative trauma, and over a longer timespan, stagnation of regeneration and a secondary drop in hepatic volume.     

X-ray interference studies of crossbridge action in muscle contraction: evidence from muscles during steady shortening

During normal muscle shortening, the myosin heads must undergo many cycles of interaction with the actin filaments sliding past them. It is important to determine what range of configurations is found under these circumstances, and, in terms of the tilting lever arm model, what range of orientations the lever arms undergo. We have studied this using the X-ray interference technique described in the previous article, focusing mainly on the changes in the first order meridional reflection (M3) as compared to isometric. The change in ratio of the heights of the interference peaks indicates how far the mean lever arm angle has moved towards the end of the working stroke; the total intensity change depends on the angle change, on the number of heads now attached at any one time, and on the dispersion of lever arm angles. The latter provides a measure of the distance over which myosin heads remain attached to actin as they go through their working strokes. Surprisingly, the mean position of the attached heads moves only about 1 nm inwards (towards the center of the A-band) at low velocity shortening (around 0.9 T0): their dispersion changes very little. This shows that they must be detaching very early in the working stroke. However, at loads around 0.5 T0, the mean lever arm angle is about half way towards the end of the working stroke, and the dispersion of lever arm angles (with a uniform dispersion) is such as to distribute the heads throughout the whole of the working stroke. At higher velocities of shortening (at 0.3 T0), the mean position shifts further towards the end of the stroke, and the dispersion increases further. The details of the measurements, together with other data on muscle indicate that the force-generating mechanism within the myosin heads must have some unexpected properties.