Using the finite element method to model the biomechanics of the asymmetric mandible before,during and after skeletal correction by distraction osteogenesis

An approach was developed to evaluate the load transfer mechanism in the temporomandibular joint (TMJ) area before, during and after mandibular ramus elongation by distraction osteogenesis (DO). In a concerted approach using computer tomography, magnetic resonance imaging (MRI), and finite element analysis, three-dimensional numerical models based on a young male patient, with a dento-facial deformity were generated. The magnitude and direction of the muscle forces acting on the mandible were assessed using both values derived from the muscles volume and cross-section as retrieved from the MRI-scan data-sets and taken from the literature. The resistance of the soft tissue envelope towards elongation during the DO-phase was also included. The finite element analyses showed that before skeletal correction by DO the load transfer was asymmetrical with high peak stresses in the affected joint. Following ramus elongation a more symmetrical loading in TMJs was predicted. The reaction forces in the TMJs during DO were low.     

Stimulus concordance and risk-assessment in hermit crabs (Coenobita clypeatus): implications for attention

Recent research has demonstrated that the topography of defensive reactions depends on factors that are extraneous to the stimulus that elicits the defensive response. For example, hermit crabs will withdraw more slowly to the approach of a simulated visual predator (i.e., the eliciting stimulus) when in the presence of a coincident acoustic stimulus. Multiple properties related to the magnitude (e.g., duration, amplitude) of the acoustic stimulus have been found to modulate the crabs' withdrawal response (Chan et al., 2010b). We demonstrate that the proximity in spatial location between a threatening visual stimulus and a potentially distracting extraneous auditory stimulus is an important determinant of anti-predator behavior in hermit crabs. We suggest that a distal relationship between the eliciting stimulus and an unrelated signal may produce greater distraction. This marks the first reported experimental evidence of this relationship in an invertebrate species.     

Training methods of military dog handlers and their effects on the team's performances

While only a few studies have analysed training methods used on working dogs, a recent survey in 303 Belgian military handlers revealed the use of harsh training methods on military working dogs (MWD). The present work aims at analysing the training methods used on Belgian MWD and the behaviour of handlers to objectify the performances of the dog handlers teams (DH teams) and the welfare of the animals.A standardized evaluation, including obedience and protection work exercises, was conducted on DH teams (n = 33). Every evaluation was done twice to assess the reliability of the observation methods. The behaviours of MWD and handlers were recorded on videotape and subsequently analysed. Results showed that handlers rewarded or punished their dogs intermittently. Stroking and patting the dogs were the most frequently used rewards. Pulling on the leash and hanging dogs by their collars were the most commonly used aversive stimuli.The team's performance was influenced by the training method and by the dog's concentration: (1) low-performance dogs received more aversive stimuli than high-performance dogs; (2) dog's distraction influenced the performance: distracted dogs performed less well.Handlers punished more and rewarded less at the second evaluation than at the first one. This suggests that handlers modified their usual behaviour at the first evaluation in view to present themselves in a positive light. During the second evaluation the dogs reacted to this higher frequency of aversive stimuli as they exhibited a lower posture after aversive stimuli. The authors cannot prove that the welfare of these dogs had been hampered, but there is an indication that it was under threat.Low team performances suggest that DH teams should train more regularly and undertake the usefulness of setting a new training system that would rely on: the use of more positive training methods, an increased training frequency, the elaboration of a course on training principles, and an improvement of dog handler relationship.     

Methodology to study intimal failure mechanics in human internal carotid arteries

While the incidence of blunt carotid artery injuries is low, the mortality rate is extremely high (40%). Clinical evidence indicates that the intimal region of the artery often sustains failure, while maintaining the integrity of the outer layers. This condition may lead to delayed ischemic symptoms, commonly reported in clinical literature. To date, the mechanical properties of the intima relative to the outer vessel layers have not been quantified in the human carotid artery. The purpose of the present study was to develop a methodology to determine the longitudinal mechanical properties of the human internal carotid artery in tension, with an emphasis on intimal failure. This was accomplished by opening the vessel at the mid-diameter level, creating an ‘I’-shaped testing specimen, subjecting the specimen to failure loading, documenting the stretch characteristics of the intimal and adventitial sides in the temporal domain, and correlating the synchronized videography with mechanical loading. Intimal failure data were quantified using stress and strain parameters in conjunction with digital videography of the intimal and adventitial sides. The present methodology can be used to determine the mechanical properties of the intima relative to ultimate carotid artery failure. These data will assist in the understanding of blunt carotid artery injuries, its diagnosis and treatment.     

Catching ants with honey: an experimental test of distraction and satiation as alternative modes of escape from flower-damaging ants

According to the distraction hypothesis, extrafloral nectaries (EFN) evolved under selection to entice ants away from floral nectaries, reducing ant-mediated damage to flowers and/or interference with pollinators. Predator-satiation, through production of nectar in either surplus flowers or EFN, provides an alternative mechanism for reducing the impact of ants as flower visitors. I tested these two hypotheses by experimentally adding EFN to flowering plants of the alpine wildflower, Polemonium viscosum, and by surveying the relationship between ant visitation and nectary number in nature. Plants of P. viscosum lack EFN and experience flower damage by ants of Formica neorufibarbus gelida. Ant behavior was compared on plants with five flowers and three experimental EFN and on controls with equal floral display, but no EFN. Addition of EFN increased flower visitation by ants. The effect of EFN on flower visitation did not depend on proximity of EFN to flowers or attractiveness of EFN to ants. Findings suggest that ants perceived patch quality on a whole plant basis, rather than responding to EFN and flowers as distinct nectar patches. Ant visitation did not keep pace with nectary number in nature. The relationship between ant visitation and nectary number per plant was weak and shallow as predicted under satiation. Ant foraging choices on experimental inflorescences showed that ants bypass flowers avoided by earlier ants, enhancing probability of escape via satiation. Results do not support the idea that EFN evolve to reduce flower visitation by ants, but show instead that nectar in surplus flowers can satiate ants and reduce their negative impacts on flower function and integrity.     

The effect of axial compression and distraction on cervical facet mechanics during anterior shear,flexion, axial rotation,and lateral bending motions

The subaxial cervical facets are important load-bearing structures, yet little is known about their mechanical response during physiological or traumatic intervertebral motion. Facet loading likely increases when intervertebral motions are superimposed with axial compression forces, increasing the risk of facet fracture. The aim of this study was to measure the mechanical response of the facets when intervertebral axial compression or distraction is superimposed on constrained, non-destructive shear, bending and rotation motions. Twelve C6/C7 motion segments (70 ± 13 yr, nine male) were subjected to constrained quasi-static anterior shear (1 mm), axial rotation (4°), flexion (10°), and lateral bending (5°) motions. Each motion was superimposed with three axial conditions: (1) 50 N compression; (2) 300 N compression (simulating neck muscle contraction); and, (3) 2.5 mm distraction. Angular deflections, and principal and shear surface strains, of the bilateral C6 inferior facets were calculated from motion-capture data and rosette strain gauges, respectively. Linear mixed-effects models (α = 0.05) assessed the effect of axial condition. Minimum principal and maximum shear strains were largest in the compressed condition for all motions except for maximum principal strains during axial rotation. For right axial rotation, maximum principal strains were larger for the contralateral facets, and minimum principal strains were larger for the left facets, regardless of axial condition. Sagittal deflections were largest in the compressed conditions during anterior shear and lateral bending motions, when adjusted for facet side.     

钛镍记忆合金牵张器复合脱细胞真皮基质增高犬牙槽嵴的初步研究

目的用成年杂种犬建立钛镍记忆合金牵张器复合脱细胞真皮基质增高犬牙槽嵴动物模型,为下一步利用钛镍记忆合金牵张器行下颌后牙牙槽嵴增高术奠定基础。方法健康成年雄性杂种犬4只。全麻下拔除双侧下颌4个前磨牙和第一磨牙,1个月后拍摄双侧后牙区X线光片,观察拔牙窝愈合情况。采用4种类型的牵张器随机在4只犬的下颌两侧行牵张手术并观察牵张后1周和1月牙槽嵴增高的情况。结果拔牙后1个月,牙槽嵴黏膜愈合良好。X线片示下颌神经管清晰可见,其上方牙槽窝内有较低密度骨质存在。放置4种牵张器牵张术后1周、1月后牙槽嵴增高的高度分别为3.24 mm、3.76 mm、4.58 mm、5.09 mm;3.15 mm、3.67 mm、4.64 mm、5.01mm,术后一周X线可见后有明显的牵张间隙,1月时牵张区有新骨形成,骨密度增高。结论犬耐受力强,后牙区下颌骨体积大,手术易操作,是理想的牙槽嵴萎缩动物模型。拔牙后1个月,拔牙创愈合良好,可以进行牵张手术。D组＂S＂形牵张器牵张后的高度比较理想,能满足后期种植体的植入。     

皮瓣移植结合骨牵张技术修复感染性胫骨复合皮肤组织缺损的临床效果观察

目的：观察皮瓣移植结合骨牵张技术修复感染性胫骨复合皮肤组织缺损的临床效果。方法：自2008年6月至2012年6月,共收治了胫骨感染性复合组织缺损16例,采用一期彻底去除病变坏死组织和病变的胫骨断端,切取同侧腓肠肌皮瓣、腓肠神经营养血管皮瓣转位、对侧小腿内侧皮瓣和游离皮瓣移植修复小腿皮肤缺损,二期行骨牵张延长术进行治疗。结果：所有16例胫骨复合组织缺损病例感染均得到了控制,移植的皮瓣顺利成活,胫骨截骨延长区成骨良好,断端骨愈合,其中2例出现针道感染,无血管神经并发症发生。骨延长2～9cm,平均延长5．5cm。外同定延长支架在停止骨延长8-20个月后拆除,双下肢等长,膝关节和踝关节功能良好。术后细菌培养＋药敏结果：金黄色葡萄球菌感染8例,表皮葡萄球菌感染4例,大肠杆菌感染1例,阴沟肠杆菌感染l例,肠球菌感染l例。结论：伤口彻底清创,胫骨断端坏死骨切除后一期行皮瓣移植,二期行骨牵张延长术是一种治疗感染性胫骨复合组织缺损的有效方法。     

Ⅳ型镶嵌式外固定器治疗下肢长骨骨缺损

目的：探讨应用IV型镶嵌式外固定器治疗下肢长骨骨缺损的临床疗效。方法：1996年4月～2008年4月应用IV型镶嵌式外固定器治疗下肢长骨骨缺损48例患者,其中股骨8例,胫骨40例。骨缺损长度为5～15cm,平均8cm。随访时间9-27个月,平均18个月。结果：48例患者肢体长度均得到恢复;骨缺损达到骨性愈合,平均愈合时间8.2个月;6例骨折成角,均〈10°;12例共25处针孔感染;所有病例无神经血管损伤表现,髋、膝、踝关节活动均未受影响。结论：IV型镶嵌式外固定器是治疗长骨复杂骨缺损、成功重建肢体长度的有效方法。     

Modeling distraction osteogenesis: analysis of the distraction rate

Distraction osteogenesis is a useful technique aimed at inducing bone formation in widespread clinical applications. One of the most important factors that conditions the success of bone regeneration is the distraction rate. Since the mechanical environment around the osteotomy site is one of the main factors that affects both quantity and quality of the regenerated bone, we have focused on analyzing how the distraction rate influences on the mechanical conditions and tissue regeneration. Therefore, the aim of the present work is to explore the potential of a mathematical algorithm to simulate clinically observed distraction rate related phenomena that occur during distraction osteogenesis. Improvements have been performed on a previous model (Gómez-Benito et al. in J Theor Biol 235:105–119, 2005) in order to take into account the load history. The results obtained concur with experimental findings: a slow distraction rate results in premature bony union, whereas a fast rate results in a fibrous union. Tension forces in the interfragmentary gap tissue have also been estimated and successfully compared with experimental measurements.