Predictive Simulations of Musculoskeletal Function and Jumping Performance in a Generalized Bird.

Jumping is a common, but demanding, behavior that many animals employ during everyday activity. In contrast to jump-specialists such as anurans and some primates, jumping biomechanics and the factors that influence performance remains little studied for generalized species that lack marked adaptations for jumping. Computational biomechanical modeling approaches offer a way of addressing this in a rigorous, mechanistic fashion. Here, optimal control theory and musculoskeletal modeling are integrated to generate predictive simulations of maximal height jumping in a small ground-dwelling bird, a tinamou. A three-dimensional musculoskeletal model with 36 actuators per leg is used, and direct collocation is employed to formulate a rapidly solvable optimal control problem involving both liftoff and landing phases. The resulting simulation raises the whole-body center of mass to over double its standing height, and key aspects of the simulated behavior qualitatively replicate empirical observations for other jumping birds. However, quantitative performance is lower, with reduced ground forces, jump heights, and muscle-tendon power. A pronounced countermovement maneuver is used during launch. The use of a countermovement is demonstrated to be critical to the achievement of greater jump heights, and this phenomenon may only need to exploit physical principles alone to be successful; amplification of muscle performance may not necessarily be a proximate reason for the use of this maneuver. Increasing muscle strength or contractile velocity above nominal values greatly improves jump performance, and interestingly has the greatest effect on more distal limb extensor muscles (i.e., those of the ankle), suggesting that the distal limb may be a critical link for jumping behavior. These results warrant a re-evaluation of previous inferences of jumping ability in some extinct species with foreshortened distal limb segments, such as dromaeosaurid dinosaurs. Simulations prédictives de la fonction musculo-squelettique et des performances de saut chez un oiseau généralisé Sauter est un comportement commun, mais exigeant, que de nombreux animaux utilisent au cours de leurs activités quotidiennes. Contrairement aux spécialistes du saut tels que les anoures et certains primates, la biomécanique du saut et les facteurs qui influencent la performance restent peu étudiés pour les espèces généralisées qui n'ont pas d'adaptations marquées pour le saut. Les approches de modélisation biomécanique computationnelle offrent un moyen d'aborder cette question de manière rigoureuse et mécaniste. Ici, la théorie du contrôle optimal et la modélisation musculo-squelettique sont intégrées pour générer des simulations prédictives du saut en hauteur maximal chez un petit oiseau terrestre, le tinamou. Un modèle musculo-squelettique tridimensionnel avec 36 actionneurs par patte est utilisé, et une méthode numérique nommée "direct collocation" est employée pour formuler un problème de contrôle optimal rapidement résoluble impliquant les phases de décollage et d'atterrissage. La simulation qui en résulte élève le centre de masse du corps entier à plus du double de sa hauteur debout, et les aspects clés du comportement simulé reproduisent qualitativement les observations empiriques d'autres oiseaux sauteurs. Cependant, les performances quantitatives sont moindres, avec une réduction des forces au sol, des hauteurs de saut et de la puissance musculo-tendineuse. Une manœuvre de contre-mouvement prononcée est utilisée pendant le lancement. Il a été démontré que l'utilisation d'un contre-mouvement est essentielle à l'obtention de hauteurs de saut plus importantes, et il se peut que ce phénomène doive exploiter uniquement des principes physiques pour réussir; l'amplification de la performance musculaire n'est pas nécessairement une raison immédiate de l'utilisation de cette manœuvre. L'augmentation de la force musculaire ou de la vitesse de contraction au-dessus des valeurs nominales améliore grandement la performance de saut et, fait intéressant, a le plus grand effet sur les muscles extenseurs des membres plus distaux (c'est-à-dire ceux de la cheville), ce qui suggère que le membre distal peut être un lien critique pour le comportement de saut. Ces résultats justifient une réévaluation des déductions précédentes de la capacité de sauter chez certaines espèces éteintes avec des segments de membres distaux raccourcis, comme les dinosaures droméosauridés. Voorspellende simulaties van musculoskeletale functie en springprestaties bij een gegeneraliseerde vogel Springen is een veel voorkomend, maar veeleisend, gedrag dat veel dieren toepassen tijdens hun dagelijkse bezigheden. In tegenstelling tot de springspecialisten zoals de anura en sommige primaten, is de biomechanica van het springen en de factoren die de prestaties beïnvloeden nog weinig bestudeerd voor algemene soorten die geen uitgesproken adaptaties voor het springen hebben. Computationele biomechanische modelbenaderingen bieden een manier om dit op een rigoureuze, mechanistische manier aan te pakken. Hier worden optimale controle theorie en musculoskeletale modellering geïntegreerd om voorspellende simulaties te genereren van maximale hoogtesprong bij een kleine grondbewonende vogel, een tinamou. Een driedimensionaal musculoskeletaal model met 36 actuatoren per poot wordt gebruikt, en directe collocatie wordt toegepast om een snel oplosbaar optimaal controleprobleem te formuleren dat zowel de opstijg-als de landingsfase omvat. De resulterende simulatie verhoogt het lichaamszwaartepunt tot meer dan het dubbele van de stahoogte, en belangrijke aspecten van het gesimuleerde gedrag komen kwalitatief overeen met empirische waarnemingen voor andere springende vogels. De kwantitatieve prestaties zijn echter minder, met verminderde grondkrachten, spronghoogtes en spierpeeskracht. Tijdens de lancering wordt een uitgesproken tegenbewegingsmanoeuvre gebruikt. Aangetoond is dat het gebruik van een tegenbeweging van cruciaal belang is voor het bereiken van grotere spronghoogten, en dit fenomeen hoeft alleen op fysische principes te berusten om succesvol te zijn; versterking van de spierprestaties hoeft niet noodzakelijk een proximate reden te zijn voor het gebruik van deze manoeuvre. Het verhogen van de spierkracht of van de contractiesnelheid boven de nominale waarden verbetert de sprongprestatie aanzienlijk, en heeft interessant genoeg het grootste effect op de meer distale extensoren van de ledematen (d.w.z. die van de enkel), wat suggereert dat de distale ledematen een kritieke schakel kunnen zijn voor het springgedrag. Deze resultaten rechtvaardigen een herevaluatie van eerdere conclusies over springvermogen bij sommige uitgestorven soorten met voorgekorte distale ledematen, zoals dromaeosauride dinosauriërs. Prädiktive Simulationen der muskuloskelettalen Funktion und Sprungleistung bei einem generalisierten Vogel Springen ist ein übliches jedoch anstrengendes Verhalten, das viele Tiere bei ihren täglichen Aktivitäten einsetzen. Im Gegensatz zu Springspezialisten, wie Fröschen und einigen Primaten, sind bei allgemeinen Arten, welche keine ausgeprägten Anpassung für Sprungverhalten aufweisen, die Biomechanik beim Springen und die Faktoren, welche die Leistungsfähigkeit beeinflussen, noch wenig untersucht. Computergestützte biomechanische Modellierungsverfahren bieten hier eine Möglichkeit, dies in einer gründlichen, mechanistischen Weise anzugehen. In dieser Arbeit werden die optimale Steuerungstheorie und Muskel-Skelett-Modellierung zusammen eingesetzt, um die maximale Sprunghöhe eines kleinen bodenlebenden Vogels, eines Perlsteisshuhns, zu simulieren und zu prognostizieren. Es wird ein dreidimensionales Muskel-Skelett-Modell mit 36 Aktuatoren pro Bein verwendet, und durch direkte Kollokation wird ein schnell lösbares optimales Steuerungsproblem formuliert, das sowohl die Abstoss- als auch die Landephase umfasst. Die daraus folgende Simulation bringt den Ganzkörperschwerpunkt auf mehr als das Doppelte seiner Standhöhe und entscheidende Aspekte des simulierten Verhaltens entsprechen qualitativ empirischen Beobachtungen für andere springende Vögel. Allerdings ist die quantitative Leistungsfähigkeit geringer, mit reduzierten Bodenkräften, Sprunghöhen und Muskel-Sehnen-Kräften. Beim Abstossen wird ein ausgeprägtes Gegenbewegungsmanöver durchgeführt. Die Durchführung einer Gegenbewegung ist nachweislich entscheidend für das Erreichen grösserer Sprunghöhen, wobei dieses Phänomen möglicherweise nur physikalische Prinzipien auszuschöpfen braucht, um erfolgreich zu sein. Die Verstärkung der Muskelleistung ist daher möglicherweise nicht zwingend ein unmittelbarer Grund für die Verwendung dieses Manövers. Eine Erhöhung der Muskelkraft oder der Kontraktionsgeschwindigkeit über die Nominalwerte hinaus führt zu einer erheblichen Zunahme der Sprungleistung und hat interessanterweise den grössten Effekt bei den weiter distal gelegenen Streckmuskeln der Beine (d.h. bei denjenigen des Sprunggelenks), was darauf hindeutet, dass die distale Gliedmasse ein entscheidendes Element für das Sprungverhalten sein könnte. Diese Ergebnisse geben Anlass zur Überprüfung früherer Schlussfolgerungen hinsichtlich der Sprungfähigkeit einiger ausgestorbener Arten mit verkürzten distalen Gliedmassen, wie beispielsweise bei dromaeosauriden Dinosauriern.

The influence of speed and size on avian terrestrial locomotor biomechanics: Predicting locomotion in extinct theropod dinosaurs.

How extinct, non-avian theropod dinosaurs moved is a subject of considerable interest and controversy. A better understanding of non-avian theropod locomotion can be achieved by better understanding terrestrial locomotor biomechanics in their modern descendants, birds. Despite much research on the subject, avian terrestrial locomotion remains little explored in regards to how kinematic and kinetic factors vary together with speed and body size. Here, terrestrial locomotion was investigated in twelve species of ground-dwelling bird, spanning a 1,780-fold range in body mass, across almost their entire speed range. Particular attention was devoted to the ground reaction force (GRF), the force that the feet exert upon the ground. Comparable data for the only other extant obligate, striding biped, humans, were also collected and studied. In birds, all kinematic and kinetic parameters examined changed continuously with increasing speed, while in humans all but one of those same parameters changed abruptly at the walk-run transition. This result supports previous studies that show birds to have a highly continuous locomotor repertoire compared to humans, where discrete 'walking' and 'running' gaits are not easily distinguished based on kinematic patterns alone. The influences of speed and body size on kinematic and kinetic factors in birds are developed into a set of predictive relationships that may be applied to extinct, non-avian theropods. The resulting predictive model is able to explain 79-93% of the observed variation in kinematics and 69-83% of the observed variation in GRFs, and also performs well in extrapolation tests. However, this study also found that the location of the whole-body centre of mass may exert an important influence on the nature of the GRF, and hence some caution is warranted, in lieu of further investigation.

Using step width to compare locomotor biomechanics between extinct, non-avian theropod dinosaurs and modern obligate bipeds.

How extinct, non-avian theropod dinosaurs locomoted is a subject of considerable interest, as is the manner in which it evolved on the line leading to birds. Fossil footprints provide the most direct evidence for answering these questions. In this study, step width-the mediolateral (transverse) distance between successive footfalls-was investigated with respect to speed (stride length) in non-avian theropod trackways of Late Triassic age. Comparable kinematic data were also collected for humans and 11 species of ground-dwelling birds. Permutation tests of the slope on a plot of step width against stride length showed that step width decreased continuously with increasing speed in the extinct theropods (p < 0.001), as well as the five tallest bird species studied (p < 0.01). Humans, by contrast, showed an abrupt decrease in step width at the walk-run transition. In the modern bipeds, these patterns reflect the use of either a discontinuous locomotor repertoire, characterized by distinct gaits (humans), or a continuous locomotor repertoire, where walking smoothly transitions into running (birds). The non-avian theropods are consequently inferred to have had a continuous locomotor repertoire, possibly including grounded running. Thus, features that characterize avian terrestrial locomotion had begun to evolve early in theropod history.

Adenomatous hyperplasia of the mucous glands in captive Archey's frogs (Leiopelma archeyi).

AIMS: To describe the gross and light microscopic characteristics of skin lesions observed on the ventral skin of captive Archey's frogs (Leiopelma archeyi) between 2000 and 2012, and to investigate their occurrence, possible aetiology and association with survival. METHODS: Postmortem skin samples were obtained for histological evaluation from 37 frogs, with and without skin lesions, that died while in captivity at Auckland Zoo between 2000 and 2012. Four frogs with skin lesions were biopsied under general anaesthesia and samples used for both light and transmission electron microscopy. The records of 94 frogs held at the University of Otago and Auckland Zoo between 2000-2012 were reviewed, which included some frogs recently collected from the wild. Information about the occurrence of skin lesions, and mortality associated with skin lesions was collated. RESULTS: Grossly the skin lesions varied in appearance; most were circular, pale grey papules, which measured from <0.5-1.5 mm in diameter with no umbilication. The overlying epidermis was not fragile and there was no associated inflammation. Contents often appeared clear or semi-transparent. Lesions were located predominantly on ventral surfaces including trunk, thighs, lower legs and forearms, and gular region, but not on digits. The number ranged from single to multiple, often confluent lesions covering the entire ventral surface of the frog. Histologically the lesions consisted of enlarged proliferating mucous glands that expanded the dermis and elevated the epidermis. They were semi-organised, solid or occasionally cavitated acinar structures with central lumina which sometimes contained mucus. Nuclei showed moderate anisokaryosis and mitotic figures were uncommon. Transmission electron microscopy did not show any infectious agents. Between 2000 and 2012, skin lesions were recorded in 35/94 (37%) frogs. The size and location of skin lesions varied over time, with some resolving and sometimes reappearing. Skin lesions were not associated with an increased risk of death. CONCLUSIONS: The skin lesions had the gross and microscopic characteristics of adenomatous hyperplasia of the dermal mucous glands. CLINICAL RELEVANCE: The aetiology of this adenomatous hyperplasia is unknown, but factors associated with the captive environment are the most likely cause. This is the first description of adenomatous hyperplasia of the cutaneous mucous glands in amphibians.

Male quality, signal reliability and female choice: assessing the expectations of inter-sexual selection.

Numerous models have attempted to explain the evolution of extravagant male ornaments found in many species. Inter-sexual indicator models postulate that male ornaments evolved as signals of quality, and that females use these signals to select the highest quality males. These models involve three traits--male quality, male signals and female preferences--and have specific expectations about the relative strengths of the phenotypic relationships between these traits. Using data from anuran species, we assessed the relative strengths of the phenotypic relationships using meta-analysis. The relative strengths of these phenotypic correlations were as expected by indicator models, providing support for indicator models of inter-sexual selection. We also found much variation in our data, suggesting that additional, untested factors may mediate inter-sexual interactions in this taxon, such as differences in the importance of quality signalling between species. These factors require investigation, in order to improve our understanding of inter-sexual selection.

Urinary hormone metabolites identify sex and imply unexpected winter breeding in an endangered, subterranean-nesting frog.

Urinary hormone analysis has proved accurate for identifying sex and breeding periods in dimorphic amphibians with known reproductive cycles. We examined whether these techniques could provide this much needed information for a monomorphic anuran with an unconfirmed mating season in the wild. We analysed urinary estrone conjugate, testosterone, and progesterone metabolites to infer the time of breeding and to identify sex in the endangered Maud Island frog, Leiopelma pakeka. Testosterone metabolites in males and estrone and progesterone metabolites in females were at their peak during winter for both wild and captive frogs. These urinary metabolite patterns were consistent with the high proportion of females exhibiting enlarged ovarian follicles in winter months. Sex identification based on urinary estrone metabolite levels was 94% correct in this monomorphic species, in which the sexes overlap in snout-to-vent length (SVL) for over half of their adult size range and in which no other sexually dimorphic trait is known. The seasonal profiles imply unexpected winter or early spring breeding in L. pakeka. Overall, these results demonstrate use of urinary hormone metabolites for reproductive monitoring and sex identification in one of the world's most threatened and evolutionarily distinct amphibians.

Urinary hormone analysis assists reproductive monitoring and sex identification of bell frogs (Litoria raniformis).

With the world currently facing a global amphibian extinction crisis, the development of techniques to help meet the needs of conservation managers and researchers studying the reproductive biology of amphibians is needed. Here, we developed enzyme immunoassays to measure estrone, testosterone, and progesterone hormone metabolites in the urine of Litoria raniformis, the southern bell frog. Concentrations of urinary estrone, testosterone, and progesterone increased during the breeding season for females (P<0.05). Concentrations of urinary testosterone and progesterone increased for males during the breeding season compared with that for months where no reproductive behaviors were observed (P<0.05). Furthermore, urinary estrone concentrations proved to be a reliable sexing tool for adult frogs, with no overlap between the sexes in 98% of cases, regardless of season. There was no difference in estrone (P=0.204) or testosterone (P=0.485) metabolite concentrations between samples taken immediately upon capture and those taken 12 to 24h later from the same individual. Progesterone metabolite concentrations were lower on Day 2 than upon collection (P=0.004). This is the first study to show that urinary hormone analysis can be a useful technique for reproductive monitoring in an amphibian. Additionally, hormone metabolite measures offer promise as sex identification tools for monomorphic species and for those whose secondary sex characteristics are visible only during the breeding season.

Cold tolerance and overwintering of an introduced New Zealand frog, the brown tree frog (Litoria ewingii).

The overwintering strategy of Litoria ewingii in Otago, New Zealand, was studied under laboratory and field conditions. Microhabitat temperature measurements showed that the frogs were often exposed to subzero temperatures. In the laboratory, Litoria ewingii tolerated freezing for up to 6 hrs at -1 degrees C, and after the completion of the freezing event (about 1 hr) at -2 degrees C. Frogs frozen with insulation survived freezing for 12 hrs at -1 degrees C. Frogs supercooled to -1.2 +/- 0.1 degrees C and -1.7 +/- 0.3 degrees C on wet and dry substrates respectively. L. Ewingii tolerated up to 47.5% of its body water frozen. Plasma glucose levels and osmolality were not increased during freezing. It is concluded that l. Ewingii cannot avoid freezing and is sufficiently freeze tolerant to survive the subzero temperatures encountered during winter in Otago.

Post mortem cohabitation-shell growth as a measure of elapsed time: a case report.

A partial calvaria, dredged from the sea-bed some years previously, was referred to us for examination. The presence of a well-established mollusc colony on the vault allowed us to establish a minimum elapsed time since death. Such a cross-disciplinary co-operative study is of great advantage in expediting a satisfactory conclusion.

Functional consequences of a novel middle ear adaptation in the central African frog Petropedetes parkeri (Ranidae).

During the breeding season, each tympanic membrane of males of the Old World treefrog Petropedetes parkeri is decorated with a single, prominent, fleshy tympanic papilla. The tympanic papilla, located dorsally on the tympanic membrane, is covered by an epidermal surface and is composed of non-ossified, spongiform tissue containing a number of globular, fluid-filled vesicles found at highest density near the papillar tip. These vesicles appear to have exit pores and are probably simple alveolar exocrine glands. Injecting sound into the pressurized vocal cavity of the male and measuring the vibration velocity response of the tympanic membrane revealed that from 0.3 to 2.0 kHz the tympanic papilla velocity amplitude is on average 20 dB lower than that of a point diametrically opposite on the ventral half of the tympanic membrane. The close agreement between the dominant frequency of the call and the frequency of the maximum spectral peak of the Fast Fourier Transform of the impulse response of the eardrum is consistent with the use of the eardrum in this species both as a call receiver and as a call radiator, similar to the function suggested for the eardrum of the male bullfrog Rana catesbeiana. Unexpectedly, surgically removing the tympanic papilla lowered the frequency of the peak vibrational amplitude, testifying to the importance of membrane tension as a dominant factor in the vibratory behavior of the eardrum. During normal positive-pressure breathing, the tympanic papillae move conspicuously, suggesting a possible rôle as a visual signal.

Electromyographic activity of the cervical musculature during dynamic lateral bending.

STUDY DESIGN: Electromyographic profiles from the neck muscles of five young, healthy men were obtained to study the muscular, activation patterns during dynamic external loading. OBJECTIVES: To examine the myoelectric activity of selected cervical muscles during dynamic loading, and to explore the reaction of the cervical muscles to different loading conditions. SUMMARY OF BACKGROUND DATA: The response of cervical muscles throughout dynamic external loading is not well understood. Electromyography provides information, within certain limitations, about the neural drive to various components of the musculature. Such information on activation, combined with geometric parameters of the musculoskeletal tissues, constitutes a tool for helping to understand the mechanism of head and neck impact-related injury. METHODS: Subjects were tested with the head and neck in the neutral and prebent positions. Dynamic loads were applied laterally to each subject by free-falling masses to create peak dynamic loads ranging from about 40 to 100 N. Force and electromyographic data were recorded, and cross-correlations from linear envelope electromyography were calculated. RESULTS: The peak electromyogram showed large differences between the two applied loads and between subjects. There were time delays (75-165 msec) between the peak applied force and the peak electromyogram. The muscles on the contralateral side demonstrated different electromyographic profiles between subjects. Within subjects, the electromyographic profiles from each muscle were consistent for the same trial conditions. CONCLUSIONS: Electromyographic profiles and the cross-correlator coefficients for cervical muscles have shown reproducible intrasubject muscle synergies, which were not sensitive to the magnitude of applied load and the posture of the head. Intersubject muscle activity patterns varied.

Factors related to quadriplegia in football and the implications for intervention strategies.

Axial compressive loading, the principal cause of spinal cord quadriplegia in American football, is produced when a player is forcibly struck on the crown of the helmet. This impact subjects the small cervical vertebrae to a large compressive force that often produces stress that exceeds the failure limit of the spine. Several factors influence the outcome in axial collisions, including the available kinetic energy, the displacement needed to dissipate the energy, and the end conditions of the collision (i.e., the position of the head). Effective intervention of this catastrophic injury requires the melding of information from the fields of biomechanics and epidemiology. From a biomechanical perspective, neck loading should be kept at a level that is below the failure limit of the cervical spine. The epidemiologic rate at which these injuries develop among football players suggests that cervical quadriplegia is rare. Thus, protective devices intended to lower the forces on the cervical spine may not succeed in dramatically reducing the incidence of this injury. Because this injury is rare, it is important to consider that introducing new protective equipment, intended for intervention of one problem (i.e., cervical quadriplegia), may lead to other injuries.

Passive stiffness of the human neck in flexion, extension, and lateral bending.

The passive bending stiffness, tolerable bending moment levels, and elastic energy storage capabilities of the cervical spine were evaluated in 40 male and 19 female volunteer subjects from a university student population, about the flexion, extension, and lateral bending axes. Bending moments were applied to the neck while subjects lay on a frictionless jig and simultaneous angular displacements of the skull relative to the rib cage were recorded. Myoelectric signals from the sternocleidomastoid and splenius capitis muscles were amplified over audio speakers to train subjects to relax their musculature. Tolerable levels of bending moments were quite low (less than 10 N m on average for all conditions) given the very large magnitude of bending moment applied to the neck estimated from impact models. Subjects tolerated greater moment and elastic energy storage in the cervical passive tissues during flexion than in both extension and in lateral bending. In addition males were able to tolerate larger applied moments, were stiffer, and stored more energy than females in all loading conditions. The data derived from this study of loading at very slow rates provide a lower limit for bending moments and for cervical spine stiffness, and yield a first approximation to dynamic bending stiffness values that may be included in models of the cervical spine.

The inappropriateness of helmet drop tests in assessing neck protection in head-first impacts.

Protecting the cervical spine in situations of axial compressive loading is indeed complex. Results from a number of crash simulations suggest that the mechanisms of head impact causing brain damage and those causing neck injury are different. The idea that neck injuries can be predicted from results of helmet drop tests or that the helmet is capable of providing protection to the cervical spine is unsupported. In head-first collisions causing axial compressive loading, the cushioning properties of the helmet alone would dictate the maximum force on the neck if both the head and neck were rigid. Since the head and neck are not rigid and appear to be as stiff or less stiff than the helmet, the cushioning influence of the helmet is minimized, so the forces experienced by the neck are dictated largely by its own properties. The helmet does not have a large influence. To be effective, the helmet would have to be much less stiff than it is at present and would have to maintain this low stiffness under very large loads. These conditions would be difficult to achieve without making the helmet disproportionately larger than it is now.

Transpleural repair of esophageal atresia without a primary gastrostomy: 240 patients treated between 1951 and 1983.

Esophageal atresia with distal tracheoesophageal fistula has been treated at one institution between 1951 and 1983 primarily by prompt transpleural repair without gastrostomy. Two hundred and seventy one patients are assigned to three time periods: (1) 1951 to 1963, prior to modern intensive care; (2) 1964 to 1973, the initial era of mechanical ventilation; and 1974 to 1983, the era of readily available ventilators and TPN. During these time periods mean birthweight decreased from 2,780 g to 2,670 g to 2,500 g, while the incidence of associated anomalies increased from 41% to 44% to 55%. Eleven patients had no operation or gastrostomy only and died. Twenty (predominantly in the early years) had staged repairs with initial gastrostomy and fistula ligation. Primary anastomosis was done in 240 patients regardless of birth weight, 229 of which were by the transpleural approach. Gastrostomy was performed primarily in 28 patients for varied indications. Operative mortality (definitive as well as staged repairs) fell over the three time periods from 44% to 15% to 7%. Anastomotic leaks occurred in 20% of patients who underwent primary repair regardless of the time period. The mortality associated with a leak, however, decreased from 88% to 47% to 0%. Anastomotic strictures requiring more than two dilatations occurred in 15% in all periods. The overall incidence of recurrent fistula was 5%. Of 200 patients surviving the initial hospitalization, follow-up longer than 2 months is available for 156 patients with a median follow-up of 30 months. There were 15 late deaths.(ABSTRACT TRUNCATED AT 250 WORDS)

Alterations in head dynamics with the addition of a hockey helmet and face shield under inertial loading.

The effect of a hockey helmet and face shield on the head and neck during inertial loading was studied. A Hybrid III Anthropometric Test Dummy (ATD) was struck from both the front and rear by a spring-loaded, instrumented striker moving at 2.9 ms-1. Data were collected from a triaxial force transducer mounted at the atlanto-occipital (a-o) junction of the ATD, a load cell in the striker, and by cinematography (250 fps). Angular kinematics of the head and moments of force about the a-o junction were determined along with impact force levels. When compared to a bare-head condition, the addition of a helmet and face shield caused an increase in head angular displacement (20-40%) but did not affect head angular acceleration. Axial and shear forces at the a-o junction did not change appreciably with the addition of a helmet and face shield. A triphasic pattern was evident for the neck moments including a small phase which represented a seating of the headform on the nodding blocks of the uppermost ATD neck segment, and two larger phases of opposite polarity which represented the motion of the head relative to the trunk during the first 350 ms after impact. No substantial differences were apparent between the helmeted and non-helmeted trials. The magnitudes of forces and moments found in the present study were well within tolerance levels reported by others (Melvin, 1979; Cheng et al., 1982). It was concluded that the increase in angular displacement of the head, with the addition of a helmet and face shield, does not place the wearer in a position of increased risk of cervical spine trauma.

Impact performance of bicycle helmets.

Seven brands of bicycle helmets were compared by means of a drop test using an instrumented Hodgson-WSU headform, on the front (F), rear (R) and left side (LS) locations from a height of 1.0m and on the right front boss (RFB) from either 1.0m or 1.75m. Acceleration signals from the headform were computer processed to yield peak acceleration and the Gadd Severity Index (GSI). Significant differences between helmets and within helmets at different locations were found. Helmets with crushable polystyrene liners were much superior to those with soft foam liners. The superiority of the polystyrene liners disappeared however when helmets were subjected to two consecutive drops to the same location (R). The results also indicated that for most cases the GSI was between 800-1200 but there were two helmets that had values in excess of 1500. Clearly not all bicycle helmets provide equivalent levels of protection and some are much superior to others.

An evaluation of football helmets under impact conditions.

The impact attenuating characteristics of a sample of 81 football helmets used in competitive high school programs were determined using a Hodgson-Wayne State University (WSU) headform and a modified National Operating Committee on Standards for Athletic Equipment (NOCSAE) test protocol. The helmets, classified by liner type as suspension (37), padded-suspension (22), and padded (22) had been in use for 6 to 8 years. Each was subjected to two consecutive right rear boss impacts from a drop height of 1.5 m, onto a rigid anvil covered with a 45 durometer hardness rubber pad. Analogue signals from a triaxial accelerometer located at the center of gravity of the headform were analogue to digital (A/D) converted at 6060.6 Hz and processed on a Hewlett Packard 9845B minicomputer to yield a resultant acceleration-time curve from which peak acceleration (gpeak) and the Gadd Severity Index (GSI) were determined. The mean gpeak was 205 g for helmets with suspension liners, 165 g for helmets with padded-suspension liners, and 156 g for helmets with padded liners. Twenty-four suspension helmets and five padded or padded-suspension helmets had GSI values greater than 1200. Using a criterion of GSI1500, the failure rate for suspension helmets was 19% compared to 2% for padded and padded-suspension helmets combined. If the criterion chosen was GSI1200, the failure rate for suspension helmets was 65% as opposed to 11% for the padded and padded-suspension helmets combined. Suspension helmets are decidedly inferior under impact conditions to the padded and padded-suspension helmets.