Exploring diagonal gait using a forward dynamic three-dimensional chimpanzee simulation.

Primates are unusual among terrestrial quadrupedal mammals in that at walking speeds they prefer diagonal rather than lateral gaits. A number of reasons have been proposed for this preference in relation to the arboreal ancestry of modern primates: stability, energetic cost, neural control, skeletal loading, and limb interference avoiding. However, this is a difficult question to explore experimentally since most primates only occasionally use anything other than diagonal gaits. An alternative approach is to produce biologically realistic computer simulations of primate gait that enable the constraints of biomechanical loading and the energetics of different modes of locomotion to be explored. In this paper we describe such a model for the chimpanzee Pan troglodytes. The simulation is able to produce spontaneous quadrupedal locomotion, and the footfall sequences generated are split between lateral and diagonal footfall sequences with no obvious energetic benefit associated with either option. However, out of 10 successful simulation runs, 5 were lateral sequence/lateral couplet gaits indicating a preference for a specific lateral footfall sequence with a relatively tightly constrained phase difference between the fore- and hindlimbs. This suggests that the choice of diagonal walking gaits in chimpanzees is not a simple mechanical phenomenon and that diagonal walking gaits in primates are selected for by multiple factors.

The 'Goldilocks' effect: preservation bias in vertebrate track assemblages.

Finite-element analysis was used to investigate the extent of bias in the ichnological fossil record attributable to body mass. Virtual tracks were simulated for four dinosaur taxa of different sizes (Struthiomimus, Tyrannosaurus, Brachiosaurus and Edmontosaurus), in a range of substrate conditions. Outlines of autopodia were generated based upon osteology and published soft-tissue reconstructions. Loads were applied vertically to the feet equivalent to the weight of the animal, and distributed accordingly to fore- and hindlimbs where relevant. Ideal, semi-infinite elastic-plastic substrates displayed a 'Goldilocks' quality where only a narrow range of loads could produce tracks, given that small animals failed to indent the substrate, and larger animals would be unable to traverse the area without becoming mired. If a firm subsurface layer is assumed, a more complete assemblage is possible, though there is a strong bias towards larger, heavier animals. The depths of fossil tracks within an assemblage may indicate thicknesses of mechanically distinct substrate layers at the time of track formation, even when the lithified strata appear compositionally homogeneous. This work increases the effectiveness of using vertebrate tracks as palaeoenvironmental indicators in terms of inferring substrate conditions at the time of track formation. Additionally, simulated undertracks are examined, and it is shown that complex deformation beneath the foot may not be indicative of limb kinematics as has been previously interpreted, but instead ridges and undulations at the base of a track may be a function of sediment displacement vectors and pedal morphology.

Simulating sauropod manus-only trackway formation using finite-element analysis.

The occurrence of sauropod manus-only trackways in the fossil record is poorly understood, limiting their potential for understanding locomotor mechanics and behaviour. To elucidate possible causative mechanisms for these traces, finite-element analyses were conducted to model the indentation of substrate by the feet of Diplodocus and Brachiosaurus. Loading was accomplished by applying mass, centre of mass and foot surface area predictions to a range of substrates to model track formation. Experimental results show that when pressure differs between manus and pes, as determined by the distribution of weight and size of respective autopodia, there is a range of substrate shear strengths for which only the manus (or pes) produce enough pressure to deform the substrate, generating a track. If existing reconstructions of sauropod feet and mass distributions are correct, then different taxa will produce either manus- or pes-only trackways in specific substrates. As a result of this work, it is predicted that the occurrence of manus- or pes-only trackways may show geo-temporal correlation with the occurrence of body fossils of specific taxa.

Anti-emetic dexamethasone and postoperative infection risk: a retrospective cohort study.

Nausea and vomiting are common complications of anaesthesia. Dexamethasone is an effective prophylaxis but is immunosuppressive and may increase postoperative infection risk. This retrospective cohort study examined the association between the administration of a single intraoperative anti-emetic dose of dexamethasone (4 to 8 mg) and postoperative infection in 439 patients undergoing single procedure, non-emergency surgery in a university trauma centre. Exclusion criteria included comorbidities, immunosuppressive medications or procedures that confer an increased infection risk. In the 10-week study period and three-month follow-up period, there were 98 documented infections (22.3% of the cohort), of which 43 were detected only on post-discharge follow-up. Anti-emetic dexamethasone was given to 108 patients (24.6%). Stepwise, multivariate logistic regression modelling identified significant associations between female gender, symptomatic reflux, respiratory disease and the risk of infection. The adjusted odds ratio for dexamethasone was 0.88 (0.5 to 1.5, P = 0.656). We did not demonstrate an association between anti-emetic doses of dexamethasone and postoperative infection.

A comparison of caudal bupivacaine and ketamine with penile block for paediatric circumcision.

BACKGROUND AND OBJECTIVES: To establish whether caudal with ketamine or penile block provide superior postoperative analgesia for paediatric circumcision. METHOD: This was a single centre, prospective, randomized, controlled, double-blind trial. Forty males (aged between 18 months and 16 yr) were randomized to receive either a penile block using 0.25 mL kg(-1) 0.5% bupivacaine (Group P), or a caudal block using 0.5 mL kg(-1) 0.25% bupivacaine with 0.5 mg kg(-1) ketamine (Group C). All of them were given a standard anaesthetic and rectal paracetamol 40 mg kg(-1) and diclofenac 1-1.5 mg kg(-1). Postoperative pain scores were assessed in recovery and the time to first analgesia, micturition and walking were recorded. RESULTS: There were no failures in either group. The time to first analgesia was longer in Group C (C median = 459 min, interquartile range 374-553 min; P median = 374 min, interquartile range 224-507 min; P < 0.05). There was a delay in time to walking in Group C (C median = 162 min, interquartile range 119-208 min; P median = 120 min, interquartile range 92-132 min; P < 0.05). There was no difference between the groups in time to waking or micturition, or the incidence of vomiting, abnormal behaviour or bleeding. CONCLUSION: Caudal bupivacaine with ketamine and penile block both provide effective postoperative analgesia for circumcision when given with non-steroidal anti-inflammatory drugs. This study shows that caudal bupivacaine with ketamine provides a longer duration of analgesia than penile block, but also causes delay in walking.

Oral transmucosal fentanyl citrate versus placebo for painful dressing changes: a crossover trial.

OBJECTIVE: Fentanyl is a potent opioid that is well absorbed via the oral mucosa. It can be given as an oral lozenge. The onset of analgesia is rapid and matches the pain profile observed at dressing changes. METHOD: Patients experiencing pain during daily dressing changes were given entonox plus either placebo or oral transmucosal fentanyl citrate (OTFC) for two consecutive dressing changes in a randomised double-blind placebo-controlled crossover trial. RESULTS: Nine patients were recruited. The mean worst pain score during dressing changes was 7/10 with placebo and 4/10 with OTFC; the reduction in pain achieved with OTFC was significant. The mean number of breaths of entonox taken during the dressing change was 27.67 with placebo and 4.67 with OTFC; the reduction in the number of entonox breaths with OTFC was significant. One patient in the OTFC group suffered nausea. CONCLUSION: Compared with placebo, OTFC improved analgesia during painful dressing changes without an increase in side-effects.