The Hughes external fixation device: studies of its biomechanical properties' effect on fracture healing and its clinical application

External skeletal fixation devices first appeared in clinical practice in the 1850's. Their use has mainly been confined to Europe although North American surgeons developed an interest in the 1930's. In the last few years, however, there has been a reawakening of interest in external fixation in North America and Great Britain leading to a proliferation of different external fixation devices.Although some experimental work has been done on the biomechanics of some of the more complex fixators very little is known about the optimal configuration of application of most devices. Additionally there is scanty information on the effect that external fixation has on bone healing.This thesis examines the Hughes unilateral external fixator from three aspects.1) Its biomechanica1 properties are examined and the stiffest mode of application defined. The effects of altering this configuration are shown. A comparison is made with the Hoffmann device.2) The effect of external fixation on bone healing is examined. A small fixator is used to immobilise rabbit tibial osteotomies and the effect on healing and bone blood flow compared with an osteotomy treated with a cast.3) A prospective study of the clinical use of the Hughes fixator is presented. An analysis is made of the use of the device in treating tibial fractures.Biomechanical study: This was undertaken using beech as a bone substitute. A jig was constructed so that different loads could be applied to a simulated fracture held by a Hughes fixator. It was found that the stiffest configuration of the Hughes occurred with the fixator bar close to the limb. The inner pin should be as close to the fracture as possible with the outer pin as far from the fracture as is practical. The effect of altering the location of the bar from a lateral to an antero-media 1 location as used on the tibia was to lower the stiffness, although only to the level of stiffness gained using a Hoffmann-Vida 1 double frame. The effect of altering the stiffest configuration was examined.Bone healing and blood flow study: New Zealand white rabbits were used to investigate bone healing and blood flow using a small external fixator designed for the experiment. Bilateral tibial osteotomies were made and one was stabilised with the small fixator with the contra-1atera1 osteotomy being treated in a long-leg cast. After a period of between one and ten weeks the rabbits were sacrificed but prior to this were injected with radioactive microspheres. Comparison of the blood flow in the two fracture sites showed a considerable increase in flow in the cast-treated leg after four weeks.A review of the histology showed that external fixation altered bone healing. The externally fixed leg showed less periosteal reaction but enhanced endochondral ossification and intra-medullary ossification.Clinical study: A three year prospective study of the use of the Hughes fixator was undertaken. The device was mainly used for the treatment of tibial fractures although humeral fractures and pelvic diastases were also treated. In addition a number of osteotomies and an arthrodesis were stabilised with the device.A study of the tibial fractures showed that the eventual outcome of the fracture was dependent on the initial reduction and the length of time tha

Two information aggregation mechanisms for predicting the opening weekend box office revenues of films: Box-office Prophecy and Guess of Guesses

Field tests were conducted on two newinformation aggregationmechanism designs. The mechanisms were designed to collect information held as intuitions about opening weekend box office revenues for movies in Australia. The principles on which the mechanisms operate and their capacity to collect information are explored. A pari-mutuel mechanism produces a predicted probability distribution over box office amounts that is, with the exception of very small films, indistinguishable from the actual revenues. The second mechanism is based on guessing the guesses of others and when applied under conditions where incentives for accuracy are unavailable still performs well against data