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
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
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
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 that