Abstract
D.Ing.
This thesis studies the application of newer generation engineering materials,
specifically carbon fibre reinforced polymers, as bone plates in cases of fractured
bones. The application of bone plates subsequent to bone fracture is a very old
orthopaedic technique that has always rendered some problems. The rigidity of
the bone plate, and thus the plated system as a whole, is of advantage during the
healing phase, but of disadvantage later. Bone remodels itself to most efficiently
perform the load bearing required of it. In a plated system, the load is born
primarily by the plate and therefore protects the underlying bone, leading to
osteoporosis and eventual atrophy. All bone plates are made of a material that
is totally foreign to the body, and in most cases these are removed after some
healing of the bone had occurred. The majority of current research programmes
with respect to bone plates are directed towards biodegradable bone plates that
reduces in mechanical strength at approximately the same rate as bone gains in
its ability to sustain loads.
The principle of stimulating bone growth in cases of delayed union and non-union
has been studied since the early 1960's. The studies revealed that bone healing
can in fact be enhanced by the introduction of a very small electric current to the
fracture site. Variations to the mechanisms and position of application of the
current, alternating or direct, are well documented. Although the physiological
healing process associated with electrical stimulus remains largely unknown, the
principle is well established.
The phenomenon of galvanic corrosion has been known since the tum of the
century. Where two dissimilar materials are in the presence of a conducting
media, the more "reactive" of the two materials will react as an anode or electron
donor to the other material. An electric current thus will flow from the one
material to the other.
Having three existing and known phenomena, namely bone plating, bone healing
stimulation and galvanic corrosion raises the question of whether these can be
combined to yield a solution superior to any current plating mechanism - a plate
that would render sufficient mechanical support but act as an electron source and
thus as a bone healing stimulus.
The purpose of this study is to assess the biological criteria determining the choice
of bone plates (inclusive of mechanical, physiological and electrical criteria) and
thereafter selecting a material suitable for this dynamic requirement.