Abstract
The outcome of peripheral nerve injuries has been poorly documented. This is due to
the heterogeneity of the injuries, the variety of surgeons from different surgical
specialities performing the repairs and a lack of objective follow up. Anecdotal
reports have suggested that injuries to purely motor nerves have a better outcome than
those affecting mixed nerves.
This aims of this work were to document the natural history of nerve injuries and their
repair under controlled conditions in order to ascertain the outcome of different types
of nerve injury and to compare the outcome of the same injuries in motor nerves and
mixed nerves. A further objective was to determine which investigations would be
useful in the assessment and follow up of peripheral nerve injuries both as predictors
of outcome and in clinical practice.
The sheep model was selected as its peripheral nerves are a similar size, and behave in
a similar manner to, human peripheral nerves. A set of six standardised nerve injuries
(normal control, neurapraxia, axonotmesis, neurotmesis and suture repair, neurotmesis
and entubulation, and nerve graft) was created in both the facial (motor) nerve and the
median (mixed) nerve. The function of the nerves and their target muscles was
assessed using nerve conduction studies (maximum conduction velocity, distribution
of conduction velocities, refractory period), single-fibre electromyography (jitter),
target muscle tension and mass, and nerve fibre morphometry.
In the carefully controlled conditions of the experiments, for both nerves the
transection injuries had a poorer outcome than the non-transection injuries. This effect
was more marked in the median nerve than in the facial nerve suggesting that the type
of nerve affected the outcome of injury. Maximum conduction velocity was
determined to be the most useful test for use in the clinical management of nerve
injuries. Distribution of conduction velocities, a nerve conduction test based on
collision theory, may be too sensitive to be of use in the management of mechanical
nerve injury but may have a valuable role in the assessment of more subtle conditions
such as neuropathies and Bell's palsy. Nerve fibre morphometry discriminated
between the different injuries and remains a useful tool in a research setting.