Key notes on plastic surgery/Adrian M. Richards

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32 GENERAL PRINCIPLES
• Group B
• These fibres are found in myelinated, preganglionic autonomic nerves.
• Group C
• These fibres are found in myelinated, postganglionic autonomic nerves.
Medical Research Council grading of nerve function
The MRC have recommended the following grading of nerve function.
Motor function Sensory function
M0 No contraction S0 No sensation
M1 Flicker S1 Pain sensation
M2 Movement with gravity eliminated S2 Pain and some touch sensation,
possible hypersensitivity
M3 Movement against gravity S3 Pain and touch with
over-reaction
M4 Movement against gravity and resistance S3+ Some 2-point discrimination
M5 Normal S4 Normal
Injury
• After transection of a nerve, traumatic degeneration occurs proximally as far as
the last node of Ranvier.
• Distally, nerves undergo wallerian degeneration.
• This process was described by Waller in 1850 and consists of:
• Degeneration of axons and myelin which are then phagocytosed by macrophages
and Schwann cells.
• Collapsed columns of nerve cells develop a bandlike appearance on electron
microscopy; these are known as the bands of Buengner.
• Neurotropism is selective, directional growth of nerve fibres towards their
appropriate receptors.
• It is mediated by nerve growth factors and consists of the following stages.
1 The proximal nerve stump sprouts many new fibres.
2 Fibres growing in an inappropriate direction atrophy.
3 Those growing in the correct direction survive and grow.
• Neurotropism is non-selective, non-directional growth of nerve fibres.
• Factors which mediate neurotropism include growth factors, extracellular matrix
components and hormones.
Classification of nerve injury
• The degree of nerve injury has been classified by both Seddon and Sunderland.
• Seddon classified nerve damage into three groups:
1 Neurapraxia
2 Axonotmesis
3 Neurotmesis.
• Sunderland expanded this classification to five groups.