The peripheral nerve is responsible for connecting the central nervous system with the different parts of the body. Its function is to transmit sensory and motor impulses.
The peripheral nerves are made up of several layers that serve as protection: the epineurium (strong and thick peripheral layer), the perineurium (fiber sheath made of collagen and elastin, which protects the nerve from compressions and tractions) and the endoneurium (innermost part). Inside the peripheral nerves is the axon surrounded by the myelin sheath, the structure that transmits the information to the body.
How and why do peripheral nerve injuries occur?
Peripheral nerve injuries are caused by two mechanisms: compression and traction. Depending on the intensity of the aggression to the nerve, the severity will be less or more severe. Thus, the patient may suffer from paralysis or reversible hypoesthesia to sections or even tearing of a nerve.
As a general rule, these are serious injuries, so they must be diagnosed and treated correctly. The consequences of incorrect management can be severe and leave permanent disabilities.
What type of injuries are the most common in peripheral nerves?
Injuries according to Seddon can be classified into:
- Neuroparaxia. Injury in which conduction is interrupted but without anatomical injury, since the nerves will be intact. It is usually reversible and the cause is usually due to compression.
- Axonotmesis. There is a loss of axon continuity solution, as well as of the myelin sheath. However, the proneurium and endoneurium are preserved.
- Neurotmesis. There is a complete rupture of the elements by fibrosis or by solution of continuity. In this lesion there is a retraction of the ends.
How are peripheral nerve injuries treated?
The principles to be followed by any specialist in Traumatology expert in nerve surgery in peripheral nerve injuries are:
- Microsurgical technique.
- Make sutures without tension.
- If there is a nerve defect, perform a graft or use a connector to avoid tension and ischemia in the area where the suture will be made. If this is not done by the specialist in peripheral nerve surgery and microsurgery, the surgery will fail.
In many cases the surgery that allows reconstruction of the peripheral nerve will involve the use of nerve grafts, which can be of two types:
- Autologous graft. They are extracted from the same patient but involve morbidity in the donor area, in addition to being a limited tissue that, depending on the extent of the lesion, will not be useful.
- Allograft. They are obtained from a cadaver donor and must be treated in order to be used. Their use has reduced morbidity and surgical damage, allowing them to be used in more extensive lesions than autologous grafts.
If, in addition, there is a loss of nerve tissue, or if a nerve suture is left in tension, there will be several alternatives:
- When the nerve defect is small (less than 7mm) a connector may be used, i.e., a bridge that will allow the nerve to grow inside.
- If the nerve defect is larger, in parts where sensitivity is more important, the use of autologous nerve grafts will be indicated. The anterior branch of the Brachialis Cutaneus Internus (BCI) or a branch of the sural nerve, for example, may be used.
- In defects in less important areas, nerve allograft can be used.
In any case, it is essential to individualize each case. In patients with neuropathic pain, in cases of neuroma, nerve allografting will allow the nerve end to be buried in the bone or muscle and the pain to disappear. If an allograft is used, the size of the incision and the morbidity of the operation will be reduced.
Sometimes the loss of nerve tissue is so great in brachial plexus injuries or in extensive injuries that the autologous graft is not sufficient. It is in these cases when allografts help to solve problems that were previously considered impossible cases.
What will the result be like after peripheral nerve surgery?
For the result to be good, it will be necessary:
- A precise microsurgical technique, performed by a surgeon with extensive training and experience.
- Adequate surgical times. Sometimes cases arrive too late. The nerve and its results are dependent, that is to say, the longer the evolution time, the worse the results. If the lesion is more than 6 months old, the results drop, and even more so in lesions of more than one year of evolution.
- Good management of nerve reconstruction techniques (grafts and nerve transfers) related to tendon transfers.
Case report: poorly healed wound of 6 months of evolution after a knife cut.
A real clinical case presents a 45-year-old female patient who cut her hand 6 months ago with a sharp knife. At the time, a correct surgical exploration of the cut was not carried out. For the last two months she claims that she cannot feel her finger and that she suffers cramps when she picks up objects between the thumb and index finger (when she makes the pincer movement).
The patient underwent surgery showing a neuroma in the section area affecting the ulnar collateral nerve of the thumb. During surgery, the proximal and distal end was identified and a 15 mm nerve allograft was performed, avoiding the use of the patient’s own graft.
The result was satisfactory, the pain disappeared and the patient recovered sensitivity and functionality. In this case the nerve allograft has allowed the patient to solve her problem, with minimal surgical aggression.