What is a nerve injury?
Nerves are the tissues that carry signals from the brain to the body and back. In the arm the signals from the brain tell the muscles to move so the arm and particularly the hand can do tasks. The hand and arm send back signals, particularly of feeling i.e. touch, what position the hand and fingers have, and also pain. In children the signals from the brain to the arm are essential for normal growth and development.
The nerves can be thought of as insulated electrical cables which allow electric impulses (the signals from the brain) to travel very fast to where they are needed. If either the outer “insulating layer” or the inner “electrical cable” is damaged then the signals will either pass slowly or weakly or NOT pass at all.
What types nerve injury occur?
Nerve injuries are defined as 3 main types with Latin names. These are explained below. In increasing severity the nerve injuries are:
Nerve stun or bruising called “neurapraxia”. The nerve injury often follows a direct blow or stretch. The commonest example is hitting one’s “funny bone”. There is tingling for a short while and then full recovery. This is a mild injury and full recovery occurs within a maximum of 6 weeks.
Internal nerve tearing called “axonotmesis”. This is a more severe injury where the electrical cable elements of the nerve are stretched and may break but the outer insulating layer is intact. Therefore the nerve can recover down the same track. Full recovery can occur but is slow and there is often some residual loss of nerve function.
Cut or ripping of the nerve called “neurotmesis”. This is the most severe injury. The nerve ends are separated and no recovery can occur unless surgery is performed to sew the nerve ends back together again. Even following surgery recovery is slow and incomplete except in children where full recovery can sometimes occur.
With many nerve injuries, especially if there is crushing/bruising of the nerve rather than a cut then there is often a mix of all the above injuries.
Cut on glass causing median nerve injury
What do they look like?
Nerve injuries may be obvious such as when there has been a cut but they are often not obvious and can be difficult to detect initially because of local pain and swelling. Even when detected the severity can easily be overlooked. As doctors we want our patients to do well so it is easy to be optimistic and diagnose a nerve stun when a more severe injury such as a nerve tearing has occurred. This may only become obvious over days/weeks/months. We see quite a few patients who come several weeks or months down the line from injury who had not appreciated the severity of the problem.
How is the diagnosis made?
The Hand specialist who sees the patient will ask questions about their injury and in particular how it occurred. They will then examine the patient looking at the injured site. The Hand specialist will look at the particular muscles that receive signals from the injured nerve and the fingers from which signals of touch are sent through the injured nerve. Thus the Hand specialist will test for muscle function and strength by asking the patient to move certain fingers/thumb or the wrist or elbow. The Hand specialist will look at movement and strength in those muscles. Late on i.e. after about 4 -6 weeks there may be evidence of reduced muscle bulk known as “wasting” of muscles. The Hand specialist will also test for feeling both by touching the hand/arm and possibly testing with specific (painless) testing equipment. Sweating in the fingers is also reduced following a nerve injury to a particular finger and testing for this may guide the Hand specialist. After several weeks patients may also have areas of excess pain/feeling from a nerve injury, so light touch such as stroking the area may feel uncomfortable with a burning feeling. This is known as hypersensitivity.
What investigations (tests) are needed?
For the milder injuries no tests are needed. For more severe injuries there are tests related to the nerve injury and tests related to other possible injuries at the time.
Tests of nerve injury: There is a limited range of tests above clinical assessment. The main test is known as an “electrical test”. The medical terms are “neurophysiological assessment” or “EMG” studies. A specialist (neurophysiologist) places electrodes on the patient’s arm and hand and sends electrical impulses (as short electrical shocks) up and down the arm. The speed and strength of transmission of the signals is measured and gives an indicator of nerve function. The testing is a little uncomfortable but is normally well tolerated by both adults and children. Unfortunately the test is of very little use before about 6 weeks from injury making assessment of patients with recent nerve injuries potentially very difficult. Patients therefore need to see experienced Hand specialists.
In theory an MRI scan should show nerves but at present the resolution is not sufficient for this to be useful below the collarbone. In time this should improve.
Tests for associated injuries: Nerve injuries can occur in association with fractures. X-rays will be helpful in assessing the fracture and this may guide the specialist as to the likely severity of any nerve injury.
What treatment is needed?
Many nerve injuries do not need treatment but recover very well. The more severe the injury the greater the need for treatment.
There are in essence three types of treatment: Removal of the cause of the nerve injury, treatment of the nerve and later reconstructive surgery.
Removal of the cause: This is not always necessary. If there has been a cut with a knife the cause will have been removed. But if there has been pressure on a nerve such as from a spike of bone following a fracture then removal of this cause may be sufficient to allow the nerve to recover. Sometimes the nerve can be “rerouted”, especially at the elbow.
Treatment of the nerve: The nerve must be protected from further injury. For example if it has been stretched following a fracture then preventing further damage such as more stretching will help the nerve to recover. This may include a sling to support the arm and possibly a splint or plaster for the arm or hand. Nerves typically need protection for up to 6 weeks from injury. If there has been a significant injury to the nerve it will need surgical exploration i.e. a surgeon needs to find and look at the nerve to see whether it needs repairing. If there has been a cut then the nerve ends can be sewn together and the nerve will recover in part by growing new nerve endings into the far end of the nerve. After a one month “rest period” the nerve regrows at about 1 mm a day (roughly an inch a month) so if the nerve is cut in the forearm or arm the recovery time is very long (many months). If there has been a broad area of nerve damage such as from a crush or stretching injury a section of nerve may be so damaged that it needs to be cut out. The nerve cannot then be sewn end to end so a bridge of nerve graft taken from elsewhere in the body (usually a less important nerve from the same arm or occasionally the leg) and sewn or glued in place to aid recovery. The repairs/grafts need to be protected in plaster/splint for 4-6 weeks.
Later reconstructive surgery: If nerve repair is not possible or fails to give a good recovery then reconstructive surgery can be considered to improve hand/arm function. Usually this is delayed for a good 6-12 months to see what recovery will occur in the nerve. Recovery of feeling (sensation) is difficult to achieve with reconstruction and is generally not undertaken except in children who can adapt better. Recovery of movement can be worthwhile. Normally this involves moving the tendon from one working muscle and rerouting it to the tendon of a muscle that is not working. The brain can then be trained to use the tendon transfer like the original muscle/tendon. This is complex specialist surgery with a long period of rehabilitation to ensure a good result but can give a dramatic recovery of function.
What happens in the next few weeks?
The care of the hand/arm in the post-injury/post-operative period is very important in helping to ensure a good result. Initially the aims are comfort and elevation.
Comfort and elevation: These are met by keeping the hand up (elevated) especially in the first few days and by use of a long acting local anaesthetic (Bupivicaine) if the hand/wrist/elbow has been operated upon. The local anaesthetic lasts at least 12 hours and sometimes 48 hours. Patients should start taking painkillers before the pain starts i.e. on return home and for at least 24 hours from there. This way most of our patients report little or any pain.
Dressings: Nerve injuries tend to need protection in a plaster or splint for 4-6 weeks, except for nerve injuries in the fingers which seem to do better with no protection beyond simple care. The treating Hand specialist will organise appropriate change of dressings/splints.
Movement: Most joint movement should be regained gained following treatment even surgery if the nerve alone has been injured. Some movement should be achieved early i.e in the first month or so even if a plaster or splint is used as it generally allows some movement. The rest of the movement occurs in the 6-12 weeks following injury i.e. following removal of plaster/splints and this time must be used productively to ensure a good result. The key is regular long gentle stretches both into straightening and into bending. Ideally these should be performed for 5 mins in each direction (feeling the stretch but without pain) once an hour. In practical terms most people manage to stretch 5-6 times a day. Elevation and icing the elbow also help reduce swelling and thus pain and improve movement.
Wound massage: The wound(s) should be massaged by the patient 3 times a day with a bland soft cream for 3 months once the wound is well healed (typically after 2 weeks, or after 4-6 weeks if protected in plaster). This is called desensitisation. It is essential following virtually all nerve injuries and many hand injuries including following surgery. Massage reduces the scar sensitivity which can be a nuisance. If this is marked hand therapy may be organised to help reduce the scar tenderness. Patients should avoid pressing heavily on the scar for 3 months following the operation as this will be quite painful. Examples of activities to avoid are using the palm to grip/twist a heavy or tight object or use the palm to help get out of a chair.
Return to daily activities: Many patients cannot return to anything but the lightest of work e.g. office work until they are out of plaster/splint but even then the extensive need for rehabilitation may prevent return to full-time work for many months following a severe nerve injury. Return to heavy manual work may take up to 6 weeks even for relatively simple injuries. The treating team should advise about this.
What are the results of treatment?
Following nerve bruising recovery should be full.
Following mild nerve stretching/crushing again recovery should be full although there may be some residual stiffness and sometimes aching especially in cold weather. This may improve for up to 3-4 years from injury.
Following more severe stretching/crushing recovery is rarely complete. In almost all cases there will be some numbness and stiffness and aching especially in cold weather. This may improve for up to 3-4 years from injury but rarely recovers fully.
If a nerve has been cut and repaired then full recovery can occur in patients under 10 but this is not guaranteed. Full recovery is very rare in adults. If the nerve is small the loss of function may be small although cut nerves have a tendency to give significant long-term pain in some cases. The severity of the long-term problems is dependent on a number of factors: which nerve is injured; the severity of the injury (crushes are worse than clean cuts); and the age of the patient (older patients do less well). Recovery in feeling and muscle power may improve for up to 2 years from injury. Cold intolerance i.e. stiffness and pain in the cold may improve for up to 3-4 years from injury.