What is nerve entrapment and what symptoms does it cause?
Nerves are the structures in the body which transmit electrical impulses to muscles and receive electrical signals from receptors recording sensation (from pressure, vibration and pain). These nerves pass through the body to the end target areas and in the process of passing through the body can be compressed in various sites. When a nerve is compressed, it can be injured. Compression reduces the blood supply to the nerve. If not severely damaged, on release, the nerve can recover and as it recovers it goes into a hyper sensory state. You may know of the sensation of having sat in the wrong position on a nerve in the leg, and your leg going numb. When you released the nerve, your leg suddenly goes hyper sensitive or prickly.
With direct trauma the nerve can be damaged. This trauma can be from a blunt injury or from penetrating injuries such as a laceration that actually cuts the nerve in half. The effects of a nerve injury gauge in severity from slightly reduced sensory loss to complete numbness and loss of movement.
What nerves can be injured?
Any nerve in the body can be injured, from the nerves in the spinal cord (as occurs in a spinal cord injury such as a diving accident or a motor vehicle accident) to the nerves to the tips of the fingers and toes. The most common nerve injured is the median nerve in the carpal tunnel, which involves compression of the median nerve in the wrist. This leads to numbness affecting the index, long and ring fingers and to some degree the thumb. The ulnar nerve can also be trapped in the “Cubital tunnel” at the inner border of the elbow. This is also known as the “funny bone” when the nerve is injured to direct pressure and leads to numbness involving the little finger and half of the ring finger. The radial nerve runs against the bone of the upper arm and there is a condition known as Saturday Night Palsy where direct pressure is applied to the radial nerve when someone who has fallen asleep in a chair has direct pressure exerted to the arm from the back of the chair. Direct pressure on the radial nerve can lead to loss of extension of the wrist, hand and fingers, with numbness on the back of the hand.
There are other nerves around the knee, known as the common peroneal nerve, which can be compressed leading to numbness on the side of the foot with difficulty lifting the foot and the toes up. In most cases, the nerves recover if the injury is as a result of a single episode. The time for the nerve to recover depends upon the type of trauma and how severe the nerve injury is.
With a laceration the nerve may require surgical repair. If it comes from compression of a tight structure in the body such as with the cubital tunnel or carpal tunnel syndrome, then the nerve will need to be released.This involves surgery to expose the nerve and de-roof it to allow it to decompress the area of compression.
This is a straight forward procedure, often performed as day surgery, but one must remember that the more severe the injury, the longer the nerve takes to recover. A nerve that has been injured will effectively take a month to start recovering and then grow back a millimetre a day. Therefore, an injury at the elbow 300 millimetres from the wrist may take 300 days to get full recovery if severely damaged. Often, as the nerve fully recovers near the final few days or weeks, it becomes hypersensitive. Use of the area that the nerve innervates is recommended to try to stimulate the nerve to recover quicker.
Are there any factors that stop the nerve recovering?
Factors that affect the recovery of the nerve are:
- Age with less recovery ability
- Recurrent traumatic episodes
- Smoking, which has a significant factor to play as it inflames the nerves, can make the pain worse and takes longer for nerves to recover.
What is a subluxing ulnar nerve and how does that have a part to play in an ulnar nerve entrapment (cubital tunnel)?
The ulnar nerve can be trapped at the inner part of the elbow and this is known as cubital tunnel, where the nerve is compressed in a tight sheath. Some people, rather than have the tight sheath, have a nerve that subluxes from behind the bump on the medial (inner) edge of the elbow to in front of that bump (medial epicondyle). This is called a subluxing ulnar nerve. It is present in up to 20% of people but in only a few does it cause any issues. On occasions it may start after trauma as subluxing nerves become inflamed, other times recurrent episodes of subluxation (rubbing) over that medial bump irritates the nerve to cause it to become unresponsive. In these cases, the treatment is to release the nerve and move the nerve in front of the medial epicondyle. This is known as transposition and is often recommended for any ulnar nerve injury so that once the nerve is decompressed it does not start subluxing over the medial bump.
The process involves mobilising the soft tissues in front of the bump and then placing the nerve in that area and securing it with a single suture to stop it from subluxing backwards. In this scenario, it is often best to keep the arm flexed for 4 weeks to allow the nerve to scar up and stay in the correct position, rather than sublux back into the unstable position.
Is a nerve injury more important to undergo treatment than other orthopaedic injuries?
In general, nerves are important structures and the longer that they have been damaged the less likely they are to recover. As such, a nerve that is injured is probably best treated more quickly than other orthopaedic injuries and as such we would recommend treatment for most nerve injuries.