Here we look at the grades of Erb’s palsy and how brachial plexus injuries are classified, depending on which nerve roots are damaged and how severe the injury is.
These classifications enable professionals to give a likely prognosis for recovery from Erb’s palsy, and will enable your child’s paediatrician to write a care plan and establish any necessary treatment.
How is brachial plexus injury classified?
To help diagnose and treat brachial plexus injuries, various classifications exist. These classifications identify the nerves injured in the brachial plexus, the symptoms of the injury and the likelihood of recovery.
In the UK the primary classification system is the Narakas classification system (developed by A.O. Narakas in 1986).
The Narakas classification system
Group 1: Group 1 represents injury to the C5 and C6 nerve roots resulting in:
- Difficulty lifting the affected arm above the head (restricted shoulder abduction)
- Difficulty rotating the shoulder away from the body (restricted external rotation)
- Difficulty bending the elbow (restricted elbow flexion)
- Difficulty twisting the forearm so that the palm of the hand is facing forward (restricted forearm supination).
As a result, a person with brachial plexus injury may present with the affected arm hanging down by their side, straightened and rotated towards the body, and with the palm of the hand facing backwards in pronation.
90% of people with a group 1 injury will return to having normal function.
Group 2: Group 2 represents injury to the C5, C6 and C7 nerve roots. In addition to the difficulties experienced above, people in group 2 also have difficulty in bending the wrist back (wrist extension).
75% of people with a group 2 injury will return to having normal function.
Group 3: Group 3 represents injury to the C5, C6, C7 and C8 nerve roots. People in this group experience complete arm paralysis.
Less than 50% recover some satisfactory function.
Group 4: Group 4 represents injury to the C5, C6, C7, C8 and T1 nerve roots. In addition to arm paralysis, people in group 4 experience Horner’s syndrome. Horner’s syndrome describes damage to a bundle of nerves that are responsible for controlling some of the muscles of the eye. As a result, people with Horner’s syndrome have a constricted pupil and droopy eyelid.
Surgery is required to repair the nerves, but few children will gain full functional recovery.
How is the severity of brachial plexus injury defined?
A three-tiered classification system to describe the severity of nerve damage was developed by Sir Herbert Seddon in 1942. It’s called the Seddon classification and it helps professionals to offer a likely prognosis.
The Seddon classification system
Neurapraxia: This is the mildest type of peripheral nerve damage when damage to the insulation around the nerve’s axon is damaged.
There is no damage to the axon itself, which is the part of the nerve fibre responsible for conducting electrical impulses to muscles.
This localised damage to the outer nerve fibres (the myelin sheath) causes an interruption in the conduction of the impulse down the axon resulting in short-term paralysis or muscle weakness.
Spontaneous recovery (remyelination) usually takes place within weeks to months.
Axonotmesis: This is more severe damage to the nerve fibres, where both the myelin sheath and the axon of the nerve are damaged but the Schwann cells and the connective tissue framework surrounding the axon (the endoneurium, perineurium and epineurium) remain intact.
Axonotmesis leads to Wallerian degeneration shortly after the injury. This is when the part of the axon between the injury and the neuron’s cell body starts to degenerate (including the myelin sheath), leaving only the outermost layer of the nerve fibre hollowed out.
When the degeneration is complete, regeneration of the axon can start from the lesion, typically within four days of the injury. New shoots grow at a pace of one millimetre per day.
The prognosis for axonotmesis is fair, but it may take months for the nerve to regrow and connect to the muscle. The process may be complicated by scar tissue forming at the site of the injury (known as neuroma). The scar tissue could interrupt the conduction of electrical impulses between the muscles and the nerve cell.
Neurotmesis: This is the most severe form of a nerve injury.
Here the axon, myelin sheath and connective-tissue framework are damaged. Electrical impulses cannot be sent to the muscles and the limb is paralysed. Wallerian degeneration will start following the injury (similar to axonotmesis) and this is when the part of the axon between the injury and the neuron’s cell body starts to degenerate. Unlike axonotmesis, the prognosis for regrowth is very poor.
Surgery may be able to repair the nerve so that some movement and feeling in the arm can be restored.
Professionals may also refer to Sunderland’s system (Sir Sydney Sunderland), which further divides Seddon’s neurotmesis classification into three subcategories.
- Neurotmesis (third degree) – the outer connective tissue framework surrounding the nerve fibres are intact/undamaged (the epineurium and perineurium), but the endoneurium is injured. This is the connective tissue that surrounds each individual myelinated axon. Spontaneous recovery is possible, but surgery may be required.
- Neurotmesis (fourth degree) – the perineurium and the endoneurium are injured and only the outer connective tissues (epineurium) remains intact. Only surgery can repair the nerve.
- Neurotmesis (fifth degree) – this is characterised by complete severance (transection) of the nerve trunk and recovery is not possible without surgery.
See also Causes of Erb’s palsy (Understanding brachial plexus injury)
See also Symptoms of Erb’s palsy
See also Treatment of Erb’s palsy