What Happens When a Nerve is Cut?
When a nerve is completely severed, a series of biological events take place. Locally, the distal segment of the nerve (the part farthest from the injury) undergoes a process called Wallerian degeneration, where the nerve fibres break down, leaving behind empty nerve sheaths. Even a small part of the proximal segment (the part closest to the injury) is affected.
The proximal end of the nerve is primed to regenerate and attempt to reconnect with the distal segment, but this cannot happen on its own if the nerve is fully severed—surgery is required to restore the connection.
Without timely intervention, particularly in motor nerves, the motor endplates (the areas where the nerve connects to muscles) begin to deteriorate, leading to muscle wasting (atrophy). Additionally, at the spinal cord, the nerve cells undergo programmed cell death (apoptosis). The cortical area of the brain that controls the injured nerve gradually loses function due to the absence of signals from the nerve. In summary, a severed nerve impacts not only the local wound but also has negative effects on the muscles, spinal cord, and brain.
Key Message: Early Nerve Repair is Critical
If a nerve is cut, it’s important to repair it as early as possible. Delays in nerve repair can lead to irreversible damage to the muscles and the central nervous system.
Prerequisites for Successful Nerve Repair
To achieve the best possible outcomes in nerve repair, certain conditions must be met:
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Skeletal stability
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Healthy tissue bed (where the nerve lies)
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Healthy nerve ends to ensure proper healing
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No undue tension on the repaired nerve
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Adequate soft tissue coverage to protect the nerve
Nerve Repair Techniques
A nerve repair can be performed using microsutures, fibrin glue, or a combination of the two. There are two main techniques for nerve repair:
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Epineurial repair: This is a simpler technique where the alignment of the nerve ends is less precise, but it causes less trauma to the nerve.
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Group fascicular repair: In theory, this provides better alignment of the nerve fibres but comes with the risks of increased scarring and longer surgery time.
Key Message: Repair Techniques and Outcomes
Although group fascicular repair might seem more precise, research has shown that the functional outcomes are not necessarily better than those of epineurial repair.
What Affects the Outcomes of Nerve Repair?
Several factors influence the outcome of nerve repair:
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Patient factors:
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Age: Younger patients generally recover better.
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Injury factors:
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Level of injury: Nerves injured closer to the body (proximal injuries) often have poorer outcomes compared to distal injuries.
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Type of nerve: Pure sensory or motor nerves may respond differently than mixed nerves.
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Condition of the nerve ends: Healthy, undamaged nerve ends are essential for optimal repair.
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Surgical factors:
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Timing of the repair: Delays in repair can reduce the chances of full recovery.
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Length of the gap between the severed nerve ends: A larger gap makes the repair more complex.
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Surgeon’s skill: Experienced microsurgeons tend to achieve better outcomes.
Key Message: Prevention is Better than Cure
Despite the significant advances in microsurgical techniques and technology, the functional outcome of a repaired nerve will never be exactly the same as it was before the injury. Therefore, preventing nerve injuries remains the best approach.