In clinical practice, injuries to the nerves around the body are common and often lead to functional disability. Due to a lack of background knowledge on pathophysiology, nerve repair outcomes were hit or miss in the past. Since Sunderland first discussed microsurgery in 1945, nerve repairs have been much more likely to work. In the last few decades, advances in microsurgery, knowledge of nerve repair, and ongoing research in molecular biology have made peripheral nerve surgery more successful.
Nerve Damage Classification
Neuropraxia, axonotmesis, and neurotmesis are the three main types of nerve damage. Temporary loss of function without disruption of nerve continuity characterizes neurapraxia. Axonotmesis is when a nerve axon and the myelin around it are destroyed, but the perineurium and epineurium stay the same. As a result of nerve damage, neurotmesis results in total incapacity.
Neurapraxia is analogous to a first-degree injury. Axonal disruption, or axonotmesis, occurs in second and third-degree neuropathies. Disruption of the axon, endoneurium and perineurium characterize a fourth-degree injury. In the fifth degree of neurotmesis, the nerve completely disintegrates. Surgeons typically utilize the Sunderland grading system to make decisions about nerve restoration.
Management of Nerve Injuries
When a nerve injury is suspected, deciding when and how to operate presents a challenge; in cases of penetrating trauma resulting in neurological disability, immediate examination and restoration of the nerve are required. But if the mechanism is caused by blunt trauma, the patient must be tested more than once to see if they can improve. In such a case, the repair can be put off for a while. Electrophysiological investigations are beneficial when determining when to perform surgery on these patients.
1. Surgical Repair
In peripheral nerve surgery, the main goal is to connect nerve ends without tension using as few nonabsorbable monofilament sutures as possible. Suture line tension is related to enhanced fibrotic reactivity and impaired regeneration. Correctly matching the motor and sensory components of nerve healing is essential for optimal results.
Using immunohistochemical and electrophysiological techniques, a motor-sensory distinction can be performed intraoperatively. Direct repair, nerve grafts, and nerve conduits are only some of the options available to bridge a gap caused by a severed nerve. When these alternatives are impossible, the superior functional outcome can also be achieved through neurotization and nerve transfers.
2. Direct Nerve Repair
If an 8-0 the suture can hold both ends of a damaged nerve without squeezing; a direct repair is suggested. The methods of epineurial, perineural, and fascicular group repair are all described as ways to heal nerves directly. The most common type of nerve repair is called epineural repair. It has several benefits, including a shorter operating time, more technical ease, and a decreased risk of harm to intraneural tissues and fascicles.
Nerve grafts and nerves with less than 5 fascicles indicate when the perineural repair would be appropriate. When a nerve has sprouted off into multiple branches, and individual fascicles can be traced back to the main trunk, this is an ideal location for a group fascicular repair. In theory, motor and sensory fascicles can be paired to prevent motor-sensory cross-innervations.
3. Repair by Nerve Grafts
Nerve grafts are advised to bridge the separated nerve ends when the gap between them is greater than 2 centimeters, and direct nerve healing is risky. In the field of nerve grafting, the three most common techniques are cable grafts, trunk grafts, and vascularized nerve grafts. In the case of cable grafts, several smaller grafts are taken from nerves that aren't crucial to the patient's health.
The sural nerve, the superficial radial sensory nerve, the anterior branch of the median antebrachial cutaneous nerve, and the lateral femoral cutaneous nerve are often used. The graft length should be 10–20% more than the nerve gap to account for shrinkage owing to fibrosis. Fibrin glue or micro neural sutures are utilized to co-apt the numerous wires to the nerve's diameter. Axonal disruption along the distal nerve branches is lessened when nerve grafts are reversed.
It is possible to repair a nerve that is more than likely to work by using a nerve transplant from a healthy nerve to a nonfunctional nerve. Still, they are linked to bad results because they are thick and can grow blood vessels from the bed. Vascularized nerve grafts use the whole nerve, including the vascular pedicle, to restore nerve functions.
4. Nerve Transfers
Restoring function to a nerve that has been damaged at its distal end requires a donor nerve from a healthy area of the body. Therefore, the surgery uses a healthy, functioning nerve to re-innervate the organ. In cases of root avulsion or roots not proven repairable, the procedure has been utilized widely in brachial plexus injuries to reinnervate the distal muscles.
5. End-to-side Neurorraphy
In an end-to-side neurorraphy procedure, nerve regeneration occurs through collateral sprouting. At their most distant end, the regrown axons leave the node of Ranvier through the epineurium of the donor's nerve. In 1993, Viterbo performed end-to-side neurorraphy on a cross-facial nerve graft to treat facial palsy. 11 patients with brachial plexus injuries treated with end-to-side neurorraphy had good outcomes, according to the study by Amr et al. The method has shown positive outcomes for other authors as well. This is a novel approach, and it may one day be used to treat peripheral nerve damage.