There are many kinds of nerve injuries, ranging from mild nerve compression lesions to severe nerve trunk cuts. Injuries to the brachial plexus present a tough challenge, where nerve roots can be torn or even avulsed from the spinal cord. Making a prompt and accurate diagnosis of a nerve injury is crucial.
For the surgeon to make good decisions about nerve repair and reconstruction, they need to know about the anatomy and neurobiology of the peripheral nerve trunk and how injury changes neurons and Schwann cells. The technique of peripheral nerve restoration contains four critical processes (preparation of nerve ending, approximation, coaptation, and maintenance).
Most of the time, nerves that have been damaged are fixed with sutures, which can be placed in different parts of the tissue. When an injury causes a nerve deficit, treatment options include nerve grafts and nerve transfers. Optimal timing for nerve healing is crucial. Due to the neurobiological benefits, an early repair is ideal. Surgery, postoperative therapy using the patient's coping mechanisms, and result evaluation are all crucial steps in treating peripheral nerve injury. In the rehabilitation phase, effective treatment of pain, allodynia, and cold intolerance are addressed.
Axons, the long extensions from the neuron's cell body, are part of the peripheral nerve trunk's fragile structure. Still, many additional cell components and intraneural blood arteries also react to stress. Depending on what caused the trauma, the prognosis for a nerve injury could be different. Even though this article is mostly about how to treat transaction and laceration injuries of peripheral nerve trunks, it is important to know that nerve injuries can range from mild ones like carpal tunnel syndrome to severe ones like brachial plexus lesions, in which spinal nerve roots are torn out of the spine.
Approximately 3% of hand injuries in the clinic involve damage to the peripheral nerve trunks. Digital nerve injuries, which often occur (6.2% per 100,000 people per year), can be caused by even minor finger injuries and lead to hand dysfunction. The effects are much more widespread when a person hurts the median or ulnar nerve in their forearm. The damage makes it hard for the patient to work and severely limits their ability to do fun things in their free time.
Nerve injuries are expensive, but not just because of the medical care they require; lost productivity accounts for the bulk of the cost (sick leave). Most people who get nerve injuries are of working age, which is the main reason. Costs to society associated with forearm median nerve injuries could be more than 50,000 Euros. Even though a total nerve injury always causes permanent damage in adults, peripheral nerve injuries can be treated in a way that leads to a satisfactory clinical outcome.
The Technique of Nerve Repair
For nerve transections, primary nerve repair is the treatment of choice. If not immediately, then no later than two days after an injury. The wound must be neatly closed when the repair is made. A nerve trunk repair method typically consists of four distinct phases.
First, the nerve ends are cleaned so the tips are healthy and there is no dead tissue (called "preparation"). When working with nerve endings, microsurgical instruments are used for precision. You can use micro scissors or a surgical blade to get rid of the dead tissue at the nerve ends. If there is a laceration or a contusion, perhaps from a gunshot, it can be hard to tell how extensive the resection needs. After the nerve ends have been prepared, an approximation should be made with the gap and tension of the nerve segments in mind (approximation).
During approximation, it's okay to move nerve ends with dissection, but you should avoid doing a lot of dissection between the fasciae. Synaptic fusion between nerve fibers. Sometimes it's best to leave just a little space between the nerve endings. A blood clot and fibrin matrix, which may include macrophages, quickly fill the void left by the injury. Schwann cells migrate into this fibrin matrix from the proximal and distal nerve segments.
The growth of proximal nerve axons is coordinated with Schwann cell proliferation (23). Stitches (maintenance) are used to keep the nerve repair in place; 9-0 or 10-0 nylon (occasionally stronger suture materials are effective in some instances) is put into the epineurium. Therefore, the repair is kept in place via interrupted epineural sutures. Multiple interrupted sutures, sometimes with thicker suture material, are used in larger nerves such as the ulnar or median nerve. Avoiding malrotation of the nerve ends is essential while placing the sutures. Finding the intraneural blood veins that run in a longitudinal direction could be helpful here.
Group fascicular nerve repair is done when an individual fascicular group can be found for attachment, usually at a distal level with clear fascicles with specific targets.
One nerve where this approach can be used is the ulnar nerve at the wrist, which has both motor and sensory branches. Surgery on a nerve is always done with surgical loupes (magnification >= 3.5), while a microscope may be useful in some cases.
Tubes for Nerve Repair
Experimentally, the regeneration process has been studied using tubes to restore nerve trunks. Clinical research compared silicone tube repair to microsurgical nerve repair for nerve damage in the median and ulnar nerves. Five years after the repairs, there were no fundamental differences between the two techniques, except for improved cold tolerance following tube repair.
Repairing tubes is a straightforward process. With the focus on tissue reaction, novel biodegradable tube materials have been developed. Humans can choose from a selection of tubes designed for many purposes. Unfortunately, there are only a few controlled clinical trials to draw on. A simple procedure was recently published in which Schwann cells are extracted from the wounded nerve segments and transferred to a tube, suggesting that this may be a viable option for future tube filling.
More and more often in recent years, surgeons have been resorting to a technique known as a nerve transfer, in which a donor's nerve is severed, the nerve's fascicles are intraneural dissected, and the fascicles are then attached to a distal nerve segment that is injured but more functionally significant.
Another option is to sever and transfer a whole distal nerve branch, such as the distal anterior interosseous nerve, to a distal nerve that has been damaged (e.g., the thenar motor branch). So, using the nerve transfer method, damage to a proximal nerve can be turned into damage to a distal nerve, which has a shorter distance to travel to heal.
When there are no proximal nerve roots, which are where axons come from, the brachial plexus is usually reconstructed by moving nerve trunks, like moving intercostal nerves to the musculocutaneous nerve.
End-to-side Nerve Repair
End-to-side nerve repair is another method that has been brought back into use. A damaged nerve's distal ends are attached end-to-side to an "uninjured" donor nerve in this operation. This is done in cases with no axon origins at the proximal nerve ends. Likely, a damage signal to the axons in the donor's nerve is necessary for the outgrowth of axons in the end-to-side connected nerve segment.