Nerve Injury

Candidate:

There are four mechanisms of nerve injury which are stretching, compression or crushing, laceration, and tumor. Stretching occurs when the nerve is elongated beyond its capacity, leading to disruption of the neural fibres. Compression or crushing occurs when the nerve is compressed or crushed, resulting in ischemia and demyelination. Laceration is the physical tearing of the nerve, and tumor growth in or around the nerve can compress and damage it.

Candidate:

Retrograde degeneration is a process that occurs in the proximal part of a nerve shortly after axonal transection. Within the zone of injury, the proximal axon undergoes traumatic degeneration extending proximally 1 to 2 nodes from the injury site to the next node of Ranvier. The cell body swells and undergoes chromatolysis. This is when the Nissl granules, which are the basophilic neurotransmitter synthetic machinery, disperse, and the cell body becomes relatively eosinophilic. The cell nucleus is displaced peripherally, reflecting a change in metabolic priority from production of neurotransmitters to production of structural materials needed for axon repair and growth, such as messenger RNA, lipids, actin, tubulin, and growth-associated proteins.

Candidate:

Wallerian degeneration is a process that occurs in the distal part of a nerve after axonal transection. Breakdown of the axon distal to the site of injury starts 48-96 hours after transection. The process starts when the macrophages ingest the distal neural tube and clear the myelin debris. This causes the tube to collapse after not receiving nutrients from the proximal end. The remaining de-differentiated schwann cells proliferate on the remaining endoneurial tubes of the extracellular matrix creating columns of cells called bands of Bungner. These then produce neurotrophic factors to guide the direction of growth. The proximal axon changes from a neuroconductive to a neuroregenerative phenotype with an increase in cellular activity. The axon tries to grow towards the distal tube via the filopodia, which are finger-like projections trying to find their growth cones in the process called contact guidance.

Candidate:

Candidate: There are three classifications of nerve injury, which are Seddon, Sunderland, and Birch and Bonney. Seddon’s classification is anatomically based and divides nerve injuries into three categories based on the presence of demyelination, the extent of damage to the axon, and the extent of damage to the connective tissues of the nerve. Neuropraxia, which is the least severe, occurs when the nerve and axon are in continuity, and there is no damage to the axons or the connective tissues. Axonotmesis, the intermediate type, is characterized by axonal damage, the continuity of the nerve’s connecting tissues, and an intact epineurium. Neurotmesis, the most severe type, occurs when the connective tissue and axons are fully transected, with disruption of the epineurium.Sunderland’s classification expands Seddon’s classification to distinguish the extent of damage to the connective tissue, dividing injuries into five grades. Birch and Bonney’s classification is clinically based and divides injuries into either conduction block (neuropraxia) or degenerative block (cutting of the nerve). In the case of a conduction block, the nerve coverings are intact, but the myelin sheath is damaged, and this may need neuroly

Candidate:

Candidate: The triple assessment approach for the management of nerve injuries is a three-pronged process that helps to identify the presence and location of a nerve injury, as well as any evidence of recovery. It involves taking a patient’s history, conducting a physical examination, and performing neurophysiology tests.

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Several patient factors can potentially impact recovery, such as age, immunocompromise, poor vascularity, diabetes, peripheral vascular disease, and smoking.

Candidate:

Several injury factors can affect the prognosis of a nerve injury. These include the time period from injury to presentation, the location of the injury (proximal nerve injuries have a worse prognosis compared to distal ones), and the type of nerve injured (those that supply both motor and sensory have a worse prognosis than motor nerves ). A clean-cut injury has a better outcome and needs to be repaired quickly, whilst blunt or crush injuries have a worse prognosis, and you need to wait for the extent of the injury to declare itself. Injuries to nerves that supply multiple muscles tend to have a worse prognosis, as do those with associated vascular injuries.

Candidate:

During a physical examination, the location of the injury should be examined, and evidence of recovery should be picked up through an advancing Tinel sign. Both motor and sensory modalities should be examined.

Candidate:

During neurophysiology tests, parameters such as latency, amplitude, and conduction velocity should be measured using nerve conduction studies (NCS). NCS detects the activity in a sensory or motor nerve by stimulating, recording, ground, and reference electrodes. Sensory nerves are typically stimulated distally and generate a sensory nerve action potential (SNAP), while motor nerves are stimulated proximally and generate a compound muscle action potential (CMAP). When there is axonal loss, there is a reduction in CMAP amplitude as function fewer motor axons exist.

Candidate:

The ladder of reconstruction is a step-by-step approach to the surgical management of nerve injuries. Two reasons for nerve exploration surgery include ongoing compression demonstrated by pain or a scan showing compression from a hematoma, and no evidence of recovery, which is demonstrated by no advancing Tinel sign (clinically) and no polyphasic units (neurophysiologically).

Candidate:

The surgical options for nerve reconstruction include neurolysis, primary/direct repair, and nerve grafting. Neurolysis involves releasing scar tissue from around a nerve in continuity. Primary/direct repair involves repairing the epineurium and is best for median, ulnar, and sciatic nerves. Nerve grafting is required when a gap can’t be bridged, such as in defects greater than 2.5 cm. Donor sites include the medial & lateral cutaneous nerves of the forearm, sural and saphenous nerves.

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Nerve Injury

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