Etiology and pathophysiology of injuries
Peripheral nerve trunks are formed by the joining of the anterior (motor) and posterior (sensory) roots. Nerve injuries can be open or closed. The main causes include wounds, bone fractures, dislocations, as well as compression of the trunk by a hematoma, callus, scars, or metal fragments.
Morphologically, two main types of injury are distinguished:
- Complete anatomical transection: rupture of axons and all sheaths (epineurium, perineurium, endoneurium) occurs. This leads to complete and persistent loss of function.
- Contusion (bruise): causes temporary conduction block. Spontaneous functional recovery is possible within 2–3 weeks.
A connective tissue scar always forms in the area of injury. If the nerve ends are widely separated or there is an obstacle in the path of regeneration (rough scars, bone fragments), a neuroma forms. It can also appear after surgical suturing if hemorrhage occurs into the trunk.
Clinical presentation
Symptomatology consists of motor, sensory, and vasomotor-secretory-trophic disorders.
- Motor disorders are characterized as peripheral paralysis or paresis. They manifest as atonia, muscle atrophy, and areflexia. Topical diagnostics are based on the level of the lesion: in proximal injuries, the function of all muscles below the injury zone is lost, whereas in distal injuries, muscles receiving branches above the injury site continue to function.
- Sensory disorders are divided into deficit symptoms (anesthesia in complete transection, hypesthesia) and irritation symptoms (hyperesthesia, pain). Pain specificity depends on the nerve: injury to the radial nerve and cutaneous nerves of the forearm and thigh results only in paresthesias, without distinct pain.
Palpatory diagnostics
Conventional palpation of the scar and the nerve projection provides crucial information about the degree of injury and the course of regeneration:
- Sign of complete conduction block: pressure on the scar causes pain projected distally, but the nerve below the injury site is painless.
- Sign of a proximal stump neuroma: very intense pain arises not only upon pressure, but also upon light percussion over the scar.
- Sign of regeneration: if after a prolonged painless period, palpation of the nerve distal to the injury site becomes painful, this is interpreted as the outgrowth of sensory fibers.
Associated complications: tetanus
Since nerve injuries are frequently associated with open and contaminated wounds, there is a high risk of developing tetanus. The pathogen toxins cause massive convulsive syndrome lasting from seconds to minutes. This can lead to muscle tears, vertebral fractures, dislocations, and respiratory failure (up to aspiration).
Emergency prophylaxis for extensively contaminated wounds:
- In unimmunized individuals: active (toxoid) + passive immunization (3,000 IU of antitoxin). The antitoxin is administered strictly in three doses using the A.M. Besredka method to prevent anaphylactic shock.
- Caution: anti-tetanus serum is not administered to children.
Treatment of developed tetanus includes radical local surgical treatment of the wound (up to amputation), administration of massive doses of anti-tetanus serum (up to 200,000 IU per day), and aggressive anticonvulsant therapy (neuroleptics, barbiturates, neuroplegic cocktails with chlorpromazine and promedol, and in cases of frequent seizures, muscle relaxants with mechanical ventilation).
Briefly: answers to topical questions
How is the Tinel sign performed in the diagnosis of nerve injuries?
The Tinel sign is elicited by percussion (tapping) over the projection of the injured nerve.
- Technique — percussion with a neurological hammer in the injury zone over the course of the nerve (e.g., over the wrist for the median nerve).
- Positive result — the appearance of pain, tingling sensations, or painful paresthesias (an "electric shock" sensation) in the area of nerve innervation, distal to the percussion site.
- Goal — to identify reactive symptoms from the affected nerve.
What types of surgical interventions are used for complete peripheral nerve transection?
In complete anatomical transection of a peripheral nerve, various types of sutures, grafting, and neurolysis are used.
- Primary suture — the optimal method for fresh injuries (no older than 12 hours), an epineurial suture is placed without tension.
- Secondary suture — performed during delayed repair.
- Microsurgical suture — a minimally invasive intrafascicular technique for suturing nerve bundles under optical magnification.
- Autografting — nerve transplantation for significant diastasis or trunk defects greater than 2 cm (the most successful donor is the sural nerve).
- Neurolysis — freeing the nerve from scar tissue, performed in old transections before assessing diastasis.
What vasomotor-secretory-trophic disorders occur in peripheral nerve injuries?
Peripheral nerve injuries result in a complex of vascular, secretory, and trophic disorders.
- Vasomotor disorders — include cyanosis, changes in skin temperature, and less commonly hyperemia (during nerve irritation).
- Secretory disorders — manifest as anhidrosis or hyperhidrosis.
- Trophic disorders — include muscle and skin atrophy, hyperkeratosis, hypertrichosis, bone osteoporosis, and trophic ulcer formation. Nail changes are also observed: they lose their luster, become dry, ridged, and brittle.
These disorders are particularly pronounced in combined injuries of the nerve and blood vessels, and are frequently encountered in lesions of the median nerve and tibial nerve.
What is the protocol for administering anti-tetanus serum according to Besredka's method?
Besredka's method consists of fractionated administration of anti-tetanus serum in small portions.
- Essence of the method — the drug is administered strictly in three doses.
- Goal — desensitization of the body and prevention of anaphylactic shock when administering heterologous (equine) serum.
- Preliminary stage — an allergic skin test is mandatory before administration to detect patient hypersensitivity to the drug.
Exact dosages and intervals between doses within this method are not detailed in the sources.
Class and exam questions
How fast do nerve fibers regenerate after injury?
Axonal regeneration is a slow process. The terminal segments of the axis cylinders grow into the peripheral segment at a rate of approximately 1 mm per day.
What does severe pain upon light percussion of a scar indicate?
This is a characteristic sign of the formation of a proximal stump neuroma—pathological proliferation of nerve tissue due to an insurmountable barrier for axons.
Can tetanus antitoxin be administered to children with open trauma?
No. According to emergency prophylaxis guidelines, the administration of anti-tetanus serum to children is strictly contraindicated.
What else to study on this topic
- Topical diagnostics of individual nerve injuries (radial, ulnar, median)
- Surgical technique for peripheral nerve repair
- Vasomotor-secretory-trophic disorders in denervation
- Schedules for routine tetanus toxoid vaccination
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