Chapter 55 - Peripheral Nerve Injuries Flashcards
What does the peripheral nervous system (PNS) connect?
It connects the periphery of the body with the central nervous system (CNS).
How many pairs of spinal nerves originate from the spinal cord?
There are 42 to 43 pairs of spinal nerves.
What are the two types of roots that attach spinal nerves to the spinal cord?
Afferent dorsal roots and efferent ventral roots.
What structures do spinal nerves exit through?
Lateral vertebral foramina or intervertebral foramina.
What is formed when the ventral rami of neighboring spinal nerves connect?
Nerve plexuses such as the cervical, brachial, and lumbosacral plexus.
Which cervical nerves form the phrenic nerve?
Cervical nerves 5, 6, and 7.
What is the primary function of the phrenic nerve?
Motor innervation of the diaphragm and sensory supply to thoracic structures.
Where is the brachial plexus located?
Immediately cranial to the first rib, between the two parts of the scalenus muscle.
What spinal nerves contribute to the brachial plexus?
Spinal nerves C6 to T2.
Which spinal nerves form the lumbosacral plexus?
Spinal nerves L4 to S2.
What major nerves arise from the lumbosacral plexus?
The femoral, obturator, sciatic, tibial, and peroneal nerves.
What components make up a nerve?
Numerous nerve fibers and their supporting soft tissues.
What does the term “nerve fiber” refer to?
The axon and its enveloping Schwann cells, myelin sheath, and surrounding endoneurium.
What is the role of the endoneurium?
It is the connective tissue layer surrounding individual nerve fibers.
What structure envelopes a bundle of nerve fibers?
The perineurium.
What surrounds fascicles of nerve fibers?
The interfascicular epineurium.
How does the epineurium function in a nerve?
It encircles the entire nerve, providing structural support.
What is neurapraxia?
A temporary conduction block due to blunt trauma without axonal damage.
Define axonotmesis.
An injury where the axon is damaged but the connective tissue layers remain largely intact.
What is the expected recovery time for neurapraxia?
Complete recovery can take up to 3 months.
What happens during third-degree axonotmesis injuries?
Disruption of endoneurial sheaths leads to disorganized axonal regrowth.
What occurs in fourth-degree peripheral nerve injuries?
Complete disruption of internal nerve structure, with scar tissue blocking regenerating axons.
What characterizes a second-degree axonotmesis injury?
The connective tissue is intact, allowing for optimal axonal regrowth.
What is the prognosis for recovery from a third-degree injury?
Rarely more than 60% to 80% of normal function is regained.
What is “neuroma-in-continuity”?
A mass of nerve fibers formed due to axonal sprouts and scar tissue.
Which types of injuries are not expected to recover without surgery?
Fourth- and fifth-degree (neurotmesis) lesions.
What is the primary limitation of Seddon and Sunderland classification systems?
They require histological examination to determine the degree of injury.
What critical concept is emphasized by both classification systems?
Axonal degeneration occurs if the axon’s continuity is affected.
What is Wallerian degeneration?
The degeneration of the distal axonal stump after axonal injury.
Which type of injury does not result in Wallerian degeneration?
First-degree injuries (neurapraxia).
What is the clinical significance of the endoneurium in nerve injury?
It provides an optimal environment for axonal regrowth in less severe injuries.
How does connective tissue damage affect axonal regrowth?
Increased damage leads to disorganized regrowth and poor recovery outcomes.
What role do Schwann cells play in peripheral nerves?
They support the axons and form the myelin sheath.
What are the implications of a nerve injury on the target organ?
If axons degenerate, the target organ loses its nerve supply, affecting function.
How do you differentiate between the degrees of peripheral nerve injury?
Based on the extent of axonal and connective tissue damage.
Why is understanding nerve anatomy important in veterinary medicine?
It aids in diagnosing and treating peripheral nerve injuries.
What is a common cause of peripheral nerve injuries in horses?
Blunt trauma or compressive injuries.
How does the anatomy of the brachial plexus relate to clinical signs of injury?
Injury can lead to weakness or paralysis of the thoracic limb muscles.
What type of nerve fibers are primarily affected in axonotmesis?
The axonal fibers, while connective tissue layers remain intact.
Why might a horse show chronic signs of nerve injury?
Due to incomplete recovery or compensation for lost function from other nerves.
What are the potential causes of acute peripheral nerve injury?
Blunt or penetrating trauma, extreme temperatures, noxious substances, electricity, ionizing radiation, ischemia, or infection/inflammation.
What is the recommended treatment for trauma-induced peripheral nerve injury in humans?
Surgery is generally considered the best option.
Surgery is generally considered Why is complete recovery after surgical intervention for peripheral nerve injury rare?
The complexity of nerve regeneration and the extent of damage often impede full recovery.
What type of nerve damage can occur as a complication of surgical procedures in horses?
Temporary and permanent damage to peripheral nerves.
What are entrapment neuropathies?
Focal compression injuries of nerve segments due to mechanical irritation.
What anatomical structures predispose the deep branch of the lateral plantar nerve to entrapment in horses?
The third metatarsal bone, vestigial metatarsal bones, and plantar fascia.
What percentage of equine neoplasms are peripheral nerve tumors?
3% to 4%.
Which types of peripheral nerve tumors are most commonly diagnosed?
Schwannomas, neurofibromas, and malignant peripheral nerve sheath tumors.
What factors contribute to postanesthetic peripheral neuropathies?
Increasing bodyweight, prolonged anesthesia, inadequate padding, malpositioning.
What complications can arise from general anesthesia in adult horses?
Postanesthetic peripheral neuropathies (PAPN) and muscle damage.
What two processes occur for target organ reinnervation after peripheral nerve injury?
Collateral sprouting of intact axons and axonal regeneration.
How long does collateral sprouting take to occur?
Over 2 to 6 months.
What is the recovery expectation if more than 90% of the axons are damaged?
Axonal regeneration becomes the primary means of reinnervation.
What is the rate of axonal regrowth after injury?
Approximately 1 mm per day.
What happens to muscle tissue if reinnervation does not occur within 12 to 18 months?
Irreversible muscle atrophy and fibrosis develop.
How long can sensory receptors regain some function after injury?
Even years after the injury.
What is the role of Schwann cells in peripheral nerve injury recovery?
They must remain intact for effective axonal regeneration.
What are common clinical signs of complete paralysis of a main motor nerve?
Abnormal posture, gait abnormalities, and muscle atrophy.
How quickly can neurogenic atrophy occur after a nerve injury?
Within 2 to 4 weeks post-injury.
What is the typical muscle mass loss in the first 14 days following denervation?
Approximately 50% of muscle mass.
What type of sensory changes might accompany muscle paralysis?
Regional cutaneous hypalgesia or analgesia.
What is electromyography (EMG) used for in diagnosing peripheral nerve injuries?
To record the electrical activity of muscles.
What is the sequence of dysfunction in focal neuropathies?
Loss of proprioception, paresis, paralysis, loss of skin sensation, and loss of pain perception.
What are autonomous zones in relation to nerve injury assessment?
Specific skin areas supplied by a single nerve used to test nerve function.
Which nerve fibers are most susceptible to compression injury?
Larger myelinated fibers, followed by motor fibers and smaller sensory axons.
What does nerve conduction studies (NCS) measure?
The response of an innervated muscle to electrical stimulation of a peripheral nerve.
What imaging techniques can aid in the localization of peripheral nerve injuries?
Ultrasonography, computed tomography, and magnetic resonance imaging.
How can NCS differentiate between neurapraxia and axonal degeneration?
Neurapraxia maintains distal nerve excitability; axonal degeneration does not.
What is the primary function of the facial nerve (VII)?
It innervates the superficial muscles of the head and controls facial expressions.
What causes facial nerve paralysis when the injury is proximal to its branching?
Complete ipsilateral facial paresis or paralysis due to nerve damage.
What are common causes of proximal facial nerve injury?
Otitis media-interna, temporohyoid osteoarthropathy, and guttural pouch mycosis.
What are the clinical signs of facial nerve injury?
Ptosis, drooping ear and lower lip, small palpebral fissure, deviation of the nose and upper lip.
How can facial nerve injury occur during anesthesia?
Compression during anesthesia and recovery or from tight-fitting halters.
What surgical procedures may lead to iatrogenic facial nerve damage?
Oral and maxillofacial surgeries, especially buccotomies.
What is the prognosis for recovery after complete transection of the facial nerve?
Recovery is unlikely after complete transection.
What are potential complications of permanent facial nerve paralysis during exercise?
Collapse of the alar folds, leading to abnormal inspiratory noise and exercise intolerance.
What surgical techniques are available to address alar fold collapse?
Alar fold resections and reinforcement with mesh or autogenous cartilage.
What recent technique has been used to maintain alar cartilage position during exercise?
Removal of a crescent-shaped segment of skin over each nostril.
What is the primary cause of acute peripheral nerve injury in horses?
Acute peripheral nerve injury can result from trauma, extreme temperatures, noxious substances, electricity, ischemia, or infection/inflammation.
Is true brachial plexus avulsion common in horses?
No, true brachial plexus avulsion has not been reported in horses.
How can brachial plexus compression mimic radial nerve injury?
Compression between the scapula and ribs can cause dysfunction that emulates symptoms of radial nerve injury.
What are the clinical signs of proximal radial nerve injury?
Signs include inability to extend joints distal to the shoulder, resulting in a dropped elbow and the hoof resting on the ground.
What is the primary function of the musculocutaneous nerve?
It innervates muscles responsible for limb adduction and elbow flexion.
What are common causes of radial nerve dysfunction?
Trauma from open wounds, fractures, hyperextension of joints, and pressure during anesthesia.
What is the main clinical sign of complete femoral nerve paralysis?
Inability to extend and lock the stifle, resulting in a crouched stance.
What differentiates ulnar nerve injury from median nerve injury?
Ulnar nerve transection leads to more pronounced and longer-lasting clinical signs compared to median nerve transection.
What is a common surgical procedure for alleviating infraorbital nerve issues?
Bilateral infraorbital neurectomy involves removing a segment of the nerve.
What is a classic sign of suprascapular nerve injury?
Atrophy of the supraspinatus and infraspinatus muscles, leading to shoulder instability known as “sweeney.”
How does chronic radial nerve injury present unusually?
t may present as difficulty protracting the limb during jumping or intermittent lameness.
What is the main function of the sciatic nerve?
It innervates the main extensor muscles of the hip and flexors of the stifle joint.
What can cause compression of the tibial nerve?
Compression can occur from deep intramuscular injections or space-occupying lesions.
What are the consequences of prolonged recumbency in horses with peripheral nerve injury?
It can lead to secondary complications like support limb breakdown or laminitis.
What is the recovery time for the suprascapular nerve if damage is minor?
Recovery from neurapraxia can occur within days or weeks.
What type of therapy can help prevent muscle atrophy in denervated muscles?
Neuromuscular electrical stimulation can help delay atrophy.
What complications can arise from infraorbital nerve surgery?
Complications include self-inflicted nasal trauma and neuroma formation.
what is the typical success rate for bilateral infraorbital neurectomy?
The success rate is around 15.8%, which is considered poor.
What are the potential sequelae of muscle paralysis in horses?
Muscle contractures and further atrophy can occur if not properly managed.
What should be done if there are no signs of improvement in nerve recovery after 90 days?
Surgical treatment should be considered if no improvement is noted.
What clinical sign indicates partial femoral nerve dysfunction?
Subtle gait abnormalities may be observed.
What anatomical structures protect the radial nerve from injury?
The radial nerve is protected by its course along the humerus but is still prone to compression in the spiral groove.
What might be a potential future treatment for peripheral nerve injuries?
Regenerative medicine, such as the use of platelet-rich plasma or mesenchymal stem cells.
What is the implication of “dropped elbow” in radial nerve injury?
It indicates the inability to extend the elbow, leading to the hoof resting on the ground.
What anatomical route does the peroneal nerve take?
It moves laterally, passing between specific muscles and crossing the stifle.
How does the femoral nerve primarily impact movement?
It innervates the quadriceps, crucial for stifle extension.
What characterizes an acute peripheral nerve injury?
It can lead to muscle weakness, paralysis, and varying degrees of atrophy.
What does complete paralysis of the sciatic nerve result in?
Flexor muscle weakness and an inability to properly position the leg.
What is a distinguishing feature of infraorbital nerve neuropathy in horses?
It may lead to headshaking, particularly following sinus surgery.
What are the most common causes of musculocutaneous nerve injury?
Transection or trauma leading to reduced elbow flexion and muscle atrophy.
What clinical presentation is observed with peroneal nerve injury?
The affected horse may drag its foot and exhibit a stiff gait.
What is a critical aspect of managing horses with peripheral nerve injuries?
Stabilizing affected joints and reducing inflammation are essential treatment goals.
How does the clinical presentation differ between ulnar and median nerve injuries?
Ulnar nerve injuries typically present with more severe and prolonged clinical signs.
What mechanical factors can lead to femoral nerve injury?
Compression during prolonged dystocia or when limbs are pulled caudally during recumbency.
How do clinical signs of obturator nerve damage present?
They can range from mild stiffness to complete paraplegia.
What is the role of manual therapy in treating peripheral nerve injuries?
It may assist in managing neuromuscular disorders in chronic cases.
What characterizes the recovery process from proximal radial nerve paralysis?
Initial recovery involves reinnervation of proximal muscle groups before distal ones.
Why is external neurolysis commonly performed?
It prepares the nerve for suture repair or nerve grafting and can also be a standalone treatment.
What instruments are typically used for external neurolysis?
A No. 15 scalpel blade and Metzenbaum scissors; fine dissection scissors may also be necessary.
What is the “rule of three” in relation to nerve repair?
Repair should be performed within 3 days for sharp lacerations, 3 weeks for blunt transections, and after 3 months for closed lesions.
What is the primary goal of surgical nerve repair?
To restore continuity between severed axonal stumps.
What is external neurolysis?
A procedure to free an injured nerve from constriction, using circumferential dissection outside the epineurium.
What does internal neurolysis involve?
Splitting an injured nerve into individual fascicles and repairing the most damaged ones.
What is considered the gold standard for treating lacerated nerves?
Direct end-to-end suture repair.
What magnification tools are required during nerve surgery?
Loupe magnification (≥3.5×) or a microscope (12–15×).
When should end-to-end nerve repair ideally be performed?
Within 3 days of the injury.
What percentage of the fascicular architecture should remain intact for optimal recovery?
At least 75%.
What are the two types of suturing techniques in nerve repair?
Epineurial and perineurial sutures.
What is the advantage of perineurial sutures?
They allow alignment of individual fascicles.
What is fibrin glue used for in nerve repairs?
To provide additional strength to the anastomosis or as an alternative to sutures.
What are common causes for failure in nerve repairs?
Inadequate tension, insufficient stump resection, and postoperative distraction.
What is the purpose of nerve grafting?
To provide components necessary for successful nerve regeneration.
What are the limitations of using autologous grafts?
Challenges in identifying suitable donor nerves, increased operative time, and potential morbidity.
Which nerve is suggested as a potential autograft source in horses?
The caudal cutaneous femoral nerve.
What must be done to the joints crossed by a graft prior to surgery?
They should be positioned in extension or flexion to minimize tension on the repair site.
What is essential for the quick revascularization of an autograft?
A healthy, well-vascularized “graft bed.”
How much longer than the interstump gap should the graft be?
Preferably 10% to 20% longer.
What is the function of nerve conduits?
To guide axonal sprouts and prevent fibrous tissue infiltration.
What is a limitation of nerve conduits in current practice?
Their successful use is limited to nerve gaps of less than 3 cm.
What is direct muscular neurotization?
Implanting a healthy nerve directly into affected muscle tissue.
What is a nerve-muscle pedicle transfer?
Transferring an expendable nerve with parts of its muscle to provide an intact motor end plate.
What does the success of nerve conduits depend on?
Their ability to promote axonal growth across nerve gaps.
What postoperative care is critical after nerve grafting?
Immobilization of the surgery site for at least 4 weeks.
How does external neurolysis contribute to nerve surgery?
It facilitates repair by relieving constriction before suturing or grafting.
What types of injuries does internal neurolysis address?
Partial nerve damage where only some fascicles are injured.
What are the two mechanisms of injury typical in peripheral nerve injuries?
Neurapraxia and axonotmesis.
What is the significance of matching fascicular structures during repair?
It helps ensure proper nerve function post-surgery.
What is the ideal method of apposing nerve ends during repair?
By suturing them in a way that maintains loose contact without undue tension.
What role does histopathology play in nerve surgery?
It helps assess tissue viability at the nerve stumps.
What challenges might arise during the harvesting of autografts?
Finding expendable nerves that match the required caliber and length.
Why is immediate intervention critical for sharp lacerations?
To preserve the fascicular anatomy and ensure better recovery chances.
What outcomes can be expected from nerve grafting?
Functional recovery depends on the quality of the graft and the repair technique used.
What factors influence the choice of surgical technique in nerve repair?
The type of injury, timing of intervention, and specific characteristics of the nerve involved.
what are the differential diagnosis of femoral nerve paralysis?
luxation of patella
rupture of the quadriceps femoris muscle
tibial crest avulsion
quadriceps femoris myopathy
the clinical signs of complete femoral nerve paralysis are
when bilaterally affected horses may not be able to rise from recumbency. When they stand, they will do so in a crouched position: stifle, hock, and fetlocks are flexed and only the toes touch the ground
the obturator nerve is from which L?
L4-L5
The obturator nerves courses along the surface of
ilial shaft before the pelvis through the cranial part of the obturator foramen
the obturator nerve innervates which muscles?
Adductor muscles
in cases of neuropraxia the nerve of suprascapular reinnervation should return when?
Assuming an axonal regrowth rate of 1 mm/day and a distance of 6.5 cm from the cranial border of the scapula (likely injury site) to the infraspinatus muscle, function should return around 70 days posttrauma.If no signs of improvement, starting with bulking of the ventral supraspinatus muscle, are noticeable after 90 days, surgical treatment should be considered
the femoral nerve (L4-L6)runs with which artery?
external iliac artery
btw psoas minor and ilipsoas muscles
locaton of peroneal nerve
passes between the biceps femoris and the lateral head of the gastrocnemius muscle. It crosses the stifle subcutaneously, just caudal to the lateral collateral ligament. The nerve then splits into the superficial and deep peroneal nerves that innervate the flexors of the hock and extensors of the digit
location of tibial nerve
The tibial nerve runs distally between the heads of the gastrocnemius muscle and crosses the stifle on the surface of the popliteus muscle.
Mention the origin and insertion of sciatic nerve
The sciatic nerve (L5–S2), or nervus ischiadicus, leaves the pelvis through the greater sciatic foramen, an opening in the sacrosciatic ligament. It continues on the lateral surface of the ligament until it reaches the caudal aspect of the coxofemoral joint, where it turns distally and splits into the tibial and peroneal nerves
which nerve promotes motor innervation to the flexors of the carpus and digit
The median (C8–T2) and ulnar nerve (T1–T2)
Median and ulnar nerve run with which artery?
brachial artery
which conditions can result in radial nerve paralysis?
Open wounds at the shoulder or brachium, fractures of the first rib, the humerus, olecranon, or C7 and T1, can result in radial nerve dysfunction. Hyperextension of shoulder and elbow, with or without simultaneous limb abduction, tightens and damages the radial nerve
Where does the radial nerve pass?
the radial nerve (C8–T1 ± C7) emerges from the caudal part of the brachial plexus. It follows the brachial artery, passes between the long and medial heads of the triceps and continues in the spiral groove to the craniolateral aspect of the humerus.
The infraorbital nerve, a purely sensory branch of the
trigeminal nerve (V), courses through the infraorbital canal before entering the face via the infraorbital foramen. It innervates the maxillary cheek teeth, the skin of the nose, skin and mucosa of the muzzle, and the upper lip.1
describe neurectomy of infraorbital nerve
Prior to surgery, it is considered good practice to complete an infraorbital nerve block at the proposed surgery site, although no consistent correlation between response to the nerve block and surgical success has been established.34,35 Bilateral infraorbital neurectomy is performed at the level of the infraorbital foramen, where a 2-cm segment of the nerve is removed.
Figure 55-3. End-to-end suture repair. (A) Preplacement of stay-sutures at 9-o’clock and 3-o’clock on a transected nerve (top) and a “neuroma in continuity” (bottom). (B) The nerve ends are trimmed back to a level where healthy epineurium is present and about 75% of the fascicular architecture appears intact. (C) The uppermost epineurium is sutured in a simple continuous or interrupted pattern, bringing the nerve ends into loose contact. The stay-sutures are now used to rotate the nerve to facilitate circumferential suturing.
Figure 55-2. Autonomous zones of innervation for major peripheral nerves of the equine limbs. a, Ulnar nerve; b, musculocutaneous nerve; c, median nerve; d, femoral nerve; e, peroneal nerve; f, tibial nerve.
Musculocutaneous nerve arises from wherE?
Arising from the cranial part of the brachial plexus, the musculocutaneous nerve receives fibers from spinal nerves C7 and C8
musculocutaneous nerve courses with which artery?
It courses to the axillary artery, where it passes below the vessel and connects with the median nerve, this large connecting branch and the two nerves form a loop (ansa axillaris) in which the vessel is encircled
musculocutaneous nerve is responsible for which movement?
ADDUCTION of the limb
The musculocutaneous nerve innervates the coracobrachial muscle, responsible for adduction of the limb and extension of the shoulder joint, as well as the biceps and brachialis muscle, both flexors of the elbow joint.
