Peroneal (fibular) nerve entrapment

Question 1

How common is peroneal (fibular) nerve entrapment?

Answer 1

• Most common mononeuropathy encountered in the lower limb
• Third most common focal neuropathy encountered overall, after median and ulnar neuropathies

Question 2

Where does peroneal (fibular) nerve entrapment occur?

Answer 2

The most frequent site of injury to the common fibular (peroneal) nerve is just below the knee as the nerve wraps around the lateral aspect of the fibula, immediately before dividing into its deep and superficial branches

Question 3

What can lead to peroneal (fibular) nerve entrapment?

Answer 3

• Most often traumatic in origin, stretch or compression is a common feature in the history
• Compression at this site is frequently produced by external pressure on the nerve due to prolonged lying, such as during surgery, palmar pressure to the fibular neck during childbirth, or prolonged hospitalization
• Crossing the legs, protracted squatting, and leg casts also can cause compression at this site

Question 4

What are clinical features of peroneal (fibular) nerve entrapment?

Answer 4

• Weakness in foot dorsiflexion and foot eversion
• The typical clinical presentation of common fibular (peroneal) neuropathy at the fibular neck is acute foot drop (difficulty dorsiflexing the foot against resistance or gravity)
• Patients describe the foot as limp; there is a tendency to trip over it unless they compensate by flexing the hip higher when walking, producing what is called a “steppage” gait
• Patients may also complain of paresthesias and/or sensory loss over the dorsum of the foot and lateral shin (superficial fibular (peroneal) nerve territory)

Question 5

Testing for peroneal (fibular) nerve entrapement

Answer 5

Electromyography (EMG) and nerve conduction studies (NCS) are very useful for identifying fibular (peroneal) neuropathy at the fibular neck

Question 6

Treatment for peroneal (fibular) nerve entrapment

Answer 6

• No specific treatment is available other than removing pressure on the nerve (such as extra cushioning while sleeping and avoidance of crossing the legs during the day)
• An ankle-foot orthosis splint, to keep the foot dorsiflexed, should be used until active movement has recovered
• Physical therapy

Question 7

Upper extremity nerve compression vs lower nerve compression surgery

Answer 7

In contrast to upper extremity neuropathies, treating compression neuropathies of the lower extremity is often not possible or of limited benefit

Question 8

Tarsal tunnel syndrome

Answer 8

Tibial nerve compression in the region of the ankles as the nerve passes under the transverse tarsal ligament

Question 9

What is meralgia paresthetica?

Answer 9

A set of symptoms caused by entrapment of the lateral femoral cutaneous nerve as it traverses below the inguinal ligament

Question 10

What is the lateral femoral cutaneous nerve?

Answer 10

The lateral femoral cutaneous nerve is a small sensory nerve that is a direct branch of the lumbar plexus.

Question 11

Clinical symptoms of lateral femoral cutaneous nerve entrapment

Answer 11

• Patients generally complain of paresthesias and pain that radiates down the lateral aspect of the thigh (more common lateral than anterolateral) toward the knee
• The pain can be quite significant. In more advanced cases, fixed sensory loss on the lateral thigh occurs

Question 12

Risk factors for meralgia paresthetica

Answer 12

Some people are especially predisposed to developing meralgia paresthetica, including those with obesity, diabetes mellitus, and advanced age
- Pregnant and postpartum patients are also at increased risk

Question 13

Treatment for meralgia paresthetica

Answer 13

• Self-limited, benign disease in most patients
• More than 90 percent of patients respond to conservative measures such as weight loss and avoiding external pressure over the inguinal ligament (eg, due to supporting heavy materials on the thigh)
• However, recurrent symptoms are common
• Anticonvulsants such as carbamazepine, phenytoin, or gabapentin may be helpful in reducing neuropathic pain for patients with persistent symptoms despite conservative measures.
• A local nerve block can also be considered
• Rarely, surgical nerve decompression or sectioning is used

Question 14

What are the different parts of a myelinated axon called?

Answer 14

• Myelin free axon regions are known as Nodes of Ranvier
• In both CNS and PNS, areas between two adjacent nodes is known as internode
• Region close to a node where the myelin sheath terminates is known as paranode, and the region just beyond the juxtaparanode

Question 15

How are damaged axons in neurons dealt with?

Answer 15

• Different response to injury depending whether it’s in the CNS or PNS
• In the CNS, glial microenvironment does not facilitate axonal regrowth and thus reconnection to original synaptic targets does normally occur
• In the PNS, glial microenvironment is capable of facilitating axonal regrowth, however functional outcome of clinical repair of large mixed peripheral nerve especially if the injury occurs some distance from the target organ or produces a long defect in the damaged nerve, is frequently poor

Question 16

Peripheral nerve structure

Answer 16

• Individual nerve fibers and their associated Schwann cells are held together by connective tissue organized into three distinctive components
• The endoneurium surrounding each individual nerve fiber (axon). Many axons with endoneurium will constitute a fascicle
• The perineurium surrounds each nerve fascicle.
  The epineurium includes dense irregular connective tissue that surrounds a peripheral nerve and fills the spaces between nerve fascicles.

Question 17

Vasculature in peripheral nerves

Answer 17

• The blood vessels that supply the nerves travel in the epineurium, and their branches penetrate into the nerve and travel within the perineurium
• Tissue at the level of the endoneurium
  is poorly vascularized; metabolic exchange of substrates and wastes in this tissue depends on diffusion from and to the blood vessels through the perineurial sheath
• The perineurium serves as a metabolically active diffusion barrier that contributes to the formation of a blood -nerve barrier

Question 18

How can peripheral nerve injury be classified into?

Answer 18

• Seddon’s classification of peripheral nerve injury
• Sunderland classification peripheral nerve injury

Question 19

What is seddon’s classification?

Answer 19

Peripheral nerve injury is often graded using Seddon’s classification :
●Grade I is neurapraxia

●Grade II is axonotmesis
●Grade III is complete nerve transection (neurotmesis) or permanent nerve injury

Question 20

.

Answer 20

,

Question 21

What is neurapraxia?

Answer 21

• A disruption of nerve function involving demyelination
• Physiologic, reversible, functional disruption of an axon
• Weakness and sensory loss are due to conduction block; this may be confirmed with electrodiagnostic studies
• The axon distal to the injury is intact, and there is nerve continuity across the site of injury
• Electromyography (EMG) is typically normal.

Question 22

Prognosis of neuropraxia

Answer 22

• Excellent recovery is expected, and may occur within hours, days, weeks, or, at the maximum, a few months
• Remyelination follows within three weeks

Question 23

What axonotmesis?

Answer 23

• Complete anatomic disruption of the axon and of its myelin sheath with continuity of its endoneurial tube
• The surrounding stroma, including the endoneurium and perineurium, remains intact
• The axon is locally but irreversibly damaged with wallerian degeneration occurring (in contrast to grade 1 injuries), and the myelin sheath is similarly involved

Question 24

What causes axonotmesis?

Answer 24

Typically occurs as a result of crush injuries, nerve stretch injuries (eg, motor vehicle accidents, falls), or percussion injuries (eg, gunshot wounds)

Question 25

What causes neuropraxia?

Answer 25

Neurapraxia is usually caused by a mild injury (eg, ischemia, mechanical compression, metabolic or toxic factors) that results in focal demyelination, but no loss of axonal integrity in the region of injury

Question 26

What is neurotmesis?

Answer 26

• The whole nerve is cut
• The axon, myelin sheath, and surrounding stroma are all irreversibly damaged
  ○ You can have a classification
  ■ Endoneurium cut
  ■ Perineum cut, epineurium intact
• Endoneurium, perineum, and epineurium cut

Question 27

When does can neurotmesis occur?

Answer 27

Occurs in association with severe lesions, such as sharp injuries, traction injuries, percussion, or exposure to neurotoxic substances

Question 28

What is the classification of nerve injury based on sunderland classification?

Answer 28

Classified into 5 grades:
- Grade 1 (equivalent to neuropraxia)
- Grade 2 (axonotmesis)
- Grade 3, 4, 5 (neurotmesis)

Question 29

Grade 1 in sunderland classification (pathology, electrodiagnostic studies, recovery)

Answer 29

• Demyelination
• Conduction block
• Excellent prognosis, up to 3 months for complete recovery

Question 30

Grade 2 in sunderland classification (pathology, electrodiagnostic studies, recovery)

Answer 30

• Demyelination and axon loss
• Axon loss on electrodiagnostic studies
• Prognosis is good, limited by “time-distance” factor

Question 31

Grade 3 in sunderland classification (pathology, electrodiagnostic studies, recovery)

Answer 31

• II + involvement of endoneurium
• Good-fair prognosis

Question 32

Grade 4 in sunderland classification (pathology, electrodiagnostic studies, recovery)

Answer 32

• III + involvement of perineurium
• Poor to no recovery

Question 33

Grade 5 in sunderland classification (pathology, electrodiagnostic studies, recovery)

Answer 33

• IV + involvement of epineurium
• No recovery

Question 34

Describe the pathological nature of peripheral nerve lesions in clinical practice

Answer 34

Most nerve lesions are mixed, consisting of a combination of neurapraxia and axonotmesis/neurotmesis, and therefore presenting as a mix of conduction block and partial axonal loss

Question 35

Describe mechanism of recovery of peripherally injured nerves

Answer 35

• Mechanisms of recovery may include resolution of conduction block (in neuropraxic lesions), distal axonal sprouting (in axonotmetic lesions), and axonal regeneration (in axonotmetic and neurotmetic lesions)
• The level of injury (proximal versus distal) also plays a factor, more favorable prognosis for distal injuries

Question 36

Lateral femoral cutaneous nerve entrapment disease name

Answer 36

Meralgia paresthetica