Hand Nerves Flashcards
Consultation is requested for a 7-year-old girl because of intravenous infiltration of a chemotherapeutic agent in the dorsal forearm. Physical examination shows firmness and swelling of the forearm and pain on passive flexion of the wrist. Which of the following is the most appropriate initial management?
A) Administration of an antidote
B) Doppler sonography of the forearm
C) Liposuction and saline flush of the affected area
D) Measurement of compartment pressures
E) Surgical excision and grafting
D) Measurement of compartment pressures
Extravasation usually remains localized, yet some patients develop necrotic problem wounds. Often initially underestimated, the extent of injury can declare itself widely with time. Compartment syndrome in an extremity extravasation should be initially ruled out either by clinical assessment or direct measurement of compartment pressures. Tissue loss can include skin, muscle, tendon, nerve, vasculature, and/or joint. Given the variable amount of soft-tissue involvement, early conservative therapy is recommended. Immediate discontinuation of the infusion at the affected site is paramount and should not be overlooked. Aspiration, liposuction, wound excision, debridement, grafts, flaps, and antidote administration have all been described in the management of extravasation injury.
A 24-year-old man comes to the office because of numbness and difficulty moving his ring and little fingers 5 months after cutting his upper arm on broken glass. Current physical examination shows inability to abduct and adduct the ring and little fingers. Sensation to light touch is diminished. Following exploration and resection of a painful, traumatic neuroma, there is a 5-cm gap in the ulnar nerve proximal to the elbow. Which of the following is the most appropriate management to restore intrinsic muscle function? A) Cadaveric nerve allografting B) Nerve transfer C) Sural nerve grafting D) Use of nerve conduit E) Vascularized nerve grafting
B) Nerve transfer
The most appropriate management for restoration of intrinsic muscle function is nerve transfer.In nerve injuries resulting in complete transection of the nerve, wallerian degeneration occurs at the site of transection, and Schwann cells in the distal nerve segment undergo apoptosis. With prolonged denervation, decreased regenerative ability with limitation in motor recovery is noted. Optimal functional recovery is dependent upon adequate reinnervation of the motor end plates and target muscles by regenerating motor axons. Over time, loss of target motor end plates via degeneration and fibrosis and replacement of muscle fibers by fat cells occur.
Nerve regeneration occurs at a rate of approximately 1 mm daily or 1 inch monthly. In a high injury to the ulnar nerve, the distance from the proximal motor axons to the intrinsic musculature precludes timely reinnervation, and intrinsic recovery is generally poor. Reinnervation of the muscle ideally should be completed within 12 to 18 months following injury to allow for recovery
In the patient who has had the delayed symptoms and high ulnar nerve injury described, the time torecovery of intrinsic function will be greater than 2 years if the injury is reconstructed directly. This estimate is based on the elapsed time and distance to the target muscles.Nerve transfer involves the use of a noncritical or expendable donor motor nerve to reinnervate a missing function. The selection of an available motor nerve donor that is closer to the target muscle can decrease the time needed for reinnervation of the muscle and help to ensure recovery before irreversible changes occur. In the scenario described, the distal portion of the anterior interosseous nerve can be used as a donor nerve to reinnervate the ulnar motor branch. Transfer of the distal anterior interosseous nerve to the motor branch of the ulnar nerve will provide motor neurons in a more distal location to reinnervate the intrinsic muscles in the desired time frame.
Nerve regeneration occurs at what rate?
Nerve regeneration occurs at a rate of approximately 1 mm daily or 1 inch monthly.
High ulnar nerve injury and intrinsic recovery
In a high injury to the ulnar nerve, the distance from the proximal motor axons to the intrinsic musculature precludes timely reinnervation, and intrinsic recovery is generally poor.
In what time frame should muscle reinnervation be performed?
Reinnervation of the muscle ideally should be completed within 12 to 18 months following injury to allow for recovery
Typically, conduits are used for:
Typically, conduits are used for sensory nerves in noncritical areas.
Gaps of up to ______ can be bridged with nerve conduits
Gaps of up to 2 to 3 cm can be bridged.
A 13-year-old boy is brought to the office because he has difficulty opening his hand and extending his fingers. History includes release of the forearm compartments to treat a pulseless hand following a supracondylar humerus fracture 2 years ago. On physical examination, passive extension of the fingers is restricted when the wrist is fully extended; it improves with full wrist flexion. Which of the following muscles is the most likely cause of the limitation described? A) Flexor carpi radialis B) Flexor carpi ulnaris C) Flexor digitorum profundus D) Flexor digitorum superficialis E) Lumbricals
C) Flexor digitorum profundus
The most likely cause of the restricted finger extension described is fibrosis of the flexor digitorum profundus muscle. The patient exhibits Volkmann ischemic contracture as a complication of late treatment (over 24 hours from the time of initial ischemia) of arterial compromise associated with the fracture. The muscle groups at the greatest risk during these ischemic episodes are within the deep flexor compartment of the forearm. This risk occurs because the arterial supply is relatively distant from the usual site of occlusion and because this compartment is relatively less distensible. In the scenario described, the flexor digitorum profundus and flexor pollicis longus are at the greatest risk. Superficial muscle groups such as the flexor carpi radialis, flexor carpi ulnaris, and the flexor digitorum superficialis typically recover some function and do not lead to contractures in the forearm. Likewise, the small muscles of the hand, such as the lumbricals, tend to be less severely injured than the deep compartment of the forearm.
What would qualify as late treatment for upper extremity ischemia?
Over 24 hours from the time of initial ischemia
Which muscle groups are at greatest risk during upper extremity ischemia?
The muscle groups at the greatest risk during these ischemic episodes are within the deep flexor compartment of the forearm.
Superficial muscle groups such as the flexor carpi radialis, flexor carpi ulnaris, and the flexor digitorum superficialis typically recover some function and do not lead to contractures in the forearm. Likewise, the small muscles of the hand, such as the lumbricals, tend to be less severely injured than the deep compartment of the forearm.
Why is the deep flexor compartment of the forearm most at risk during an ischemic episode?
The greater risk occurs because the arterial supply is relatively distant from the usual site of occlusion and because this compartment is relatively less distensible.
A 24-year-old man comes to the office because he says the ring and little fingers of his right hand “catch” when he puts his hand in his pocket and that he “pokes” himself in the eye when washing his face. History includes repair of a complete transection of the right ulnar nerve at the wrist 1 year ago. On physical examination, he is unable to extend the interphalangeal joints of the ring and little fingers when the metacarpophalangeal joints are flexed. Photographs are shown. Which of the following tendon transfers is the most appropriate management?
A) Extensor indicis proprius (EIP) to adductor
B) EIP to extensor digiti minimi
C) EIP to first dorsal interosseous
D) Flexor digitorum superficialis (FDS) of the little finger to A2 pulley
E) FDS of the little finger to lateral band
E) FDS of the little finger to lateral band
Of the tendon transfer choices offered, only the FDS transfer to the lateral band (of both the ring and little fingers) will correct the loss of interphalangeal joint extension described, thereby diminishing the tendency for the flexed/abducted finger to catch on pocket edges. The clinical scenario and photographs demonstrate failure of the intrinsic muscle function to return following a low ulnar nerve repair. The deformities demonstrated include ulnar clawing of the little finger primarily, abduction of the little finger (Wartenbergsign), hyperflexion of the interphalangeal joint of the thumb, and atrophy of the intrinsics (especially notable in the hypothenar eminence on the lateral view). Of these deformities, the patient is bothered primarily by the little finger deformity.
Correction of clawing can be achieved actively or passively. Patients who can extend the interphalangeal joints while hyperextension of the metacarpophalangeal joints is blocked (Bouvier test) can achieve correction of clawing with active or passive transfers. Active transfers attempt to re-create the normal function of the intrinsics by directing pull through the lateral bands. Passive transfers re-create the intrinsic function of metacarpophalangeal joint flexion (similar to externally blocking hyperextension) but do not extend the interphalangeal joints. EIP transfers are useful for correction of the lateral pinch functions of the intrinsic minus hand. An EIP transfer to the adductor tendon re-creates the thumb component of lateral pinch, while the EIP transfer to the first dorsal interosseous tendon would improve the index function in pinch.
EIP transfer to the extensor digiti minimi is one method used to reduce hyperabduction of the little finger. This would not correct the flexion deformity at the level of the proximal interphalangeal joint.FDS transfer to the A2 pulley provides a passive transfer, which, based on the patient’s inability to extend the interphalangeal joints during the Bouvier test, would not correct the deformity.
Active transfers for correcting ulnar clawing: General concept
Active transfers attempt to re-create the normal function of the intrinsics by directing pull through the lateral bands.
Passive transfers for correcting ulnar clawing: General concept
Passive transfers re-create the intrinsic function of metacarpophalangeal joint flexion (similar to externally blocking hyperextension) but do not extend the interphalangeal joints.
Bouvier test
Correction of clawing can be achieved actively or passively. Patients who can extend the interphalangeal joints while hyperextension of the metacarpophalangeal joints is blocked (Bouvier test) can achieve correction of clawing with active or passive transfers.
A 25-year-old right-hand dominant man is brought to the emergency department after sustaining a stab wound to the right arm in a bar fight. Physical examination shows a 2 × 1-cm laceration over the antecubital fossa. He is unable to flex the interphalangeal joint of the thumb and the proximal interphalangeal joint of the index finger. Which of the following nerves is most likely injured? A) Lateral antebrachial cutaneous B) Median C) Musculocutaneous D) Radial E) Ulnar
B) Median
Median nerve palsy is marked by the inability to oppose the thumb or flex the thumb at the interphalangeal joint. The inability to flex the index finger at the proximal interphalangeal joint is also noted. The lateral antebrachial cutaneous nerve provides sensory innervation to the lateral aspect of the arm. The median antebrachial cutaneous nerve innervates the skin of the anterior and middle surfaces of the forearm to the level of the wrist. This nerve does not innervate any muscles. Radial nerve palsy is marked by the inability to extend the fingers, thumb, and wrist. Patients with radial nerve palsies have difficulty grasping objects. The results of tendon transfers to restore function in patients with radial nerve palsies are among the best and most predictable outcomes. Ulnar nerve palsy symptoms include a “claw” deformity, with flexion deformities of the ring and little fingers. In later stages, profound muscle wasting of the both hypothenar eminence and the first web space is seen.
Symptoms of median nerve palsy
Median nerve palsy is marked by the inability to oppose the thumb or flex the thumb at the interphalangeal joint. The inability to flex the index finger at the proximal interphalangeal joint is also noted.
The lateral antebrachial cutaneous nerve innervates what?
The lateral antebrachial cutaneous nerve provides sensory innervation to the lateral aspect of the arm.
The median antebrachial cutaneous nerve innervates what?
The median antebrachial cutaneous nerve innervates the skin of the anterior and middle surfaces of the forearm to the level of the wrist. This nerve does not innervate any muscles.
Symptoms of radial nerve palsy
Radial nerve palsy is marked by the inability to extend the fingers, thumb, and wrist. Patients with radial nerve palsies have difficulty grasping objects.
Symptoms of ulnar nerve palsy
Ulnar nerve palsy symptoms include a “claw” deformity, with flexion deformities of the ring and little fingers. In later stages, profound muscle wasting of the both hypothenar eminence and the first web space is seen.
A 55-year-old man with bilateral carpal tunnel syndrome comes to the outpatient surgical unit for elective surgical intervention of the dominant right hand. He will be the tenth procedure of the day for the surgeon performing the operation. The surgeon favors an open technique; he has performed 150 carpal tunnel operations since finishing his hand fellowship 3 years ago. Which of the following is most likely to increase the risk of wrong-site surgery?
A) The elective nature of the procedure
B) Only one surgeon is involved in the operation
C) The procedure will be performed using an open technique
D) The surgeon has a high volume of cases scheduled for the same day
E) The surgeon has only been practicing independently for 3 years
D) The surgeon has a high volume of cases scheduled for the same day
A Joint Commission review of a series of sentinel events identified a number of factors contributing to the increased risk of wrong-site surgery, such as emergency cases; unusual physical characteristics, including morbid obesity or physical deformity; unusual time pressures to start or complete the procedure; unusual equipment or setup in the operating room; multiple surgeons involved in the case; and multiple procedures being performed during a single surgical visit. A large series of wrong-site hand surgeries showed an increased rate of wrong-site surgery with increasing surgeon age and experience, and a direct correlation with increasing surgical case volumes.
A 34-year-old man is brought to the emergency department 2 hours after sustaining injuries to the right wrist when he punched a glass window. Surgical exploration shows a complete laceration of the median nerve at the level of the wrist. A 1-cm gap between the proximal and the distal stumps of the nerve is noted. Which of the following treatments is most likely to provide the best functional outcome? A) Multistrand nerve grafting B) Nerve transfer C) Nerve transposition D) Primary epineurial repair E) Single-strand nerve grafting
D) Primary epineurial repair
The need for nerve grafting is dependent upon many parameters, such as the length of the gap, the excursion of the nerve, the wound bed, and vascularity, among others. For clean, sharp injuries with nerve gaps measuring less than 1 cm in a large peripheral nerve such as the median, most authors agree that primary repair of the nerve results in the best outcome. Autologous nerve grafting should be reserved for cases in which there is tension on the nerve ends with primary repair. Both multistrand nerve grafting and single-strand nerve grafting produce similar outcomes and are inferior to primary repair. Nerve transfer would only be considered if there were no proximal nerve to repair to the distal nerve. Nerve transposition would only be appropriate for gaining length in the ulnar nerve, where the switch from the extensor side of the elbow to the flexor side results in increased relative length in the nerve
When should primary nerve repair be performed in the upper extremity?
For clean, sharp injuries with nerve gaps measuring less than 1 cm in a large peripheral nerve such as the median, most authors agree that primary repair of the nerve results in the best outcome. (Acute setting)
When should autologous nerve grafting be performed, instead of primary nerve repair?
Autologous nerve grafting should be reserved for cases in which there is tension on the nerve ends with primary repair.
Multistrand nerve grafting versus single strand nerve grafting
Both multistrand nerve grafting and single-strand nerve grafting produce similar outcomes and are inferior to primary repair
A 40-year-old man who is an avid cyclist comes for evaluation of a 5-week history of numbness and tingling of the ring and little fingers of the left hand. Conservative management has failed. Physical examination shows weakness of grip strength. Sensation over the dorsal ulnar aspect of the hand is intact, and results of elbow flexion testing are negative. Which of the following structures are most appropriate for surgical release?
A ) Osborne ligament and arcade of Struthers
B ) Osborne ligament and volar carpal ligament
C ) Pisohamate ligament and volar carpal ligament
D ) Transverse carpal ligament and arcade of Struthers
E ) Transverse carpal ligament and pisohamate ligament
C ) Pisohamate ligament and volar carpal ligament
The patient described has ulnar tunnel syndrome or compression of the ulnar nerve in the Guyon canal. Sensory sparing onthe dorsal ulnar aspect of the hand suggests a lesion distal to the origin of the dorsal cutaneous branch of the ulnar nerve. Nerve conduction studies and electromyography can be used to confirm the diagnosis. Conservative treatment includes activity modification, splinting, and administration of a nonsteroidal anti-inflammatory drug.
The most appropriate management of this condition is exploration of the entire ulnar tunnel and release of the pisohamate and volar carpal ligaments. The ulnar tunnel, whichis 4 to 4.5 cm in length, begins at the proximal volar carpal ligament and ends at the fibrous edge of the hypothenar muscles. Zone I is the region of the tunnel proximal to the bifurcation of the nerve. Zone II is the area around the deep motor branch, which ends at the pisohamate ligament, and Zone III is the area surrounding the superficial branch. The ulnar nerve courses between the volar carpal ligament and the transverse carpal ligament.
The Osborne ligament and the arcade of Struthers are potentialsites of compression of the ulnar nerve at the elbow, or cubital tunnel syndrome. The fascia of Osborne, or the cubital tunnel retinaculum, is a band bridging the two origins of the flexor carpi ulnaris muscle and the medial epicondyle. The arcade of Struthers is 8 to 10 cm proximal to the medial epicondyle and extends from the medial intermuscular septum to the medial head of the triceps.
Release of the transverse carpal ligament is appropriate for management of compression of the median nerve at the wrist, or carpal tunnel syndrome.
Conservative management of Ulnar tunnel compression
Conservative treatment includes activity modification, splinting, and administration of a nonsteroidal anti-inflammatory drug.
Ulnar tunnel syndrome: What suggests compression distal to the dorsal cutaneous branch?
Sensory sparing onthe dorsal ulnar aspect of the hand suggests a lesion distal to the origin of the dorsal cutaneous branch of the ulnar nerve.
Management of ulnar tunnel syndrome
The most appropriate management of this condition is exploration of the entire ulnar tunnel and release of the pisohamate and volar carpal ligaments.
Ulnar tunnel: Anatomy
The ulnar tunnel, whichis 4 to 4.5 cm in length, begins at the proximal volar carpal ligament and ends at the fibrous edge of the hypothenar muscles.
The ulnar nerve courses between the volar carpal ligament and the transverse carpal ligament.
Ulnar tunnel: Zone I
Zone I is the region of the tunnel proximal to the bifurcation of the nerve.
Ulnar tunnel: Zone II
Zone II is the area around the deep motor branch, which ends at the pisohamate ligament
Ulnar tunnel: Zone III
Zone III is the area surrounding the superficial branch.
The fascia of Osborne
The fascia of Osborne, or the cubital tunnel retinaculum, is a band bridging the two origins of the flexor carpi ulnaris muscle and the medial epicondyle.
Potential sites of compression of the ulnar nerve at the elbow:
The Osborne ligament and the arcade of Struthers are potential sites of compression of the ulnar nerve at the elbow, or cubital tunnel syndrome.
The arcade of Struthers
The arcade of Struthers is 8 to 10 cm proximal to the medial epicondyle and extends from the medial intermuscular septum to the medial head of the triceps.
A 45-year-old man is brought to the emergency department immediately after sustaining injuries to the right upper extremity during a motorcycle collision. On admission, physical examination shows a flaccid and insensate right upper extremity, and x-ray studies show no abnormalities. Follow-up nerve conduction studies 4 weeks later show preservation of sensory nerve action potentials and evidence of fibrillations and denervation in the motor action potentials from the paravertebral muscles, biceps, triceps, and deltoid. The nerve injury is most likely located at which of the following levels of the nerve? A ) Anterior division B ) C5 and C6 trunk C ) Lateral cord D ) Preganglionic root E ) Subscapular nerve
D ) Preganglionic root
Following a traction injury to the brachial plexus, the nerves may rupture, be avulsed at the level of the spinal cord, or significantly stretch but remain intact. There are five possible levels where the nerve can be injured: (1) root, (2) anterior branches of the spinal nerves, (3) trunk, (4) cord, and (5) peripheral nerve. Root injuries may be further localized with respect to the dorsal root ganglion. Infraganglionic (postganglionic) injuries are located distal to the dorsal root ganglion, and supraganglionic (preganglionic) lesions are located proximal to the ganglion. With both types of lesions, patients will have the symptom of loss of muscle function. In supraganglionic injuries, the nerve has been avulsed from the spinal cord, separating the motor nerve fibers from the motor cell bodies in the anterior horn cells. The sensory fibers and cell bodies are still connected at the dorsal root ganglion; however, the efferent fibers entering the dorsal spinal column have been disrupted. Thus, sensory nerve action potentials will be preserved in patients with supraganglionic injuries, while motor nerve action potentials will be absent. In infraganglionic injuries, both the motor and sensory nerve cells have been disrupted, so there will be abnormalities in both motor and sensory action potentials. An injury to the C5 and C6 roots would show preservation of triceps function, as would an injury to the medial or lateral cord.
Possible levels of injury of the brachial plexus
There are five possible levels where the nerve can be injured: (1) root, (2) anterior branches of the spinal nerves, (3) trunk, (4) cord, and (5) peripheral nerve.
Sub levels of brachial plexus root injuries
Root injuries may be further localized with respect to the dorsal root ganglion:
- Infraganglionic (postganglionic) injuries are located distal to the dorsal root ganglion
- Supraganglionic (preganglionic) lesions are located proximal to the ganglion.
Supraganglionic brachial plexus injuries
In supraganglionic injuries, the nerve has been avulsed from the spinal cord, separating the motor nerve fibers from the motor cell bodies in the anterior horn cells. The sensory fibers and cell bodies are still connected at the dorsal root ganglion; however, the efferent fibers entering the dorsal spinal column have been disrupted. Thus, sensory nerve action potentials will be preserved in patients with supraganglionic injuries, while motor nerve action potentials will be absent.
Infraganglionic brachial plexus injuries
In infraganglionic injuries, both the motor and sensory nerve cells have been disrupted, so there will be abnormalities in both motor and sensory action potentials.
A 48-year-old woman has numbness and paresthesia of the right hand 2 years after mastectomy and radiation therapy. She reports no pain or night waking. Symptoms have not improved with cock-up wrist splints or injection of a corticosteroid into the carpal tunnel. Physical examination shows swelling and weakness of the right arm, most prominently in the C5-C6 distribution; no varicosities, stasis ulcers, dermatitis, or symptoms of Horner syndrome are noted. Allen test is normal. Electromyography shows myokymia. CT scan shows diffuse swelling but no mass. Which of the following is the most likely diagnosis?
A ) Acute ischemic injury
B ) Carpal tunnel syndrome
C ) Chronic venous insufficiency
D ) Radiation-induced brachial plexopathy
E ) Tumor recurrence
D ) Radiation-induced brachial plexopathy
The most likely diagnosis is radiation-induced brachial plexopathy, which can occur when radiation therapy is directed at the chest, axillary region, thoracic outlet, or neck. The incidence is 1.8 to 4.9% of those patients receiving radiation therapy to the above areas and is most common in patients with underlying breast or lung carcinoma. Patients often have sensory symptoms, with swelling and a generalized weakness of the arm.
Eighteen percent of patients have pain in the shoulder, wrist, or hand. The neurologic findings are most prominent in the C5-C6 distribution. The lymphatic-vascular system may show prominent lymphedema of the involved extremity without cyanotic or dusky features. There should be no disturbance of arterial or venous circulation in the involved extremity and no changes in the limb to suggest venous insufficiency (ie, varicosities, stasis ulcers, or dermatitis). The Allen test should be normal. Horner syndrome is not present in patients with radiation-induced brachial plexopathy.Eighty percent of patients with tumor infiltration into the brachial plexus come to the office because of pain in the shoulder, upper arm, elbow, and ring and little fingers. Symptoms progress to atrophy and weakness of the C7-T1 distribution with persistent pain and occasional Horner syndrome. CT scan shows a discrete mass with circumscribed tissue infiltration. Electromyography shows segmental slowing.
Patients with acute ischemic injury have symptoms of paresthesia in the C5-C6 nerve distribution and acute, nonprogressive weakness and sensory loss. CT angiography woulddemonstrate subclavian artery segmental obstruction. Electromyography shows segmental slowing.
Patients with carpal tunnel syndrome often have night waking and experience a period of symptomatic relief after injection of a corticosteroid into the carpal tunnel.
Chronic venous insufficiency does not typically have neurologic sequela
When does radiation induced brachial plexopathy occur?
In what % of patients?
Can occur when radiation therapy is directed at the chest, axillary region, thoracic outlet, or neck. The incidence is 1.8 to 4.9% of those patients receiving radiation therapy to the above areas
Presentation of radiation induced brachial plexopathy
- Sensory symptoms, with swelling and a generalized weakness of the arm.
- 19% of patients have pain in the shoulder, wrist, or hand.
- The neurologic findings are most prominent in the C5-C6 distribution.
The lymphatic-vascular system may show prominent lymphedema of the involved extremity without cyanotic or dusky features. There should be no disturbance of arterial or venous circulation in the involved extremity and no changes in the limb to suggest venous insufficiency (ie, varicosities, stasis ulcers, or dermatitis). The Allen test should be normal.
Presentation of patient with tumor infiltration into the brachial plexus
80% of patients with tumor infiltration into the brachial plexus come to the office because of pain in the shoulder, upper arm, elbow, and ring and little fingers. Symptoms progress to atrophy and weakness of the C7-T1 distribution with persistent pain and occasional Horner syndrome.
A 54-year-old woman comes to the office because of a 6-year history of weakness and numbness of the left hand. Physical examination shows decreased sensation in the thumb, index, long, and ring fingers. No other sensory abnormalities are noted. Examination of which of the following muscles is most likely to confirm a diagnosis? A ) Abductor pollicis brevis B ) Adductor pollicis C ) First dorsal interosseous D ) Flexor digiti minimi E ) Flexor pollicis brevis
A ) Abductor pollicis brevis
The examination of the patient described suggests an injury or compression neuropathy of the median nerve.
The only intrinsic muscle innervated by the median nerve (recurrent branch) that can be reliably tested separately from the ulnar intrinsic muscles is the abductor pollicis brevis. The adductor pollicis, first dorsal interosseous, and flexor digiti minimiare all completely innervated by the ulnar nerve. The flexor pollicis brevis muscle has dual innervation from both the ulnar (deep head) and median (superficial head) nerves.
What is the only intrinsic muscle that can be tested independently of the ulnar intrinsic muscles
The only intrinsic muscle innervated by the median nerve (recurrent branch) that can be reliably tested separately from the ulnar intrinsic muscles is the abductor pollicis brevis.
Innervation of the flexor pollicis brevis muscle
The flexor pollicis brevis muscle has dual innervation from both the ulnar (deep head) and median (superficial head) nerves
A 30-year-old woman comes to the emergency department after cutting herself with a kitchen knife. Surgical exploration shows that the median nerve had been cut at the distal forearm. The distal nerve is relatively fixed, but the proximal nerve has been lifted and twisted. Immediate repair is planned. The motor fibers of the proximal nerve end are most likely in which of the following locations relative to the sensory fibers? A ) Dorsal and radial B ) Dorsal and ulnar C ) Volar and radial D ) Volar and ulnar
C ) Volar and radial
At the level of the distal forearm, the median nerve is a mixed nerve comprised of both motor (20%) and sensory (80%) fibers. The motor fibers become the thenar branch, which innervates the abductor pollicis brevis (AbPB), opponens pollicis (OP), and flexor pollicis brevis (FPB). The FPB is located distal to the AbPB and OP and also has innervation from the ulnar nerve, which is why patients with median nerve injuries can sometimes still bring the thumb to the little finger. The thenar nerve can be injured with acarpal tunnel release procedure. After coursing into the carpal tunnel, these median nerve motor fibers leave the median nerve volar and radial to the sensory fibers of the median nerve through a variety of branching patterns.
When patients have clean-cut injuries to nerves, the nerves can be repaired primarily. In a contaminated, dirty wound caused by a crush and mutilating injury, it can be difficult to determine the nonviable nerve required for debridement before repair. In the scenario described, the nerve ends are labeled with a permanent suture for later identification and repair at a second stage. In general, sensory-only nerves can be repaired by epineurial approximation, and group fascicular repair can be considered for mixed nerves.
At the level of the distal forearm, the median nerve is a ______ nerve comprised of:
At the level of the distal forearm, the median nerve is a mixed nerve comprised of both motor (20%) and sensory (80%) fibers.
The ______ branch of the median nerve innervates what muscles?
The motor fibers of the thenar nerve become the thenar branch, which innervates the:
- abductor pollicis brevis (AbPB)
- opponens pollicis (OP)
- flexor pollicis brevis (FPB). The FPB is located distal to the AbPB and OP and also has innervation from the ulnar nerve, which is why patients with median nerve injuries can sometimes still bring the thumb to the little finger.
Why would a patient with a median nerve injury sometimes be able to bring the thumb to the little finger?
The FPB is located distal to the AbPB and OP and also has innervation from the ulnar nerve, which is why patients with median nerve injuries can sometimes still bring the thumb to the little finger.
After coursing into the carpal tunnel, the course of the median nerve motor fibers, relative to the sensory fibers:
After coursing into the carpal tunnel, these median nerve motor fibers leave the median nerve volar and radial to the sensory fibers of the median nerve through a variety of branching patterns.
A 68-year-old woman comes to the office because of a 4-year history of numbness and tingling in the tips of the thumb, index, and long fingers. The symptoms have become progressively severe and now wake her at night. Physical examination shows decreased strength of thumb opposition and thenar atrophy. Sensation to pinprick is diminished over the median nerve distribution. Which of the following findings is most likely on electrodiagnostic testing?
Median sensory latency, Median motor latency, Fibrillations
A ) Decreased || decreased || absent
B ) Decreased || decreased || present
C ) Unchanged || unchanged || absent
D ) Increased || increased || absent
E ) Increased || increased || present
E ) Increased || increased || present
The most likely finding on electrodiagnostic testing is increased median sensory latency, increased median motor latency, and presence of fibrillations. For the patient described, compression of the median nerve results in numbness and paresthesias in the median nerve distribution. The disease has progressed to the point where physical findings include decreased strength and thenar atrophy, indicating the presence of denervation and median nerve damage. On nerve conduction studies (NCS), the sensory and motor latency measurements detect the time necessary for a signal to travel across a segment of nerve from a stimulating electrode to a recording electrode. In the presence ofnerve compression, demyelination results and conduction is slowed, resulting in a longer time and increased latency (measured in milliseconds). On electromyography (EMG), the needle examination will assess the presence of denervation changes, manifested as fibrillations and positive sharp waves. These are signs of ongoing nerve injury and muscle denervation. Spontaneous muscle activity with fibrillation potentials is the earliest sign of denervation. In severe carpal tunnel syndrome, examination of the median-innervated abductor pollicis brevis muscle will reveal changes. There may also be alteration in the motor unit potentials caused by chronic episodes of denervation and reinnervation.Carpal tunnel syndrome remains a clinical diagnosis based on historyand physical examination. Clinical suggestion may be confirmed by electrophysiologic testing, but false-negative and false-positive results may occur.
On nerve conduction studies, the latency measurements detect what?
On nerve conduction studies (NCS), the sensory and motor latency measurements detect the time necessary for a signal to travel across a segment of nerve from a stimulating electrode to a recording electrode.
EMG needle examination:
On electromyography (EMG), the needle examination will assess the presence of denervation changes, manifested as fibrillations and positive sharp waves. These are signs of ongoing nerve injury and muscle denervation.
EMG: Earliest sign of denervation
Spontaneous muscle activity with fibrillation potentials is the earliest sign of denervation.
Volkmann ischemic contracture occurs when forearm compartment pressure is above 30 mmHg for a minimum of approximately how many hours? A ) Less than 2 B ) 3-5 C ) 6-12 D ) 18-24 E ) Greater than 24
C ) 6-12
Permanent neuromuscular damage occurs at 12 hours, leading to subsequent Volkmann contracture. Timeline of ischemia, shown experimentally, is capillary endothelial damage at 3 hours; partially reversible muscle and nerve injury occurs at 6 hours.
Upper extremity ischemia: Permanent neuromuscular damage occurs when?
Permanent neuromuscular damage occurs at 12 hours, leading to subsequent Volkmann contracture.
Upper extremity ischemia: Timeline
Timeline of ischemia, shown experimentally, is:
3 hours: capillary endothelial damage
6 hours: partially reversible muscle and nerve injury
A 30-year-old man who works as an ironworker is brought to the emergency department after falling 20 ft and impaling his right upper arm on a picket fence. Surgical exploration shows a complete transection of the ulnar nerve 6 in (15.2 cm) above the elbow with a 2-cm nerve gap. The median and radial nerves are intact. Which of the following procedures is most likely to result in maximal recovery of intrinsic muscle function?
A ) Anterior transposition of the ulnar nerve at the elbow followed by primary repair
B ) Interposition nerve grafting using the lateral antebrachial cutaneous nerve
C ) Nerve transfer of the distal anterior interosseous nerve to the deep motor branch of the ulnar nerve
D ) Tendon transfer of the extensor digiti quinti to the extensor digitorum communis
E ) Vascularized radial nerve grafting
C ) Nerve transfer of the distal anterior interosseous nerve to the deep motor branch of the ulnar nerve
High ulnar nerve injuries, ie, above the elbow, have routinely yielded unsatisfactory results with minimal return of intrinsic function and resultant claw hand deformity. This poor recovery of motor function of the intrinsic muscles of the hand occurs despite meticulous neurorrhaphy technique and regardless of whether nerve graft or primary repair is performed. The principal reason for poor results is the long distance between the site of injury and the muscle motor endplates. During the many months required for the regenerating axons to traverse this gap, the target muscles are undergoing atrophy and fibrosis. The rate of nerve regeneration is approximately 1 inch per day. Motor endplates become refractory to reinnervation after about 15 to 18 months. In contrast, sensory return from high nerve injuries is usually adequate.
The key to nerve transfer is to convert a high nerve injury to a low nerve injury. In this case, the original injury is over 15 inches from the ulnar nerve innervations of the intrinsic muscles. The likelihood of any intrinsic muscle function is poor. By transferring the distal anterior interosseous nerve at the level of the pronator quadratus to the deep motor branch of the ulnar nerve, the distance that the reinnervating nerve has to travel is much shorter, thus preserving the muscle structure.
The other options presented are all inappropriate because they do not address the length of time it will take the nerve to grow to the motor endplates.
High ulnar nerve injuries: Reason for poor results?
The principal reason for poor results is the long distance between the site of injury and the muscle motor endplates. During the many months required for the regenerating axons to traverse this gap, the target muscles are undergoing atrophy and fibrosis.
Motor endplates become refractory to reinnervation after how long?
Motor endplates become refractory to reinnervation after about 15 to 18 months.
Sensory return from high nerve injuries
Sensory return from high nerve injuries is usually adequate.
The key to nerve transfer is what?
The key to nerve transfer is to convert a high nerve injury to a low nerve injury.
Morbidity of transferring the distal anterior interosseous nerve at the level of the pronator quadratus:
The loss of pronator quadratus function is insignificant.
Determining the need for nerve transfer:
When determining the need for nerve transfer, the time vs. distance constraints can be guided by the “Rule of 18.” The Rule of 18 states: “The number of inches from the site of nerve injury to the supplied muscle added to the number of months the muscle has been denervated should be less than the number 18 in order for the primary nerve reconstruction to be attempted successfully.” In other words, the nerve must be able to get to the muscle before 18 months from the initial injury.
Rule of 18:
When determining the need for nerve transfer, the time vs. distance constraints can be guided by the “Rule of 18.” The Rule of 18 states: “The number of inches from the site of nerve injury to the supplied muscle added to the number of months the muscle has been denervated should be less than the number 18 in order for the primary nerve reconstruction to be attempted successfully.” In other words, the nerve must be able to get to the muscle before 18 months from the initial injury.
A newborn who sustained a traction injury to the shoulder during delivery because of the use of forceps has complete palsy of the left upper extremity. Surgical intervention is indicated if there is no spontaneous biceps recovery by what age? A ) 6 weeks B ) 6 months C ) 18 months D ) 24 months E ) 36 months
B ) 6 months
Most experts will perform surgery on infants who are between 3 and 6 months of age. At 3 months of age, if biceps function is absent, there is a poor prognosis. Early on, 92% will recover spontaneously. If biceps function is noted, surgery is not recommended. At 3 months of age, the child is retested by electromyography if there is no biceps function, although there is poor correlation with final results. The final evaluation is cervical myelography.
Traction injury in a newborn: At what point is the prognosis poor
At 3 months of age, if biceps function is absent, there is a poor prognosis.
___% newborns with traction injury recover spontaneously <3 months of age
Early on, 92% will recover spontaneously.
Age range appropriate for surgery for newborn traction injury
Most experts will perform surgery on infants who are between 3 and 6 months of age.
A 23-year-old man is brought to the emergency department after sustaining a single gunshot wound to the right upper arm. Physical examination shows a high radial nerve palsy. Which of the following is the most appropriate first step in management of potential nerve injury?
A ) Immediate surgical exploration and primary nerve repair if nerve is lacerated
B ) Immediate surgical exploration and repair with a nerve graft if nerve is lacerated
C ) Immediate surgical exploration, resection of devitalized nerve, and suture tagging of nerve ends for delayed repair
D ) Observation with electromyography six weeks after injury followed by exploration and repair if no return of function
E ) Observation with electromyography six months after injury followed by exploration and repair if no return of function
D ) Observation with electromyography six weeks after injury followed by exploration and repair if no return of function
In general, nerve injuries associated with open wounds should be explored and repaired early. If the nerve injury resulted from a relatively clean laceration or wound, it should be explored and repaired immediately. Crush or significant soft-tissue injury prohibits early nerve repair until the extent of devitalized tissue can be determined and the soft-tissue repair is stable.
Although gunshot wounds are technically open injuries, they should be treated as closed or blunt nervetrauma because the etiology of the trauma is predominately heat and shock. The majority of nerve dysfunction spontaneously recovers after gunshot wounds. Thus, the most logical first step in treatment is observation for at least six weeks at which time electrodiagnostic studies can be undertaken.
If there is not complete clinical return of function within six weeks, electrodiagnostic studies should be performed for baseline function and repeated at 12 weeks if clinical return of function is still not complete. If electromyography does demonstrate motor unit potentials, expectant management should be continued as full function should return. Electrodiagnostic studies should not be delayed for six months because long-term function is significantly decreased if nerve repair is delayed longer than three months.
Lack of clinical or electrical evidence of reinnervation at three months requires surgical exploration. A nerve that has been completely divided or fails to conduct intraoperatively should be managed withresection of scar tissue and repair of the nerve gap with an interpositional nerve graft. An in-continuity lesion should undergo neurolysis of nonfunctioning nerve units and nerve grafting. The functioning units can remain intact
When should a nerve be repaired immediately versus delayed?
If the nerve injury resulted from a relatively clean laceration or wound, it should be explored and repaired immediately. Crush or significant soft-tissue injury prohibits early nerve repair until the extent of devitalized tissue can be determined and the soft-tissue repair is stable.
Gunshot wounds should be treated as _______ wounds re: nerve trauma, because:
Although gunshot wounds are technically open injuries, they should be treated as closed or blunt nervetrauma because the etiology of the trauma is predominately heat and shock.
Management of nerve injury after gunshot injury
The majority of nerve dysfunction spontaneously recovers after gunshot wounds. Thus, the most logical first step in treatment is observation for at least six weeks at which time electrodiagnostic studies can be undertaken.
Nerve injury after gunshot wound: When should these be managed expectantly?
If there is not complete clinical return of function within six weeks, electrodiagnostic studies should be performed for baseline function and repeated at 12 weeks if clinical return of function is still not complete. If electromyography does demonstrate motor unit potentials, expectant management should be continued as full function should return.
Nerve injury after gunshot wound: When should these be managed surgically?
Lack of clinical or electrical evidence of reinnervation at three months requires surgical exploration.
Operative approach to nerve injury following a gunshot wound
A nerve that has been completely divided or fails to conduct intraoperatively should be managed with resection of scar tissue and repair of the nerve gap with an interpositional nerve graft. An in-continuity lesion should undergo neurolysis of nonfunctioning nerve units and nerve grafting. The functioning units can remain intact.
A 52-year-old man comes to the office because he has had a clinical diagnosis of carpal tunnel syndrome including numbness and dysesthesia of the thumb, index, and long fingers of both hands for the past four months. He says his symptoms worsen at night and when his wrist position changes while driving. Electrodiagnostic studies show delayed motor and sensory latencies and slowed conduction velocity at the wrist, indicating a conduction block of the median nerve. This block is most likely caused by localized nerve ischemia that results in which of the following?
A ) Blocking of calcium channels
B ) Failure to maintain the resting nerve potential at −30 mV
C ) Opening of sodium channels
D ) Prevention of nerve membrane depolarization
E ) Thickening of the myelin sheath
D ) Prevention of nerve membrane depolarization
Local nerve ischemia prevents depolarization. A charge is maintained across the axon membrane with the interior of the axon having a charge of −90 mV. When the resting membrane potential reaches −50 mV, the membrane depolarizes. Since there is a relatively greater concentration of K+ ions on the inside of the axon, there is a slow leak of K+ ions, which causes the inside of the axon to become less negative. The ATP-dependent pump imports K+ and exports Na+, maintaining the normal resting membrane potential at −90 mV. Maintenance of this ionic charge separation across the membrane requires energy, and the mechanism stops when the energy supply is interrupted, as with local ischemia. This is one of the mechanisms for conduction block that occurs with nerve compression. Various membrane channels consist of proteins embedded in the phospholipid membrane bilayer that allow passage of Na+, Ca2+, and K+ ions. With chronic nerve compression, the myelin sheath disintegrates and saltatory conduction between nodes of Ranvier ceases.
Local nerve ischemia prevents ____________.
Local nerve ischemia prevents depolarization.
Resting charge of a nerve
A charge is maintained across the axon membrane with the interior of the axon having a charge of −90 mV.
At what charge does a nerve depolarize?
When the resting membrane potential reaches −50 mV, the membrane depolarizes.
What causes an axon to be less negative?
Since there is a relatively greater concentration of K+ ions on the inside of the axon, there is a slow leak of K+ ions, which causes the inside of the axon to become less negative.
Actions on electrolytes of the ATP-dependent pump on a nerve
The ATP-dependent pump imports K+ and exports Na+, maintaining the normal resting membrane potential at −90 mV.
