Uper Limb Nerve Injuries Flashcards
Result of injury to cell body (soma)
Absolute death of neuron. No regeneration (hence danger of cervical spine injuries…where all the cell bodies are)
Result of mild compression to axon (not cell body)? Result of severe compression? How will severe compressions manifest?
- Axon stimulation (funny bone)
- May interfere with transmission along axon
- Anatomical damage, resulting in DEGENERATION DISTAL to injury site (axon will shorten). Cell body unaffected. Manifestation of injury is simply muscle weakness
Describe regeneration process.
Starts with 2 week delay after injury, after which axon regenerates at 1 mm a day
How are nerves able to regenerate, reaching the targeted muscle?
Nerves are surmounted by endoneurium and schwann cells. So when the nerve is compressed and the axon dies, the schwann cells and the endoneurium are still there. So follow the tunnel.
What is the case of healing if there is a full laceration.
Surgery to rejoin the connecting tissue (schwann cells and endoneurium…but in all actually it, you are really only suturing the EPI…not ENDO…neurium)(reestablishing the severed path). The degenerate axon will then be replaced as it is in compression injuries
What innervates the serratus anterior and where does it run?? Where does serratus anterior attach to scapula? What is job of this muscle?
Long thoracic nerve, which runs on lateral side, downward along the serratus anterior muscle. And serratus anterior attaches to MEDIAL border of scapula. Serratus anterior protracts and upwardly rotates scapula, often working ISOtonically to keep scapula up against chest wall (try pressing against a wall….serratus anterior presses against it.)
What injures the long thoracic nerve?
- Downward force on scapula, pulling down on the serratus anterior and thus long thoracic nerve. Falling object from sky onto shoulder will do this
- Chest blunt trauma…construction worker is impaled by a beam, screwing up ribs and compressing long thoracic nerve significantly against the chest wall.
* 3.* Surgical trauma on MEDIAL wall of axilla during axillary lymph node dissection when checking for breast cancer
Result of damaging long thoracic nerve
Winged scapula, since serratus anterior attaches medial border of scapula to the chest wall…so cutting this removes ability to hold the medial border against it. End result = limiting range of motion in abduction and flexion at shoulder.
What does axillary nerve innervate?
Deltoid and teres minor
Describe order of muscles the axillary nerve passes, superiorly to inferiorly, and the associated injuries.
- Head of the humerus (glenohumeral dislocation). Remember that the humerus is the most commonly dislocated joint in the human body. Also remember that when it is dislocated, the humerus is pulled INFERIORLY due to gravity, pulling axillary nerve down with it.
- Surgical neck of humerus. Remember that the surgical neck is the most common point of injury to the humerus. Inferior side moves down, superior side moves upward. Screws up the nerve since the nerve is pinned up against this neck.
Job of teres minor, deltoid, and infraspinatus
Externally rotate and abduct the arm. Deltoid and infraspinatus are best at this tho
What muscles take L if you cut axillary? What functions suffer as a result?
Deltoid. Supraspinatus is innervatred by suprascapular nerve, which softens blow in terms of ability to abduct, but the deltoid does remaining abduction after th efirst 15 degrees.
Clinical presentation of axillary nerve injury
Atrophy of deltoid
What does the radial nerve innervate
Entire posterior arm, skin of posterior hand, skin of posterior forearm. Also a major extensor.
Generalization about nerve injuries
Longer nerves are injured more frequently
Where does radial nerve pass, and what injuries are associated with them?
- Lateral wall of the axilla, coursing the humerus. Note humerus comes out of quadrangular interval and that the humerus head is above the radial nerve
- Shaft of the humerus.. So, try not to break it
- Head of radius…so do not injure the radius
- Deep branch of the radius is protected well, but the superficial branch at the wrist is too close to the skin surface to not be in danger.
Where do you see effects of a nerve injury? Where should you conduct tests in the case of testing the effects of a nerve injury?
Distal from the point of injury. So test distal points of that specific nerve in order to more quickly confirm certain nerve injuries
How to test radial nerve injury most distally. Where is the sensory innervation of radial nerve in the hand?
Have patient extend (Bend hand backwards) wrist. You could also tell patient to hold hand straight out. If the hand cannot stay flat out, this would also indicate a radial nerve injury. Radial skin innervation is posterior metacarpals 1 (thumb), 2 and 3
How to damage radial nerve
- Upward pressure on floor of axilla (sleeping with arm penetrated by chair or improperly using a crutch)
- Glenohumeral dislocation. Rememeber that during a dislocation, the humerus is dragged inferiorly, which would strain the humerus
- Midshaft fracture of humerus. remember radial nerve runs right next to it at the shaft. Triceps would be fine, and the biceps never came in contact. but the later side of posterior side of arm would suffer.
- Radial head dislocation. This is the location of Common Extensor Tendon (lateral arm of humerus).
- Laceration or compression at dorsum of wrist. Note that radial nerve passes superfically here, so can easily be lacerated or compressed. Note that there so muscle or motor loss loss to posterior side of hand, but you would lose sensation
Note about distal injuries in general
Tend to have fewer clinical findings
Where does the median nerve pass? Note that it is on anterior side
- Passes the arm and does nothing. Work starts in forearm
- Supracondylar region of humerus (the distal end of the humerus)
- DIRECTLY THROUGH pronator teres
- Passes under the flexor retinaculam (carpal tunnel). Note that there is a palmar cutaneous branch of the median nerve that goes straight to palm of hand. There is also a recurrent branch that goes to the 3 thenar muscles and the first and 2nd lumbrical muscle
- Goes to the digits
List consequences of damaging the median nerve
- Upon proximal or distal lesion, loss of opposition because no innervation by opponens pollicis (innervated by median nerve). So test opposition ability to test distal motor function of median nerve. Or you could have them grip a sheet of paper and try to take it out of their hand.
- Check for passive hand position. If it looks like a claw (flex of IP and extend of IP). Mean antagonist muscles are taking over. In other words, they can’t flex digit 2 and 3 (sign of benediction)
- Lack of sensation in digits 1 to 4.5 on anterior sire and distal portions of digits 2 and 3 on posterior side.
Describe L taken if median nerve lesion is on proximal side of arm
Loss of flexion of DIP of Digits II and III (FDP)
Proximal or Distal Lesion
Loss of FDS of Digits II-V Loss of FDP of Digits II-III Loss of FPL & FPB
What injury screws up the median nerve?
- Elbow dislocation in which ulna is sent posteriorly
- Supracondylar fracture (distal humerus). Rememebr that the median nerve crosses here
- Wrist laceration. Rmemeber that the median nerve sits in the MIDDLE, between palmaris longus and flexor carpi digitalis. Also note that flexor pollisis longus is also here, but it is fine.The brevis muscle is not fine.
- Lunate dislocation. This leads to carpal tunnel entrapment. This makes sense since carpal tunnel has 9 tendons and the median nerve passing through it. Common injury.
- Pronator teres entrapment. More common in muscle builders. Pronator teres becomes culprit when, instead of pronating the forearm, it becomes an added source of motor unit recruitment, enabling it to flex at the elbow with biceps and brachialis. In other words, hypertrophy
- Compressing carpal tunnel (during sleep). Get a brace tp prevent this in post menopausal women
