2.4.2. Anat Lab Tuesday - Forearm

Question 1

Name the purely sensory nerve that is located on the radial (lateral) side of the wrist. What part of the hand does this nerve provide sensation to?

Answer 1

Superficial branch of the radial nerve

Provides sensation to the radial side of the dorsum of the hand

Note: If injured, it can be extremely sensitive/irritable to the patient

Question 2

Identify the labeled items:

Answer 2

1. Flexor carpi radialis
2. Palmaris longus
3. Flexor carpi ulnaris
4. Brachioradialis

Question 3

List the superficial muscles of the anterior forearm (there are 4)

Answer 3

1. Flexor carpi radialis
2. Palmaris longus
3. Flexor carpi ulnaris
4. Brachioradialis

Question 4

Identify the following structures:

(Note, this is an oblique view of the right forearm)

Answer 4

1. Flexor digitorum superficialis
2. Pronator teres
3. Brachioradialis (cut and reflected)
4. Flexor carpi radialis (cut and reflected)
5. Radial artery
6. Superficial branch of the radial nerve
7. Radius

Question 5

Identify the following structures:

Answer 5

1. Flexor digitorum profundus
2. Flexor pollicis longus
3. Pronator quadratus
4. Superficial flexor group - reflected
5. Flexor digitorum profundus (index finger)

Question 6

Identify the following structures:

Answer 6

1. Flexor pollicis longus
2. Median nerve
3. Superficial branch of the radial nerve
4. Ulnar nerve
5. Flexor digitorum profundus
6. Flexor carpi ulnaris tendon (cut)

Question 7

Identify the following structures:

Answer 7

1. Flexor digitorum profundus
2. Flexor pollicis longus
3. Pronator quadratus
4. Flexor digitorum profundus (index finger)

Question 8

Identify the following structures:

Answer 8

1. Brachial artery
2. Ulnar artery
3. Radial artery

Question 9

Identify the following structures.

Bonus - what nerve are you most worried about if this bone breaks in the middle?

Bonus Bonus - what are the symptoms of damage to that nerve in that area of the bone?

Answer 9

1. Capitulum
2. Trochlea
3. Medial epicondyle
4. Lateral epicondyle
5. Coronoid fossa

Bonus: A mid-humeral fracture can be associated with damage to the radial nerve

Bonus Bonus: The characteristic clinical sign of radial nerve injury is WRIST-DROP. When the radial nerve is injured in the radial groove, the triceps is normally only weakened (because only the medial head is affected), and muscles in the posterior compartment of the forearm are paralyzed.

Question 10

Identify the following structures:

Answer 10

1. Medial epichondyle
2. Lateral epicondyle
3. Olecranon fossa

Question 11

Identify the following structures (anterior view):

Answer 11

1. Head of ulna
2. Styloid process of ulna
3. Ulnar tuberosity
4. Coronoid process
5. Ulnar interosseous border
6. Styloid process of radius
7. Radial tuberosity

Question 12

Identify the following structures:

Answer 12

1. Head of radius
2. Radial tuberosity
3. Styloid process of radius
4. Interosseous border

Question 13

What bone is this? Identify the numbered structures.

Answer 13

This is the ulna!

1. Olecranon process
2. Coronoid process
3. Trochlear notch

Question 14

Pronator teres:

Origin (2)

Insertion

Innervation

Main Action

Answer 14

Origin: Medial epicondyle of humerus and coronoid process of ulna

Insertion: Middle of lateral surface of radius (pronator tuberosity)

Innervation: Median Nerve (C6-C7)

Main Action: Pronates forearm and flexes elbow joint

Question 15

Flexor carpi radialis:

Origin

Insertion

Innervation

Main Action

Answer 15

Origin: Medial epicondyle of humerus

Insertion: Base of 2nd and 3rd metacarpals

Innervation: Median nerve (C6-C7)

Main Action: Flexes and ABducts wrist joint

Question 16

Palmaris Longus:

Origin

Insertion

Innervation

Main Action

Answer 16

Origin: Medial epicondyle of the humerus

Insertion: Distal half of flexor retinaculum and palmar aponeurosis

Innervation: Median nerve (C7-C8)

Main Action: Flexes wrist joint and tightens palmar aponeurosis

Question 17

Flexor carpi ulnaris:

Origin (2)

Insertion (3)

Innervation

Main Action

Answer 17

Origin: 1) Humeral head: medial epicondyle of humerus

                                     2) Ulnar head: olecranon and posterior border of ulna

Insertion: Pisiform, hook of hamate, and 5th metacarpal

Innervation: Ulnar nerve (C7-C8)

Main Action: Flexes and adducts wrist joint

Question 18

Flexor digitorum superficialis:

Origin (2)

Insertion

Innervation

Main Action

Answer 18

Origin: 1) Humero-ulnar head: medial epicondyle of humerus, ulnar collateral ligament, and coronoid process of ulna

2) Radial head: superior half of anterior border of the radius

Insertion: Bodies of middle phalanges of medial four digits

Innervation: Median Nerve (C7, C8, T1)

Main Action: Flexes proximal interphalangeals (PIPs) of medial four digits; acting more strongly, it flexes metacarpophalangeal (MCPs) and wrist joint

Question 19

Flexor digitorum profundus:

Origin

Insertion

Innervation (2)

Main Action

Answer 19

Origin: Proximal three quarters of medial and anterior surfaces of ulna and interosseous membrane

Insertion: Bases of distal phalanges of medial four digits

Innervation: 1) Medial Part: Ulnar nerve (C8-T1)

2) Lateral Part: Median Nerve (C8-T1)

Main Action: Flexes distal interphalangeals (DIPs) of medial four digits; assists with flexion of wrist joint

Question 20

Flexor pollicis longus:

Origin

Insertion

Innervation

Main Action

Answer 20

Origin: Anterior surface of radius and adjacent interosseous membrane

Insertion: Base of distal phalanx of thumb

Innervation: Anterior interosseous nerve from median (C8-T1)

Action: Flexes interphalangeal (IP) joints of 1st digit (thumb) and assists flexion of wrist joint

Question 21

Pronator quadratus:

Origin

Insertion

Innervation

Main Action

Answer 21

Origin: Distal fourth of anterior surface of ulna

Insertion: Distal fourth of anterior surface of radius

Innervation: Anterior interosseous nerve from median (C8-T1)

Main Action: Pronates forearm; deep fibers bind radius and ulna together

Question 22

Which way does the palm face when the radius spins into pronation?

Answer 22

Palm faces down

Question 23

Which way does the palm face when the radius spins into supination?

Answer 23

Palm is up

Question 24

Which bone is the forearm rotates, and which bone in the forearm cannot rotate?

Explain the function of the stationary bone and the motion of the rotating bone.

Answer 24

The radius rotates, and the ulna does not.

The proximal ulna is like a big crescent wrench that grips the humerus at the elbow, allowing the elbow to move like a big hinge.

The radius spins in an arc around the stable ulna.

Question 25

The "head" of the ulna is on which end of the bone? (Proximal or distal)

Answer 25

Distal

Question 26

What are the two pivot points of the forearm? What type of joints are they?

Answer 26

The two pivot points are the proximal and distal radioulnar joints. They are synovial joints, and must be normal in order to allow the spinning to occur.

Question 27

If a patient's proximal and/or distal radioulnar joints are not normal, what won't they be able to do?

Answer 27

They will not be able to perform pronation and supination movements

Question 28

The radius contributes more to the _____ joint, while the ulna contributes more to the _____ joint

Answer 28

The radius contributes more to the wrist (radiocarpal) joint The ulna contributes more to the elbow joint

Question 29

Which bone in the forearm does not directly contact bones in the wrist?

Answer 29

The ulna does not directly contact the bones in the wrist, but it moves via the triangular fibrocartilage complex and the articular disc that are positioned at the end of the ulna

Question 30

What is the function of the anular ligament?

Answer 30

It encircles/stabilizes the radial head while the radius "spins" around the ulna in supination and pronation

Question 31

The dorsal radial tubercle (Lister's tubercle) acts as a "pulley" for which tendon?

Answer 31

The extensor pollicis longus (EPL)

Question 32

Which tubercle does the extensor pollici longus (EPL) use as a "pulley"? What is the resulting motion of this "pulley system"?

Answer 32

The dorsal radial tubercle, also called Lister's tubercle Allows elevation of the thumb

Question 33

What does the pulley system between Lister's tubercle and the Extensor Pollicis Longus tendon unfortunately predispose the tendon to, and why?

Answer 33

Predisposes the tendon to rupture in rheumatoid arthritis and in fractures of the distal radius This is due to the inflammation and friction that can develop at Lister's tubercle as the tendon makes its turn toward the thumb. This can wear the tendon down.

Question 34

Where is the most common location for a radius fracture to occur?

Answer 34

The distal radius

Question 35

Which artery is located in the "anatomical snuff box"?

Answer 35

The radial artery (passes diagonally from the anterior surface of the radius to the dorsal surface of the hand)

Question 36

Describe the course of the ulnar artery through the forearm.

Answer 36

Descends inferomedially and then directly inferiorly, deep to superficial (pronator teres and palmaris longus) and intermediate (flexor digitorum superficialis) layers of flexor muscles to reach medial side of forearm; passes superficial to flexor retinaculum at wrist in ulnar canal to enter hand

Question 37

Which artery does the common interosseous artery originate from, and where does it branch off?

Answer 37

The ulnar artery in the cubital fossa, distal to bifurcation of brachial artery

Question 38

What two arteries originate as terminal branches of the common interosseous artery? Describe their courses in the forearm.

Answer 38

The two arteries are the anterior interosseous artery and the posterior interosseous artery. The anterior interosseous passes distally on the anterior aspect of the interosseous membrane to the proximal border of the pronator quadratus; it then pierces the membrane and continues distally to join the dorsal carpal arch on the posterior aspect of the interosseous membrane. The posterior interosseous passes to the posterior aspect of the interosseous membrane, giving rise to recurrent interosseous artery; it then runs distally between superficial and depp extensor muscles, supplying both; it is replaced distally by the anterior interosseous artery.

Question 39

What three structures separate the flexor compartment from the extensor compartment? What is their surgical significance?

Answer 39

The interosseous membrane, the radial artery and the subcutaneous medial border of the ulna. they are useful guides in planning surgical incisions because no important nerves cross these structures.

Question 40

What are the general clinical findings of a median nerve injury?

Answer 40

Injury causes a predictable pattern of sensory loss in the hand: - numbness to the radial-sided 3 1/2 digits - loss of thumb opposition (the ability to raise the thumbtip up away from the palm in order to touch the fingertips)

Question 41

Explain how the nerve branches that are proximal and distal to a nerve injury are affected.

Answer 41

Any branches that departed the nerve proximal to the injury will still function. Any branches distal to the injury will not function.

Question 42

What are the general clinical findings of an anterior interosseous nerve injury?

Answer 42

Injury causes loss of tip-to-tip pinch between the thumb and index finger.

Question 43

What are the general clinical findings of an ulnar nerve injury?

Answer 43

Injury causes a predictable pattern of sensory loss in the hand: - Numbness to the ulnar-sided 1 1/2 digits - Loss of coordination of the hand due to loss of the function of the intrinsic muscles of the fingers (muscles that originate and insert within the hand)

Question 44

What are the general clinical findings of a radial nerve injury?

Answer 44

- Injury causes "wrist drop" (due to the loss of the wrist extensor muscles), which causes loss of power grip, since the fist cannot be raised up to assume its power-grip position - Causes a predictable pattern of sensory loss (numbness) to the radial-sided dorsal skin of the hand

Question 45

What are the general clinical findings of an injury to the superficial branch of the radial nerve?

Answer 45

Injury causes a predictable pattern of sensory loss over the back (dorsum) of the thumb and 1st webspace on the radial side.

Question 46

What are the general clinical findings of an injury to the deep branch of the radial nerve?

Answer 46

This nerve is renamed the posterior interosseous nerve after it pierces the supinator muscle on the dorsal/extensor side of the forearm Injury causes loss of full extension of the central digits (the patient cannot fully open their hand)

Question 47

For extremity incisions, is it better to have latitudinal or longitudinal ones? Why?

Answer 47

Longitudinal because the vessels and nerves run in this direction; there is less danger of transecting them

Question 48

The posterior (extensor) compartment paradoxically contains one flexor muscle. What is the muscle, what is it innervated by, and what joint does it flex?

Answer 48

The brachioradialis muscle is innervated by the radial nerve (just like all of the extensors in the posterior compartment). It is considered a flexor of the elbow joint.

Question 49

True or False: If nerves are microscopically repaired after a laceration injury, they can fully recover and function as the did before the injury occurred.

Answer 49

FALSE!!!! Nerves, even if microscopically repaired, never regain full function once they are transected. They can, however, under optimal circumstances, recover from certain compression type injuries. But after a laceration, the injured nerves can only regenerate up to a point and are never the same as before the injury.

Question 50

Name the two branches that the radial nerve branches into in the lateral cubital fossa. What does these two nerves do?

Answer 50

1) The superficial branch of the radial nerve is sensory to the skin over the dorsum of the thumb and radial-sided digits. 2) The deep branch of the radial nerve is RENAMED the posterior interosseous nerve after piercing the supinator muscle distal to the elbow on the extensor surface of the forearm. The posterior interosseous nerve motors the extensors of the forearm.

Question 51

Why is it easier for some infections to rapidly spread between the hand and forearm (especially synergistic (flesh-eating) infections)?

Answer 51

Fascial septae divide the forearm into anterior (flexor) and posterior (extensor) compartments. These compartments do not communicate with those of the arm, but do continue into the hand. This makes it easier for infections to spread between the hand and forearm.

Question 52

# Define "synergistic infection." What do they cause? What are the clinical symptoms? How do you treat them? BONUS: What organisms are the usual culprits? (2)

Answer 52

Synergistic infection: infections that are due to two or more organisms that work together to spread rapidly by elaborating enzymes (collagenases) that dissolve collagen and by destroying tissue as they spread. They cause rapidly-spreading necrosis that can become life threatening within HOURS and are considered surgical emergencies. Clinical symptoms include pain and tachycardia (rapid heart rate) and sometimes elaborate gas in the soft tissues, which is seen on imaging and/or felt as "crepitance" - a crunchy or bubbly feel to the soft tissues when palpated. Treatment: These infections must be immediately opened and debrided aggressively and packed open until the infection has resolved. Intravenous antibiotics are also administered. BONUS: Microaerophilic streptococcus and anaerobic staphylococcus