Anterior Forearm & Palmar Hand

Question 1

Anterior Compartment of the Forearm nerve innervation and exceptions

Answer 1

• Superficial group (cross elbow) and deep group (do not cross elbow)
• Most of the anterior forearm muscles are innervated by the median nerve (C6-T1) (compartment rule: “mostly median”)
• Exceptions: 1½ muscles are innervated by the ulnar nerve (flexor carpi ulnaris and the ulnar half (to digits 4 and 5) of flexor digitorum profundus)

Question 2

Anterior Compartment of the Forearm Actions

Answer 2

• Flex wrist joint
• Flex fingers (e.g., at MCP and IP joints)
• Pronate forearm (palm posterior)
• Abduct (radial deviation)/adduct (ulnar deviation) wrist joint

Question 3

Superficial Group, Anterior Compartment of Forearm Rules

Answer 3

• Mostly median nerve innervation
• Common origin: Medial Epicondyle of the Humerus
• Medial epicondylitis (“Golfer’s elbow”): inflammation of common flexor origin and periosteum of the medial epicondyle

Question 4

What are the muscles of the Superficial Group, Anterior Compartment of Forearm

Answer 4

1) Pronator teres
2) Flexor carpi radialis
3) Flexor carpi ulnaris
4) Palmaris longus (absent in ~15% of people)
5) Flexor digitorum superficialis (FDSF)

Question 5

Pronator teres

Answer 5

• Insertion: midshaft of radius
• Action: pronate forearm
• Innervation: median nerve

Question 6

Flexor carpi radialis

Answer 6

• Insertion: radial (lateral) side of hand
• Action: flex and abduct wrist joint
• Innervation: median nerve

Question 7

Flexor carpi ulnaris

Answer 7

• Insertion: ulnar (medial) side of hand
• Action: flex and adduct wrist joint
• Innervation: ulnar nerve

Question 8

Palmaris longus

Answer 8

-Insertion: palmar aponeurosis
-Action: flex wrist joint
-Innervation: median nerve
(absent in ~15% of people)

Question 9

Flexor digitorum superficialis (FDSF)

Answer 9

• Insertion: middle phalanges of digits 2-5
• Action: flex digits 2-5 (MCP and PIP joints), flex wrist joint
• Innervation: median nerve

Question 10

Deep Group, Anterior Compartment of Forearm Rules and muscles

Answer 10

• Origins: ulna, radius, interosseous membrane
• Mostly median nerve innervation

1) Flexor digitorum profundus (FDP)
2) Flexor pollicis longus (pollex=thumb)
3) Pronator quadratus

Question 11

Flexor digitorum profundus (FDP)

Answer 11

• Insertion: distal phalanges of digits 2-5
• Action: flex digits 2-5 (MCP, PIP, and DIP joints), flex wrist joint
• Innervation:
  1) Lateral (radial) ½ (to digits 2, 3) = median nerve
  2) Medial (ulnar) ½ (to digits 4, 5) = ulnar nerve

Question 12

Flexor pollicis longus (pollex=thumb)

Answer 12

• Action: flex thumb (CMC, MCP and IP joints), flex wrist joint
• Innervation: median nerve

Question 13

Pronator quadratus

Answer 13

• Insertion: distal radius
• Action: pronate forearm
• Innervation: median nerve

Question 14

Describe Flexor Retinaculum

Answer 14

• Band of deep fascia holding long flexor tendons in place as they cross the wrist joint
• Tendons are surrounded by synovial sheaths (allow tendons to move freely)
• The flexor retinaculum forms the roof of the carpal tunnel

Question 15

Describe Contents of the carpal tunnel (deep to flexor retinaculum)

Answer 15

• median nerve (note: compression of this nerve in the carpal tunnel can lead to carpal tunnel syndrome, see below for more info)
  1) tendons of flexor digitorum superficialis
  2) tendons of flexor digitorum profundus
  3) tendon of flexor pollicis longus

Question 16

What are the Compartments of the Palm

Answer 16

1) Thenar compartment
- Contains the 3 thenar muscles acting on the thumb (pollex)

2) Adductor compartment
- Contains the adductor pollicis muscle

3) Hypothenar compartment
- Contains the 3 hypothenar muscles acting on digit 5

4) Central compartment
- Deep to palmar aponeurosis, in center of palm
- Contains the long flexor tendons (tendons of flexor digitorum superficialis and flexor digitorum profundus) and lumbricals
- Untreated infections of the central compartment can spread through the carpal tunnel and into the anterior compartment of the forearm

5) Interosseous compartments
- Between the metacarpals
- Contain the interossei

Question 17

Describe the innervation of the Intrinsic Muscles of the Hand and the Thenar Muscles

Answer 17

-Most of the intrinsic muscles are innervated by the ulnar nerve (C8-T1), but some are innervated by the median nerve (C8-T1)

• Thenar Muscles: Form the thenar eminence
• Innervation: recurrent branch of the median nerve

1) Abductor pollicis brevis
- Action: abduct thumb (CMC joint)

2) Flexor pollicis brevis
- Action: flex thumb (CMC and MCP joints)

3) Opponens pollicis
- Action: opposition of thumb (CMC joint)

Question 18

Describe the Adductor Compartment Muscle

Answer 18

• Adductor pollicis (oblique and transverse heads)
• Innervation: ulnar nerve
• Action: adduct thumb (CMC joint)

(NOTE: NOT part of the thenar eminence)

Question 19

Describe Hypothenar Muscles

Answer 19

• Form the hypothenar eminence
• Innervation: ulnar nerve

1) Abductor digiti minimi
- Action: abduct digit 5 (MCP joint)

2) Flexor digiti minimi brevis
- Action: flex digit 5 (CMC and MCP joints)

3) Opponens digiti minimi
- Action: opposition of digit 5 (CMC joint)

Question 20

Describe the Central Compartment Muscles

Answer 20

• Lumbricals (n=4)
• Origin: tendons of flexor digitorum profundus
• Insertion: extensor expansions of digits 2-5
• Action: flex MCP joints and extend PIP & DIP joints of digits 2-5
• Innervation: median nerve (lateral ½), ulnar nerve (medial ½)

Note: Remember: the innervation for flexor digitorum profundus is split [lateral ½ (digits 2 & 3) = median nerve, while medial ½ (digits 4 & 5) = ulnar nerve]. The lumbricals take origin from these tendons and share this split innervation. The lumbricals to digits 2 & 3 are innervated by the median nerve, while lumbricals to digits 4 & 5 are innervated by the ulnar nerve.

Question 21

Describe the Interossei

Answer 21

-Innervation: ulnar nerve

1) Palmar interossei (n=3)
- Action: adduct (“PAD”) MCP joints of digits 2, 4, & 5 (digit 3 is the axis)

2) Dorsal interossei (n=4)
- Action: abduct (“DAB”) MCP joints of digits 2-4

Question 22

Describe the Median Nerve

Answer 22

• Does NOT innervate structures in the arm
• Courses through the cubital fossa
• “Mostly median nerve”: innervates most of the muscles of the anterior forearm
• Travels deep to flexor retinaculum, within the carpal tunnel –> Can be compressed here (carpal tunnel syndrome)
• Recurrent branch: motor to the 3 thenar muscles
• Common and proper digital nerves: motor to lumbricals to digits 2 & 3; sensory to skin on lateral palm and lateral 3½ digits

Question 23

What would happen is there was a Proximal Lesion of the Median Nerve (e.g., in the arm):

Answer 23

1) Pronation lost
2) Flexion and abduction of wrist weakened dramatically
3) Flexion of MCPs, PIPs and DIPs of digits 2-3 lost (flexion of MCPs and PIPs of digits 4-5 weakened)
4) Affects abduction (weakened), flexion and opposition (lost) of the thumb (due to loss of the 3 thenar muscles & flexor policis longus)
5) Lumbricals to digits 2 and 3 paralyzed (MCP flexion, PIP & DIP extension weakened)
6) Skin of the lateral palm and lateral 3½ digits anesthetized

Test: pad-to-pad opposition of thumb; cutaneous sensation tip of digit 2

Question 24

Describe Carpal Tunnel Syndrome

Answer 24

Results from any significant reduction in the size of the carpal tunnel (e.g., inflammation of the synovial sheaths of the flexor tendons). Patients with this condition experience a progressive weakening of the thenar muscles, which weakens their grip. In addition, the resulting loss of sensation (usually not full anesthesia) on lateral 3½ digits also affects grip.
Surgery (partial to full opening of the flexor retinaculum) may be required, but often more conservative treatments can alleviate symptoms.

Question 25

Describe the Ulnar nerve

Answer 25

- Does NOT innervate structures in the arm - Passes posterior to the medial epicondyle of the humerus, within cubital tunnel (area of the “funny bone”) --> Can be compressed here (cubital tunnel syndrome) - Susceptible to damage with a fracture of the medial epicondyle - Innervates flexor carpi ulnaris, medial (ulnar) ½ of flexor digitorum profundus - Travels superficial to the flexor retinaculum with the ulnar artery -Due to its location superficial to the flexor retinaculum, suicide attempts by wrist slashing can sever the ulnar nerve, resulting in full paralysis and anesthesia of the innervated structures -Deep branch: motor to hypothenar muscles, interossei, lumbricals to digits 4 & 5, and adductor pollicis -Common and proper digital nerves: sensory to skin on medial aspect of the palm and medial 1½ digits (also medial aspect of dorsal hand)

Question 26

Describe Proximal Lesion of the Ulnar Nerve (e.g., in the arm):

Answer 26

1) Flexion and adduction of the wrist weakened 2) Flexion of DIPs of digits 4-5 lost 3) Affects grip (hypothenar & adductor pollicis muscles paralyzed) 4) Intricate hand movements affected. Interossei muscles paralyzed (adduction/abduction of digits 2-5 lost), lumbricals to digits 4 & 5 paralyzed (MCP flexion, PIP & DIP extension affected). 5) Skin of medial palm and medial 1½ digits anesthetized Test: adduct/abduct digits 2-5, cutaneous sensation tip of digit 5

Question 27

Describe the Brachial and Ulnar artery

Answer 27

-Brachial artery gives rise to the ulnar and radial arteries in the cubital fossa Ulnar artery - Gives rise to ulnar recurrent arteries (anastomoses around elbow) - Gives rise to common interosseous artery, which divides into: 1) Anterior interosseous artery supplies the deep aspect of the anterior forearm, the deep aspect of the distal posterior forearm, and the dorsal hand 2) Posterior interosseous artery supplies the posterior forearm - Travels with ulnar nerve along medial aspect of forearm - Courses superficial to flexor retinaculum with ulnar nerve (can palpate ulnar pulse here) - Gives rise to superficial palmar arch which provides primary blood supply to the common and proper digital arteries - Ulnar artery anastomoses with the radial artery via the superficial and deep palmar arches

Question 28

Describe the Radial artery

Answer 28

- Gives rise to radial recurrent artery (anastomoses around elbow) - Supplies anterior and posterior compartment muscles on the lateral aspect of the forearm - The pulse rate is usually measured on the radial artery at the wrist, where it lies lateral to the tendon of flexor carpi radialis - Gives rise to deep palmar arch which provides modest blood supply to the digital arteries (exception: main blood supply to the thumb) - Radial artery anastomoses with the ulnar artery via the deep and superficial palmar arches

Question 29

Describe the deep veins

Answer 29

- Accompany arteries and have the same names (e.g., ulnar, radial) - Typically paired - Communicate with superficial veins