Anterior Forearm and Palmar Hand

Question 1

Anterior compartment of the forearm

• Which group crosses elbow and which does not?
• Most of anterior forearm is innervated by?
• At what spinal level?
• What are the two muscle exceptions?

Answer 1

Anterior compartment of the forearm

• Superficial group crosses elbow
• Deep group does NOT cross elbow
• Most of anterior forearm is innervated by the median nerve (C6-T1)
• Flexor carpi ulnaris and ulnar half of flexor digitorum profundus are innervated by ulnar

Question 2

Superficial group of the anterior compartment of the forearm

• What are the 5 muscles?
• Innervated by? Exception?
• Common origin?
• Insertion? Action? Innervation?

Answer 2

Superficial group of the anterior compartment of the forearm

• Most of innervation is medial nerve
• Origin: medial epicondyle of the humerus / common flexor origin
• Medial epicondylitis: Golfer’s elbow, inflammation

Pronator teres

• Insertion: lateral (midshaft) radius
• Action: pronate forearm
• Innervation: median nerve

Flexor carpi radialis (radialis = radial deviation)

• Insertion: radial side of hand
• Action: flex and abduct wrist
• Innervation: median nerve

Flexor carpi ulnaris

• Insertion: ulnar side of hand
• Action: flex and adduct wrist
• Innervation: ulnar nerve

Palmaris longus (most superficial, absent in 15% of people)

• Insertion: palmar aponeurosis
• Action: flex wrist
• Innervation: medial nerve

Flexor digitorum superficialis

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

Question 3

Deep group of the anterior compartment of the forearm

• What are the 3 muscles?
• Origins? (3)
• Innervation rule?
• Insertion? Action? Innervation?

Answer 3

Deep group of the anterior compartment of the forearm

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

Flexor digitorum profundus

• Insertion: distal phalanges of digits 2-5
• Action: flex digits 2-5 at the MCP, PIP, and DIP joints, and flex wrist
• Innervation: 2,3 are median and 4,5 are ulnar

Flexor pollicus longus

• Action: flex pollicus at the CMC, MCP, and IP joints, and flex wrist
• Innervation: median nerve

Pronator quadratus

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

Question 4

Flexor retinaculum and carpal tunnel

• What is the flexor retinaculum?
• Tendons are surrounded by?
• Forms the roof of?
• Contents of the carpal tunnel?

Answer 4

Flexor retinaculum

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

Carpal tunnel contents

• Median nerve
• Tendons of flexor digitorum superficialis (4)
• Tendons of flexor digitorum profundus (4)
• Tendon of flexor pollicus longus (1)

Question 5

Compartments of the palm

• What are five compartments of the palm?
• What is contained in each?
• Where can untreated infections spread in the central compartment and through what?

Answer 5

Compartments of the palm

• Thenar compartment: 3 thenar muscles acting on the thumb
• Adductor compartment: adductor pollicus muscle
• Hypothenar compartment: 3 hypothenar muscles acting on digit 5
• Central compartment
  
  • Deep to palmar aponeurosis
  • Contains the long flexor tendons (flexor digitorum superficialis and flexor digitorum profundus)
  • Untreated infections in the central compartment can spread through the carpal tunnel and into the anterior compartment of the forearm
• Interosseous compartments
  
  • Between metacarpals
  • Contain the interossei muscles

Question 6

Intrinsic muscles of the hand

• ​3 muscles of the thenar compartment? Action and innervation?
• Muscle of the adductor compartment? Action and innervation?
• 3 muscles of the hypothenar compartment? Action and innervatinon?
• Muscles of the central compartment? Origin, insertion, action, and innervation?
• 2 muscles of the interossei compartment? Action and innervation?

Answer 6

Intrinsic muscles of the hand

• Most are innervated by the ulnar nerve (C8-T1)

Thenar compartment

• Form the thenar eminence
• 3 pollicis muscles
• Innervation: recurrent branch of the median nerve
• Abductor pollicus brevis (lateral)
  
  • Action: abduct thumb at CMC joint
• Flexor pollicus brevis (middle)
  
  • Action: flex thumb at CMC and MCP joints
• Opponens pollicus (deep)
  
  • Action: opposition of thumb (CMC joint)

Adductor compartment (one muscle)

• Adductor pollicis
  
  • Action: adduct thumb at CMC joint
  • Innervation: ulnar nerve
  • NOT part of thenar eminence

Hypothenar compartment (digiti minimi)

• Form the hypothenar eminence
• 3 digiti minimi muscles
• Innervation: ulnar nerve
• Abductor digiti minimi
  
  • ​Action: abduct digit 5 at MCP joint
• Flexor digiti minimi brevis
  
  • Action: flex digit 5 at CMC and MCP joints
• Opponens digiti minimi
  
  • Action: opposition of digit 5 at CMC joint

Central compartment (lumbricals)

• Lumbricals (4)
  
  • Origin: tendons of flexor digitorum profundus
  • Insertion: extensor expansions of digits 2-5
  • Action: flex MCP joints and extend PIP and DIP joints of digits 2-5
  • Innervation: median nerve for 2-3 and ulnar nerve for 4-5
  • Bye bye muscles!

Interossei compartment (2)

• Palmar interossei (3)
  
  • Action: adduct MCP joints of digits 2, 4, and 5
  • PAD
  • Innervation: ulnar nerve
• Dorsal interossei (4)
  
  • Action: abduct MCP joints of digits 2-4
  • DAB
  • Innervation: ulnar nerve

Question 7

What are the sensory innervations of the hand for the median and ulnar nerves?

Answer 7

Sensory innervation of the hand

• Median nerve: lateral palm, palmar aspects of lateral 3.5 digits, and dorsal aspects of the distal halves of lateral 3.5 digits
• Ulnar nerve: skin on the medial palm, medial dorsal hand, and palmar and dorsal aspects of medial 1.5 digits

Question 8

Median nerve

• Mostly innervates?
• Courses through?
• Where can it be compressed?
• If there is a proximal lesion of the median nerve, what will be lost, weakened, and not affected?

Answer 8

Median nerve

• Does NOT innervate arm
• Mostly innervates anterior forearm
• Courses through cubital fossa
• Travels deep the flexor retinaculum within the carpal tunnel (can be compressed here)
• Recurrent branch: gives motor innervation to the 3 thenar muscles
• Common and proper digital nerves: motor to lumbricals to digits 2 and 3, and sensory to skin on lateral palm and lateral 3.5 digits

Proximal lesion of the median nerve (e.g. in the arm)

• Prontation lost
• Flexion and abduction of wrist weakened
• Flexion of MCPs, PIPs, and DIPs of digits 2-3 lost
• Flexion of MCPs and PIPs of digits 4-5 weakened
• Thumb abduction weakened
• Flexion and opposition of thumb lost (due to loss of 3 thenar muscles and flexor pollicus longus)
• Skin on lateral palm, palmer aspects of lateral 3.5 digits, and dorsal aspects of distal halves of lateral 3.5 digits anesthetized
• (Flexion of DIPs digits 4-5 NOT affected)
• (Adduction of thumb NOT affected)
• Test: opposition of thumb, flexion of DIPs of digits 2-3, cutaneous sensation tip of digit 2, “Hand of Benediction” when asked to make a fist

Question 9

Carpal tunnel syndrome

• What is it?
• What muscles are weakened?
• Where do you have loss of sensation?

Answer 9

Carpal tunnel syndrome

• Compression of median nerve
• Results from reduction in size of carpal tunnel, e.g. inflammation of the synovial sheaths of the flexor tendons
• Weakening of thenar muscles, which weakens their grip
• Loss of sensation (but not full anesthesia) on lateral 3.5 digits also affects grip
• Can do surgery to open flexor retinaculum

Question 10

Ulnar nerve

• Passes posterior to? Within the?
• Where can the ulnar nerve be compressed?
• Suspectible to damage with a fracture to?
• Innervates what muscles?
• Travels superficial to?
• If there is a proximal lesion, what actions will be lost, weakened, paralyzed, and anesthetized?

Answer 10

Ulnar nerve

• Does NOT innervate arm
• Passes posterior to the medial epicondyle of the humerus within the cubital tunnel (area of the “funny bone”)
  
  • Can be compressed here (cubital tunnel syndrome)
  • Susceptible to damage with a fracture the medial epicondyle
• Innervates flexor carpi ulnaris and ulnar half of flexor digitorum profundus
• Travels superficial to the flexor retinaculum with the ulnar artery
  
  • Due to this location, suicide attempts by wrist slashing can severe the ulnar nerve, resulting in full paralysis and anesthesia of the innervated structures
• Deep branch: motor to the hypothenar, interossei, lumbricals to digits 4-5, and adductor pollicis
• Common and proper digital nerves: sensory to skin on medial aspect of the palmar and dorsal hand, and palmar and dorsal aspects of the medial 1.5 digits

Proximal lesion of the ulnar nerve (e.g. in the arm)

• Flexion and adduction of the wrist weakened
• Flexion of DIPs of digits 4-5 lost
• Affects grip: hypothenar and adductor pollicis muscles paralyzed
• Intricate hand movements affected: interossei muscles paralyzed (adduction and abduction of digits 2-5 lost), lumbricals to digits 4-5 paralyzed (MCP flexion, PIP and DIP extension affected)
• Skin of medial palm and medial 1.5 digits anesthetized
• Test: adduct and abduct digits 2-5 and cutaneous sensation tip of digit 5

Question 11

Arteries

• Where does the brachial artery branch into ulnar and radial arteries?
• Ulnar artery
  
  • Gives rise to what two arteries?
  • Second artery divides into?
  • Ulnar artery travels with ulnar nerve where?
  • It is superficial to what?
  • You can palpate ulnar pulse where?
  • Gives rise to what arch?
  • How does it anastomose with the radial artery?
• Radial artery
  
  • Gives rise to what artery?
  • Supplies what?
  • Where do you measure pulse rate?
  • Gives rise to what arch?

Answer 11

Brachial artery gives rise to the ulnar and radial arteries in the cubital fossa

Ulnar artery

• Gives rise to the ulnar recurrent arteries (anastomose around elbow)
• Gives rise to the common interosseous artery, which divides into:
  
  • Anterior interosseous artery: supplies deep aspect of anterior forearm, deep aspect of distal posterior forearm, and dorsal hand
  • Posterior interosseous artery: supplies posterior forearm
• Travels with the ulnar nerve along the medial aspect of the forearm
• Courses superficial to the flexor retinaculum with the ulnar nerve (can palpate ulnar pulse here)
• Gives rise to the superficial palmar arch: supplies common and proprer digital arteries
• Ulnar artery anastomoses with the radial artery via the superficial and deep palmar arches

Radial artery

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