Week 6 - The Hand Flashcards
Which muscles are included in the intrinsic muscle group of the hand?
- Thenar muscles
- Hypothenar muscles
- Lumbricals
- Interossei
What are the 2 groups of muscles that can be found in the hand?
Extrinsic: located in the anterior and posterior compartments of the forearm, control crude movements
Intrinsic: located within the hand itself, responsible for the fine motor functions of the hand
What are the thenar muscles?
3 short muscles
- Opponens pollicis (largest muscle, lies underneath the other 2 muscles, from the tubercle of the trapezium and the associated flexor retinaculum to the metacarpal of the thumb)
- Abductor pollicis brevis (from the tubercles of the scaphoid and trapezium and from the associated flexor retinaculum, to the lateral side of proximal phalanx)
- Flexor pollicis brevis (from the tubercle of the trapezium and associated flexor retinaculum to the base of the proximal phalanx of the thumb)
What innervates the thenar muscles?
Median nerve
What is the action of the opponens pollicis?
Opposes the thumb, by medically rotating and flexing the metacarpal on the trapezium
What are the actions of the abductor pollicis brevis?
Abducts the thumb
What are the actions of the flexor pollicis brevis?
Flexes the MCP joint of the thumb
What are the hypothenar muscles?
- Opponens digiti minimi (from the hook of hamate and associated flexor retinaculum, to the medial margin of metacarpal V)
- Abductor digiti minimi (from the pisiform and the tendon of the flexor carpi ulnaris, to the base of the proximal phalanx of the little finger)
- Flexor digiti minimi brevis (from the hook of hamate and adjacent flexor retinaculum, to the base of the proximal phalanx of the little finger)
What innervates the hypothenar muscles?
Ulnar nerve
What are the actions of the opponens digiti minimi?
Rotates the metacarpal of the little finger towards the palm, producing opposition
What are the actions of the abductor digiti minimi?
Abducts the little finger
What are the actions of the flexor digiti minimi brevis?
Flexes the MCP joint of the little finger
What are the lumbricals?
- There are 4 lumbricals in the hand
- Each are associated with a finger
- They are crucial to finger movement, linking the extensor tendons to the flexor tendons
What innervates the lumbricals?
- Medial 2 lumbricals = ulnar nerve
- Lateral 2 lumbricals = median nerve
What are the interossei muscles?
- Muscles that are located between the metacarpals
- Can be divided into 2 groups: dorsal and palmar
- Dorsal: from the medial and lateral surfaces of a metacarpal, to the extensor hood and proximal phalanx of each finger
- Palmar: from a medial or lateral surface of a metacarpal, to the extensor hood and proximal phalanx of the same finger
What innervates the interossei muscles?
Ulnar nerve
What are the actions of the interossei muscles?
- Dorsal: abducts the fingers at the MCP joint (DAB)
- Palmar: adducts the fingers at the MCP joint (PAD)
- They also assist the lumbricals in flexion at the MCP joints and extension at the IP joints
What other muscles (I.e. Not intrinsic hand muscles) can be found in the palm?
- Palmaris brevis
- Adductor pollicis
Where is the palmaris brevis found?
- From the palmar aponeurosis and flexor retinaculum
- To the dermis of the skin on the medial margin of the hand
What are the actions of the palmaris brevis?
- Wrinkles the skin of the hypothenar eminence
- Deepens the curvature of the hand, improving grip
What innervates the palmaris brevis?
Ulnar nerve
Where does the adductor pollicis originate from/attach to?
Has 2 heads:
- 1 head: from metacarpal III
- Other head: from adjacent areas of metacarpals II and III, and the capitate
- Both attach to the base of the proximal phalanx of the thumb
What are the actions of the adductor pollicis?
Adducts the thumb
What innervates the adductor pollicis?
Ulnar nerve
What is the blood supply to the hand?
- There is a good supply, with many anastomosing arteries
- Majority are superficial arteries (allows for heat loss when needed)
- The radial and ulnar arteries interconnect to form 2 arches, from which branches to the digits emerge
- The radial artery contributes mainly to the supply of the thumb and lateral side of the index finger
- The ulnar artery contributes mainly to supply of the rest of the digits and medial side of the index finger
How does the ulnar artery enter the hand?
- It moves into the hand anteriorly to the flexor retinaculum and laterally to the ulnar nerve
- It then divides into 2 branches: superficial palmar arch and deep palmar arch
Where is the superficial palmar arch found?
- Anterior to the flexor tendons in the hand
- Just deep to the palmar aponeurosis
What arises from the superficial palmar arch?
The common digital arteries
How does the radial artery enter the hand?
- It enters dorsally, crossing the floor of the anatomical snuffbox
- It turns medically and moves between the heads of the adductor pollicis
- It then anastomoses with the deep palmar branch of the ulnar artery, forming the deep palmar arch
What is the carpal tunnel?
- A narrow passageway found on the anterior portion of the wrist
- Serves as the entrance to the palm for several tendons and the median nerve
How is the carpal tunnel formed?
By 2 layers:
A deep carpal arch
- Concave on the palmar side
- Formed laterally by the scaphoid and trapezium tubercles
- Formed medially by the hook of hamate and the pisiform
Flexor retinaculum
- Thick connective tissue
- Turns the carpal arch into the carpal tunnel by bridging the space between the medial and lateral parts of the arch
- Originates on the lateral side and inserts on the medial side of the carpal arch
What are the contents of the carpal tunnel?
Tendons:
- Tendon of flexor pollicis longus
- 4 tendons of flexor digitorum profundus
- 4 tendons of flexor digitorum superficialis
Median nerve
What happens to the median nerve after it passed through the carpal tunnel?
It divides into 2 branches
- Recurrent branch (supplies the thenar muscles)
- Palmar digital
What does the palmar digital (median) nerve innervate?
- Sensory innervation: the palmar skin and dorsal nail beds of lateral 3.5 digits
- Motor innervation: lateral 2 lumbricals
What is carpal tunnel syndrome?
Compression of the median nerve with the carpal tunnel
- It can cause weakness and atrophy of the thenar muscles if left untreated
What can cause carpal tunnel syndrome?
- Thickened ligaments and tendon sheaths
- Most often idiopathic (unknown)
How can you test for carpal tunnel syndrome?
- Tap the nerve in the carpal tunnel to elicit pain in median nerve distribution
- Hold the wrist in flexion for 60 seconds to elicit numbness/pain in median nerve distribution
How can you treat carpal tunnel syndrome?
- Use a splint to hold the wrist in dorsiflexion overnight to relieve symptoms
- If unsuccessful, can use corticosteroid injections in the carpal tunnel
- In severe cases, surgical decompression of the carpal tunnel may be required
What is a Boxer’s fracture?
A fracture of the 5th metacarpal neck
- Usually caused by a clenched fist striking a hard object
- The distal part of the fracture is displaced posteriorly, producing shortening of the affected finger
What is a scaphoid fracture?
- Most common carpal bone fracture
- Causes pain and tenderness in the anatomical snuffbox
- Needs to be fixed quickly, since it may cut off the blood supply to the proximal part of the bone (will cause a vascular necrosis)
- If undiagnosed, patient is likely to develop wrist arthritis
What is the effect of a superficial laceration at the wrist?
May damage the palmar cutaneous branch of the median nerve
- Hence loss of sensation over the skin overlying the thenar eminence
- No motor deficit
Mainly damages skin
No penetration of major blood vessels
What are the effects of a deep laceration at the wrist?
- Ulnar nerve damage (results in claw hand deformity, sensory loss in medial 1.5 digits only)
- Median nerve and its palmar cutaneous branch injury (results in ape thumb deformity, sensory loss on lateral palm and in the lateral 3.5 digits)
- Tendons in carpal tunnel may be damaged
- Radial and ulnar artery may be damaged
What is the effect of a laceration to the palm?
- May damage tendons
- Superficial or/and deep artery arches may be damaged depending on depth of wound
- Median/ulnar nerve damage
How can Erb’s palsy occur?
Excessive increase in the angle between the neck and the shoulder
- This stretches (or can even tear) the nerve roots, causing damage
- Can occur as a result of a difficult birth or shoulder trauma
What nerves are affected in Erb’s palsy?
- Musculocutatneous
- Axillary
- Suprascapular
- Subclavian
Which muscles are paralysed in Erb’s palsy?
- Supraspinatus
- Infraspinatus
- Subclavius
- Biceps brachii
- Brachialis
- Coracobrachialis
- Deltoid
- Teres minor
Which motor functions are affected in Erb’s palsy?
Movements that are lost or greatly weakened:
- Abduction at shoulder
- Lateral rotation of arm
- Supination of forearm
- Flexion at shoulder
Which sensory functions are affected in Erb’s palsy?
There is a loss of sensation down the lateral side of arm
What is the characteristic presentation of Erb’s palsy?
Affected limb hangs limply - “waiter’s tip”:
- Medially rotated by unopposed actin of the pectoralis major
- Forearm is pronated due to the loss of biceps brachii
What type of injury is Erb’s palsy?
An upper brachial plexus injury
What is Klumpke’s palsy?
A lower brachial plexus injury
How can Klumpke’s palsy occur?
By excessive abduction of the arm
- E.g. Someone catching a branch of the arm
Which nerves are affected by Klumpke’s palsy?
Nerves derived from the T1 root
- Ulnar and median
Which muscles are paralysed by Klumpke’s palsy?
All of the small muscles of the hand
What is the sensory effect of Klumpke’s palsy?
Loss of sensation along medial side of arm
What is the characteristic presentation of Klumpke’s palsy?
Clawed appearance of hand
- The MCP joints are hyperextended and the IP joints are flexed
What is the most common way of damaging the ulnar nerve at the elbow?
Fracture of the medial epicondyle
What is the effect on motor functions following ulnar nerve injury at the elbow?
Paralysed muscles: flexor carpi ulnaris, medial half of flexor digitorum profundus, interossei, medial 2 lumbricals
- Flexion of the wrist can still occur, but is accompanied by abduction
- Abduction and adduction of the fingers cannot occur since interossei muscles are paralysed
- Movement of the little and ring fingers is greatly reduced, due to paralysis of the medial 2 lumbricals
Which sensory functions are affected following ulnar nerve injury at the elbow?
All sensory branches are affected
- Loss of sensation over the areas that the ulnar nerve innervates
What is a sign of ulnar nerve injury at the elbow?
Patient cannot grip paper placed between fingers
How can ulnar nerve injury at the wrist occur?
Laceration at the wrist
Which motor functions are affected following ulnar nerve damage at the wrist?
- The interossei are paralysed, so abduction and Adduction of the fingers cannot occur
- Movement of the little and ring fingers is greatly reduced, due to paralysis of the medial 2 lumbricals
Which sensory functions are affected following ulnar nerve damage at the wrist?
- The palmar branch and superficial branch are usually severed, but the dorsal branch is unaffected
- Sensory loss over palmar side of medial 1.5 fingers only
What is a characteristic sign of ulnar nerve damage at the wrist?
Patient cannot grip paper placed between fingers
- For long term cases: a hand deformity called ulnar claw develops
- – Hyperextension of the MCP joints of the little and ring fingers (due to paralysis of the medial 2 lumbricals and the now unopposed action of the extensor muscles)
- – Flexion at the IP joints
How can median nerve injury occur at the wrist?
Commonly in lacerations just proximal to the flexor retinaculum
What motor functions are affected following median nerve injury at the wrist?
- Thenar muscles are paralysed
- Lateral 2 lumbricals are paralysed
- This affects opposition of the thumb and flexion of the index and middle fingers
What sensory functions are affected following median nerve injury at the wrist?
Lack of sensation over the area that the median nerve innervates
What is the characteristic sign of median nerve injury at the wrist?
- The thenar eminence is wasted, due to atrophy of the thenar muscles
- If the patient tries to make a fist, only the little and ring fingers can flex completely
- This results in a characteristic shape of the hand known as ‘hand of benediction’
How can median nerve injury occur at the elbow?
Commonly by supracondylar fracture of the humerus
Which motor functions are affected following median nerve injury at the elbow?
- The flexors and pronators in the forearm are paralysed, with the exception of the flexor carpi ulnaris and medial half of flexor digitorum profundus
- The forearm is constantly supinated
- Flexion is weak (often accompanied by adduction, because of the pull of the flexor carpi ulnaris)
- Flexion at the thumb is also prevented, as both the longus and brevis are paralysed
- The lateral 2 lumbrical muscles are paralysed
- The patient will not be able to flex at the MCP joints or extend at the IP joints of the index and middle fingers
What are the characteristic signs of median nerve injury at the elbow?
- Wasted thenar eminence
- Hand of benediction
