The Wrist and Hand

Question 1

What are the 3 classes of bone in the hand?

Answer 1

Carpal bones (Most proximal) – A set of eight irregularly shaped bones. These are located in the wrist area.

Metacarpals – There are five metacarpals, each one related to a digit

Phalanges (Most distal) – The bones of the fingers. Each finger has three phalanges, except for the thumb, which has two.

Question 2

Describe the organisation of the carpal bones

Answer 2

In the proximal row, the bones are (lateral to medial):

Scaphoid

Lunate

Triquetrum

Pisiform – A sesamoid bone, formed within the tendon of the flexor carpi ulnaris

In the distal row, the bones are (lateral to medial):

Trapesium

Trapezoid

Capitate

Hamate – has a projection on its palmar surface called the hook of hamate

Question 3

Describe the organisation of the metacarpal bones

Answer 3

Metacarpal I – Thumb.

Metacarpal II – Index finger.

Metacarpal III – Middle finger.

Metacarpal IV – Ring finger.

Metacarpal V – Little finger.

Question 4

What are the phalanges?

Answer 4

The phalanges are the bones of the fingers. The thumb has a proximal and distal phalanx, while the rest of the digits have proximal, middle and distal phalanges.

Question 5

What is the difference between the intrinsic and extrinsic muscles of the hand?

Answer 5

• The extrinsic muscles are located in the anterior and posterior compartments of the forearm. They control crude movements, and produce a forceful grip.
• The intrinsic muscles of the hand are located within the hand itself. They are responsible for the fine motor functions of the hand.

Question 6

What are the thenar muscles?

Answer 6

The thenar muscles are three short muscles located at the base of the thumb. The muscle bellies produce a bulge, known as the thenar eminence. They are responsible for the fine movements of the thumb.

The median nerve innervates all the thenar muscles.

• opponens pollicis
• abductor pollicis brevis
• flexor pollicis brevis

Question 7

Give the attachments, innervation and action of Opponens Pollicis

Answer 7

The opponens pollicis is the largest of the thenar muscles, and lies underneath the other two.

Attachments: Originates from the tubercle of the trapezium, and the associated flexor retinaculum. It inserts into the lateral margin of the metacarpal of the thumb.

Actions: Opposes the thumb, by medially rotating and flexing the metacarpal on the trapezium.

Innervation: Median nerve.

Question 8

Give the attachments, innervation and action of Abductor Pollicis Brevis

Answer 8

This muscle is found anteriorly to the opponens pollicis and proximal to the flexor pollicis brevis.

Attachments: Originates from the tubercles of the scaphoid and trapezium, and from the associated flexor retinaculum. Attaches to lateral side of proximal phalanx.

Actions: Abducts the thumb.

Innervation: Median nerve.

Question 9

Give the attachments, innervation and actions of Flexor Pollicis Brevis

Answer 9

The most distal of the thenar muscles.

Attachments: Originates from the tubercle of the trapezium and from the associated flexor retinaculum. Attaches to the base of the proximal phalanx of the thumb.

Actions: Flexes the MCP joint of the thumb.

Innervation: Median nerve.

Question 10

Name the hypothenar muscles

Answer 10

• Opponens Digiti Minimi
• Abductor Digiti Minimi
• Flexor Digiti Minimi Brevis

Question 11

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Answer 11

The opponens digit minimi lies deep to the other hypothenar muscles.

Attachments: Originates from the hook of hamate and associated flexor retinaculum, inserts into the medial margin of metacarpal V.

Actions: It rotates the metacarpal of the little finger towards the palm, producing opposition.

Innervation: Ulnar nerve.

Question 12

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Answer 12

The most superficial of the hypothenar muscles.

Attachments: Originates from the pisiform and the tendon of the flexor carpi ulnaris. It attaches to the base of the proximal phalanx of the little finger.

Actions: Abducts the little finger.

Innervation: Ulnar nerve.

Question 13

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Answer 13

This muscles lies laterally to the abductor digiti minimi.

Attachments: Originates from the hook of hamata and adjacent flexor retinaculum, and inserts into the base of the proximal phalanx of the little finger.

Actions: Flexes the MCP joint of the little finger.

Innervation: Ulnar Nerve.

Question 14

What are the lumbricals?

Answer 14

These are four lumbicals in the hand, each associated with a finger. They are very crucial to finger movement, linking the extensor tendons to the flexor tendons.

Denerveration of these muscles is the basis for the ulnar claw and hand of benediction.

Attachments: Each lumbrical originates from a tendon of the flexor digitorum profundus. They pass dorsally and laterallly around each finger, and inserts into the extensor hood.

Actions: The flex at the MCP joint, and extend at the IP joints of each finger.

Innervation: The medial two lumbricals (of the little and ring fingers) are innervated by the ulnar nerve. The lateral two lumbricals (of the index and middle fingers) are innervated by the median nerve.

Question 15

What are the interossei muscles?

Answer 15

The interossei muscles are located between the metacarpals. They can be divided into two groups; the dorsal and palmar interossei.

In addition to their individual actions, the interossei also assist the lumbricals in flexion and MCP joints, and extension at the IP joints.

Question 16

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Answer 16

The most superficial of all dorsal muscles, these can be palpated on the dorsum of the hand. There are four dorsal interossei muscles.

Attachments: Each interossei originates from the lateral and medial surfaces of the metacarpals. They attach into the extensor hood and proximal phalanx of each finger.

Actions: Abduct the fingers at the MCP joint.

Innervation: Ulnar nerve.

Question 17

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Answer 17

These are located anteriorly on the hand. There are three palmar interossei muscles.

Attachments: Each interossei originates from a medial or lateral surface of a metacarpal, and attaches into the extensor hood and proximal phalanx of same finger.

Actions: Adducts the fingers at the MCP joint.

Innervation: Ulnar nerve.

Question 18

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Answer 18

This is a small, thin muscle, found very superficially in the subsutaneous tissue of the hypothenar eminence.

Attachments: Originates from the palmar aponeurosis and flexor retinaculum, attaches to the dermis of the skin on the medial margin of the hand.

Actions: Wrinkles the skin of the hypothenar eminence and deepens the curvature of the hand, improving grip.

Innervation: Ulnar nerve.

Question 19

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Answer 19

This is large triangular muscle with two heads. The radial artery passes anteriorly through the space between the two heads, forming the deep palmar arch.

Attachments: One head originates from metacarpal III, the other from the capitate, and adjacent areas of metacarpals II and III. They both attach into the base of the proximal phalanx of the thumb.

Actions: Adductor of the thumb.

Innervation: Ulnar nerve.

Question 20

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Answer 20

The wrist joint is formed by:

Distally – The proximal row of the carpal bones (except the pisiform).

Proximally – The distal end of the radius, and the articular disk.

The ulna is not part of the wrist joint – it articulates with the radius, just proximal to the wrist joint, at the distal radioulnar joint. It is prevented from articulating with the carpal bones by a fibrocartilginous ligament, called the articular disk, which lies over the superior surface of the ulna.

Together, the carpal bones form a convex surface, which articulates with the concavesurface of the radius and articular disk.

Question 21

Describe the vasculature and innervation of the wrist

Answer 21

The wrist joint receives blood from branches of the dorsal and palmar carpal arches, which are derived from the ulnar and radial arteries

Innervation to the wrist is delivered by branches of three nerves:

Median nerve – Anterior interosseous branch.

Radial nerve – Posterior interosseous branch.

Ulnar nerve – deep and dorsal branches.

Question 22

How is stability of the wrist joint achieved?

Answer 22

Joint capsule: Like any synovial joint, the capsule is dual layered. The fibrous outer layer attaches to the radius, ulna and the proximal row of the carpal bones. The internal layer is comprised of a synovial membrane, secreting synovial fluid which lubricates the joint.

Palmar radiocarpal – It is found on the palmar (anterior) side of the hand. It passes from the radius to both rows of carpal bones. Its function, apart from increasing stability, is to ensure that the hand follows the forearm during supination.

Dorsal radiocarpal – It is found on the dorsum (posterior) side of the hand. It passes from the radius to both rows of carpal bones. It contributes to the stability of the wrist, but also ensures that the hand follows the forearm during pronation.

Ulnar collateral – Runs from the ulnar styloid process to the triquetrum and pisiform. Works in union with the other collateral ligament to prevent excessive lateral joint displacement.

Radial collateral – Runs from the radial styloid process to the scaphoid and trapezium. Works in union with the other collateral ligament to prevent excessive lateral joint displacement.

Question 23

Describe movements of the wrist

Answer 23

The wrist is an ellipsoid type synovial joint, allowing for movement along two axes. This means that flexion, extension, adduction and abduction can all occur at the wrist joint.

All the movements of the wrist are performed by the muscles of the forearm.

Flexion – Produced mainly by the flexor carpi ulnaris, flexor carpi radialis, with assistance from the flexor digitorum superficialis.

Extension – Produced mainly by the extensor carpi radialis longus and brevis, and extensor carpi ulnaris, with assistance from the extensor digitorum.

Adduction – Produced by the extensor carpi ulnaris and flexor carpi ulnaris

Abduction – Produced by the abductor pollicis longus, flexor carpi radialis, extensor carpi radialis longus and brevis.

Question 24

What is the anatomical snuffbox?

Answer 24

The anatomical snuffbox (also known as the radial fossa), is a triangular depression found on the lateral aspect of the dorsum of the hand. It is located at the level of the carpal bones, and best seen when the thumb is abducted.

Question 25

What are the borders of the anatomical snuffbox?

Answer 25

Ulnar (medial) border: Tendon of the extensor pollicis longus.

Radial (lateral) border: Tendons of the abductor pollicis longus and extensor pollicis brevis.

Proximal border: Styloid process of the radius.

Floor: Carpal bones; scaphoid and trapezium.

Roof: Skin.

Question 26

What are the contents of the anatomical snuffbox?

Answer 26

• The radial artery crosses the floor of the anatomical snuffbox in an oblique manner. It runs deep to the extensor tendons. The radial pulse can be palpated in some individuals by placing two fingers on the proximal portion of the anatomical snuffbox.
• Subcutaneously, terminal branches of the superficial branch of the radial nerve run across the roof of the anatomical snuffbox, providing innervation to the skin of the lateral 3 1/2 digits on the dorsum of the hand, and the associated palm area.
• Also subcutaneously, the cephalic vein crosses the anatomical snuffbox, having just arisen from the dorsal venous network of the hand.

Question 27

What is the carpal tunnel?

Answer 27

The carpal tunnel is a narrow passageway found on the anterior portion of the wrist. It serves as the entrance to the palm for several tendons and the median nerve.

Question 28

What are the borders of the carpal tunnel?

Answer 28

Carpal Arch:

Concave on the palmar side

Formed laterally by the scaphoid and trapezium tubercles

Formed medially by the hook of the 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.

To find where the carpal tunnel begins on yourself, locate your distal wrist crease, which aligns with the entrance of the carpal tunnel.

Question 30

What are the contents of the carpal tunnel?

Answer 30

The carpal tunnel contains a total of 9 tendons, surrounded by synovial sheaths, and the median nerve.

Tendons:

• The tendon of flexor pollicis longus
• 4 tendons of flexor digitorum profundus
• 4 tendons of flexor digitorum superficialis

The 8 tendons of the flexor digitorum profundus and flexor digitorum superficialis are surrounded by a single synovial sheath.

The tendon of flexor pollicis longus is surrounded by its own synovial sheath. These sheaths allow free movement of the tendons.

Question 31

Describe the branching of the median nerve in the carpal tunnel

Answer 31

Once it passes through the carpal tunnel, the median nerve divides into 2 branches: the recurrent branch and palmar digital nerves.

The palmar digital nerves give sensory innervation to the palmar skin and dorsal nail beds of the lateral three and a half digits. They also provide motor innervation to the lateral two lumbricals. The recurrent branch supplies the thenar muscle group.