Wrist and Hand - Chapter 5, Biomechanics

Why are the wrist and hand considered complex structures?

Contains many bones/joints/ligaments/muscles and performs fine movements

What are prehensile hands?

Hands capable of grasping objects

What allows humans to have prehensile hands?

Thumb’s ability to perform opposition, allowing it to touch other fingers

What structures contribute to the thumb’s movement?

Thumb joint, thenar muscles, hypothenar muscles

How many carpal bones make up the wrist?

Eight

Which bones form the proximal row of the carpals?

Scaphoid, lunate, triquetrum, pisiform

Which bones form the distal row of the carpals?

Trapezium, trapezoid, capitate, hamate

Which carpal bone is most commonly fractured?

Scaphoid (navicular)

Which carpal bone is the largest?

Capitate

Which carpal bone can be palpated on the palm near the little finger?

Hamate (hook of hamate)

How many metacarpal bones are in the hand?

Five

Which metacarpal belongs to the thumb?

The first metacarpal

How many phalanges are in the hand?

Fourteen

How are the thumb and fingers different in the number of phalanges?

Thumb: 2 (proximal and distal); Fingers: 3 (proximal, middle, distal)

What bones form the radiocarpal joint?

Radius and proximal row of carpal bones

What bones form the midcarpal joints?

Between the proximal and distal rows of carpals

What are intercarpal joints?

Joints between carpal bones within the same row

What are carpometacarpal (CM) joints?

Joints between the distal carpal bones and the metacarpals

What are metacarpophalangeal (MP) joints?

Joints between the metacarpals and proximal phalanges

Which interphalangeal joints are found in the fingers?

Proximal interphalangeal (PIP), distal interphalangeal (DIP)

Which interphalangeal joint is found in the thumb?

Interphalangeal (IP) joint

Which ligament forms the roof of the carpal tunnel?

Flexor retinaculum (transverse carpal ligament)

What is the function of the flexor retinaculum?

Holds the flexor tendons close to the wrist

What are extensor retinacula?

Bands that hold the extensor tendons against wrist during extension

What causes carpal tunnel syndrome?

Compression of median nerve beneath flexor retinaculum due to swelling or inflammation

What four movements occur at the wrist?

Flexion, extension, radial deviation, ulnar deviation

At which joints does wrist flexion primarily occur?

Radiocarpal joint

At which joints does wrist extension primarily occur?

Midcarpal joints

What is radial deviation?

Movement of the hand toward the thumb

What is ulnar deviation?

Movement of the hand toward the little finger

What movements occur at the MP joints?

Flexion, extension, abduction, adduction

What movements occur at the PIP, DIP, and thumb IP joints?

Flexion and extension only

What are extrinsic muscles of the hand?

Muscles that originate on humerus, radius, or ulna and insert into hand

What are the five major anterior wrist muscles?

Flexor carpi radialis, flexor carpi ulnaris, flexor digitorum superficialis, palmaris longus, flexor digitorum profundus

What is the action of flexor carpi radialis?

Wrist flexion and radial deviation

What is the action of flexor carpi ulnaris?

Wrist flexion and ulnar deviation

What is the action of flexor digitorum superficialis?

Flexes PIP joints and assists wrist and MP flexion

What is the action of palmaris longus?

Wrist flexion and tightening of palmar aponeurosis

What is the action of flexor digitorum profundus?

Flexes DIP joints of digits 2-5

What are the five major posterior wrist muscles?

Extensor carpi radialis longus and brevis, extensor carpi ulnaris, extensor digitorum, extensor digiti minimi

What is the action of extensor carpi radialis longus?

Wrist extension and radial deviation

What is the action of extensor carpi radialis brevis?

Wrist extension and radial deviation

What is the action of extensor carpi ulnaris?

Wrist extension and ulnar deviation

What is the action of extensor digitorum?

Extends wrist, MP, PIP, and DIP joints of digits 2-5

What is the action of extensor digiti minimi?

Extends little finger and assists wrist extension

What is the action of extensor indicis?

Extends index finger and assists wrist extension

What are intrinsic hand muscles?

Muscles that both originate and insert within the hand

Which muscles make up the hypothenar eminence?

Abductor digiti minimi, flexor digiti minimi brevis, opponens digiti minimi

What does the abductor digiti minimi do?

Abducts little finger

What does the flexor digiti minimi brevis do?

Flexes little finger

What does the opponens digiti minimi do?

Helps bring little finger toward thumb (opposition)

What are the lumbricals?

Intrinsic muscles that flex MP joints and extend IP joints

What do the dorsal interossei do?

Abduct the fingers

What do the palmar interossei do?

Adduct the fingers

Which muscles are the thumb’s extrinsic muscles?

Extensor pollicis longus and brevis, abductor pollicis longus, flexor pollicis longus

What is the action of extensor pollicis longus?

Extends the thumb

What is the action of extensor pollicis brevis?

Extends the thumb at the MP joint

What is the action of abductor pollicis longus?

Abducts the thumb

What is the action of flexor pollicis longus?

Flexes the thumb

Which muscles make up the thenar eminence?

Abductor pollicis brevis, flexor pollicis brevis, opponens pollicis, adductor pollicis

What does the abductor pollicis brevis do?

Abducts the thumb

What does the flexor pollicis brevis do?

Flexes the thumb

What does the opponens pollicis do?

Produces opposition of the thumb

What does the adductor pollicis do?

Adducts the thumb

What movements can the thumb perform?

Flexion, extension, abduction, adduction, opposition

How do thumb movement planes differ from most joints?

Flexion and extension occur in frontal plane, abduction and adduction occur in sagittal plane