Anatomical snuff box and intrinsic muscles of the hand

Question 1

What are the borders of the anatomical snuff box?

Answer 1

Lateral/anterior border:
Abductor pollicis longus -> to base of 1st metacarpal
Extensor pollicis brevis -> to base of proximal phalanx
Floor: scaphoid, (radial artery), trapezium.
Medial/posterior border:
Extensor pollicis longus -> to base of distal phalanx

Question 2

What is the clinical significance of the anatomical snuff box?

Answer 2

Radial pulse + palpate scaphoid

Question 3

What is the origin, insertion and action of the lumbricals?

Answer 3

Origin: flexor digitorum profundus tendons
Insertion: extensor hoods d2-5
Link flexor to extensor tendons
Extend interphalangeal joints + flex MCP joints 
Precision grip (hold pen / pinch)

Question 4

What is the origin, insertion and action of the palmar interossei?

Answer 4

3 palmar interossei, sit between metacarpals.
Origin: 2nd, 4th, 5th metacarpals.
Insertion: extensor hoods d2, d4, d5.
PAD: Palmar ADduct MCP joints relative to d3. no palmar interossei for d1 (performed by adductor pollicis) or d3.

Question 5

What is the origin, insertion and action of the dorsal interossei?

Answer 5

4 dorsal interossei, sit between metacarpals.
Origin: metacarpals
Insertion: extensor hoods d2, d3(x2), d4.
DAB: dorsal abduct MCP joints relative to D3.
No dorsal interossei for D1 or D5 (performed by thenar + hypothenar muscles).

Question 6

What is the origin and action of the thenar and hypothenar muscles?

Answer 6

Flexor retinaculum + adjacent carpal bones
Thenar -> fine movements of thumb (d1)
Hypothenar -> fine movements of little finger (d5)

Question 7

What are the 3 thenar muscles?

Answer 7

Opponens pollicis (deepest) -> inserts into 1st metacarpal, draws thumb across little finger during opposition. 
Abductor pollicis brevis -> into proximal phalanx, abducts thumb. 
Flexor pollicis brevis -> into proximal phalanx, flexes thumb.

Question 8

What are the 3 hypothenar muscles?

Answer 8

Opponens digiti minimi (deepest) -> into 5th metacarpal, draws little finger towards thumb during opposition.
Abductor digiti minimi -> into proximal phalanx, abducts little finger.
Flexor digiti minimi -> flexes little finger.

Question 9

Which muscle adducts the thumb?

Answer 9

Adductor pollicis (deep to thenar muscles):
Oblique head -> base 2nd and 3rd metacarpal + carpal bones
Transverse head -> 3rd metacarpal
Insertion: proximal phalanx