STRUCTURE OF THE HAND

1
STRUCTURE OF THE HAND

• Carpals (8) scaphoid, lunate, triquetral,
  pisiform, trapezium, trapezoid, capitate, and
  hamate
• Metacarpals (5) proximal base, medial body, and
  distal head
• Phalanges (14) proximal, medial, distal (the
  thumb has only proximal and distal)

2
JOINTS OF THE WRIST

• The wrist joints are composed of the radiocarpal
  joints and the intercarpal joints
• radiocarpal joint formed by the distal end of the
  radius, an articular disk, and (3) of the (4)
  carpal bones in the proximal row (scaphoid,
  lunate triquetral)
• intercarpal joints are divided into (3) groups
  the joints between the proximal row bones the
  joints between the distal row bones and the
  midcarpal joint, the joint between the (2) rows

3
JOINTS OF THE HAND

• There are (12) hinge joints and (5) universal
  joints in the hand allowing for (22) degrees of
  freedom note the thumbs carpometacarpal joint
  is also called a saddle joint permitting
  extensive and unique mvts.
• Hinge joints (within the phalanges) 1 dof
• Universal joints (MP) 2 dof

4
MUSCLES OF THE WRIST AND HAND

• Six principle muscles act on the wrist, although
  the extrinsic muscles of the hand can act as
  agonists flexor carpi radialis, flexor carpi
  ulnaris, flexor digitorum superficialis, extensor
  carpi radialis longus, extensor carpi radialis
  brevis, and extensor carpi ulnaris

5
MUSCLES OF THE WRIST AND HAND

• Intrinsic muscles of the hand are sub-divided
  into (3) groups those of the thumb (thenar
  eminence) on the radial side, those of the little
  finger (hypothenar eminence)on the ulnar side,
  and those in the middle of the hand and between
  the metacarpals.
• (11) small intrinsic muscles are involved with
  mvt of the fingers (4) lumbricals, (4) dorsal
  interossei, (3) palmar interossei

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MUSCLES OF THE WRIST AND HAND

• (3) muscles act only on the little finger
  abductor digiti minimi, flexor digiti minimi
  brevis, opponens digiti minimi
• (8) muscles act on the thumb, (4) are intrinsic
  to the hand (flexor pollicis brevis, opponens
  pollicis, abductor pollicis brevis, adductor
  pollicis) extrinsic muscles are (extensor
  pollicis longus, extensor pollicis brevis,
  abductor pollicis longus, flexor pollicis longus

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FUNCTION OF THE HAND

• Opposition is a movement by which the pulp
  surface of the thumb is placed squarely in
  contact with--or dramatically opposite to-the
  terminal pads of one or all of the remaining
  digits
• This mvt and the resultant manueverability of the
  thumb separate us from other primates abduction,
  circumduction rotation

8
FUNCTION OF THE HAND

• Opposibility index total length of thumb x
  100/total length of index finger
• A low index denotes a long first finger and a
  short thumb, in primates the mean values are
  between 40 and 65.
• Orangutans mean 40
• humans mean 60

9
FUNCTION OF THE HAND

• What movement of the thumb separates Old World
  monkeys and apes from New World monkeys and
  prosimians?
• Which primates are closest to our opposibility
  factor? (apes, gorillas, baboons and mandrills)

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MOVEMENTS OF THE HAND

• Thomas Ellis (1804-1878) noted that the true
  position of rest in the hand lies somewhere
  about a mean between the ranges of easy movement
  Explain?
• How did Ellis come to this description?

11
MOVEMENTS OF THE HAND

• Two Classes of Movement of the Hand
• Prehensile movements an object, fixed or free,
  is held by a gripping or pinching action between
  the digits and the palm
• Nonprehensile movements include pushing,
  lifting, tapping, and punching movements of the
  fingers

12
MOVEMENTS OF THE HAND

• There are two main patterns and two subsidiary
  prehensile patterns
• Main
• precision - thumb held against pulp (pulp to
  pulp)
• power - thumb held against palm
• Subsidiary
• hook - without thumb
• scissors - without thumb
• The type of grip used is a function of the
  activity itself does not depend on the shape or
  size of the object gripped.

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MOVEMENTS OF THE HAND

• How is this generalization effected by very small
  or very large objects?
• Differentiate the prehensile patterns in Old
  World and New World Primates.
• Regarding tools, should function dictate design?

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FUNCTION OF THE HAND

• What did your observational experiment yield
  regarding the (4) grips?