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Biomechanics > Elbow/forearm > Flashcards

Elbow/forearm Flashcards

1
Q

What it normal cubitus valgus?

A

15 degrees angle from longitudinal axix

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2
Q

What is excessive cubitus valgus?

A

20-25 degrees deviated laterally

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3
Q

What is gun stock?

A

Cubitus varum where forearm is deviated midline 5 degrees

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4
Q

What can cubitus valgus damage if overstretched?

A

ulnar nerve

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5
Q

What reinforces the articular capsule?

A

oblique bands of fibrous tissue

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6
Q

What does the medial collateral ligament consist of?

A

anterior, posterior and transverse fiber bundles

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7
Q

Which ligaments: anterior, posterior, transverse, are the strongest?

A

anterior

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8
Q

Which fibers provide most significant resistance against valgus force?

A

anterior

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9
Q

Where to anterior fibers arise and insert?

A

anterior part of medial epicondlye

medial part of coronoid process of ulna

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10
Q

Why are some anterior fibers taut throughout sagittal plane movement?

A

fibers span both sides of axis of rotation

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11
Q

What do anterior fibers provide?

A

articular stability throughout entire ROM

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12
Q

Where do posterior fibers attach and insert?

A
  • posterior part of medial epicondyle

- medial margin of olecranon process

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13
Q

What do posterior fibers resist?

A

valgus force

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14
Q

Transverse fibers insert and attach

A

cross from olecranon to coronoid process of ulna

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15
Q

What are dynamic medial stabilizers of the elbow?

A

proximal fibers of wrist flexor and pronator group of muscles also resist excessive valgus-producing strain at elbow, most notably by flexor carpi ulnaris

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16
Q

How can anterior capsule be injured?

A

excessively hyperextended

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17
Q

The MCL is susceptible to injury from what?

A

valgus-producing forces to elbow in non–weight-bearing activities, such as pitching baseball and spiking volleyball

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18
Q

The lateral collateral ligament complex is composed of what?

A

radial collateral ligament

lateral (ulnar) collateral ligament

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19
Q

Where does the lateral collateral ligament originate?

A

lateral epicondyle and immediately splits into two fiber bundles

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20
Q

Where does the radial collateral ligament go?

A

fans out to blend with annular ligament

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21
Q

Where does the lateral ulnar collateral ligament attach?

A

distally to supinator crest of ulna

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22
Q

The fibers of the LCL become taut during what action?

A

full flexion

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23
Q

Why are the lateral collateral ligament and anterior fibers called “guy wires?”

A

provide medial-lateral stability to ulna during sagittal plane motion

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24
Q

LCL complex and posterior-lateral aspect of capsule are primary stabilizers against what?

A

varus-producing force

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25
Q

Rupture of the elbow cause what?

A
  • increase varus adduction

- increase posterior-lateral rotary instability

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26
Q

What can instability of LCL be expressed as?

A

-excessive external rotation with subsequent subluxation of both humero-ulnar and humeroradial joints

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27
Q

What motion increases tension of MCL (anterior fiber)?

A

valgus

extension and flexion

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28
Q

What motion increases tension of MCL (posterior fiber)?

A

valgus

flexion

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29
Q

What motion increases tension of radio collateral ligament?

A

varus

external rotation

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30
Q

What motion increases tension of lateral (ulnar) collateral ligament?

A

varus

external rotation and flexion

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31
Q

What motion increases tension of annular ligament?

A

direction of radius, external rotation

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32
Q

What are the primary valgus or varus stabilizers?

A
  • anterior fibers of MCL

- lateral (ulnar) collateral ligament

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33
Q

What is maximal range of passive motion to elbow?

A

5° beyond neutral (0°) extension through 145° of flexion

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34
Q

What is the functional arc of motion

A

b/w 30° and 130° of flexion

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35
Q

What articulates the humero-ulnar joint?

A

concave trochlear notch of ulna and convex trochlea of humerus

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36
Q

Hyaline cartilage covers about _____ of articular surface on trochlea, compared with only ____ on trochlear notch

A

300°, 180°

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37
Q

What limits motion of humero-ulnar joint within sagittal plane?

A

natural congruency and shape of joints

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38
Q

What is required for humero-ulnar joint to be fully extended?

A

extensibility required in dermis anterior to elbow, flexor muscles, anterior capsule, and anterior fibers of medial collateral ligament

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39
Q

What can limit full extension?

A

excessive ectopic bone formation around olecranon

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40
Q

What does full extension require?

A

that prominent tip of olecranon process become wedged into olecranon fossa

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41
Q

In a health humero-ulnar joint, what stabilizes extension?

A

articular congruency and ↑ tension in stretched connective tissues

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42
Q

What is the action of the humero-ulnar joint during flexion?

A

concave surface of trochlear notch rolls and slides on convex trochlea

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43
Q

What can lead to neuropathy?

A

Stretching of ulnar nerve from prolonged or repetitive elbow flexion activities

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44
Q

What does full elbow flexion require?

A

elongation of posterior capsule, extensor muscles, ulnar nerve and certain portions of collateral ligaments, especially posterior fibers of MCL

45
Q

How to severe elbow injuries effect the humero-ulnar joint?

A

trochlear notch of ulna may dislocate posterior to trochlea of humerus

46
Q

How is the humeroradial joint articulated?

A

b/w cuplike fovea of radial head and reciprocally shaped rounded capitulum

47
Q

How to flexion and extension affect the humeroradial joint?

A

consist of fovea of radius rolling and sliding across convexity of capitulum

48
Q

Where is the medial lateral axis of rotation during humeroradial joint flexion?

A

center of capitulum

49
Q

What structures are stretched taut during humeroradial joint flexion?

A
  • posterior capsule

- lateral (ulnar) collateral ligament

50
Q

What structures are slackened during humeroradial joint flexion?

A

anterior capsule

51
Q

What binds the radius and ulna together?

A

interosseous membrane and proximal and distal radio-ulnar joints

52
Q

Where does forearm rotation occur?

A

an axis of rotation that extends from radial head through ulnar head—an axis that intersects and connects both radio-ulnar joints

53
Q

What binds the radius and ulna together?

A

interosseous membrane and proximal and distal radio-ulnar joints

54
Q

What does the set of radio-ulnar joints allow?

A

the forearm to rotate into pronation and supination

55
Q

Where is the axis of rotation in forearm rotation?

A

axis extends from radial head through ulnar head-an axis that intersects and connects both radio-ulnar joints

56
Q

In full supination the radius and ulna are ________?

57
Q

Moving into full pronation, the radius______?

A

crosses over the ulna

58
Q

Where does the axis of rotation extend when in pronation?

A

obliquely across forearm from radial head to ulnar head

59
Q

What forms the distal segment in the forearm complex?

A

radius and carpal bones

60
Q

What forms the proximal segment in the forearm complex?

A

humerus and ulna

61
Q

Where does the thumb stay during pronation?

A

with the radius

62
Q

What is the zero reference position of the forearm?

A

thumb up position midway between complete pronation and supination

63
Q

What is the average forearm rotation?

A

75 degrees of pronation and 85 degrees of supination

64
Q

How much rotation do ADL require?

A

100 degrees of rotation, 50 of that from pronation and 50 from supination

65
Q

A decrease in pronation and supination can be compensated for by what?

A

internally and externally rotating the shoulder

66
Q

Pronation and supination require simultaneous movements where?

A

proximal and distal radio-ulnar joints

67
Q

Pronation and supination also require movement where?

A

adjacent humeroradial joint

68
Q

Where does supination occuur?

A

proximal radio-ulnar joint

69
Q

What happens during supination?

A

rotation of radial head with fibro-osseous ring formed by annular ligament and radial notch of ulna

70
Q

What prohibits standard roll and slide?

A

tight constraint of radial head by fibro-osseous ring

71
Q

During supination, what do the radius and carpal bones rotate?

A

fixed humerus and ulna

72
Q

During pronation and supination proximal end of radius rotates where?

A

both proximal radio-ulnar and humeroradial joints

73
Q

What are the arthrokinematics at humeroradial joint?

A

spin of fovea of radial head against rounded capitulum of humerus

74
Q

What is the screw home mechanism of elbow?

A

Natural proximal migration of radius and associated ↑ joint compression of humeroradial joint

75
Q

What can significantly disrupt functional mobility of entire distal upper extremity?

A

pain or limited motion at humeroradial joint

76
Q

Pronation and supination in a weight bearing positin?

A

humerus and ulna rotate relative to stationary radius and hand

77
Q

Where is the GH joint during pronation and supination with radius and hand held fixed?

A

partially internally rotated

78
Q

Where are the ulna and radius positioned with radius and hand held fixed?

A

parallel -rod placed through epicondyle of humurus helps with orientation of this position

79
Q

With radius and hand held firmly fixed with ground, pronation of forearm occurs by what?

A

external rotation of humerus and ulna

80
Q

Rotation of humerus transferred, nearly degree for degree, to rotating ulna how?

A

because of tight structural fit of humero-ulnar joint

81
Q

Moving back to full supinated position with radius hand held fixed involved what?

A

internal rotation of humerus and ulna relative to fixed radius and hand

82
Q

What muscle rotates the humerus relative to fixed scapula during pronation of the forearm from weight bearing position?

A

infraspinatus

83
Q

What muscle rotates the ulna relative to fixed radius during weight bearing pronation?

A

pronator quadratus

84
Q

What are the arthrokinematics of the radio-ulnar joint during pronation while radius and hand are stationary?

A
  • at proximal radio-ulnar joint annular ligament and radial notch of ulna rotate around fixed radial head
  • capitulum of humerus spinning relative to fovea of fixed radius
  • distal radio-ulnar joint head of ulna rotates around fixed ulnar notch of radius
85
Q

At the proximal radio-ulnar joint, what are the arthrokinematics in weight bearing?

A

annular ligament and radial notch of ulna rotate around fixed radial head

86
Q

At the distal radio-ulnar joint, what are the arthorkinematics in weight bearing?

A

convex ulnar head rolls and slides in opposite directions on concave ulnar notch of radius?

87
Q

At the proximal radio-ulnar joint what are the arthrokinematics in non-weight bearing?

A

radial head rotates within ring formed by annular ligament and radial notch of the ulna

88
Q

At the distal radio-ulnar joint, what are the arthrokinematics in non-weight bearing?

A

concavity of ulnar notch of radius rolls and slides in similar directions on convex ulna head

89
Q

What do muscles that attach distally on the ulna do?

A

flex or extend the elbow, but possess no ability to pronate or supinate the forearm

90
Q

What do muscles that attach distally on the radius do?

A

flex or extend the elbow, but can also pronate or supinate the forearm

91
Q

What are the primary flexors of the elbow?

A

Biceps brachii, brachialis, brachioradialis and pronator teres

92
Q

When do the biceps produce its maximal EMG signal?

A

when performing both flexion and supination simultaneously (spoon to mouth)

93
Q

What is the sole function of the brachialis?

A

flex the elbow

94
Q

Which muscle of the elbow generates the greatest of any muscle crossing elbow?

A

brachialis

95
Q

What muscle is the longest of all elbow muscles?

A

brachioradialis

96
Q

The brachioradialis causes what actions?

A

full elbow flexion and rotation of the forearm

97
Q

The pronator teres has only what percentage of physiological cross sectional area of the brachialis?

98
Q

What are the primary extensors of the elbow?

A

triceps, anconeus

99
Q

What allows the long head of the triceps to extend and adduct the shoulder?

A

attachment on the infraglenoid tubercle

100
Q

What movement does the anconeus allow?

A

longitundinal and medial-lateral stability across humero-ulnar joint

101
Q

What shoulder motion occurs with pronation?

A

internal rotation

102
Q

What shoulder motion occurs with supination?

A

external rotation

103
Q

How many degrees does supination alone allow?

A

180 degrees

104
Q

How many degrees does pronation alone allow?

A

170 degrees

105
Q

Rotation at the shoulder in addition to pronation/supination allows for how much rotation

A

360 degrees

106
Q

What are the primary supinator muscles?

A

supinator

biceps

107
Q

What are the secondary muscles of supination?

A

extensor pollicis longus, and extensor indicis

brachioradialis (from pronated position)

108
Q

What are the primary pronator muscles?

A

pronator teres and pronator quadratus

109
Q

What are the secondary pronators?

A

flexor carpi radialis,
palmaris longus
brachioradialis (from supinated position)

Biomechanics (13 decks)

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