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2 Biomechanics > Elbow > Flashcards

Elbow Flashcards

1
Q

Joints of Elbow

A

Humeroulnar
Humeroradial
Radioulnar, proximal and distal

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2
Q

Elbow joint is made of…

A

humeral ulnar and humeral radial

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3
Q

M/L axis of elbow

A

runs superior
due to asymmetry of trochlea, ulnar deviates laterally

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4
Q

Cubitus valgus

A

carrying angle
average is about 13°

generally greater on dominant arm and naturally increases with age

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5
Q

Excessive Cubitus Valgus

A

angle exceeds 20-25°

can be caused by severe fracture or growth plate injury

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6
Q

Cubits Varus

A

forearm neutral, or projects medially
can be caused by severe fracture or growth plate injury

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7
Q

Capsule of elbow

A

relatively thin, covers humeroulnar, humeroradial, and proximal radioulanar joints

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8
Q

MCL of elbow

A

has anterior fibers, posterior fibers, transverse fibers

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9
Q

Anterior fibers of MCL

A

most resistance to valgus force
taut through flexion and extension

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10
Q

Posterior fibers of MCL

A

thickening of peromedial capsule
taut in valgus and end range flexion

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11
Q

Transverse fibers of MCL

A

ulna to ulna, limited stability

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12
Q

Radial collateral ligament

A

Lateral epicondly to annular ligament
some varus resistance

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13
Q

LCL of elbow

A

lateral epicondyle to supinator crest
resists varus and end range flexion
forms a sling that prevents radial head to dislocate

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14
Q

Humeroulnar joint type

A

HINGE

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15
Q

Humeroradial joint type

A

PIVOT

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16
Q

Elbow joint characteristics

A

modified hinge
1 degree of freedom, sagittal plane
Frontal/transverse = accessory motions

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17
Q

Flexion/Extension ulna on humerus

A

Concave on convex
Flexion: roll/slide are anterior
Extension: roll/slide are posterior

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18
Q

Flexion/Extension radius on humerus

A

Concave on convex
Flexion: roll/slide are anterior
Extension: roll/slide are posterior

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19
Q

Function of interosseus membrane

A

firmly bind radius and ulna together
attachment for extrinsic hand muscles
transmit force proximally through upper limb

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20
Q

Components of interosseus membrane

A

central band: thickest
oblique cord: limits distal migration of radius to ulna
Distal oblique: only present 40% of time, stability

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21
Q

Proximally directed Force Transmission

A

closed chain force, 80% through radiocarpal joint

interosseus membrane is pulled taut, allows compressive forces to cross the elbow towards the humeroulnar joint

both joints share the compressive load

muscles will also pull the radial head towards capitulum, increases force at humeroradial joint; IM helps to transfer some force to humeroulnar

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22
Q

Distally directed force transmission

A

distal force relaxes IM
stresses oblique cord and annukar ligament
brachioradialis stops radius from moving from capitulum

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23
Q

Proximal Radioulnar Joint

A

shares capsule with elbow joints
Annular ligament helps to attach ulna to the radius

24
Q

Distal radioulnar joint

A

little osseous stability, some connective tissue
has a articular disc that is triangular
capsular ligaments are continuation of disc
tissues hold ulna against ulnar notch

25
Q

Radioulnar joint characteristics

A

Modified Pivot
1 degree of freedom
does pronation/supination

26
Q

Proximal radioulnar joint movements

A

Axis is through heads of bones
convex on concave

Roll/Slide in Pronation: roll
RollSlide in Supination: roll

tight annular ligament prohibits standard movements

27
Q

Distal radioulnar joint movements

A

Axis is through heads
Cave on Vex

Supination: Roll/Slide are Lateral
Pronation: Roll/Slide are Medial

IM stays stable during motion

28
Q

Humeroradial joint pronation/supination

A

Axis through heads
Cave on Vex

Pronation: Medial rotation
Supination: Lateral rotation

29
Q

Closed pack position for elbow

A

extension and supination

30
Q

Closed chain movement

A

humerus and ulna rotate relative to fixed radius and hand

rotation of humerus is transferred to rotating ulna, nearly degree for degree

31
Q

Proximal radioulnar closed chain

A

Cave on vex motion
pronation/supination causes ulna/annular ligament on radius motion

32
Q

Distal radioulnar joint, closed chain

A

Vex on cave
pronation on supination is ulna on radius (ulnar notch)

33
Q

Elbow Flexors

A

Biceps brachii
brachialis
Brachioradialis

34
Q

Biceps brachii

A

maximal activation during combine flexion and supination

35
Q

Brachioradialis

A

moment arm increases when active

proximal attachment closer than distal attachment for joint action

greater % of muscle belly over joint axis

flexing muscle creates bowstring effect that increases its flexion MA

36
Q

Moment Arms for Flexor muscles

A

Brachioradialis = greater at 120°
Brachialis = greater at 100-120°
Biceps Brachii = greater at 100°

Brachioradialis has the greatest moment arm/production of force

37
Q

Elbow Extensor

A

Triceps Brachii
Anconeus

38
Q

Triceps Brachii

A

muscles not activated all at once
goes from medial to lateral to long head

39
Q

Anconeus

A

Poor elbow extensor
first muscle to turn on
high % of type 1 fibers (ideal for stability/fatiguing)

40
Q

Elbow extensor MAs

A

Triceps moment arm highest near full extension
triceps torque occurs between 80-90°

41
Q

GH adductors/horizontal adduction

A

Pec major and anterior deltoid can act as adductors during closed chain motion to extend elbow

42
Q

Any muscle that supinates or pronates the forearm must have attachments where?

A

humerus/ulna to radius/hand

43
Q

Supination/pronation associated with movement at shoulder

A

Supination –> GH ER
Pronation –> GH IR

44
Q

Supination muscles

A

supinator
biceps brachii
brachioradialis if pronated

45
Q

Biceps brachii as a supinator

A

3x PCSA compared to supinator
wraps around radius during pronation
action as supinator greatest at 90° elbow angle

MA doesn’t change with supination
length/tension optimized just under 90°
line of pull of biceps optimized just after 90°

46
Q

High powered supination

A

biceps only active during high force tasks
best to perform with elbow at 90°
triceps (on the ulna) acts an antagonist to prevent flexion of elbow during supination

also needs extensor counter torque

47
Q

Supinator muscle

A

has superficial and deep fibers
weak humerus attachment and poor MA for flex/ext
significant supinator at all angles and effort levels

48
Q

Brachioradialis w/pronation & supination

A

brachioradialis is supinator when arm is pronated, until 10° of supination

brachioradialis is a pronator past 10° of supination

49
Q

Pronator muscles

A

pronator teres
pronator quadratus
brachioradialis

50
Q

Pronator teres

A

two heads
secondary elbow flexor, triceps action is needed to stabilize elbow during pronation

51
Q

Pronator quadratus

A

most active and consistent pronator, regardless of force or flexion
action perpendicular to axis of rotation
compresses radius against ulnar head during pronation, stabilizing joint

52
Q

UCL injury acute mechanisms

A

External valgus force to elbow
FOOSH (extended elbow forced into valgus
ulnar nerve, ant capsule, pronator/flexor muscles
compression fracture to humeroradial joint

53
Q

UCL Injury chronic mechanism

A

repetitive valgus strain
valgus torques high during late cocking, acceleration
can be fixed with tommy john surgery

54
Q

During a FOOSH mechanism for injury, what structure helps transmit force from the medial to lateral side of the forearm?

A

central band of the interosseous membrane

55
Q

The pronation/supination axis of rotation runs between which landmarks?

A

radial head and ulnar head

2 Biomechanics (9 decks)

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