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1022 THEORY > Week 8 Elbow Biomechanics and Common Conditions > Flashcards

Week 8 Elbow Biomechanics and Common Conditions Flashcards

1
Q

joints of elbow complex (elbow joint, forearm)

A

elbow joint:
humeroradial joint
humeroulnar joint

forearm:
superior (proximal) radioulnar joint
inferior (distal) radioulnar joint

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2
Q

classification of the elbow joint

A

compound modified hinge joint

modified hinge joint = ulna rotates about its own longitudinal axis in flexion and extension

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3
Q

alignment 對齊 - coronal plane of elbow joint

coronal plane = front/ back

A

‘carrying angle’ = normal valgus (10-15 degrees)
excessive cubitus valgus = >20 degrees
cubitus varus =<5 degrees

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4
Q

alignment - sagittal plane of elbow joint

sagittal plane = left/ right

A

humeroulnar joint - encouraging flexion
alignment: anterior curvature of distal humerus and proximal ulna allow ROM flexion and limit extension

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5
Q

What is used to rely on stability of humeroulnar joint

A

50% bony shape:
- olecranon: prevent anterior dislocation
- coronoid process: prevent posterior dislocation

50% ligaments and passive restraints:
- MCL, LCL, capsule
- the ratio varies depending on degree of flexion/ extension
- any muscle activity will also provide a joint compressive force that increases joint stability 任何肌肉活動也會提供關節壓縮力，進而增加關節穩定性

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6
Q

ligamentous stability - MCL

medial (ulnar) collateral ligament

A
  • resists valgus forces
  • anterior fibers (band) taut in full E, posterior fibers (band) taut in full F
  • in 20-120 degrees flexion, MCL are main limit to valgus stress – In flexed positions, overstretching may cause medial instability 在彎曲位置時，過度伸展可能會導致內側不穩定
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7
Q

ligamentous stability - LCL

lateral (radial) collateral ligament

A
  • resist varus force
  • blends with annular ligament
  • stabilises head of radius
  • provides posterolateral stability to elbow complex & some resistance to longitudinal distraction

Both collateral ligaments dense with 密集著 sensory receptors – aid 幫助 proprioceptive and detect safe passive tension in ligaments and capsule 偵測韌帶和關節囊的安全被動張力

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8
Q

degrees of elbow ROM: flexion/ extension

A

normal AROM: -5/ 145 degrees
PROM up to 150-160 degrees
functional ROM less

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9
Q

what limits the extension of elbow

A
  • close packed position full extension
  • olecranon in olecranon fossa
  • anterior bands MCL
  • tension/ shortening of biceps
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10
Q

what limits the flexion of elbow

A

AROM:
- soft tissue opposition
- tricpes/ biceps
- swelling/ pain limiting ROM

PROM:
- coronoid process in coronoid fossa
- soft tissue apposition
- posterior capsule
- posterior LCL/ MCL
- passive length triceps

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11
Q

factors that contributing to ROM of elbow

A

1. type of motion (active/ passive)

2. position of forearm (supinated/ pronated)
- forearm pronated –> ROM of flexion decreased

3. position of shoulder (flexion/ extension)
- length of 2 joint muscles (LH of triceps, both heads of biceps)

4. presence of increased intra-articular pressure 關節內壓力增加 (effusion)

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12
Q

radioulnar joints

in supination? in pronation?

A

supination:
- radius & ulna parallel

pronation:
- radius crosses over the ulna
- ulna remains stationary

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13
Q

radioulnar joint kinematics

proximal and distal joint

A

proximal joint: spinning of radial head within the fibro-osseous ring

distal joint: concave surface of the ulnar notch of radius slides around the convex ulnar head

can refer back to nettler’s atlas plate 425 carpal articular surface

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14
Q

what is the function of interosseous membrane of radioulnar joint

A

ensures the radius and ulna do not splay apart/ stabilises both proximal & distal radioulnar joints

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15
Q

why interosseous membrane of elbow is so important?

A
  • Elbow sustains large loads during everyday activities – lifting, WB, pushing, falling (FOOSH)
  • Axial loads – 80% axial load is transmitted through radius
  • Problem: proximal radius has small surface area and is not well equipped to withstand forces
  • Solution: Interosseous membrane distributes proximally directed force to ulna
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16
Q

elbow distraction

A
  • holding a load
  • not resisted by interosseous membrane
  • resisted by oblique cord, annular ligament, actively by brachioradialis
17
Q

muscle function: elbow flexors
1/ biceps brachii

A
  • peak moment arm: 80-100 degrees
  • poor flexor in 0 degrees extension
  • over 100 degrees of flexion, force is distracting 分散 force at elbow
  • influenced by forearm and shoulder position
18
Q

muscle function: elbow flexors
2/ brachialis

A
  • powerhouse of elbow flexion
  • greatest moment arm (MA) at 100 degrees flexion
  • unaffected by forearm/ shoulder position
19
Q

muscle function: elbow flexors
3/ brachioradialis

A
  • large average moment arm (peaks 100-120 degrees flexion)
  • large joint compression force: stability

EMG studies:
little contribution to slow, unresisted elbow flexion
increases activity in mid-prone (increase speed/ resistance)

20
Q

muscle function: elbow extensors
triceps brachii and anconeus

A
  • generate large and dynamic extensor torques through high velocity concentric and eccentric activities (throw, push)
  • not affected by forearm position, LH of triceps influenced by shoulder position
  • medial head recruited first for unresisted elbow extension
  • medial and lateral head generate 70-90% isometric torque
  • anterior deltoid acting as stabilising synergist to allow efficient elbow extension

elbow extensors like properly fitted crutches
–> hand grip raised 1-2cm from optimal height = increase resistance for elbow extensors to overcome

21
Q

muscle function: elbow supinators

A
  • supinators produce about 25% greater isometric torque than the pronators
22
Q

muscle function: elbow pronators
pronator teres and pronator quadratus

A
  1. pronator teres
    - small role as elbow flexor
    - assist when increases power required
  2. pronator quadratus
    - most active, regardless of 無論 resistance/ elbow position
    - assist with stability at distal radioulnar joint
23
Q

valgus injuries - chronic

A
  • throwing, pitching 投球, tennis
  • valgus stress: repetitive stretching of anterior band of MCL, increased compressive forces on lateral side at radiocapitellar joint
24
Q

posterior dislocations fractures

A
  • acute 急性, high force mechanism
  • FOOSH/ posterior force in elbow flexion
  • disruption of both collateral ligaments
  • often with associated # of coronoid process/ radial head

what neurovascular structures would be at risk?
MUST assess distal radial pulses - urgent reduction required if absent

25
Q

olecranon fracture

A
  • FOOSH/ direct trauma
  • tender over 壓痛 olecranon and pain with resisted triceps contraction

If non displaced and stable:
immobilise in posterior splint for 2-3 weeks
remove splint to start AROM

If displaced:
ORIF and AROM exercises after 1 week

26
Q

supracondylar fracture

A
  • more common in adolescents
  • anterior humeral line and fat pad sign
  • FOOSH
  • unstable and high rate of neurovascular complications
  • do no flex arm –> this can occlude 閉合 brachial artery
  • often ORIF: sling and cast
  • pins removed 4-6 weeks
  • children typically do not get stiffness but adults do
27
Q

radial head fractures

A
  • FOOSH
  • most minimally displaced or non displaced 移位最小或無移位
  • hard to see on X-ray
  • sail - fat pad sign
  • splint and early commencement of ROM
  • displaced requires surgical
28
Q

elbow injury management

immobilisation

A
  • regain ROM and strength (priority extension)
  • Mx of pain and swelling
  • proprioceptive re-training
  • functional weight bearing activities activities of daily living (ADL) training
  • consider superior/ inferior RU joint functioning
  • mindful of associated neurovascular injuries
  • risk of contracture of soft tissue and biceps anterior elbow
29
Q

complications 併發症 of elbow joint

A
  • stiffness; lost of terminal extension
  • neurovascular damage

1022 THEORY (10 decks)

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