Week 8 Elbow Biomechanics and Common Conditions Flashcards
joints of elbow complex (elbow joint, forearm)
elbow joint:
humeroradial joint
humeroulnar joint
forearm:
superior (proximal) radioulnar joint
inferior (distal) radioulnar joint
classification of the elbow joint
compound synovial modified hinge joint
modified hinge joint = ulna rotates about its own longitudinal axis in flexion and extension
alignment 對齊 - coronal plane of elbow joint
coronal plane = front/ back
‘carrying angle’ = normal valgus (10-15 degrees)
excessive cubitus valgus = >20 degrees
cubitus varus = < 5 degrees
observe in supination forarm
alignment - sagittal plane of elbow joint
sagittal plane = left/ right
humeroulnar joint - encouraging flexion
alignment: anterior curvature of distal humerus and proximal ulna allow ROM flexion and limit extension
What stabilise elbow joint?
- humeroulnar joint
- MCL
- LCL
stability - humeroulnar joint
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
ligamentous stability - MCL
medial (ulnar) collateral ligament
- 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
ligamentous stability - LCL
lateral (radial) collateral ligament
- less defined than MCL
- two fibre bundles: radial/ ulnar
- resist varus force at elbow
- blends with (supports) annular ligament
- stabilises head of radius
- provides posterolateral stability to elbow complex
- provides 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
degrees of elbow ROM: flexion/ extension
normal AROM: 145/ -5 degrees
PROM up to 150-160 degrees
functional ROM less
what limits the extension of elbow
- close packed position full extension
- olecranon in olecranon fossa
- anterior bands MCL
- tension/ shortening of biceps
what limits the flexion of elbow
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
factors that contributing to ROM of elbow
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)
- extra fluid in the joint stretches the capsule and limits full ROM
radioulnar joints
in supination? in pronation?
supination:
- radius & ulna parallel
pronation:
- radius crosses over the ulna
- ulna remains stationary
radioulnar joint kinematics
proximal and distal joint
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
what is the function of interosseous membrane of radioulnar joint
ensures the radius and ulna do not splay apart
/ stabilises both proximal & distal radioulnar joints
why interosseous membrane of elbow is so important?
- 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
elbow distraction
- holding a load –> distally applied force - distraction at elbow
- not resisted by interosseous membrane
- resisted by
oblique cord, annular ligament, actively by brachioradialis
muscle function: elbow flexors
1/ biceps brachii
- 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
muscle function: elbow flexors
2/ brachialis
- powerhouse of elbow flexion
- greatest moment arm (MA) at 100 degrees flexion
- unaffected by forearm/ shoulder position
muscle function: elbow flexors
3/ brachioradialis
- 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)
muscle function: elbow extensors
triceps brachii and anconeus
- 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 deltoid acting as stabilising synergist to allow efficient elbow extension- medial head recruited first for unresisted elbow extension
- medial and lateral head generate 70-90% isometric torque
elbow extensors like properly fitted crutches
–> hand grip raised 1-2cm from optimal height = increase resistance for elbow extensors to overcome
muscle function: elbow supinators
pronators and supinators must have one attachment on humerus and ulnar, and one attachment on the radius
- supinators produce about 25%
greater isometric torquethan the pronators
muscle function: elbow pronators
pronator teres and pronator quadratus
pronators and supinators must have one attachment on humerus and ulnar, and one attachment on the radius
- pronator teres
- small role as elbow flexor
- assist when increases power required - pronator quadratus
- most active, regardless of 無論 resistance/ elbow position
- assist with stability at distal radioulnar joint
valgus injuries - chronic
- throwing, pitching 投球, tennis
- valgus stress: repetitive stretching of anterior band of MCL, increased compressive forces on lateral side at radiocapitellar joint
posterior dislocations fractures
- 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
olecranon fracture
- 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 移位:
ORIF and AROM exercises after 1 week
supracondylar fracture
*****cbl
- 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
radial head fractures
- 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
elbow injury management
immobilisation
-
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
complications 併發症 of elbow joint
- stiffness; lost of terminal extension
- neurovascular damage
