Kinesiology of Elbow & Forearm Flashcards
What is the normal carrying angle of the elbow?
13°
What might be the functional significance of normal cubitus valgus?
Keeping carried objects away from the side of the thigh during walking
What could be the effect of excessive cubitus valgus?
Structures under stretch (e.g. ulnar nerve)
- Structures crossing the cubital fossa on the medial side
What does the articular capsule enclose?
(elbow)
- Humero-ulnar joint
- Humeroradial joint
- Proximal radio-ulna joint
What ligaments is the articular capsule (elbow) strengthened by?
- Medial collateral ligament (anterior fibers)
- Medial collateral ligament (posterior fibers)
- Radial collateral ligaments
- Lateral (ulnar) collateral ligaments
- Annular ligament
What kind of stability does the medial collateral ligament (anterior fibers) provide?
Provides:
- Articular stability throughout sagittal plane movement
- Significant resistance against a valgus (abduction) produced force to elbow
- Strongest & stiffest ligament of elbow
What kind of stability does the medial collateral ligament (posterior fibers) provide?
Resists valgus-produced force & becomes taut in extreme elbow flexion
- Less defined compared to anterior fibres
What increases tension of radial collateral ligaments?
Varus force on elbow
What increases tension of lateral (ulnar) collateral ligaments?
- Varus force
- External rotation
- Flexion
What increases the tension of the annular ligament?
- Distraction of radius
How does the annular ligament provide stability to the elbow joint?
The fovea of the radius is shallow while the capitulum is large
Annular ligament reinforces/protects the “connection” between the fovea & capitulum (keeps both in place)
What is the medial collateral ligament susceptible to?
Injury
- When extended elbow is violently forced into excessive valgus (e.g. fall onto outstretched & supinated arm)
- Non-weight bearing valgus producing –> repetitive strain (e.g. overhead activities like baseball/pitchers)
What are the ligaments in the lateral collateral ligament complex?
Radial collateral ligament
Lateral (ulnar) collateral ligament
What are the fibres of the medial collateral ligament?
- Anterior fibers (Strongest & stiffest)
- Posterior fibres
- Transverse fibers (Poorly developed)
What does the fibro-osseous ring consist of?
Annular ligament
Radial notch of ulna
(The head of radius articulates with proximal ulnar by fibro-osseous ring)
What is the articular disc at the distal radio-ulnar joint known as?
Triangular fibrocartilage
How does the lateral ulnar collateral ligament provide stability?
Distal attachment to ulna = forms a sling that supports radial head = prevents excessive ext. rotation
Taut at full flexion
What does the triangular fibrocartilage complex (TFCC) consist of?
(7)
- Articular disc (triangular fibrocartilage)
- Distal radio-ulnar joint capsular ligament
- Palmar ulnocarpal ligament
- Ulnotriquetral ligament
- Ulnolunate ligament
- Ulnar collateral ligament
- Fascia sheath of extensor carpi ulnaris tendon
What is the terrible triad injury of the elbow?
- Elbow joint dislocation (with ligamentous injury)
- Fracture of radial head
- Fracture of coronoid process
E.g. falling onto outstretched & supinated arm = injury to MCL + above 3 components
What structures stabilize the humero-ulnar joint?
- Well-fitting joint surfaces
- Joint capsule
- Medial collateral ligament
- Biceps brachii
- Brachialis
- Triceps brachii
- Anconeus
What structures stabilize the humeroradial joint?
- Joint capsule
- Lateral collateral ligament complex
- Biceps brachii
- Brachialis
- Triceps brachii
- Anconeus
What structures stabilise the proximal radio-ulnar joint?
- Joint capsule
- Annular ligament
- Quadrate ligament
- Interosseous membrane
- Biceps brachii
- Brachialis
- Triceps brachii
What structures stabilise the distal radio-ulnar joint?
- Triangular fibrocartilage complex (TFCC)
- Volar & dorsal radioulnar ligaments
- Extensor carpi ulnaris tendon sheath - Pronator quadratus
- Interosseous mbn
What is the role of the interosseous mbn?
- Most fibres of the interosseous mbn referred to as central band –> binds radius firmly to ulna (distal oblique fibres are small & poorly developed)
- Serves as attachment site for extrinsic muscles of hand
- Provides a mechanism of transmitting force proximally thru upper limb
How does the interosseous mbn transmit force?
Fiber direction usually from radius to ulnar so some of the force is transferred across mbn to ulna
- 20% of force crosses the medial side of the wrist
What increases the likelihood of radial fracture?
80% of compression force is directed through the radiocarpal joint = inc. likelihood
(some of the force directed to ulna thru interosseous mbn)
Why does a distracting force cause deep ache in brachioradialis & other tissues)?
Distal pull of radius slackens interosseous mbn = larger demands on other tissues (oblique cord of interosseous mbn & annular ligament)
Brachioradialis & other tissues contracts = assist with holding of humerus & load firmly against capitulum (humerus)
Which joints are involved in elbow flexion/extension?
- Humero-ulnar joint
- Humeroradial joint
What soft tissues must be sufficiently extensible for full elbow extension?
- Dermis anterior to elbow (free of scars, burns, etc)
- Flexor muscles
- Anterior capsule
- Anterior fibres of medial collateral ligament (some)
What soft tissues must be sufficiently extensible for full flexion of elbow?
- Posterior capsule
- Extensor muscles
- Ulnar nerve
- Collateral ligaments (esp posterior fibres of medial collateral ligament)
Arthrokinematics of elbow flexion at humero-ulnar joint
Concave trochlear notch (ulna) rolls & slides on convex trochlea (humerus)
Arthrokinematics of elbow flexion at humeroradial joint
Concave fovea (radial head) rolls & slides on the convex capitulum (humerus)
What factors allow the humeroradial joint to resist valgus-producing force?
- Shape of angulation of proximal radius
- Size & depth of fovea
- Compression forces produced by activation of muscles crossing elbow
(provides 50% of resistance against valgus-producing force)
What occurs at the proximal radioulnar joint during supination?
Radial head rotates within fibro-osseous ring (formed by annular ligament & radial notch of ulna) = tight constraint of radial head = X roll & slide
What occurs at the distal radioulnar joint during supination?
Concave ulnar notch of radius rolls & slides in similar direction on ulnar head
What is the primary stabiliser of the distal radio-ulnar joint?
TFCC
- Includes capsular ligaments of distal radio-ulnar joint & ulnar collateral ligament
What are the structures restricting full supination?
- Pronator teres
- Pronator quadratus
- Flexor carpi radialis
- Extrinsic finger flexors
- TFCC (esp. palmar capsular ligament at distal radio-ulnar joint & interosseous mbn
- Quadrate ligament
What are the structures restricting full pronation?
- Biceps
- Supinator
- Radial wrist extensors
- Extensor pollicis longus
- TFCC (esp. dorsal capsular ligament at distal radio-ulnar joint)
At the end of supination, what structure is stretched to max length?
Palmar capsular ligament = creates stiffness = stabilizes joint
What occurs to the dorsal capsular ligament at the distal radio-ulnar joint and the palmar capsular ligament during full pronation?
Dorsal capsular ligament = elongates & tension increases
Palmar capsular ligament = slackens to ~70% of original length
What can happen with a strenous pull on pronated hand?
Can cause radial head to slip through distal end of annular ligament
- Children more susceptible bc ligaments are lax = sharp pull on arm can dislocate
AKA pulled elbow syndrome, nurse maid’s elbow, babysitter’s elbow
What are the elbow flexors?
Brachialis
Biceps brachii
Brachioradialis
Pronater teres
What are the elbow extensors?
Triceps brachii
Anconeus
What are the forearm pronators?
Pronator quadratus
Pronator teres
What are the forearm supinators?
Biceps brachii
Supinator
What does the musculocutaneous nerve innervate?
Biceps brachii
Coracobrachialis
Brachialis
Continues as sensory nerve to skin over lateral forearm
Formed by C5-C7 spinal nerve roots
What does the radial nerve innervate?
Triceps brachii
Anconeus (radial groove)
Brachioradialis
Extensor carpi radialis longus
Extensor carpi radialis brevis
Supinator
Extensor carpi ulnaris
Extensor digitorum
Extensor digiti minimi
Extensor pollicis brevis
Extensor pollicis longus
Extensor indicis
Abductor pollicis longus
Postero-lateral aspect of distal forearm
Formed by C5-T1 spinal nerve roots
What does the median nerve innervate?
Pronator teres
Flexor carpi radialis
Palmaris longus
Flexor digitorum superficialis
Flexor digitorum profundus (lateral half)
Flexor pollicis longus
Pronator quadratus
Abductor pollicis brevis
Opponens pollicis
Flexor pollicis brevis
Lumbricals (lateral half)
Formed from C6-T1 spinal nerve roots
What does the ulnar nerve innervate?
Flexor carpi ulnaris
Flexor digitorum profundus (medial half)
Palmaris brevis
Abductor digiti minimi
Opponens digiti minimi
Flexor digiti minimi
Adductor pollicis
Formed from C8-T1 spinal nerve roots
Innervation of the elbow flexors
Brachialis = Musculocutaneous nerve (C5, 6)
Biceps brachii = Musculocutaneous nerve (C5, 6)
Brachioradialis = Radial nerve (C5, 6)
Pronator teres = Median nerve (C6, 7)
Innervation of elbow extensors
Triceps brachii = Radial nerve (C7, 8)
Anconeus = Radial nerve (C7, 8)
Innervation of forearm pronators
Pronator quadratus = Median nerve (C8, T1)
Pronator teres = Median nerve (C6, 7)
Innervation of forearm supinators
Biceps brachii = Musculocutaneous nerve (C5, 6)
Supinator = Radial nerve (C6)
When does biceps brachii have maximal EMG (electromyography)?
During flexion & supination
- Relatively low EMG when flexion is performed w pronated forearm
Function of brachioradialis?
- Always working = flex., ext., pronate, supinate
- Maximal shortening causes full elbow flexion & rotation of forearm to near neutral position
- Longest elbow muscle
Function of brachialis?
Sole function = flex elbow
- Largest muscle crossing elbow = generates greatest force of any muscle crossing elbow
Are flexion torques or extensor torques greater?
Flexion torques ~70% greater than extensor torques
Why are flexor torques when forearm is supinated greater than when forearm is pronated?
Flexor torques when supinated 20-25% greater than when pronated
Bc increased flexor moment arm (longer) of biceps & brachioradialis when forearm is in/approaches supination (longer moment arm = more torque generated)
At what angle does the primary elbow flexors produce the greatest torque?
90°
Max internal torque by flexors is at 90° which corresponds to greatest external torque (gravity) at 90°
Elbow flexion when shoulder extended
- Biceps brachii stretched over shoulder joint
- Muscle lengthened beyond optimal length for force prod. = prod. less force = contraction speed dec.
Passive insufficiency
Elbow flexion when shoulder flexed
- Biceps brachii shortened over shoulder joint
- Places muscle closer to optimal length = contract more efficiently & faster
Active insufficiency
Why is the speed of elbow flexion contraction slower with shoulder extension (compared to with shoulder flexion)?
Shoulder extension = passive insufficiency
Shoulder flexion = active insufficiency
Function of triceps brachii
Extend & adducts shoulder
- 3 heads; long head has extensive volume (exceeds other elbow muscles)
- Medial head (distal fibres) attached to posterior capsule = draws capsule taut during extension
- articularis cubiti (sort of part of triceps)
Anconeus
Small triangular muscle
- Spans the posterior side of elbow
- Small cross-sectional area
- Small moment arm for extension
- function: differing opinions
How does shoulder flexion neutralize the tendency of elbow extensors extending the shoulder?
Extensors stabilize flexed elbow through isometric con- traction/low–velocity eccentric activation
Anterior delt. produces shoulder flexion torque = drives limb forward = neutralises shoulder extension of triceps long head = minimises rate & amt of shortening required by triceps to extend elbow
What is a stable position at the elbow and how is it produced?
90° flexion (like arm wrestling position)
Strong isometric coactivation of elbow flexor & extensor muscles in a position near 90° flexion
What is the law of Parsimony?
Hierarchy of muscle recruitment depending on demand on muscle
Nervous system tends to activate fewest muscles/muscle fibres possible for control of a given joint action
- E.g. for lower level extensor torque = only anconeus & medial head of triceps; when more dynamic/resisted extensor torque needed = nervous system selects larger, polyarticular long head of triceps
At what angle is the largest torque produced by elbow extensors?
90°
Why does
- shoulder internal rotation often occur w pronation
- shoulder external rotation often occur w supination?
Eliminate contribution by shoulder
= elbow held flexed to 90° w medial epicondyle of humerus pressed against side of body
Why do the supinator muscles produce 25% greater isometric torque than the pronators?
Supinator muscles possess about twice the physiologic cross-sectional area as pronator muscles
The supinator & pronator produces a force that acts with ____________ about the axis of rotation
The supinator & pronator produces a force that acts with an internal moment arm about the axis of rotation
Which supinator muscle is recruited first?
Supinator
- recruited first & for low-power supination tasks
When is the biceps brachii recruited for supination?
During higher power supination activites (esp. those assoc. w elbow flexion)
When recruited, triceps & post. delt. required to neutralise undesired biceps action of shoulder & elbow (prevent biceps from flexing elbow & shoulder)
Which pronator muscle is consistently used during all pronation movements?
Pronator quadratus!
- Most active
- Used during all pronation movements regardless of power demand
- Simult. compresses ulnar notch of radius directly against ulnar head = stabilises distal radio-ulnar joint throughout range of pronation
When is biceps brachii most effective as a supinator?
When elbow is flexed to ~90° (therefore elbow is naturally held in this position during many high-powered supination tasks)
Hierarchic recruitment of muscles in elbow extension from gentle unresisted movement to highly resisted extension
Anconeus (recruited first, gentle unresisted movement)
Medial head of triceps
Lateral head of triceps
Long head of triceps (recruited last)
Hierarchic recruitment of muscles in elbow flexion from gentle unresisted movement to highly resisted extension
Brachialis (recruited first)
Biceps brachii/brachioradialis
Hierarchic recruitment of muscles in forearm supination from gentle unresisted movement to highly resisted extension
Supinator (recruited first)
Biceps brachii
