Elbow Kinesiology

carrying angle (normal cubitus valgus)

frontal plane alignment of humerus to radius/ulna

• population average: 13 degrees, 6 degree SD

• females generally > males

• dominant > non-dominant

carrying angle

shifts the medial to lateral axis of rotation superiorly for elbow flexion and extension

articulations of the elbow/forearm complex

humero-ulnar joint

humero-radial joint

proximal radio-ulnar joint

distal radio-ulnar joint

elbow flexion/extension

actions of humero-ulnar and humero-radial joints

forearm pronation/supination

actions of proximal radio-ulnar joint and distal radio-ulnar joint

humeroulnar and humeroradial joints

modified hinge joint

• minimal axial rotation and ABD/ADD of ulna during flexion/extension movements

humeroulnar joint

relatively tight fit

• trochlea of humerus and trochlear groove of ulna

• most of passive stability from joint congruency

humeroradial joint

minimal bony stability

• capitulum of humerus and cuplike fovea of radial head

• minimal sagittal plane stability

important for resistance to valgus forces on the elbow

articular capsule

surrounds humeroulnar, humeroradial and proximal radioulnar joints

• thin, some anterior thickening

medial (ulnar) collateral ligament

resist valgus forces

anterior, posterior, transverse bands

lateral (radial) collateral ligament

resist varus forces

two bands: radius and ulna

muscle active stability of humeroulnar and humeroradial joints

medial common flexor tendon to medial epicondyle

lateral common extensor tendon to lateral epicondyle

anterior stabilization from elbow flexor group

medial common flexor tendon to medial epicondyle

• wrist flexor/pronator muscles

• assist with stabilization against valgus forces

lateral common extensor tendon to lateral epicondyle

wrist extensor/supinator muscles

humeroulnar arthrokinematics open chain

concave trochlear notch of ulna moving on convex trochlea of humerus

humeroulnar flexion

anterior roll, anterior glide

concave trochlear notch of ulna moving on convex trochlea of humerus

humeroulnar extension

posterior roll, posterior slide

concave trochlear notch of ulna moving on convex trochlea of humerus

humeroradial arthrokinematics open chain

concave radial head fovea moving on convex capitulum of humerus

humeroradial flexion

anterior roll, anterior glide

concave radial head fovea moving on convex capitulum of humerus

humeroradial extension

posterior roll, posterior glide

concave radial head fovea moving on convex capitulum of humerus

proximal and distal radioulnar joints

allow for pronation and supination

• plane: transverse/horizontal

• axis: oblique axis from radial head to ulnar head

  • bisects both

• radius moving around a stable ulna (OKC)

proximal radioulnar joint periarticular connective tissue

annular ligament (75% coverage) and radial notch (25% coverage) support radial head

• within joint capsule with humero-ulnar and humeroradial joints

distal radioulnar joint periarticular connective tissue

articular disc of triangular fibrocartilage complex (TFCC)

• continuous with anterior and posterior radioulnar ligaments

• includes ulnar collateral ligaments of wrist

minimal bone congruency stability

interosseous membrane

• supports radius and ulna along shaft

• inferior direction radius to ulna

• transmits compression forces

• unable to assist with distraction forces

  • radial head subluxation (nursemaid’s elbow)

compression force on the forearm

pronator teres, supinator

proximal radioulnar joint muscles active stability

• generally, common flexor and extensor groups proximally

pronator quadratus

distal radioulnar joint muscles active stability

• generally, wrist flexor/extensor tendons

simultaneously

in pronation and supination, proximal and distal radioulnar joints must work ___________

spin

pronation and supination requires a ______ of the fovea of radial head on the capitulum of humerus

• stabilizes radial head on capitulum with pronation > supination

PRUJ OKC arthrokinematics

convex radial head moving on concave radial notch of ulna

PRUJ pronation

anterior roll, posterior glide

convex radial head moving on concave radial notch of ulna

PRUJ supination

posterior roll, anterior glide

convex radial head moving on concave radial notch of ulna

DRUJ OKC arthrokinematics

concave ulnar notch of radius moving on convex head of ulna

DRUJ pronation

anterior roll, anterior glide

• limited by dorsal carpal ligaments

concave ulnar notch of radius moving on convex head of ulna

DRUJ supination

posterior roll, posterior glide

• limited by palmar carpal ligaments

concave ulnar notch of radius moving on convex head of ulna

PRUJ/DRUJ CKC pronation and supination

occur with a fixed hand/radius

requires rotation of ulna → humerus → GHJ

• through stable humeroulnar joint

NOT TESTED ON THIS

musculocutaneous nerve

innervation of biceps brachii, brachialis

radial nerve

brachioradialis innervation

median nerve

pronator teres innervation

radial nerve

triceps brachii and anconeus innervation

elbow flexion primary muscles

biceps brachii, brachialis, brachioradialis, pronator teres

flexion torque

approximately 70% greater than extension torque

90 degrees of elbow flexion

flexion torque is maximal at approximately

supination, pronation

flexion torque is 25% greater in _________ compared to __________

brachialis

largest muscle crossing the elbow

• distally attaches to ulna

• functions regardless of pronation/supination position

biceps brachii

physiologic advantage to combining elbow flexion with shoulder extension

• attaches scapula to radius

• posterior deltoid + biceps brachii

• increases biceps elbow flexion torque

flexion torque

decreased concentric contraction velocity increases

biceps length-tension relationship

same 90 degree elbow flexion position

2 cm shortening difference based on shoulder position

triceps brachii and anconeus

elbow extension primary muscles

shoulder extension

long-head of triceps to infraglenoid tubercle of scapula

sequence of elbow extension activation

with increasing force demand

anconeus → medial head → lateral head → long head

extension torque

increasing moment arm with increasing extension

maximal __________ ________ at approximately 90 degrees flexion (when anatomic GHJ position)

• greater influence from length-tension of triceps vs moment arm

triceps brachii function

static stability in UE weight bearing

• isometric, low-velocity eccentric to stabilize a fixed elbow

• prevents buckling

generate large dynamic extensor torque

• standing from chair, pushing open door, throwing ball

• typically combined with shoulder flexion

  • maintains length-tension, avoids active insufficiency

anterior deltoid

opposes shoulder extension torque

forearm pronation/supination muscles must

attach on both sides of axis of rotation (humerus/ulnar to radius)

produce force acting with internal moment arm around axis of rotation

forearm pronation/supination

more perpendicular to the axis of rotation the better

pronator quadratus

is closest to perpendicular to axis of rotation

supinators, pronators

_______ produce 25% greater torque than ________

• R hand vs L hand dominance example!

forearm pronation/supination

functionally works with shoulder ER/IR for nearly 360 degrees of hand rotation

supinator

recruited first for low-power supination activities at all elbow flexion angles

biceps brachii

recruited for high-power supination activities

• ideally with elbow flexed close to 90 degrees

• need co-contraction of triceps to prevention elbow flexion

pronator quadratus

more consistently recruited for all pronation movements

• line of pull assists with distal radioulnar joint stability and arthrokinematics

pronator teres

recruited more for high-power pronation activities

• triceps co-contraction required to isometrically resist elbow flexion