biomechanics unit 2, ACJ, SCJ, GHJ

what motion causes anterior tilting of scapula?

acromion tilts forward, inferior angle tilts backwards

what makes up the inferior GH ligament?

anterior band, posterior band, axillary pouch

what is the smallest moment arm of the GHJ?

anterior deltoid

muscles responsible for GHJ flexion

anterior deltoid, coracobrachialis, biceps brachii

muscles responsible for GHJ abduction

anterior deltoid, middle deltoid, supraspinatous

what degree does the subscapularis produce greatest moment arm at GHJ?

at 30 degrees of flexion or abduction

muscles responsible for GHJ external rotation

infraspinatus, teres minor, posterior deltoid - passive tension subscapularis, middle GH ligament, coracohumeral ligament

what ligament restricts depression at SCJ?

interclavicular

what does the coracoclavicular ligament do at the AC joint?

ligament suspends the scapula and UE from clavicle

sternoclavicular joint

links appendicular skeleton to axial skeleton

the clavicle convex ____ and concave ____

longitudinally; transverse

muscles that posterior tilt scapula

lower trap pulls inferior, serratus anterior pulls anterior

what muscles cause depression of scapula?

lower trapezius, pectoralis minor, subclavius, lats

What muscles retract the scapula?

middle trapezius, rhomboids, lower trap

what are the RTC muscles?

supraspinatus, infraspinatus, teres minor, subscapularis

what structures live in subacromial space

supraspinatus, subacromial bursa, biceps LH, superior capsule

what type of joint is the SC joint

synovial saddle joint

posterior band of the inferior GH ligament

taut at 90 degrees abduction and IR

what would happen if there was no coracoclavicular ligament?

the scapula and arm will sag down from clavicle

GHJ IR and ER plane and axis

transverse plane, vertical axis

horizontal adduction/abduction plane and axis

transverse plane, vertical axis

what muscles cause elevation of scapula?

upper trapezius levator scapulae rhomboids

Muscles that upwardly rotate the scapula

upper trapezius, lower trapezius, serratus anterior

Is the superior GH ligament taut in anatomical position?

yes

normal amount of space in subacromial bursa

1 cm

6 principles for proper arm abduction kinematics

1. scapulohumeral rhythm 2. SC elevation + AC upward rotation 3. clavicle retracts at SCJ 4. scapula posteriorly tilts and ER's 5. clavicle posteriorly rotates 6. GHJ external rotates

how much can the GHJ abduct by itself?

120 degrees

how many degrees of freedom does the AC joint have

3

how many degrees of freedom does the SCJ have?

3

how many degrees of freedom does the GHJ have?

3, greatest ROM than any joint in the body

how much more muscle force do the internal rotators produce than external rotators?

40-70% more torque

when is the middle GH ligament taut?

45-90 degrees abduction

what position is the anterior band of the inferior GH ligament taut

90 degrees abduction and ER - resists anterior translation - strongest and thickest part of band

axillary pouch is taut at what position

90 degrees abduction, resists inferior translation

arthrokinematics of internal rotation GHJ

head rolls anterior slide posterior

arthrokinematics adduction GHJ

head rolls inferior, slides superior

arthrokinematics abduction GHJ

head rolls superior, slides inferior

Protraction/retraction of the clavicle at the SCJ plane and axis

horizontal plane; vertical axis

arthrokinematics external rotation GHJ

humeral head rolls posterior and slides anterior

what are the consequences of downwardly rotated scapula on subacromial space?

impingement of subacromial contents

a tight posterior capsule of the GHJ will have what effect on subacromial space?

impingement of the subacromial space can occur

coracohumeral ligament resists...

inferior translation and some ER

Retraction of SCJ, the shoulder does what?

shoulder extension

what motion of the arm causes retraction of scapula?

shoulder extension

what motion causes posterior tilitng of scapula?

shoulder extension - acromion tilts backwards and inferior angle tilts forward

protraction of the SCJ, the arm does what?

shoulder flexion

what motion of arm causes protraction of scapula?

shoulder flexion

what motion causes depression of scapula?

shoulders going down

what motion causes scapular elevation?

shrugging shoulders up

Arthrokinematic flexion/extension GHJ

spin

horizontal adduction/abduction of GHJ

starts from 90 degrees, moves anterior for adduction, posterior for abduction

muscles responsible for GHJ internal rotation

subscapularis, pec major, lats, teres major, anterior deltoid

what muscles are in between the scapulothoracic joint?

subscapularis, serratus anterior, erector spinae

Plane of scapula

In anatomical position, glenoid angles 30 degrees from frontal plane (internally rotated)

what are the dynamic stabilizers of the GHJ

RTC, biceps LH (restricts superior and anterior translation)

arthrokinematics of SCJ clavicle depression?

Roll inferior slide superior - convex-on-concave

force couple of scapular upward rotation

The upper trapezius muscle pulls up, the lower trapezius muscle pulls down, and the lower fibers of the serratus anterior muscle pull outward in a horizontal direction.

What does the coracoacromial ligament do?

attaches the coracoid process to the acromion process. prevents upward displacement of the head of the humerus. extrinsic and acts like a wall.

what occurs at the SCJ and ACJ when scapula depression

clavicle depression and AC upward rotation

what occurs at the SCJ and ACJ when scapula downwardly rotates

clavicle depression, AC downward rotation

what occurs at the SCJ and ACJ when scapula elevates

clavicle elevates AC downward rotates

what occurs at the SCJ and ACJ when scapula upwardly rotates

clavicle elevation and AC upward rotation

what occurs at the SCJ and ACJ when scapula protracts

clavicle protracts, AC internally rotates

what occurs at the SCJ and ACJ when scapula retracts

clavicle retracts, AC externally rotates

glenoid humeral joint

concave glenoid fossa, convex humeral head

The sternum is shaped to the clavicle and ____ transverse and ____ longitudinally

convex; concave

what ligament restricts elevation at SCJ?

costoclavicular

what ligament restricts retraction at the SCJ?

costoclavicular

what are the consequences of downwardly rotated scapula on GHJ?

decreases compressive forces, risking subluxation or dislocation inferior. plastic deformation on superior capsular structures

a tight posterior capsule of the GHJ will have what effect on humeral head during elevation?

displace the humeral head to far anterior

what is scaption

elevation of the arm in scapular plane - halfway between pure abduction in frontal plane and flexion in sagittal plane

GHJ abduction/adduction plane and axis

frontal plane, AP axis

upward rotation/downward rotation of ACJ plane and axis

frontal plane, sagittal axis

elevation/depression of the clavicle at the SCJ plane and axis

frontal plane; sagittal axis (anterior to posterior)

what are the static stabilizers of the GHJ

glenoid labrum, ring deepens concavity 50% of fossa

Acromioclavicular joint

gliding or plane joint, no roll or slide. acromion and clavicle join

scapulothoracic joint

not a true joint. Space between the scapula and the thoracic cage

Muscles that anteriorly tilt the scapula

pectoralis minor

muscles responsible for GHJ adduction/extension

posterior deltoid, lats, teres major, triceps LH, pec major (sternocostal head)

muscles responsible for GHJ extension

posterior deltoid, lats, teres major, triceps LH, pec major (sternocostal head)

what is rotator cuff interval?

region between supraspinatus and subscapularis

what does the superior GH ligament do

resists ER, inferior, and anterior translation

what does the middle GH ligament do?

resists anterior translation

what does the acromioclavicular ligament do?

restrains posterior translation and posterior axial rotation of the AC joint

muscles that downwardly rotate scapula

rhomboids, pec minor, lats

arthrokinematics of SCJ clavicle protraction?

roll and slide anterior - concave-on-convex

arthrokinematics of SCJ clavicle retraction?

roll and slide posterior - concave-on-convex

arthrokinematics of SCJ clavicle elevation?

roll superior slide inferior - convex-on-concave

what is a common site for anterior dislocation of the GHJ?

rotator cuff interval

GHJ flexion/extension plane and axis

sagittal plane and medial-lateral axis (frontal) - spin

rotation of the clavicle at the SCJ plane and axis

sagittal plane, longitudinal axis (medial lateral axis)

What muscles protract the scapula?

serratus anterior

Elevation of the SCJ, the arm does what?

shoulder abduction

what motion of the arm causes upward rotation of the scapula?

shoulder abduction

what motion of the arm causes downward rotation of the scapula?

shoulder adduction from abducted position

Depression of the SCJ, the arm does what?

shoulder adduction, arm back to side