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
