Shoulder

Question 1

Where do the proximal stabilizers orginate?

Answer 1

originate on spine, ribs, and cranium and insert on scapula and clavicle
Examples include serratus anterior and trapezius

Question 2

Where do distal mobilizers originate?

Answer 2

originate on scapula and clavicle and insert on humerus or forearm
Examples include deltoid and biceps brachii

Question 3

which are activated first - proximal stabilizers or distal mobilizers?

Answer 3

proximal stabilizers - there must be “balance” of the two for optimal function
example:
with a paralyzed serratus anterior muscle, the deltoid muscle is unable to express its full abduction

Question 4

What are the primary elevators of the ST joint?

Answer 4

Upper trapezius
Levator scapulae
Rhomboids

Functionally, these muscles support posture of shoulder girdle (scapula and clavicle) and upper extremity

Question 5

What are the primary depressors of the ST joint?

Answer 5

Lower trapezius (act directly on scapula)
Latissimus dorsi (act indirectly on scapula)
Pectoralis minor (act directly on scapula)
Subclavius (stabilizes the SC joint)

Question 6

What are the primary protractors of the ST joint?

Answer 6

Serratus anterior*

Question 7

What are the primary retractors of the ST joint?

Answer 7

Middle trapezius* Main
Rhomboids
Lower trapezius

Question 8

What are the primary upward rotators of the ST joing?

Answer 8

Serratus anterior
Upper and lower trapezius
These muscles also provide stable attachments for more distal mobilizers, such as deltoid and rotator cuff muscles

Question 9

What are the primary downward rotators of the ST joint?

Answer 9

Rhomboids

Pectoralis minor

Question 10

If the upper trapezius is paralyzed - what type of joint dislocation and/or subluxation would the person be more prone too?

Answer 10

inferior subluxation and dislocation
Although variable, ideal posture of shoulder girdle incorporates slightly elevated and relatively retracted scapula, with glenoid fossa facing slightly upward
Clinical test = Shoulder abduction with arms bent at 90 – see if the upper trap fires to get the arm into abduction

Question 11

what is the ideal posture of the shoulder girdle?

Answer 11

Although variable, ideal posture of shoulder girdle incorporates slightly elevated and relatively retracted scapula, with glenoid fossa facing slightly upward
Clinical test = Shoulder abduction with arms bent at 90 – see if the upper trap fires to get the arm into abduction

Question 12

How do “rounded shoulders” present themselves regarding the scapula?

Answer 12

Scapulas slightly depressed, downwardly rotated, and protracted

Question 13

Posture can lead to same biomechanical stress on SC and GH joints described in paralysis

Answer 13

Scapulae become slightly internally rotated and anteriorly tilted—posture predisposing to impingement of tissues within subacromial space
Abnormal scapular posture may be associated with generalized laxity of connective tissues, muscle fatigue or weakness, GH joint capsule tightness, abnormal cervicothoracic posture or simply habit or mood

Question 14

does the subclavius muscle act directly or indirectly on scapula?

Answer 14

indirectly - through its inferior pull on the scapula

Subclavius’s near parallel line of force with shaft of clavicle suggests this muscle important in compressing and thereby stabilizing SC joint

Question 15

how does the latissimus dorsi act on the shoulder girdle? directly or indirectly? how does it accomplish its movement?

Answer 15

Lower trapezius and pectoralis minor act directly on scapula
Latissimus dorsi depresses shoulder girdle indirectly, primarily by pulling humerus inferiorly

Question 16

what joint is the force of scapular protraction transferred through?

Answer 16

GH - employed for pushing and reaching activities

Question 17

SC has a _______ axis of rotation

Answer 17

Vertical - this is what gives it leverage for protraction

Question 18

strenght of protraction torque produced by Serratus Anterior is a result of _________ multiplied by _________ origination at __________ AOR at ______ joint

Answer 18

Strength of protraction torque primarily result of muscle force multiplied by internal moment arm (IMA) originating at vertical AOR at SC joint
((LOOK UP!!))

Question 19

Which retractor has optimal line of force to produce this motion?

Answer 19

Middle Trapezius

secondary retractors = rhomboids and lower trapezius

Question 20

during what motions are the Retractors of the shoulder primarily active?

Answer 20

during pulling activities such as climbing and rowing

• retractors secure scapula to axial skeleton

Question 21

Secondary Retractors as antagonists to one another

Answer 21

during vigorous retraction effort, elevation tendency of rhomboids neutralized by depression tendency of lower trapezius

Line of forces of both muscles combine to produce pure retraction

Question 22

with complete paralysis of trapezius - scapula tends to “drift” slightly into ________ as a result of partially unopposed protraction action of _________

Answer 22

Scapula tends to “drift” slightly into protraction as result of partially unopposed protraction action of serratus anterior muscle

Question 23

muscles that elevate (abduct/flex) the humerus at GH joint

name which muscles are primary abductors & which are primary flexors

Answer 23

Anterior (ABDUCT & FLEXION)
and middle deltoid (ABDUCT)
Supraspinatus (ABDUCT)
Coracobrachialis (FLEXION)
Biceps (long head) (FLEXION)

Question 24

Term “elevation” of arm describes active movement of bringing arm overhead without specifying exact plane of motion - name the 3 groups that the elevators are separted into

Answer 24

(1) muscles that elevate (i.e., abduct or flex) humerus at GH joint; (2) scapular muscles that control upward rotation of scapulothoracic joint; and (3) rotator cuff muscles that control dynamic stability and arthrokinematics at GH joint

Question 25

scapular muscles that control upward rotation of ST joint

Answer 25

Serratus anterior

Trapezius

Question 26

rotator cuff muscles that control dynamic stability and arthrokinematics at GH joint

Answer 26

Supraspinatus
Infraspinatus
Teres minor
Subscapularis

Question 27

When are the middle deltoid and supraspinatus first activated during elevation and when are they most active during elevation?

Answer 27

Both muscles activated at onset of elevation, reaching maximum level near 90° of abduction

Question 28

What is the function of the middle deltoid and supraspinatus muscle during abduction?

Answer 28

During abduction, both muscles help stabilize humeral head within functional concavity formed by inferior capsule of joint

Question 29

if the supraspinatus muscle is paralyzed - is abduction of the GH still possible?

Answer 29

With supraspinatus paralyzed or tendon ruptured, full abduction often difficult or not possible b/c of altered arthrokinematics at GH joint

Question 30

if deltoid muscle paralyzed, is supraspinatus still capable of producing arm abduction?

Answer 30

With deltoid paralyzed, supraspinatus muscle capable of fully abducting GH joint, although abduction torque reduced

Question 31

if ________ and __________ muscles are paralyzed - full active abduction is not possible

Answer 31

Full active abduction not possible with paralysis of both deltoid and supraspinatus

Question 32

Research has shown that extreme upper fibers of infraspinatus and subscapularis muscles have limited moment arm to abduct GH joint - why does this occur?

Answer 32

Occurs b/c upper fibers of these muscles pass slightly superior to joint’s AP AOR
Although considered only secondary abductors, they play primary role in establishing dynamic stabilization and directing joint’s arthrokinematics (functions described later)

Question 33

in addition to upward rotation, what other functions does the serratus anterior have on the scapula?

Answer 33

In addition, serratus anterior can posteriorly tilt and externally rotate scapula
Line of force of lower fibers of serratus anterior pulls inferior angle of (upwardly rotated) scapula forward
Although speculative, this forward pull on inferior angle, in conjunction with other forces, may tilt glenoid region of scapula posteriorly
Also, serratus anterior produces external rotation torque on scapula by generating force that passes medial to vertical axis of AC joint
External rotation torque helps secure medial border of scapula firmly against thorax

Question 34

where is the GH axis (abductors) AOR during abduction?

Answer 34

near humeral head

Question 35

where is the scapular axis (from upward rotators) during abduction?

Answer 35

near acromion

Question 36

upper trapezius upwardly rotates scapula indirectly by its______________ pull on ___________

Answer 36

its superior-and-medial pull on clavicle
EMG ACTIVATION
Upper trapezius shows significant rise in EMG activation at initiation of shoulder abduction, then continues gradual rise in amplitude throughout remainder of ROM
Upper trapezius elevates clavicle throughout early phase of abduction while simultaneously balancing inferior pull of lower trapezius during late phase of abduction

Question 37

lower trapezius upwardly rotates scapula by its __________ pull on the _____________

Answer 37

Lower trapezius upwardly rotates scapula by its inferior-and-medial pull on root of spine of scapula
EMG ACTIVATION
Lower trapezius particularly active during later phase of shoulder abduction

Question 38

Serratus Anterior shows gradual _______ in EMG amplitude throughout entire range of shoulder abduction

Answer 38

increase

Question 39

during abduction - where does the Middle Trapezius line of force run through?

Answer 39

AOR of rotating scapula

Question 40

Middle Trapezius activation during abduction

Answer 40

very active during shoulder abduction

MT robbed of its leverage to contribute upward rotation torque
However, MT still contributes needed retraction force on scapula, which along with rhomboid muscles, helps to neutralize strong protraction effect of serratus anterior
Net force dominance b/w middle trapezius and serratus anterior during elevation of arm helps determine final retraction-protraction position of upward rotated scapula

Question 41

____________ and ______________ control mechanics of scapular upward rotation

Answer 41

serratus anterior and trapezius

Serratus anterior has greater leverage for this motion
Both muscles synergists in upward rotation but are agonists and antagonists as they oppose, and thus partially limit, each other’s strong protraction and retraction effect

Question 42

which muscle has greatest leverage for shoulder abduction?

Answer 42

serratus anterior

Question 43

paralysis of upward rotators of STJ: Trapezius

Answer 43

Complete paralysis of trapezius causes moderate to marked difficulty in elevating arm overhead
Tasks may still be accomplished through full ROM as long as serratus anterior fully innervated
Elevation of arm in pure frontal plane particularly difficult with trapezius paralysis b/c this action requires MT generate strong retraction force on scapula

Question 44

paralysis of upward rotators of STJ: Serratus Anterior

Answer 44

Paralysis of serratus anterior muscle causes significant disruption in normal shoulder kinesiology:
Disability may be slight with partial paralysis, or profound with complete paralysis
Persons with complete paralysis of SA have great difficulty actively elevating arm
Difficulty exists even though trapezius and GH abductor muscles fully innervated

Question 45

Contraction of normal SA upwardly _______scapula, thus allowing middle deltoid and supraspinatus to ________ humerus in ______ rotary direction as scapula

Answer 45

Contraction of normal SA upwardly rotates scapula, thus allowing middle deltoid and supraspinatus to rotate humerus in same rotary direction as scapula
With SA paralysis, middle deltoid and supraspinatus dominate scapular kinetics, producing paradoxic (and ineffective) downward rotation

Question 46

“winging” of the scapula a result from the scapula being ________ rotated and slightly ________tilted and ___________ rotated

Answer 46

In addition to downwardly rotated position, scapula also slightly anteriorly tilted and internally rotated (evidenced by “flaring” of scapula’s inferior angle and medial border)

Question 47

“winging” can cause adaptive shortening of what muscle?

Answer 47

pectoralis minor - direct antagonist to serratus anterior

↑ passive tension in pectoralis minor further promotes anteriorly tilted and internally rotated position of scapula