Shoulder Flashcards
Where do the proximal stabilizers orginate?
originate on spine, ribs, and cranium and insert on scapula and clavicle
Examples include serratus anterior and trapezius
Where do distal mobilizers originate?
originate on scapula and clavicle and insert on humerus or forearm
Examples include deltoid and biceps brachii
which are activated first - proximal stabilizers or distal mobilizers?
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
What are the primary elevators of the ST joint?
Upper trapezius
Levator scapulae
Rhomboids
Functionally, these muscles support posture of shoulder girdle (scapula and clavicle) and upper extremity
What are the primary depressors of the ST joint?
Lower trapezius (act directly on scapula) Latissimus dorsi (act indirectly on scapula) Pectoralis minor (act directly on scapula) Subclavius (stabilizes the SC joint)
What are the primary protractors of the ST joint?
Serratus anterior*
What are the primary retractors of the ST joint?
Middle trapezius* Main
Rhomboids
Lower trapezius
What are the primary upward rotators of the ST joing?
Serratus anterior
Upper and lower trapezius
These muscles also provide stable attachments for more distal mobilizers, such as deltoid and rotator cuff muscles
What are the primary downward rotators of the ST joint?
Rhomboids
Pectoralis minor
If the upper trapezius is paralyzed - what type of joint dislocation and/or subluxation would the person be more prone too?
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
what is the ideal posture of the shoulder girdle?
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
How do “rounded shoulders” present themselves regarding the scapula?
Scapulas slightly depressed, downwardly rotated, and protracted
Posture can lead to same biomechanical stress on SC and GH joints described in paralysis
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
does the subclavius muscle act directly or indirectly on scapula?
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
how does the latissimus dorsi act on the shoulder girdle? directly or indirectly? how does it accomplish its movement?
Lower trapezius and pectoralis minor act directly on scapula
Latissimus dorsi depresses shoulder girdle indirectly, primarily by pulling humerus inferiorly
what joint is the force of scapular protraction transferred through?
GH - employed for pushing and reaching activities
SC has a _______ axis of rotation
Vertical - this is what gives it leverage for protraction
strenght of protraction torque produced by Serratus Anterior is a result of _________ multiplied by _________ origination at __________ AOR at ______ joint
Strength of protraction torque primarily result of muscle force multiplied by internal moment arm (IMA) originating at vertical AOR at SC joint
((LOOK UP!!))
Which retractor has optimal line of force to produce this motion?
Middle Trapezius
secondary retractors = rhomboids and lower trapezius
during what motions are the Retractors of the shoulder primarily active?
during pulling activities such as climbing and rowing
- retractors secure scapula to axial skeleton
Secondary Retractors as antagonists to one another
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
with complete paralysis of trapezius - scapula tends to “drift” slightly into ________ as a result of partially unopposed protraction action of _________
Scapula tends to “drift” slightly into protraction as result of partially unopposed protraction action of serratus anterior muscle
muscles that elevate (abduct/flex) the humerus at GH joint
name which muscles are primary abductors & which are primary flexors
Anterior (ABDUCT & FLEXION) and middle deltoid (ABDUCT) Supraspinatus (ABDUCT) Coracobrachialis (FLEXION) Biceps (long head) (FLEXION)
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
(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
scapular muscles that control upward rotation of ST joint
Serratus anterior
Trapezius
rotator cuff muscles that control dynamic stability and arthrokinematics at GH joint
Supraspinatus
Infraspinatus
Teres minor
Subscapularis
When are the middle deltoid and supraspinatus first activated during elevation and when are they most active during elevation?
Both muscles activated at onset of elevation, reaching maximum level near 90° of abduction
What is the function of the middle deltoid and supraspinatus muscle during abduction?
During abduction, both muscles help stabilize humeral head within functional concavity formed by inferior capsule of joint
if the supraspinatus muscle is paralyzed - is abduction of the GH still possible?
With supraspinatus paralyzed or tendon ruptured, full abduction often difficult or not possible b/c of altered arthrokinematics at GH joint
if deltoid muscle paralyzed, is supraspinatus still capable of producing arm abduction?
With deltoid paralyzed, supraspinatus muscle capable of fully abducting GH joint, although abduction torque reduced
if ________ and __________ muscles are paralyzed - full active abduction is not possible
Full active abduction not possible with paralysis of both deltoid and supraspinatus
Research has shown that extreme upper fibers of infraspinatus and subscapularis muscles have limited moment arm to abduct GH joint - why does this occur?
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)
in addition to upward rotation, what other functions does the serratus anterior have on the scapula?
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
where is the GH axis (abductors) AOR during abduction?
near humeral head
where is the scapular axis (from upward rotators) during abduction?
near acromion
upper trapezius upwardly rotates scapula indirectly by its______________ pull on ___________
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
lower trapezius upwardly rotates scapula by its __________ pull on the _____________
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
Serratus Anterior shows gradual _______ in EMG amplitude throughout entire range of shoulder abduction
increase
during abduction - where does the Middle Trapezius line of force run through?
AOR of rotating scapula
Middle Trapezius activation during abduction
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
____________ and ______________ control mechanics of scapular upward rotation
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
which muscle has greatest leverage for shoulder abduction?
serratus anterior
paralysis of upward rotators of STJ: Trapezius
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
paralysis of upward rotators of STJ: Serratus Anterior
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
Contraction of normal SA upwardly _______scapula, thus allowing middle deltoid and supraspinatus to ________ humerus in ______ rotary direction as scapula
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
“winging” of the scapula a result from the scapula being ________ rotated and slightly ________tilted and ___________ rotated
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)
“winging” can cause adaptive shortening of what muscle?
pectoralis minor - direct antagonist to serratus anterior
↑ passive tension in pectoralis minor further promotes anteriorly tilted and internally rotated position of scapula
