Musculature of the Shoulder Flashcards
elevation
require muscle activity to overcome or control the weight of the limb and its load
usually involves glenohumeral flexion and/or ABD and scap upward rotation
muscles included in elevation
deltoid
supraspinatus
infraspinatus and teres minor
subscapularis
biceps
pec major
deltoid in elevation
middle deltoid is always active
anterior deltoid is for flexion
posterior deltoid is for extension
when are the anterior and middle heads optimally aligned for elevation
in the scapular plane
30-45 degrees in front of the coronal plane
when the humerus is in plane of the scapula
what happens as the humerus continues to elevate
fibers of the deltoid are becoming actively insufficient
more motor units are recruited to maintain tension
how can we prevent active insufficiency of the deltoid during elevation
the deltoid is strongly dependent on simultaneous scapular movement
what else is the deltoid actively dependent on during elevation
intact rotator cuff
w/ a complete rupture of RC, deltoid actively will result in a shrug rather than ABD
how does the deltoid depend on the RC during elevation
as the deltoid draws the humeral head up
the RC tugs on the head and centers it in the glenoid fossa
supraspinatus during elevation
working in all active planes of elevation
will provide a depressing force, offsetting the deltoid’s superior shearing effect
has secondary functions as well
how does the supraspinatus provide a depressing force
tendon will become shorter and widen and push down (vertical motion)
keeps the humeral head away from the acromion by depressing it
secondary functions of the supraspinatus during elevation
acts as a vertical steerer of the humeral head
assists in maintaining the stability of the dependent arm
infraspinatus and teres minor in elevation
compress the GH joint
act in a force couple to depress the humeral head during elevation, allowing for humeral rotation
serve as a posterior barrier against translation
subscapularis in elevation
acts synergistically w/ the posterior cuff muscles to depress and compress the humeral head
biceps in elevation
long head can assist with ABD when the humerus is in ER
pec minor in elevation
only contributes to flexion of GH
muscles that perform extension GH joint
posterior deltoid
latissimus dorsi
teres major
infraspinatus
teres minor
triceps
middle deltoid
ER GH joint muscles
infraspinatus
posterior deltoid
teres minor
muscles that help with ER beyond 30 degrees
scapular adductors
trapezius
rhomboids
stabilize the origin of the infraspinatus, posterior delt and teres minor, preventing the medial border of the scap from winging
IR GH joint muscles
subscapularis
teres major
pectoralis major
latissimus dorsi
anterior deltoid muscles
what are the scapulothoracic muscles
traps (all)
serratus anterior
levator scap
rhomboids
pec minor
what do the scapulothoracic muscles do
provide a stable yet mobile base from which the GH joint and associated muscles can function
upward rotation muscles (ST)
serratus anterior and trapezius force couple
middle traps and rhomboids
4 functions of serratus anterior and trapezius force couple
orient the scapula
provide scapular upward rotation
prevent impingement
provide a stable base
- orient the scapula
will maintain the glenoid fossa in an appropriate position to support the humeral head
- provide scapular upward rotation
this will maintain efficient length of the deltoid fibers through the ROM
this enhances the power and stabilizing effect
- prevent impingement
the upward rotation will prevent impingement of the RC and bursa in the subacromial space
- provide a stable base
for the axiohumeral and scapulohumeral muscles that are moving the arm against gravity
middle traps and rhomboid upward rotation
active in humeral elevation, esp ABD
stabilizing synergists to the muscles tha rotate the scapula
contract eccentrically to control the motion created by the traps-serratus anterior force couple
muscles of shoulder depression
latissimus dorsi and pectoralis muscles
shoulder depression
forceful downward movements of the arm in relation to the trunk
forceful movement of the trunk upward in relation to the fixed arm
what does the scapula tend to do during humeral motion
rotate downward and ADD
lattissimus dorsi during downward rotation when the arm is free
adduct, medially rotate, and extend the humerus
adduct and depress the scap
lattissimus dorsi during downward rotation when the arm is fixed
lifting the body up as in a seated push up
reverse action of a muscle
pectoralis major during upward rotation
primary depressors of the shoulder complex
pectoralis minor
will assist with depression
acts directly on the scapula to depress and rotate downward
scapulohumeral rhythm
essential for normal shoulder function
synchronous motion of the humerus and scapula during arm elevation
coordinated movements of the shoulder of the shoulder girdle provide the smoothest and greatest ROM possible for the upper extremity
can GH motion alone have full ROM
not for full ROM in flexion or ABD
the rest of the motion is contributed by the scapulothoracic joint through SC and AC linkages
ration of scapulohumeral rhythm
2:1
for every 2 degrees of humeral movement
there is 1 degree of scapular motion
what joints are included in scapulohumeral rhythm
scapulothoracic
GH
SC
AC
what chain is the scapulothoracic joint
closes kinematic chain
movement of the scap can only occur through movement of the SC and AC joints
if movement occurs in one place
movement will occur is another place
phase one of scapulohumeral rhythm
the setting phase
when the humerus elevates up to 30 degrees of ABD or 60 degrees of flexion
scapula seeks a position of stability on the thoracic wall
where does motion primarily take place during phase 1
GH joint
what does the scap begin to do during the setting phase
scapula begins to link with the clavicle
ligaments and capsule tighten so they will move together
phase 2 of scapulohumeral rhythm
occurs from 30 degrees of ABD and 60 degrees of flexion to 150 degrees of both motions
GH contribution decreases and scapulothoracic joint increases and upwardly rotates
how does upward rotation occur (phase 2)
upper and lower traps w/ the serratus anterior
AC motion is prevented d/t the conoid ligaments, so motion must occur elsewhere –> SC joint –> clavicle elevates
clavicular elevation causes 30 degrees of upward rotation
clavicular elevation (90 degrees) is checked by the costoclavicular ligs
AC joint permits some winging and tipping to maintain contact b/w the scap and thoracic wall
by this point there is 90 degrees of either flexion or ABD
as phase 2 continues
upward rotation is restrained by the costoclavicular ligaments and coracoclavicular ligaments
muscles continue to produce force, coracoid continues to move inferiorly, causing more clavicular rotation
this carries the scap through another 30 degrees of upward rotation
continued winging and tipping of the scap via the AC joint
phase 3
ranges from 150-180 degrees of flexion or ABD
GH contribution increases and ST decreases
to complete ABD the humerus must ER
for full flexion, the scap must ABD and upwardly rotate (keeps the glenoid in good alignment w/ shaft of the humerus)
rotator cuff
supraspinatus
infraspinatus
teres minor
subscapularis
“S.I.T.S” muscles
important role of the RC
shoulder elevation and reinforcing the joint capsule
what does the RC do during shoulder elevation
will secure the humerus to the glenoid fossa and compress the joint
adds dynamic stability to the shoulder
what does the RC do during ABD
ER the humerus (infraspinatus and teres minor) at the end of ROM of ABD
force couple in RC
deltoid/supraspinatus with infraspinatus and teres minor
without adequate strength of the RC muscles
there is risk of injury
