Lecture 5: The shoulder complex Flashcards
What four joints make up the shoulder complex?
Glenohumeral Joint
Sternoclavicular Joint
Acromioclavicular Joint
Scapulothoracic Joint
What joint provides the greatest mobility in the body?
Glenohumeral Joint
What are the three components of the shoulder complex?
Clavicle
scapula
humerus
The GH joint connects what?
the humerus and the scapula
What serve as a primary mechanism for securing the shoulder girdle to the to the thorax AND providing a stable base of support for the upper extremity movements?
Muscle force
What is dynamic stabilization?
A moving segment or segments is limited very little by passive forces such as capsules or ligaments and instead relies heavily on active forces or dynamic muscular control
Give two examples of the shoulder weight bearing:
a gymnast on parallel bars
a grandparent using a cane
What joint is the only structural attachment of the UE to the axial skeleton? (everything else is muscular)
Sternoclavicular Joint
The SC joint has how many rotary and translatory degrees of freedom?
3
Rotations at the SC joint produce movement where?
The clavicle and the scapula
The SC joint is classified as a _____ ________ joint due to the sternoclavicular disc proving glide and rotation in all three planes.
plane synovial
Does the superior joint of the medial clavicle articulate with the manubrium?
no; it articulates with the SC disk and interclavicular ligament
Does the inferior joint of the medial clavicle articulate with the manubrium?
Yes, as well as the first costal cartilage
What is the purpose of the SC joint disk?
Increases congruency and absorbs forces
Where does the SC joint disk attach?
post/sup clavicle, manubrium, first costal cartilage, and ant/post fibrous capsule
During shoulder motion, the disk acts like a _____ or pivot point for the medial end of the clavicle
hinge
The SC disk is considered part of the ________ with elevation and depression and part of the ________ during protraction and retraction
manubrium
clavicle
What are the three ligaments that the SC joint relies on for the majority of its support?
anterior and posterior SC ligaments
costoclavicular ligament
intervclavicular ligament
What part of the SC joint holds on to the entire weight of the arm?
Capsule
The anterior and posterior SC ligaments do what?
reinforce the capsule
checks ant/post translation of clavicle
The _____________ ligament is a very strong ligament between the clavicle and first rib and has two segments or laminae
costoclavicular
The anterior fibers of the costoclavicular ligament run from the 1st rib to clavicle in what direction?
laterally
The posterior fibers of the costoclavicular ligament run from the 1st rib to clavicle in what direction?
medially
The costoclavicular ligament does what?
Checks elevation of lateral clavicle
May help with inferior glide of medial clavicle
Counters the superior pull of the SCM and supra hyoid mm
The posterior fibers of the costoclavicular ligament resist ______ movement of the clavicle, absorbing some of the force that would otherwise be imposed on the disk
medial
What ligament stabilizes the clavicle and keeps it relatively still?
costoclavicular ligament
What is the job of the interclavicular ligament?
Resists excessive depression of distal clavicle and superior glide of medial clavicle
Which joint is LESS stable, SC or AC?
AC joint
What are the motions at the SC joint?
elevation/depression around an a/p axis
protraction/retraction around a vertical axis
anterior/posterior rotation around the long axis
The lateral clavicle has about how many degrees of elevation (upward rotation)?
~48 degrees
The lateral clavicle has about how many degrees of depression (downward rotation)?
~15 degrees
With SC joint elevation, the lateral end of the clavicle moves _______ and the medial end glides _______
up
down
With protraction, the lateral clavicle rotates ________ and the medial clavicle slides _________ about how many degrees?
anteriorly
15-20 degrees
With retraction, the lateral clavicle rotates ________ and the medial clavicle slides _________ about how many degrees?
posteriorly
30 degrees
Anterior/Posterior rotation of the clavicle typically occurs in one direction from neutral… what direction is it? about how many degrees of a/p rotation does the clavicle have?
posterior
50 degrees
What joint of the shoulder complex has a low incidence of OA and dislocation? Why is this the case?
SC joint
Strong force-disipating structures such as the disk and ligaments prevent excessive intra-articular motion
The ______________ joint is made more for mobility and less for stability
acromioclavicular
What joint attaches the scapula to the clavicle?
AC joint
What is the function of the AC joint?
Allows scapular rotation in 3d during arm movement, increasing UE ROM
Adjustments of tipping and int/ext rotation
transmission of forces from UE to clavicle
The AC joint consists of the articulation between the _______ end of the ________ and a small _____ on the ________ of the scapula
lateral
clavicle
facet
acromion
What joint is actually a fibrocartilagenous union through 2 years of age?
AC joint
The AC capsule is relatively _____ and cannot maintain the integrity of the joint without the reinforcement of the ________ and _______ _____________ ligaments.
weak
superior
inferior
acromioclavicular
What job does the superior AC ligament perform?
resists small opposing forces applied to the distal clavicle along with deltoid and trap muscles
What job does the inferior AC ligament perform?
resists small rotary and translatory forces- not as strong as the superior ligament
Why is the joint support of the superior AC ligament greater than that of the inferior?
Aponeurotic fibers of the trapezius and deltoids muscles reinforce the superior ligament, making it stronger.
What ligament firmly unites the undersurface of the clavicle and the coracoid of the scapula limiting upward rotation of the scapula at the AC joint and medial scapular displacement, transferring forces to the SC joint?
Coracoclavicular ligament
What are the two portions of the coracoclavicular ligament called and where are they relatively located?
Trapezoid- lateral, quadrilateral, and horizontal
conoid- medial, posterior, and triangular and vertical
What does the trapezoid part of the coracoclavicular ligament do?
resists posteriorly directed forces
What does the conoid part of the coracoclavicular ligament do?
resists superior/inferior forces
One of the most critical roles of the coracoclavicular ligament is the coupling of what two motions to help flip the clavicle posteriorly?
posterior rotation of the clavicle and scapular rotation during elevation of the arm
Shoulder flexion and abduction results in the _________ tipping of the scapula
posterior
Internal and External rotation of the scapula through the AC joint results in ___________ and _________ movements of the glenoid fossa
(Maintains the scapula with the curve of the thorax while the clavicle protracts and retracts)
anteromedial
posterolateral
Shoulder shrug results in _______ tilting of the scapula
anterior
Upward and downward rotation of the scapula tilts the _______ _____ up and down
glenoid fossa
During upward rotation of the scapula, the ________ process and the _______ _______ of the scapula moves away from the clavicle
coracoid
superior border
Unlike the sternoclavicular joint, the __ joint is susceptible to both trauma and degenerative changes.
AC
Trauma to the AC joint is most typically caused by what?
Falling on shoulder with arm ADducted
What types of problems will you see more of- AC or SC joint?
AC
What “joint” is formed by the articulation between the scapula and the thorax?
Scapulothroacic joint
Why is the scapulothroacic joint not an actual anatomical joint?
It is not a union of bony segments by fibrous, cartilaginous, or synovial tissues
The motions of the AC, SC, and ST joints are all interdependent– what type of kinetic chain is this?
Closed chain
Of the three: AC, ST, and SC joints, which motion is most commonly measured due to its accessibility?
ST joint motion
What is the typical rest position of the scapula?
Between ribs 2-7
about 2” from the midline (give or take)
Slight internal rotation (protraction) ~ 30-45 degrees (it rests against the rib cage)
Anterior tilt ~10-15 degrees
Up rotation ~5-10 degrees
How many degrees of upward rotation are required for arm elevation from the ST joint (along with external rotation and posterior tipping)?
60 degrees
What are the secondary scapular motions?
Anterior and posterior tipping
internal and external rotation
What are the primary scapular motions?
upward rotation and downward rotation
elevation and depression
protraction and retraction
Excessive internal rotation is also referred to as _________ ________.
Scapular Winging
Scapular elevation occurs through elevation of the clavicle at the _____ joint and may include subtle adjustments in a/p tilting and I/E rotation at the ____ joint to keep the scapula in contact with the thorax
SC
AC
Scapular protraction and retraction are interchangeable with scapular _________ and _______
abduction and adduction
2/3 of SC joint __________ rotation will couple with ST upward rotation.
1/3 of clavicular _________ will couple with ST upward rotation
posterior
elevation
ST joint stability is dependent on:
AC & SC joints
Muscles of scapula and thorax
The glenohumeral joint is a ____ ____ ______ synovial joint with how many degrees of freedom?
ball and socket
3
The humeral head is larger than the glenoid fossa making it inherently _________
unstable
Scapular motion can affect GH joint motion. Why?
The glenoid fossa of the scapula make up the proximal part of the GH joint
True or False: The Glenoid is always perpendicular to the plane of the scapula
FALSE
The glenoid is not always perpendicular to the plane of the scapula
How does the labrum benefit the glenoid?
It enhances the depth of the glenoid by 50% making it more concave and also adding stability for the humeral head
What part of the labrum is attached to the glenoid and is not mobile?
The inferior aspect
What muscle attaches on the superior end of the labrum?
The long head of the biceps
What is considered the distal articular surface of the GH joint?
Humeral head
In anatomical position the humeral head faces _________, ____________, and _________.
medially
superiorly
posteriorly
What is the typical angle of inclination of the humerus?
~130-150 degrees
What is the typical angle of retroversion/torsion of the humerus?
~30 degrees posterior
Increase in humeral retroversion results in increased range of _______ rotation and decreased range of _______ rotation. This is common in throwing athletes
lateral
medial
The GH joint is surrounded by a large, loose capsule that is taut ___________ and slack ___________ and ___________ with the arm dependent at the side.
superiorly
anteriorly
inferiorly
When is the capsule around the GH joint the tightest (closed pack position)?
when the humerus is abducted and laterally rotated
Where is the GH joint most susceptible to dislocations?
Anteriorly
What are the 4 ligaments surrounding the GH joint capsule?
Superior GH Ligament
Middle GH Ligament
Inferior GH Ligament
Coracohumeral Ligament
When is the Superior GH Ligament taut? What movement does it resist?
at 0 degrees
Resists anterior and inferior humeral translation
When is the Middle GH Ligament taut? What movement does it resist?
45 degrees
Resists anterior humeral translation
When is the Inferior GH Ligament taut? What movement does it resist?
45 degrees
Resists inferior, superior, and posterior humeral translation
Where do anterior GH joint dislocations typically occur, especially in FOOSAs?
Foramen of Weitbrecht
What does the coracohumeral ligament do?
Works with Superior GH for stability of dependent arm
Resists lateral rotation of humerus while in adduction
What is the coracoacromial arch formed by?
Coracoid process
Acromion
Coracoacromial Ligament
Inferior surface of the AC joint
What is the purpose of the coracoacromial arch?
Forms a vault over the humeral head
What lies within the subacromial space?
rotator cuff tendons
a portion of the long head of biceps brachii tendons
and the subacromial bursa
What muscle is especially susceptible to impingement in the subacromial/subdeltoid space
supraspinatus
When is the subacromial space the smallest?
at 90 degree of humeral elevation
You may not see the effects of supraspinatus impingement in angles larger than 60 degrees. Why?
The suprspinatus does not work in these ranges
How far can the GH joint flex and extend?
Flexion- 120 degrees
Extension- 50 degrees
When is GH joint IR/ER rotation restricted?
When the arm is at the side
The GH joint needs what other movement to complete full abduction in the frontal plane?
Lateral (external) rotation
When is adduction/abduction the greatest in the GH joint? (What position is the humerus in?)
Scaption (in the plane of the scapula)
In regard to arthrokinematics, the GH joint is a _______ humeral head moving on a _______ glenoid fossa. For humeral elevation, _________ glide is necessary for full ROM without impingement.
convex
concave
inferior
Below 90 degrees, only the superior segment of the GH joint capsule is taut and the _______ _____ muscles are actively stabilizing the GH joint.
rotator cuff
At the end range of motion, the GH joint capsule tightens and translates the humeral head in what direction?
The least resistant
What is/are the prime mover(s) for GH abduction?
deltoid
supraspinatus
The posterior deltoid is used for _________
extension
The anterior deltoid is used for _______
flexion
What is the initial action of the deltoid?
superior translation shear
Can the deltoid independently abduct/elevate the arm? Why or why not?
No
It needs forces opposing the upward pull of the deltoid
What produces rotation and compression as well as the translatory pull that counteracts the deltoid pull?
Rotator Cuff Muscles
What rotator cuff muscles can also laterally rotate to clear the greater tubercle from under the acromion?
Teres minor and infraspinatus
What muscle can produce nearly full ROM for GH abduction alone while also stabilizing due to its long MA?
Supraspinatus
What is considered the “painful arc” produced by rotator cuff tendinopathy or tears?
between 60 and 120 degrees
What muscle can flex and abduct the GH jt if the arm is already in ER?
Long head of the biceps
What two tendons can become painful during repeated elevation, especially if they’re impinged below the arch?
Supraspinatus and Biceps tendon
What are the three benefits of scapulohumeral rhythm?
distributes forces across all 4 joints providing more ROM with more stability
Maintains glenoid in optimal position for humeral head through the range
maintains good length-tension relationship of humeral muscles and prevents active insufficiency with upward rotation of the scapula
