Lecture 24 - Functional Anatomy of Shoulder Joint Complex Flashcards
What 7 structures compose the shoulder complex
- Glenohumeral Joint
- Labrum
- Capsule
- Ligaments
- Scapulothoracic Joint
- Sternoclavicular Joint
- Acromioclavicular Joint
What is the glenohumeral joint
A triaxial synovial joint that rotates around 3 axes/degrees of freedom
What is the glenoid of the glenohumeral joint
It is concave and pear shaped structure that faces laterally, anteriorly and superiorly
What is the humeral head of the glenohumeral joint
It is a convex structure that is larger articulates 1/3 with the glenoid fossa and faces superiorly, medially and posteriorly
What is the glenoid labrum
It is a fibrocartilage ring (tissue) that surrounds the glenoid, deepens the fossa, and supplies a vacuum effect to seal and stabilize the glenohumeral joint
Where does the joint capsule arise from and insert into?
The glenoid neck and labrum and inserts into the articular margin of the humeral neck
How is the joint capsule reinforced
Superiorly and anteriorly by superior, middle and inferior glenohumeral ligaments
Where does the superior glenohumeral ligament arise from
Its a robust thin tissue that is a small depression above lesser tubercle and blends with coracohumeral ligament that arises from margin of glenoid and labrum
What is the function of the superior glenohumeral ligament
1) Provides restraint to inferior translations of humeral head when arms are adducted
2) Limits external rotation from 0-45 degrees abduction
3) Aids in stability anteriorly and inferiorly
T or F: The superior glenohumeral ligament is not tensioned with biceps during throwing
F, it is
What is the attachments of the middle glenohumeral joint
It arises from anterior superior glenoid and labrum and inserts into lower part of lesser tuberosity
What are the 2 functions of the middle glenohumeral ligament
- Limits external rotation when arm is at side
- Provides restraint to anterior humeral translation with the arm in mid-range of abduction up to 45 degrees
What is the attachment of the inferior glenohumeral ligament
Attaches from anterior/posterior mid glenoid and labrum (hammock type axillary pouch)
What are the 2 functions of the inferior glenohumeral ligament?
- Anterior band limits anterior translation when glenohumeral joint is abducted up to 90 degrees
- During internal rotation the posterior band limits posterior translation of the humerus
What is the attachment/insertion of the coracohumeral ligament
It attaches near root of the coracoid and inserts into the humerus and transverse ligament
What are the 4 functions of the coracohumeral ligament
- Limits external rotation below 60 degrees of flexion
- Works with the superior glenoid ligament
- Restraint for flexion and extension
- Acts as a tunnel for the bicep
T or F: The scapulothoracic joint is a true joint
F, it is a pseudojoint
Where is the scapulothoracic joint found
- Between anterior portion of the scapula and posterior thorax and rib cage (plane of scapula)
Where is the sternoclavicular joint located
Between the medial end of the clavicle and lateral portion of the sternum (saddle-shaped)
What is the most important ligament surrounding the sternoclavicular joint and why?
The posterior sternoclavicular ligament which increases anterior and posterior translation
Where is the acromioclavicular joint located
Between he lateral end of the clavicle and medial end of the acromion
How many degrees of freedom does the acromioclavicular joint have
3
What 2 ligaments compose the acromioclavicular joint and their function
- Conoid: Resists elevation and protraction
- Trapezoid: Resists acromioclavicular joint compression and clavicle elevation/protraction
Describe the Scapulohumeral Rhythm
180 degree of shoulder elevation is caused by humeral elevation while 60 degrees of that is due to scapular rotation (2:1 ratio)
Force Couple
Occurs when 2 groups of muscles work together to produce a movement or provide joint stability
Describe the Deltoid-Rotator Cuff Force Couple
During initial arm movement the larger deltoid has an upward and outward force caused by superior migration of humerus that is counteracted by inferior and medial directed force of the infraspinatus, subscapularis and teres minor (rotator cuff)
What force couple produces the largest amount of force
Deltoid-Rotator Cuff
Supraspinatus movement
Provides a direct compressing force on the humeral head into the glenoid maximally between 45-90 degrees of abduction (gone at 150 degrees)
Infraspinatus and Teres Minor 2 Functions
- Depress humerus allowing supraspinatus to compress and prevent sub-acromial compression
- External rotator and eccentrically decelerates internal rotation (Concentrically -> lateral rotation)
Do muscles work harder concentrically or eccentrically
eccentrically
Subscapularis 2 functions
- Active in all movements of humeral head that require compression and depression
- Acts eccentrically to decelerate external rotation (concentric -> medial rotation)
3 functions of the long head of the biceps
- Increases glenohumeral compression with supraspinatus
- Applies longitudinal compressive force during deceleration activities
- Increases anterior stability in abduction/external rotation by resisting translational stress
Describe the upper trapezius and serratus anterior force couple 4 functions
to produce upward movement of scapula during elevation by:
1) Rotating scapula for optimal glenohumeral joint function
2) Maintaining efficient length-tension of deltoid
3) Preventing impingement of rotator cuff from subacromial structures
4) Providing stable scapular base to enable appropriate recruitment of scapular-humeral muscles
Describe how the serratus anterior/lower trap is involved with the upper trap/levator scapula in the upper trapezius and serratus anterior force couple
Lower portion of SA and LT work in conjunction with the UT and LS to create upward rotation of the scapula
T or F: Lower trap and serratus anterior are the primary components of upward rotation and stabilization of the scapula when the shoulder is abducted past 90 degrees
T
What happens to patients with impingement syndrome of the upper trapezius and serratus anterior force couple
Show decreased activity of serratus anterior and delay in firing lower traps and middle traps, so dominance occurs in the upper traps and levator scapula causing faulty scapulohumeral patterns
