Lecture 2: Glenohumeral Joint

What type of joint is the Glenohumeral joint?

synovial ball and socket

Is the Glenohumeral joint a stable joint?

no, its incongruent

Since the GH joint is incongruent, what does it allow?

increase movement

What does the GH joint rely heavily on for stability?

soft tissues like the labrum, ligaments, and rotator cuff muscles

What is the close packed position for the GH joint?

90° abduction with external rotation

What is the function of the labrum in the glenoid fossa?

the labrum increases the articulating surface length and depth of the glenoid fossa

What is the labrum made of?

connective tissue continuous with the joint

What does SLAP tear stand for?

Superior Labrum Anterior to Posterior tear

Where does a SLAP tear occur at?

where the biceps tendon anchors to the labrum

How is the GH joint capsule of positioned at rest?

the joint is surrounded by a loose capsule that is taut superiorly and slack anteriorly and inferiorly

Where in the capsule is the weakest and providing little stability?

inferiorly

What is the function of the Superior Glenohumeral Ligament (SGHL)?

helps stabilize the shoulder by preventing inferior (downward) displacement of the humeral head and limiting external rotation of the arm

What is the function of the Middle Glenohumeral Ligament?

helps to resist anterior (forward) translation of the humeral head, especially when the arm is in a position of abduction and external rotation

What is the function of the Inferior Glenohumeral Ligament?

helps stabilizes the shoulder in overhead movements and extremes of abduction and external rotation

Which ligaments of the GH joint is the most important?

Inferior Glenohumeral Ligament (IGHL)

Which ligament in the GH joint is most impacted in Adhesive Capsulitis (frozen shoulder)?

Inferior Glenohumeral Ligament (IGHL)

Why is the IGHL most impacted in Adhesive Capsulitis (frozen shoulder)?

because of its role in stabilizing the shoulder during extreme ranges of motion (abduction and external rotation)

What is the capsular pattern loss of ROM in Adhesive Capsulitis?

ER > ABD > IR

Where does the coracohumeral ligament goes from and to?

coracoid process to greater tubercle

What is the function of the Coracohumeral Ligament?

provides passive support to the joint against the force of gravity

What does the Subdeltoid (Subacromial) bursa separate?

supraspinatus tendon from acromion process, coracoid process and coracoacromial ligament

What is the function of the subacromial (subdeltoid) bursa?

permits smooth gliding between the humerus, supraspinatus and surrounding structures

How does gravity act on the humerus?

gravity acts as a pure translatory force through the humerus

What counteracts the downward pull of gravity on the humerus?

superior joint capsule, superior GH ligament, coracohumeral ligament

When additional mass is added to the upper extremity, what becomes more active?

the supraspinatus

What role does the supraspinatus play in passive GH joint stability?

its passive tension helps support and stabilize the GH joint

What effect does deltoid activation have on the shoulder joint?

it generates a superiorly translatory force (compression) toward the coracoacromial arch

What effect do the deltoids have on the shoulder joint if the deltoids were to act unopposed?

little abduction will occur and poor glenohumeral arthrokinematics will occur as there would be little rotator cuff activity

What is the role of the rotator cuff to the GH joint?

contributes to the stability of the joint as their tendons blend with the GH joint capsule

How does the subscapularis, infraspinatus, and teres minor contribute to GH joint stability?

their combine efforts create a rotatory force directed toward the glenoid, increasing joint stability

How does the infraspinatus, subscapularis, and teres minor counteract the deltoid’s superior force?

their inferior (distractive) translatory force negates the deltoid’s superior translatory force

How does the deltoid, teres minor and infraspinatus contribute to humeral head movement?

they form a force couple that causes the humeral head to spin the glenoid fossa

What makes the supraspinatus different from the other 3 rotator cuff muscles?

line of pull is opposite to the others and it has a compressive force, while the other 3 have a distractive force

What role does the supraspinatus play in humeral movement?

it assists in humerus abduction and helps steer the humeral head in the glenoid fossa

How does gravity and the supraspinatus influence humeral head movement?

gravity creates a downward translatory force, while the supraspinatus lifts the humerus into abduction

What role does the subscapularis play in humeral stability?

it controls the anterior displacement of the humerus

What is the role does Teres Minor and Infraspinatus during humerus abduction?

they externally rotate the humeral head and help prevent posterior displacement of the humerus

What are 5 common causes of GH dysfunction?

1.) large or full-thickness rotator cuff tears

2.) trauma and high levels of pain

3.) adhesive capsulitis

4.) fractures

5.) ETC

How do we get full ROM?

GH + Scapular thoracic w/ linkages with the SC and AC joints

What is scapulohumeral rhythm?

the coordinated movement between the GH joint and the ST joint to allow full arm motion

How much does the GH joint contribute to arm flexion and abduction?

contributes 120° of flexion and 90-120° of abduction

How does the ST joint assist in arm elevation?

it upwardly rotates the glenoid by 60°, helping elevate the arm

What is the ratio of GH to ST movement in scapulohumeral rhythm?

The GH and ST joints move in a 2:1 ratio—for every 3° of arm movement, 2° come from the GH joint, and 1° from the ST joint

In the setting phase of scapulohumeral rhythm, what happens in the initial 30° of abduction and 60° of flexion?

the scapula is stable and motion is primarily occurring at the GH joint

What is the GH to ST joint movement in Phase 1 of shoulder abduction?

the GH and ST joints move in a 1:1 ratio

How much does the GH joint and scapula contribute to motion in Phase 1?

the GH joint abducts 30° and the scapula upwardly rotates 30­°, bringing total motion to 90°

What happens at the SC joint during Phase 1 of shoulder abduction?

the clavicle elevates at the SC joint

What occurs at 90° of shoulder abduction in Phase 2?

the GH joint has reached 90°, but an additional 90° is needed to reach full abduction

How does the GH joint contribute to the final phase (Phase 2) of abduction?

the GH joint abducts another 60° to help lift the arm higher

How does the scapula contribute to reaching full 180° of abduction (Phase 2)?

the scapula upwardly rotates by another 30° to assist in full arm elevation

What happens at the SC joint in the final phase of abduction (Phase 2)?

the clavicle rotates posteriorly at the SC joint to allow full shoulder movement

What force couple causes scapular upward rotation?

serratus anterior and the trapezius muscles

How can ST upward rotation occur?

only with AC and SC motion

Where does the first 30° of ST upward rotation occur?

it occurs around the SC joint axis

How is the additional 30° of ST upward rotation achieved?

it is gained by the posterior rotation of the clavicle

How does increased shoulder elevation affect joint compression and impingement?

as shoulder flexion or abduction increases, joint compression increases (some degree of impingement is normal)

What structures contribute to optimal deltoid function?

depends on the deltoid, the upward rotators of the scapula, and the rotator cuff

With an absence of upward rotators, how much would the deltoids only be able to abduct to?

about 90°

How much would the deltoids and upward rotators would be only about to elevate if the rotator cuff were to disappear?

about 120°

How does the supraspinatus contribute to GH joint stability with and without added weight?

• without weight, it helps with elevation

• with weight it works more actively to improve stability via increased compressive forces

What muscle shows increased activity during shoulder abduction?

trapezius

During shoulder flexion, which muscle exhibits increased activity and why?

the serratus anterior exhibits increased activity during flexion because greater protraction is needed compared to abduction

Between the trapezius and serratus anterior, which of these two is the stronger muscle?

trapezius is stronger than serratus

What happens to scapular upward rotation when the serratus anterior is absent?

the scapula can still upwardly rotate, but the range is reduced and the motion is weak

What is the effect on scapular upward rotation when the trapezius is absent?

without the trapezius, the range of upward rotation is very limited and the movement is weak

How does the mid trapezius and rhomboids stabilize the scapula during abduction/flexion?

they eccentrically contract to provide dynamic stabilization during these movements