Shoulder joint stability

Question 1

How stable is the glenohumeral joint?

Answer 1

Unstable -> most frequently dislocated joint -> ant. dislocation common -> humeral head descends inferiorly and ends up anterior.

Question 2

Which factors increase stability of the shoulder joint?

Answer 2

Coracoacromial arch -> prevents superior dislocation Glenohumeral ligaments -> superior, middle, inferior -> supports anterior of joint.
Glenoid labrum -> deepens glenoid fossa
Long heads of biceps + triceps
Tendons of rotator cuff muscles

Question 3

Which structure helps to sling the joint above and below?

Answer 3

Long head of biceps, passes through joint capsule -> supraglenoid tubercle
Long head of triceps -> infraglenoid tubercle
Splint joint

Question 4

What are the properties of the tendons of the rotator cuff muscles?

Answer 4

4 muscles. Insert on humerus close to joint -> fuse with joint capsule, forms cuff around joint.

Question 5

What are the rotator cuff muscles and what is their origin and insertion?

Answer 5

Supraspinatus -> supraspinous fossa
Infraspinatus -> infraspinous fossa
Teres minor -> inferior aspect of scapula
Insertion (above) -> greater tubercle of humerus
Supcapsularis -> subscapular fossa -> lesser tubercle
Surround joint on all sides except inferiorly

Question 6

What are the functions of the rotator cuff muscles?

Answer 6

Together: stabilise humeral head on glenoid fossa -> concavity compression.
Supraspinatus -> initiate abduction
Infraspinatus -> lateral rotation
Teres minor -> lateral rotation
Subscapularis -> medial rotation

Question 7

What are the rotator cuff muscles and what is their origin and insertion?

Answer 7

Supraspinatus -> supraspinous fossa
Infraspinatus -> infraspinous fossa
Teres minor -> inferior aspect of scapula
Insertion (above) -> greater tubercle
Supcapsularis
Surround joint on all sides except inferiorly.

Question 8

What is the origin, insertion and actions of the teres major?

Answer 8

Origin: inferior angle of scapula
Insertion: medial lip of bicipital groove
Performs medial rotation, stabilises the humerus during abduction -> eccentric contraction.

Question 9

What is the most common rotator cuff injury?

Answer 9

Supraspinatus impingement -> repetitive overhead activities.
Limited space for tendon under coracoacromial arch
Common in athletes (throwers)