The shoulder Joint Flashcards
What type of joint is the shoulder joint?
- Known as the Glenohumeral joint
- Synovial joint
- Ball and socket
- Most mobile: Wide range of movements in multiple planes
- Least stable: Most commonly dislocated
What bony surfaces form the joint?
Glenoid fossa - a shallow cavity.
In the living state, the glonoid fossa and the head of the humerus would be covered with a layer of articular cartilage.
Head of the humurous - hemisphere
4:1 disproportionate in area of articular surfaces - contribute to stability.
Glenoid cavity deepened by glenoid labum (a fibrocartilagenous rim).
What does this Xray show?
Why is the shoudler joint unstable?
- Shallow glenoid fossa
- Disproportion of articular surfaces
- Multiplanar movements
- Lax capsule
How is stability of the shoulder joint achieved?
- Rotator cuff muscles (most important)
- Other muscles
- Ligaments
- Capsule
What is the joint capsule attatched to?
- Glenoid labrum and margins of glenoid fossa
- Anatomical neck of humerus
- Dips down medially to surgical neck (laxity for full abduction)
- Bridges intertubular groove
Tough by lax to allow movement
Small opening anteriorly
- Synovial membrane of SJ communicates with subscapular bursa
What does the synovial membrane line?
- Capsule
- Intra capsular bone, up to edge of articular cartilage
- Tendon of long head of the biceps within joint cavity.
The tendon acquires a tubular sleeve of synovium as it enters joint, which surrounds it up to its insertion
What ligaments does the shoulder joint have?
- Intracapsular Ligaments
- 3 Gleno-humeral ligaments (superior, middle, inferior)
- 3 fibrous bands -extend from glenoid labrum to humerus
- Part of the fibrous capsule
- Reinforces capsule anteriorly
- Can only be seen from inside the capsule.
What are the three extracapsular ligaments of the shoulder joint?
- Caracoacamial ligament (CAL) - Between Acromion and caracoid process
- Coracohumeral ligament - From base of caracoid process to anterior part of greater tubercle
- Transverse humeral ligament - Holds the tendon of long head of biceps in place during shoulder movement. (yellow arrow)
Why is the coraco acromial arch important?
This arch is formed by the coracoacromial ligament, acromion and the coracoid process.
- A strong structure of bone and ligament (osseoligamentous structure)
- Overlies the humeral head
- Prevents upper displacement of humerus
- Clinically inportant in the ‘painful arc’ syndrome
What are the four rotator cuff muscles of the shoulder?
- Supraspinatus
- Infraspinatus
- Teres minor
- Subscalularis
S.I.T.S
Where do the rotator cuff muscles arise and insert from?
- Supraspinatus, Infrapinatus and Teres Minor arise from the dorsal aspect of the scapula.
- All 3 muscles inserted into Greater tubercle of humerus
- Supraspinatus tendon passes under coraco-acromial arch.
- Subscapularis arises from the ventral aspect of the scapula
- Sunscapularis muscle inserted into lesser tubercle
What are the overall roles of the rotator cuff muscles?
- The tendons blend to form a cuff
- Cuff fuses with capsule and strengthens it
- Tone in muscles holds the head close to glenoid cavity
- Supraspinatous tendon is separated from coraco acromial arch (CAA) by the bursa.
What is the action of supraspinatus?
Initiation and first 15° of abduction.
n - suprascapular C5,6
What is the action of Infraspinatus?
Lateral (external) rotation of the arm
n - suprascapular C5,6
What is the action of Teres minor?
Lateral rotation of the arm, weak adductor
n - axillary C5,C6
What is the action of Subscapularis?
Medial (internal) rotation of the arm
n - upper and lower subscapular nerves - C5,C6
What other muscles stabalise the shoulder joint?
- Deltoid
- Long head of biceps (attached to supra-glenoid tubercle)
- Long head of triceps. (attached to infra glenoid tubercle)
Summarise what provides static and dynamic stability of the shoulder joint.
- Tendons of the rotato cuff (Dynamic) (anteriorly, posteriorly, superiorly)
- Coracoacromial arch (superiorly)
- Gleno-humeral (intracapsular) ligaments (anteriorly, inferiorly)
- Coraco-jumeral ligament (superiorly)
- Deepening glenoid cavity by labrum (circumferentially)
- Splinting effect of:
- The long head of the bicepts (dynamic, superiorly)
- The long head of the triceps (dynamic, inferiorly)
- Other muscles (dynamic)
- Deltoid (anteriorly, posteriorly, superiorly)
- Pectoralis major (anterior)
- Corachobrachialis (anteriorly)
Inferior part of joint is least supported.
What are the two bursa of the shoulder joint?
- Subacromial Bursa - Facilitates movement of supraspinatus tendon under the coraco acromial arch and deltoid
- Subscapular bursa - Facilitates movement of subscapularis tendon over scapula and communicates with joint cavity.
What structures are present in the space between the acromion and the head of the humerus?
Intersposed in this space are the:
- Subacromial Bursa
- Supraspinatus tendon
- Capsule
- Tendon of Long head of Biceps
During abduction, there is a risk of soft tissue impingement between Head of humerus ans Acromion.
What is the blood supply to the shoudler joint?
- Anterior circumflex humeral artery
- Posterior circumflex humeral artery
- Suprascapular artery
What is the nerve supply to the shoudler joint?
- Axillary nerve
- Suprascapular
- Lateral pectoral nerves
These are all from the brachial plexus (C5,C6)
What are the shoulder joint movements?
These movements occur at the Glenohumeral and Scapulothoracic joint. (scapula moves over thorax as if there was a joint).
