After completing “The Shoulder Joint” section, you will be able:
- To describe the 3 bones
- To explain the 2 joints
- To summarise the 4 ligaments
- To identify the 4 rotator cuff muscles and demonstrate their action
- To validate knowledge by completing the quiz
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The shoulder joint is made from 3 bones:
Bones of The Shoulder Joint
These bones articulate to form 2 joints within the shoulder joint:
1. Acromioclavicular (AC) joint:
- Plane synovial (gliding) joint between the clavicle and the acromion of the scapula.
2. Glenohumeral joint:
- Ball and socket joint between the humeral head and the glenoid cavity of the scapula.
- Large humeral head and shallow glenoid cavity, allows mobility however it is unstable.
- To increase the stability, the labrum, joint capsule (ligaments) and muscles (rotator cuff, deltoid, pectoralis major) surround the glenoid cavity.
* Imagine the glenohumeral joint as a golf ball (ball) on a tee (socket). The golf ball is the humeral head, the golf tee is the glenoid cavity. Just like a golf ball on a tee, the joint is unstable which commonly leads to dislocation *
4 LIGAMENTS: (REMEMBER: LIGAMENTS = BONE → BONE)
- The joint capsule is a lax fibrous sheath that covers the shoulder joint.
- The ligaments (1,2,3) of the shoulder joint are thickenings of the joint capsule that provide joint capsule stability.
- The laxity of the ligaments allows for free movement of the shoulder joint.
There are 4 main ligaments of the shoulder joint:
1. Glenohumeral ligaments:
- Glenoid cavity → Anterior neck of the humerus.
- Stabilises the anterior aspect of the shoulder joint.
2. Coroacohumeral ligament:
- Base of the coracoid process → greater tubercle of the humerus.
- Strengthens and supports anterior and superior part of the joint capsule.
3. Transverse humeral ligament:
- Transverse across from greater tubercle of humerus → lesser tubercle of the humerus.
- Stabilises the tendon of the long head of the bicep muscle.
4. Coracoacromial ligament:
- Coracoid process → overlies the shoulder joint preventing superior shoulder displacement.
4 ROTATOR CUFF MUSCLES:
The rotator cuff muscles make up the main strength for the stability of the shoulder joint. There are four rotator cuff muscles, that work as a group to hold the large head of the humerus in the shallow glenoid cavity:
TIP: * Mnemonic Alert * The SITS muscles:
- S – Supraspinatus = ABDuction
- I – Infraspinatus = external rotation
- T – Teres Minor = ADDuction and external rotation
- S – Subscapularis = ADDuction and internal rotation
Moore K, Dalley A, Agur A. (2014). Clinically Oriented Anatomy. 7th ed. Philadelphia: Wolters Kluwer.
Teach Me Anatomy. (2017). The Shoulder Joint. [online]. Available at: http://teachmeanatomy.info/upper-limb/joints/shoulder/ [accessed 1 March 2017].
Tortora G, Derrickson B. (2011). Principles of Anatomy and Physiology. 13th ed. Chichester: John Wiley & Sons.