Structures (anterior to posterior)
Subclavian vein Anterior scalene muscle Subclavian artery Brachial plexus trunks Middle scalene muscle
Coracoid process attachments
Ligaments
There are two coracoclavicular ligaments, which are frequently injured in acromioclavicular joint injuries.
Shoulder joint
Stability: The glenohumeral joint sacrifices stability for mobility. Its shallow articulation provides minimal bony stability, so dynamic soft tissue restraints are critical during motion. Instability is most common in the anterior direction, exacerbated with arm in extreme abduction and external rotation. While their impact is indirect, muscle groups that impact scapulothoracic stability are also important for shoulder stabilisation, as they allow the rotator cuff to act effectively.
| Essential | Supplementary | |
|---|---|---|
| Static | Glenoid labrum | |
| Joint capsule | ||
| Inferior > middle > superior glenohumeral ligaments | ||
| Negative intra-articular pressure | Glenohumeral articulation (including anteverted orientation) | |
| Coracoacromial arch | ||
| Coracohumeral ligament | ||
| Posterior joint capsule | ||
| Dynamic | Rotator cuff muscles | |
| Long head of biceps brachii | ||
| Scapular stabilisers (Trapezius, serratus anterior) | Deltoid | |
| Proximal humerus attachments (Pec. major, lat. dorsi, teres major) | ||
| Scapular stabilisers (rhomboids, levator scapulae) |
Negative intra-articular pressure: As the shoulder is a highly-mobile joint and hangs in neutral with with gravitational traction, negative intra-articular pressure optimises the articulation between the glenoid and humeral head. This is why joint effusion, haemarthrosis associated with fracture or post-arthroscopy appearances often demonstrate inferior pseudosubluxation.
Shoulder abduction is performed in three stages, each stage controlled by a different muscle:
Initiation: Initial 15-30° is performed by supraspinatus.
True glenohumeral abduction: 15-90° is performed by middle fibres of deltoid.