Movements of the Shoulder Girdle
Overview
Movements of the shoulder girdle are movements of the scapula relative to the thorax. They always involve coordinated movement at both the sternoclavicular and acromioclavicular joints.
Scapular movements may occur independently of or combined with glenohumeral movement.
Movements and Muscles
| Movement | Description | Muscles |
|---|---|---|
| Elevation | Scapula moves upward (shrugging) | Upper fibres of trapezius + levator scapulae |
| Depression | Scapula moves downward (drooping) | Gravity + lower fibres of serratus anterior + pectoralis minor |
| Protraction | Scapula moves forward, away from spine (pushing/punching) | Serratus anterior + pectoralis minor |
| Retraction | Scapula moves toward spine (squaring shoulders) | Rhomboids + middle fibres of trapezius |
| Lateral (forward) rotation | Inferior angle moves laterally; glenoid faces upward | Upper and lower fibres of trapezius + lower fibres of serratus anterior |
| Medial (backward) rotation | Inferior angle moves medially; glenoid faces downward | Gravity; levator scapulae + rhomboids |
Clavicular Movement Associated with Scapular Movement
Each scapular movement is associated with a movement of the clavicle at the sternoclavicular joint:
| Scapular Movement | Clavicular Movement | SC Joint Compartment |
|---|---|---|
| Elevation | Lateral end elevates; medial end depresses | Inferolateral compartment |
| Depression | Lateral end depresses; medial end elevates | Inferolateral compartment |
| Protraction | Lateral end moves forward; medial end moves backward | Superomedial compartment |
| Retraction | Lateral end moves backward; medial end moves forward | Superomedial compartment |
| Lateral rotation | Clavicle rotates around its long axis | Inferolateral compartment |
Lateral Rotation of Scapula
The most important scapular movement for overhead function:
- Scapula rotates around the coracoclavicular ligament (as a pivot)
- Inferior angle moves laterally and forward, glenoid faces upward
- Essential for abduction above 120°
- Serratus anterior rotates inferior angle laterally; trapezius (upper + lower fibres) depresses medial end of spine — synergistic action turns glenoid upward
Without lateral rotation of scapula, overhead abduction is impossible.
Serratus Anterior — Key Scapular Muscle
- Inserted mainly into inferior angle of scapula
- Rotates inferior angle laterally
- Essential for full abduction
- Injury to long thoracic nerve (nerve to serratus anterior): winging of scapula; arm cannot be raised beyond 90°; loss of pushing and punching actions
Ligaments of the Scapula
Coracoacromial Ligament
- Triangular; from lateral border of coracoid process to tip of acromion
- With the coracoid and acromion forms the coracoacromial arch (secondary socket for humeral head)
Suprascapular Ligament
- Converts the scapular notch into a foramen
- Suprascapular nerve passes below the ligament
- Suprascapular artery and vein pass above the ligament (mnemonic: Army goes over the bridge, Navy goes under the bridge)
Spinoglenoid Ligament
- Bridges the spinoglenoid notch
- Suprascapular nerve and vessels pass beneath it to reach the infraspinous fossa