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M01.03.011 The Scapula
The scapula, commonly known as the shoulder blade, is a triangular, flat bone. It connects the upper limb to the trunk by articulating with the humerus at the glenohumeral joint and the clavicle at the acromioclavicular joint. It serves as an attachment site for 17 muscles, playing a key role in shoulder movement and stability.
Anatomical Features of the Scapula
1. Costal (Anterior) Surface
- Location: Faces the ribcage.
- Key Features:
- Subscapular fossa: A large concave depression where the subscapularis muscle (a rotator cuff muscle) originates.
- Coracoid process:
- Hook-like projection beneath the clavicle.
- Serves as an attachment for three muscles:
- Pectoralis minor
- Coracobrachialis
- Short head of the biceps brachii
| Feature | Description | Associated Structures |
|---|---|---|
| Subscapular fossa | Large concave depression | Subscapularis muscle |
| Coracoid process | Hook-like projection | Pectoralis minor, coracobrachialis, short head of biceps brachii |
2. Lateral Surface
- Location: Faces the humerus.
- Key Features:
- Glenoid fossa: Shallow cavity that articulates with the humerus to form the glenohumeral (shoulder) joint.
- Supraglenoid tubercle: Attachment site for the long head of the biceps brachii.
- Infraglenoid tubercle: Attachment site for the long head of the triceps brachii.
| Feature | Description | Associated Structures |
|---|---|---|
| Glenoid fossa | Shallow cavity | Glenohumeral joint |
| Supraglenoid tubercle | Roughening superior to glenoid fossa | Long head of biceps brachii |
| Infraglenoid tubercle | Roughening inferior to glenoid fossa | Long head of triceps brachii |
3. Posterior Surface
- Location: Faces outward.
- Key Features:
- Spine: Prominent ridge dividing the surface into two regions:
- Supraspinous fossa: Smaller, convex area; origin of the supraspinatus muscle.
- Infraspinous fossa: Larger, convex area; origin of the infraspinatus muscle.
- Acromion: Extension of the spine that forms the acromioclavicular joint with the clavicle.
- Spine: Prominent ridge dividing the surface into two regions:
| Feature | Description | Associated Structures |
|---|---|---|
| Spine | Transverse ridge dividing the posterior surface | Landmark for supraspinous and infraspinous fossae |
| Acromion | Projection over the glenohumeral joint | Acromioclavicular joint |
| Supraspinous fossa | Area above the spine | Supraspinatus muscle |
| Infraspinous fossa | Area below the spine | Infraspinatus muscle |
Articulations
- Glenohumeral Joint: Formed by the glenoid fossa of the scapula and the head of the humerus.
- Acromioclavicular Joint: Formed by the acromion of the scapula and the clavicle.
Clinical Relevance
Fractures of the Scapula
- Incidence: Rare, often associated with severe trauma (e.g., high-speed collisions or sports injuries).
- Presentation: Severe chest trauma.
- Management:
- Surgical fixation is typically unnecessary.
- Surrounding muscle tone stabilizes bone fragments during healing.
Key Points to Remember
- The scapula connects the upper limb to the trunk via the glenohumeral and acromioclavicular joints.
- It serves as an attachment site for 17 muscles, critical for upper limb movement.
- The costal, lateral, and posterior surfaces have distinct anatomical landmarks and functions.
- Fractures are uncommon but indicate significant trauma.