Shoulder Blade
Scapula
location_on Posterior thoracic wall, overlying ribs 2 through 7
A large, flat, triangular bone that connects the humerus to the clavicle. The scapula sits on the posterior aspect of the thoracic cage and provides attachment points for 17 muscles, making it one of the most muscularly connected bones in the body. It has no direct bony connection to the axial skeleton, relying entirely on muscles for its position and stability.
Key Anatomical Features
- Acromion process articulates with the clavicle
- Coracoid process serves as attachment for biceps and pectoralis minor
- Glenoid cavity forms the socket of the shoulder joint
- Spine of scapula divides posterior surface into supraspinous and infraspinous fossae
- Subscapular fossa covers the entire anterior surface
- Inferior angle is a palpable landmark at the level of the T7 spinous process
Muscle Attachments
| Muscle | Attachment | Action |
|---|---|---|
| Trapezius | Spine of scapula and acromion | Elevates, retracts, and rotates scapula |
| Deltoid | Spine of scapula and acromion | Abducts the arm |
| Supraspinatus | Supraspinous fossa | Initiates arm abduction |
| Infraspinatus | Infraspinous fossa | Laterally rotates the arm |
| Subscapularis | Subscapular fossa | Medially rotates the arm |
| Serratus anterior | Medial border | Protracts and stabilizes scapula |
| Rhomboid major | Medial border below spine | Retracts the scapula |
| Teres major | Inferior angle and lower lateral border | Adducts and medially rotates the arm |
Joints and Articulations
| Joint | Type | Connects to |
|---|---|---|
| Glenohumeral joint | Synovial ball-and-socket | Humerus |
| Acromioclavicular joint | Synovial plane | Clavicle |
Common Pathologies
Scapular fracture
Rare fracture usually resulting from high-energy trauma such as car accidents. Accounts for less than 1% of all fractures and indicates severe thoracic trauma.
Winged scapula
Medial border protrudes from the back due to long thoracic nerve injury, weakening the serratus anterior muscle. Can result from axillary surgery or direct nerve trauma.
Scapulothoracic bursitis
Inflammation of the bursa between the scapula and thoracic wall causing pain and crepitus with arm movement.
Snapping scapula syndrome
Audible or palpable grinding between the scapula and thoracic wall during shoulder motion, caused by bony or soft tissue abnormalities.
Clinical Relevance
Scapular fractures indicate severe thoracic trauma. Always assess for associated injuries including pneumothorax, rib fractures, pulmonary contusion, and brachial plexus damage. The scapula is protected by thick muscle layers, so fracture implies significant force. The glenoid cavity is shallow and covers only about one-third of the humeral head, making the shoulder the most commonly dislocated joint.
Development and Ossification
The scapula ossifies from 8 centers. The body begins ossification during the 8th week of fetal development from an intramembranous center. The coracoid appears around age 1, and the acromion from two centers that appear at puberty. Complete fusion occurs between ages 20 and 25.
Did You Know?
- The word scapula comes from the Latin word for shovel or digging tool
- Scapulimancy was an ancient practice of reading cracks in heated shoulder blades to predict the future
- The scapula has no direct bony connection to the axial skeleton and is held in place entirely by muscles
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