Scapula is a flat bone, a broad, thin bone that lies against the back of the chest wall. Commonly called the shoulder blade, it provides attachment sites for muscles and forms joints with the clavicle, or collarbone, and the humerus, the upper arm bone. Its movements help position the arm.
Where is the scapula located?
The left scapula and right scapula lie on opposite sides of the upper back, over the posterior ribs. Each is roughly triangular, with its pointed lower end directed downwards and its joint-bearing outer corner directed towards the shoulder.
Within the skeletal system, the scapula and clavicle form the pectoral girdle, the bony framework connecting the upper limb to the trunk. The scapula has no direct joint with the ribs or vertebral column. Instead, muscles hold it against the chest wall while allowing it to slide and rotate.
The subscapularis muscle lies between the scapula and the serratus anterior muscle, which covers the adjacent ribs. Together, these intervening muscles separate the bone from the chest wall. The clavicle extends forwards and medially, towards the body's midline, from the scapula to the sternum, or breastbone.
What are the surfaces, borders and angles?
The costal surface faces the ribs and is also called the anterior surface. Its broad concavity, the subscapular fossa, provides attachment for the subscapularis muscle. A fossa is a depression in a bone.
The posterior surface faces backwards. A prominent ridge called the scapular spine divides it into the supraspinous fossa above and the infraspinous fossa below. These depressions accommodate the supraspinatus and infraspinatus muscles respectively.
The margins and corners provide useful orientation landmarks:
- Superior border: the upper edge, containing the suprascapular notch near the base of the coracoid process.
- Medial border: the edge nearest the vertebral column.
- Lateral border: the thicker outer edge extending towards the shoulder joint.
- Superior angle: the upper corner where the superior and medial borders meet.
- Inferior angle: the lower tip where the medial and lateral borders meet.
- Lateral angle: the expanded outer corner that bears the glenoid cavity, the shallow socket for the humerus.
What are the main scapular landmarks?
The scapular spine extends across the posterior surface and continues laterally as the acromion. The acromion projects over the shoulder joint and meets the clavicle. The coracoid process is a hook-like projection extending forwards from the upper part of the scapula; a process is a projecting part of a bone.
| Landmark | Position | Main anatomical role |
|---|---|---|
| Scapular spine | Across the posterior surface | Separates the posterior fossae and provides muscle attachment |
| Acromion | Lateral continuation of the spine | Joins the clavicle and provides muscle attachment |
| Coracoid process | Projects forwards above the glenoid cavity | Provides attachment for muscles and ligaments |
| Glenoid cavity | At the lateral angle | Receives the head of the humerus |
| Suprascapular notch | On the superior border | Forms a passage for the suprascapular nerve beneath a ligament |
The suprascapular nerve passes beneath the superior transverse scapular ligament, a strong connective-tissue band spanning the notch. The suprascapular artery normally passes above this ligament. The nerve supplies the supraspinatus and infraspinatus muscles.
Which joints does the scapula form?
The glenohumeral joint, commonly called the shoulder joint, lies between the glenoid cavity and the rounded head of the humerus. It is a synovial joint: the joint surfaces are covered by cartilage and enclosed within a capsule containing lubricating fluid. A fibrocartilage rim called the glenoid labrum deepens the shallow socket.
The acromioclavicular joint connects the acromion to the lateral end of the clavicle. Ligaments, bands of connective tissue joining bones, stabilise this connection. The coracoclavicular ligament connects the coracoid process to the clavicle and helps maintain their relationship.
The scapulothoracic articulation describes the scapula's movement over the chest wall. Unlike the other connections, it is not a true synovial joint: muscles and connective tissues lie between the scapula and ribs rather than opposing cartilage-covered joint surfaces.
Which muscles attach to the scapula?
Attachments to the scapula allow the muscular system to move both the shoulder blade and the humerus. The rotator cuff is a group of muscles whose tendons surround the shoulder joint and help hold the humeral head against the glenoid cavity. Its muscles arise from the scapula: subscapularis, supraspinatus, infraspinatus and teres minor.
Other important attachments include:
- Trapezius and deltoid: attach to the scapular spine and acromion.
- Serratus anterior: attaches along the costal aspect of the medial border.
- Rhomboid muscles and levator scapulae: attach along parts of the medial border.
- Pectoralis minor, the short head of biceps brachii and coracobrachialis: attach to the coracoid process.
- Long head of biceps brachii and long head of triceps brachii: attach above and below the glenoid cavity respectively.
How does the scapula help arm movement?
The scapula provides a movable base for the shoulder joint. As the arm rises, the scapula rotates so that the glenoid cavity faces more upwards. Movement at the shoulder joint therefore works together with movement of the shoulder blade.
The scapula can also move upwards, downwards, towards the vertebral column or around the chest wall away from it. Its muscle attachments both produce these movements and stabilise the bone while the arm moves.
How can you orient the scapula in the 3D model?
In the 3D model beside this article, select a scapula and isolate it, then rotate and zoom to examine its orientation. Use rotation to view the selected bone from different directions, and zoom to adjust the size of the view without changing its orientation.
Hide or fade other selected parts to reduce overlap, or switch layers to change the view. You can also cut a section along a sagittal, coronal or transverse plane, or pull selected parts apart.