The scapula (shoulder blade) is a flat, triangular bone located on the posterior side of the shoulder. It is surrounded by muscles and does not directly articulate with the ribs, allowing it to move freely across the back of the thoracic cage. 

The scapula plays a key role in anchoring the upper limb and serving as a site for numerous muscle attachments.

The scapula has three borders (superior, medial, and lateral) and three angles (superior, inferior, and lateral).

The lateral angle contains the glenoid cavity, a shallow socket that articulates with the head of the humerus to form the glenohumeral joint. Just above and below this cavity are the supraglenoid and infraglenoid tubercles, which serve as attachment points for arm muscles.

On its posterior surface, the scapula features a prominent ridge called the spine, which divides the bone into two fossae: the supraspinous fossa above and the infraspinous fossa below. 

These fossae provide attachment areas for muscles that move the shoulder. 

The spine extends laterally to form the acromion, which creates the bony tip of the shoulder and articulates with the clavicle. 

Another important projection is the coracoid process, a hook-like structure on the anterior side that serves as an attachment point for ligaments and muscles of the chest and arm.

The anterior surface of the scapula contains the subscapular fossa, a broad depression that also provides space for muscle attachment. 

Altogether, the scapula has three fossae:

• supraspinous fossa

• infraspinous fossa 

• subscapular fossa

all of which are important for muscle function and shoulder movement.

The clavicle and scapula move together as a functional unit, allowing the shoulder to perform complex motions such as lifting, rotating, and extending the arm. 

The acromioclavicular joint connects the clavicle to the scapula and is supported by ligaments, especially the strong coracoclavicular ligament. Injuries to this joint, such as ligament tears, can result in a condition known as a “shoulder separation,” often seen in contact sports.

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