Scapula

The scapula (shoulder blade) is a flat triangular bone that serves as the attachment site for 17 muscles involved in arm and shoulder movement. It forms two important joints: the glenohumeral joint (shoulder joint) via the glenoid cavity, and the acromioclavicular joint via the acromion. The scapula enables a wide range of arm movements through coordinated scapular rotation, elevation, depression, protraction, and retraction.

The scapula lies on the posterior thoracic wall, overlying approximately ribs 2 through 7. It is a floating bone with no direct bony connection to the axial skeleton — it is held in place entirely by muscles. The spine of the scapula, a prominent ridge on its posterior surface, is easily palpable and leads to the acromion, which projects over the shoulder joint.

Scapular winging occurs when the medial border of the scapula protrudes abnormally from the posterior chest wall, resembling a wing. The most common cause is paralysis of the serratus anterior muscle due to injury of the long thoracic nerve (C5–C7), which is vulnerable to traction injuries. Less commonly, trapezius weakness from spinal accessory nerve damage causes lateral winging.