The scapula (shoulder blade) does not directly connect to the ribs via ligaments or bony articulations. Instead, it "connects" functionally through muscles.
Here's a breakdown:
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No Direct Articulation: Unlike many bones that connect via joints formed by ligaments and cartilage, the scapula doesn't have any direct joint connections to the rib cage.
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Muscular "Connection": The scapula is held in place and moves against the rib cage (specifically, the posterior aspect of the thorax) primarily by several muscles. These muscles act as the primary means of stabilization and movement:
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Serratus Anterior: This muscle originates on the ribs and inserts along the medial border of the scapula. It protracts (moves forward) and upwardly rotates the scapula, and also holds the scapula against the rib cage, preventing "winging" (excessive prominence of the medial border of the scapula).
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Trapezius: This large muscle has multiple parts that attach to the scapula (spine and acromion) and to the skull and vertebral column. The trapezius helps elevate, retract, and rotate the scapula.
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Rhomboids (Major and Minor): These muscles originate from the vertebral column and insert along the medial border of the scapula. They retract and downwardly rotate the scapula.
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Levator Scapulae: As the name suggests, this muscle elevates the scapula. It originates from the cervical vertebrae and inserts into the superior angle of the scapula.
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Subscapularis: While the primary action of this muscle is internal rotation of the humerus, it fills the subscapular fossa (the large concavity on the ventral surface of the scapula) and assists in stabilization of the scapula against the rib cage. The ventral surface of the scapula abuts the thoracic rib cage.
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Scapulothoracic Joint: While not a true synovial joint (joint with a capsule), the space between the scapula and the rib cage is often referred to as the scapulothoracic joint or articulation. Movement here is essential for full shoulder range of motion. The coordinated movement between the glenohumeral (shoulder) joint, the acromioclavicular joint, the sternoclavicular joint, and the scapulothoracic articulation is known as scapulohumeral rhythm.
In summary, the scapula is functionally connected to the ribs through a complex arrangement of muscles that allow for a wide range of shoulder movements and stability.
