Which joint within the shoulder complex attaches directly to the ribcage?

The sternoclavicular joint is the correct choice because it is the only joint in the shoulder complex that has a direct anatomical connection to the ribcage. This joint connects the clavicle (collarbone) to the sternum (breastbone), forming a stable base for the shoulder girdle. Its attachment allows for movements such as elevation, depression, and rotation of the shoulder.

Other joints in the shoulder complex, such as the acromioclavicular joint, glenohumeral joint, and scapulothoracic articulation, do not have a direct attachment to the ribcage. The acromioclavicular joint links the clavicle to the acromion of the scapula, while the glenohumeral joint connects the humerus to the scapula. The scapulothoracic articulation, although it plays a crucial role in shoulder movement, is not a true anatomical joint and is formed by the interaction of the scapula with the thoracic ribcage through muscles and fascia. Hence, the connection of the sternoclavicular joint to the ribcage makes it unique among the joints in the shoulder complex.