What is the only articulation between the upper extremity and the thorax?

• A. Shoulder joint
• B. Sternoclavicular joint
• C. Acromioclavicular joint
• D. Thoracic inlet

Answer: (B)

The correct answer is the sternoclavicular joint, as it is the only direct articulation between the upper extremity and the thorax. This joint connects the clavicle (collarbone) to the sternum (breastbone) and is critical for providing stability and movement in the shoulder region. The sternoclavicular joint allows for a range of motions, including elevation, depression, protraction, and retraction of the shoulder.

In the context of the shoulder and upper extremity movement, the shoulder joint (glenohumeral joint) is a ball-and-socket joint that provides a wide range of motion but does not directly connect to the thorax. The acromioclavicular joint connects the clavicle to the acromion of the scapula, facilitating shoulder movement but is not a direct link to the thorax. The thoracic inlet is an anatomical region that allows structures to pass between the thorax and upper body but is not an articulation in itself.