Final answer:
The needle is inserted in the glenohumeral joint during a shoulder arthrogram. This joint is formed by the articulation between the head of the humerus and the glenoid cavity of the scapula.
Step-by-step explanation:
The needle is inserted in the glenohumeral joint during a shoulder arthrogram. The glenohumeral joint is a ball-and-socket joint formed by the articulation between the head of the humerus and the glenoid cavity of the scapula. It provides the widest range of motions and has a loose articular capsule supported by ligaments and the rotator cuff muscles.