The structure indicated is the acromioclavicular joint.
The shoulder joint complex consists of the three joints:
- Glenohumeral joint
- Acromioclavicular joint
- Sternoclavicular joint
The acromioclavicular joint is formed between the acromion of the scapula and the clavicle. It is a small synovial joint that is stabilised by the following ligaments:
- Acromioclavicular ligament (consists of superior and inferior parts)
- Coracoclavicular ligaments
The coracoclavicular ligaments consist of two parts:
- Trapezoid ligament
- Conoid ligament
Learn more about the shoulder joint in this anatomy tutorial.