Ligaments are soft tissue structures that connect bones to bones. Three ligaments support the acromio-clavicular joint; the cocrocoacromial, corococlavicular and acromioclavicular ligaments. Four ligaments make up the joint capsule that connects the humerus to the glenoid; superior, middle, inferior and posterior glenohumeral ligaments. The inferior glenohumeral ligament splits into a front and a back half. These act like a hammock to support the humerus in the joint. The joint capsule is a water tight bag that surrounds the joint and prevents it from dislocating. Ligaments are only tight at the extremes of movement. This allows the large range of movement seen in the shoulder.

              

 

 

 

This is a diagram view of the shoulder joint from the side with the humeral head removed. It shows how the ligaments and tendons surround the joint