The acromioclavicular joint is where the acromion, part of the shoulder blade (scapula), and the collar bone (clavicle) meet. The glenohumeral joint is where the ball (humeral head) and the socket (the glenoid) meet.
Rotator cuff anatomy
The rotator cuff connects the upper arm bone to the shoulder blade. It is made up of the tendons of four muscles:
The deltoid muscle forms the rounded curve of the shoulder. Tendons attach muscle to bone. Muscles move bones by pulling on the tendons.
The muscles of the rotator cuff keep the bone tight in the socket. The socket is shallow and flat. It is rimmed with soft tissue called the labrum that makes a deeper socket that molds to fit the humeral head.
The joint capsule surrounds the shoulder joint. It is a fluid filled sac that lubricates the joint. It is made up of ligaments. Ligaments are soft tissue that holds bone to bone.
Shoulder injuries can happen to any part of the shoulder.