The shoulder is one of the most complex joints in the body. It is made up of the humerous (upper arm bone) fitting into the scapula to make a ball and socket joint. The main dynamic stabiliser of the shoulder joint is the rotator cuff. The rotator cuff is a group of four muscles that are positioned around the shoulder joint. The muscles are named:
- Teres minor
The rotator cuff muscles interlock to work as a unit. Their job is to stabilise the shoulder joint and help keep it stable during movement.
The four tendons of the rotator cuff muscles join together to hold the head of the bony surface at the top of the upper arm bone (the humerus) in direct contact with the other shoulder joint surface on the shoulder blade (glenoid fossa of the scapula).
There is a space underneath the acromion of the scapula (point of your shoulder), called the subacromial space. One of the rotator cuff muscle tendons – supraspinatus – passes through here. The subacromial space is filled by the subacromial bursa and this tendon. This is a fluid-filled sac which helps the rotator cuff to move smoothly. It has a large number of pain sensors.
Rotator cuff disorders or swelling in this bursa will cause subacromial pain, or impingement pain. This is commonly seen in athletes who do repetitive overhead movements such as pitching.