Though referring to the shoulder most often refers to the ball and socket glenohumeral joint, the shoulder is made up of 4 distinct joints including the glenohumeral, the acromioclavicular, the scapulothoracic, and the sternoclavicular joints. This blog is the first of a series of blogs discussing the basic anatomy and injuries to different parts of the shoulder complex.
BURSA: A bursa is a fluid-filled sac that is located in the body in areas of high friction. The main bursa of the shoulder is the subacromial bursa that is located between a rotator cuff muscle and a bony part of the shoulder.
CARTILAGE: There are two types of cartilage in the shoulder: fibrous and hyaline. Hyaline cartilage covers the surface of the humeral head (the “ball” of the ball and socket joint). Fibrous cartilage (also called the labrum in the shoulder) is strong and helps to protect the bone “socket” and allows for pressure resistance.
LIGAMENTS: Ligaments are non-contracting tissues that connect two bones to each other. They help stabilizes the shoulder and limit excess movement. The shoulder has several ligaments, including but not limited to the coracoclavicular, acromioclavicular, glenohumeral, coracoacromial, transverse humeral, and coracohumeral ligaments.
TENDONS/MUSCLES: Tendons are on the end of muscles where they connect muscle to bone. There are several muscles and tendons that cross the shoulder joint. That is one reason why the shoulder joint may be so complicated. Anytime a tendon/muscle crosses a joint, it plays a role in the movement of that joint. The more a joint moves, the more susceptible it is to getting injured.
The shoulder is the most mobile joint in the body. With increased mobility comes an increase in the susceptibility to injuries. Injuries often happen when a joint is forced into too much motion in one or more directions. The following blogs will talk specifically about the different structures of the shoulder and different types of injuries that may occur.