The shoulder is one of the largest and most complex joints in the body. It is an elegant piece of machinery. To better understand shoulder surgery, it is important to understand the anatomy of the shoulder and how the shoulder works. It is extremely complex, with a design that provides maximum mobility and range of motion; the shoulder has the greatest range of motion of any joint in the body. The important structures of the shoulder can be divided into several categories as listed below:
- Bones and joints
- Ligaments and tendons
- Muscles
- Nerves
- Blood vessels
- Bursae
Understanding how the different layers of the shoulder are built and connected is necessary to understand its function in the human body. The deepest layer of the shoulder includes the bones and the joints. The next layer is made up of the ligaments of the joint capsule. The tendons and the muscles come next. These tendons and muscles help stabilize the joints of the shoulder while giving it motion.
The shoulder is made up of three bones:
- Scapula (shoulder blade)
- Clavicle (collar bone)
- Humerus (arm bone)
These bones are joined together by soft tissues (ligaments, tendons, muscles and joint capsule) to form a platform for the arm to work. A joint is formed where two or more bones meet. There are three joints in the shoulder, which include:
- Glenohumeral joint – a ball-and-socket joint where the humerus meets the glenoid on the scapula; this joint is informally known as the shoulder joint.
- Acromioclavicular joint – a gliding joint where the acromial process on the scapula links to the collar bone (clavicle).
- Sternoclavicular joint – a double gliding joint between the sternum (breastbone) and the clavicle (collar bone).
The shoulder also has one articulation, which is the relationship between the scapula (shoulder blade) and the chest wall. The main joint of the shoulder is the glenohumeral joint. This joint comprises a ball (the humeral head) on a golf-tee-shaped joint (the glenoid of the scapula). The bones of the shoulder are covered by several layers of soft tissues. The top layer is the deltoid muscle, a muscle just beneath the skin, which gives the shoulder a rounded appearance. The deltoid muscle helps to bring the arm overhead. Directly beneath the deltoid muscle is the sub-deltoid bursa, a fluid-filled sac, analogous to a water balloon.