The shoulder is one of the most sophisticated and complicated joints of the body. It has the greatest range of motion of any joint. The co ordinated activity of numerous muscles working together in patterns is necessary to achieve this.
It is made up of four joints and five groups of bones.
To allow such a wide range of movement, shoulder joints need to be able to move freely rather than being fixed, but require a system of complex ligaments and muscles to keep it in the correct place.
Arthritis of the shoulder involves the swelling and damage of the joint. There are three main types of shoulder arthritis: Osteoarthritis of the shoulder, Rheumatoid Arthritis and Post traumatic shoulder arthritis after an accident. Some other words you might hear associated with shoulder arthritis are shoulder bursitis, rotator cuff tendonitis (both associated with Shoulder Impingement Syndrome) and adhesive capsulitis or "frozen shoulder" (this is the term to describe the symptoms when the connective tissue surrounding the glenohumeral joint become inflamed and stiff).
The rotator cuff is made up of the tendons of four muscles. It surrounds the head of the humerus just as a cuff surrounds the wrist at the end of a sleeve. One part of these muscle attachments is located below the top of the shoulder. These tendons lie between two opposite, movable bones and are therefore easily damaged. The tendons keep the head of the humerus within the joint and provide stability when the arm is moved.
Shoulder impingement occurs when the tendons of the rotator cuff and the subacromial bursa become compressed (squashed) against the acromian (a bone which sticks out from the scapula). If these tissues continually rub against bone, as time passes they become irritated and inflamed. This could be as a result of acromioclavicular joint arthritis, thickening or calcification (hardening due to the accumulation of calcium deposits) of the coracoacromial ligament, structural abnormalities of the acromion or weakness of the rotator cuff muscles.
The shoulder is the most mobile joint in the human body. The shoulder joint is formed by the upper arm (humerus) and the shoulder socket (Glenoid). Total shoulder arthroplasty replaces both components of the "ball and socket" joint.
As is usual in joint replacement surgery, the ball at the humeral head is replaced by a metal device. The socket component is replaced by a smooth plastic device which replicates the function of the natural cartilage surface.