Shoulder arthritis can affect either of the two joints in the shoulder complex. The first joint is called the acromioclavicular joint (AC joint). It is a joint between the clavicle (collar bone) and the acromion (roof of the shoulder). The AC joint moves a little when the shoulder moves and can be injured in a shoulder separation. The second joint is the glenohumeral joint (GH joint). This is the ball and socket joint which connects the top part of the arm (humerus) to the shoulder blade (scapula). This joint allows the shoulder to have a wide range of motion in all directions.
Two types of arthritis can be seen in the shoulder complex. The first type is Osteoarthritis (OA) is the typical “wear-and-tear” arthritis, which can present at any age but typically appears in later life. In some cases, OA can present after an injury or fracture to the shoulder and is called post-traumatic arthritis. The second type of arthritis is the inflammatory arthritis. Rheumatoid arthritis (RA) is a common example. This arthritis affects patients at an earlier age. It typically affects multiple joints in the body (elbows, knees, etc.).
When arthritis affects the shoulder joint, the lining on one or both sides of the joint called cartilage starts to wear out. Cartilage is a very smooth surface which allows the joint to move with very little friction and no pain. When the cartilage disappears, the undersurface of the cartilage starts to rub against the opposite side of the joint. This leads to a far less smooth motion (crepitus) which can be felt or heard. Furthermore, the undersurface has nerve endings which causes pain on motion. This pain can get progressively worse and can interfere with sleep and activities of daily living (combing hair, reaching things above shoulder level).
The essential part of the surgery is to remove the damaged area and replace it with a shoulder prosthesis (artificial joint). To get to the shoulder joint an incision is made on the front of your shoulder. After exposing the shoulder joint, the damaged ends of the bone are removed. The bone is prepared for the placement of the artificial joint. The artificial joint is made of metal, usually a titanium or a cobalt-chrome alloy. The stem is placed inside the humerus bone. Bone cement may be used to secure the stem in the humerus. The glenoid component is made of a special plastic. The glenoid is cemented into place. Not all patients require a glenoid component. The final decision to use a glenoid component is made during the surgery. Patients with osteoarthritis and inflammatory arthritis generally benefit from the placement of a glenoid component. After the components are in place, the shoulder joint is checked to make sure that the shoulder is stable and has the potential for good motion after rehabilitation.
For a reverse shoulder replacement procedure, much of the surgery is the same as the total shoulder replacement. The shoulder joint is a ball-and-socket joint that consists of a ball at the top of the arm bone (humerus) that fits into a socket at the shoulder blade (scapula). A reverse shoulder replacement uses an artificial device to replace the damaged shoulder joint in a reversed manner — a ball at the shoulder and a socket at the end of the arm. A hole is made down the center of the arm bone to insert the stem of the socket implant and secure it with special cement. A ball-shaped implant is affixed to the socket of the shoulder blade using screws. Proper alignment of these two pieces is critical to the success of the surgery. Any imbalance will cause rotation issues that can result in damage to the shoulder.
The difference in therapy between a total shoulder replacement and a reverse total shoulder replacement is that with the reverse, patients do not start therapy until after six weeks of rest, to where with a total shoulder replacement patients start therapy a week after surgery.