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Shoulder Anatomy

The shoulder is the most mobile joint in the body, which is why we are able to position our hand so freely for dressing, grooming, hygiene, reaching, and playing sports. The shoulder is comprised of three main bones: the collarbone (clavicle), the shoulder blade (scapula) and the upper arm bone (humerus). The upper end of the humerus is a smooth, rounded head (ball) that fits into the glenoid cavity (socket) of the shoulder blade. Although the shoulder is often referred to as a “ball and socket” joint, in reality it more closely resembles a golf ball sitting on a tee. In a normally functioning shoulder, the four muscle-tendon units that comprise the rotator cuff (supraspinatus, infraspinatus, teres minor and subscapularis) help provide the stability to keep the golf ball centered on the tee.

Common Reasons for Shoulder Replacement


Osteoarthritis (degenerative arthritis), the most common form of arthritis, affects nearly 21 million people in the United States. It is defined by degradation of the cartilage that lines the joint (“wear and tear”). Age, genetics, activity level, occupation, and co-existing medical conditions play a role in the development of osteoarthritis. As the cartilage continues to wear, the joint becomes inflamed and can result in severe pain, limited mobility and strength, and sleep disruption. If non-surgical treatment options such as medication, physical therapy, or lifestyle changes fail to provide relief, Dr. Diaz may recommend total shoulder replacement.

Rotator Cuff Deficiency and Cuff Tear Arthritis

Because the shoulder joint is stabilized by muscles and tendons rather than by bone, the shoulder has great flexibility, allowing us to position our hand in space with great freedom. However, this great degree of motion has a trade off, as the stability of the shoulder is dependent upon the integrity of the four muscle-tendon units (supraspinatus, infraspinatus, teres minor and subscapularis) that comprise the rotator cuff. Most people with a painful rotator cuff tear can be treated arthroscopically. Chronic, massive tears of the
rotator cuff are often irreparable and can result in cuff tear arthritis of the shoulder. The degenerated muscles lose their ability to keep the humerus centered on the glenoid, causing your arm bone to move upward and out of the socket, and not allowing you to position your hand in certain ways that can affect reaching overhead, dressing, playing sports, turning a steering wheel, eating, etc. Cuff tear arthritis is often characterized by severe pain and limited mobility of the shoulder, and in most patients is reliably treated with reverse shoulder replacement.

Other causes: Complex Fractures of the Upper Humerus, Post-Traumatic Arthritis, and Rheumatoid Arthritis

Types of Shoulder Replacement

Anatomic Total Shoulder Replacement

Shoulder replacement surgery replaces the damaged part of your shoulder to recreate the natural contours of the bones in a healthy shoulder. During surgery, Dr. Diaz will remove the damaged bone and cartilage and replace with new surfaces to allow for pain free range of motion. In treatment of osteoarthritis with good rotator cuff function, the ball resembles the native ball in shape and is made of metal, and the socket is made of a medical grade plastic (polyethylene). This is called anatomic total shoulder replacement.

Reverse Total Shoulder Replacement

If you are a candidate for surgery and you have pain and dysfunction from a massive, irreparable rotator cuff tear and/or arthritis, Dr. Diaz may recommend a reverse shoulder replacement. In this procedure, the anatomy of the shoulder is reversed by attaching a metal ball (glenosphere) to the glenoid and the plastic socket (humeral liner) to the upper humerus. If you are having a reverse shoulder
replacement, the system will help restore pain-free shoulder function by empowering the triangular muscle on the outside of your shoulder called the deltoid to become the main functioning muscle in the absence of a healthy rotator cuff.

Shoulder Replacement

The Right Choice For You

Dr. Diaz will consider a number of factors when selecting the shoulder implant that is right for you. Your age, the status of your rotator cuff, your activity level, and your general health are among the most important variables.

If you are scheduled for shoulder replacement surgery with Dr. Diaz, please review Preparing For and Recovering From Shoulder Replacement.

For a list of post-op shoulder home exercises: Click Here.

Total Shoulder Replacement Patient Brochure(opens in a new tab)


Arthritis – Base of the Thumb

Arthritis at the base of the thumb is a genetic predisposition: like graying and thinning of the hair, it comes with age and it shows up earlier in some families. Patients with arthritis of the base of the thumb report pain and weakness with pinching and grasping.

Carpal Tunnel Syndrome

Carpal tunnel syndrome is essentially a pinched nerve in the wrist. There is a space in the wrist called the carpal tunnel where the median nerve and nine tendons pass from the forearm into the hand. Carpal tunnel syndrome happens when swelling in this tunnel puts pressure on the nerve.

Cubital Tunnel Syndrome

Cubital Tunnel Syndrome is a condition that involves pressure or stretching of the ulnar nerve (also known as the “funny bone” nerve), which can cause numbness or tingling in the ring and small fingers, pain in the forearm, and/or weakness in the hand.

de Quervain Syndrome

Patients with de Quervain syndrome have painful tendons on the thumb side of the wrist. Tendons are the ropes that the muscle uses to pull the bone. You can see them on the back of your hand when you straighten your fingers.

Dupuytren’s Disease

Dupuytren’s disease is an abnormal thickening of the tissue just beneath the skin known as fascia. This thickening occurs in the palm and can extend into the fingers. Firm pits, nodules and cords may develop that can cause the fingers to bend into the palm, in which case it is described as Dupuytren contracture.

Dr. Diaz is honored to be carrying on the tradition of excellence in the treatment of Dupuytren Disease set forth by Dr. Charles Eaton, MD. To learn more about ongoing research efforts related to Dupuytren Disease and connect with others, visit The Dupuytren Research Group.

Elbow Fractures

Elbow fractures may result from a fall, a direct impact to the elbow, or a twisting injury to the arm. Sprains, strains or dislocations may occur at the same time as a fracture. X-rays are used to confirm if a fracture is present and if the bones are out of place.

Extensor Tendon Injuries

Extensor tendons are just under the skin. They lie next to the bone on the back of the hands and fingers and straighten the wrist, fingers and thumb. They can be injured by a minor cut or jamming a finger, which may cause the thin tendons to rip from their attachment to bone.

Flexor Tendon Injuries

The muscles that bend (flex) the fingers are called flexor muscles. These flexor muscles move the fingers through cord-like extensions called tendons, which connect the muscles to bone. Deep cuts can injure the tendons and nearby nerves and blood vessels.

Ganglion Cysts

Ganglion cysts are very common lumps within the hand and wrist that occur adjacent to joints or tendons. The most common locations are the top of the wrist, the palm side of the wrist, the base of the finger on the palm side, and the top of the end joint of the finger.

Hand Fractures

The hand is made up of many bones that form its supporting framework. This frame acts as a point of attachment for the muscles that make the wrist and fingers move. A fracture occurs when enough force is applied to a bone to break it.

Mallet Fingers

A mallet finger is a deformity of the finger caused when the tendon that straightens your finger (the extensor tendon) is damaged. When a ball or other object strikes the tip of the finger or thumb and forcibly bends it, the force tears the tendon that straightens the finger. The force of the blow may even pull away a piece of bone along with the tendon.

Trigger Finger

Trigger finger/thumb occurs when the pulley at the base of the finger becomes too thick and constricting around the tendon, making it hard for the tendon to move freely through the pulley. Sometimes the tendon develops a nodule (knot) or swelling of its lining.

Tennis Elbow – Lateral Epicondylitis

Lateral epicondylitis, commonly known as tennis elbow, is a painful condition involving the tendons that attach to the bone on the outside (lateral) part of the elbow.

Wrist Sprains

Arthritis at the base of the thumb is a genetic predisposition: like graying and thinning of the hair, it comes with age and it shows up earlier in some families. Patients with arthritis of the base of the thumb report pain and weakness with pinching and grasping.

Wrist Fractures – Distal Radius Fracture

The wrist is made up of eight small bones and the two forearm bones, the radius and ulna. Wrist fractures may occur in any of these bones when enough force is applied to the wrist, such as when falling down onto an outstretched hand.