Shoulder Anatomy and Function

How a Healthy Shoulder Works

Your shoulder is the most moveable joint in the body. It is made up of three bones:

  • the collarbone, or clavicle
  • the shoulder blade, or scapula
  • and the upper arm bone, or humerus

There are also two important joints that allow for movement:

  • The acromioclavicular joint connects the upper part of the shoulder blade (the acromion) to the collarbone.
  • The glenohumeral joint, also known as the shoulder joint, is a ball-and-socket joint that connects the upper arm to the shoulder blade. This joint allows free movement of the arm so that it can rotate in a circular fashion.

Although the shoulder is the most moveable joint in the body, it is unstable because the ball (the humerus) is larger than the socket (the glenoid) that holds it. To maintain stability, the bones of the shoulder are held in place by muscles, tendons, and ligaments. Tendons are tough cords of tissue that attach muscles to bone, and ligaments attach bones to each other for stability.

The rotator cuff is made up of four muscles and their tendons, which act to hold the upper arm (humerus) to the socket of the shoulder (glenoid fossa). The rotator cuff also provides mobility and strength to the shoulder joint. Two sac-like structures, called bursae, allow smooth gliding between the bone, muscle, and tendon. They also cushion and protect the rotator-cuff structures from the upper part of the scapula (the acromion).

What causes shoulder pain?

According to the AAOS about 23,000 people have shoulder replacement surgery each year. This compares to more that 700,000 Americans a year who have knee and hip replacement surgery*. Shoulder problems may arise because of injury to the soft tissues of the shoulder, overuse or underuse of the shoulder, or even because of damage to the tissues.

Shoulder problems result in pain, which may be localized to the joint or travel to areas around the shoulder or down the arm. Damage to the shoulder joint may result in instability of the joint, and pain is often felt when raising the arm or when soft tissues are trapped between the bones (impingement). Impingement is particularly common in sports activities that involve repetitive overhead arm motions, such as pitching baseballs.

You may have a shoulder injury if:

  • Your shoulder is stiff and doesn’t allow full normal movement.
  • Your shoulder lacks strength to perform your daily activities.
  • Your shoulder feels as if it’s slipping out of place (upper arm bone “popping” or a feeling that your arm is sliding out of the shoulder socket).

Another common cause of shoulder pain is arthritis. The most common type of arthritis is osteoarthritis (OA) — sometimes called degenerative arthritis because it is a “wearing out” condition involving the breakdown of cartilage in the joints. OA can occur without a shoulder injury, but this seldom happens since the shoulder is not a weight-bearing joint like the knee or hip. Instead, shoulder OA commonly occurs many years following a shoulder injury, such as a dislocation, that has led to joint instability and damage, allowing OA to develop.

Your Treatment Options for Shoulder Pain

Following an orthopaedic evaluation of your shoulder, your doctor will review and discuss the results with you. Based on his or her diagnosis, your treatment options may include:

  • Medication
  • Physical therapy
  • Shoulder joint fluid supplements (injections that provide temporary pain relief)
  • Total shoulder joint replacement

When joint pain and stiffness become severe enough to affect your daily life and comfort, and when that pain is not relieved by other treatment options, shoulder replacement may be recommended.

*AAOS.org — January 2006.

About Shoulder Replacement

Replacement of an arthritic or injured shoulder is less common than knee or hip replacement. However, shoulder replacement typically offers all the same benefits as those procedures — including joint pain relief and the restoration of more normal joint movement.

Restoring your movement is particularly important in the shoulder, because it’s the mechanism that allows your arm to rotate in every direction. If you’re experiencing severe shoulder pain and reduced shoulder movement, there are probably many daily activities you can no longer do — or do as comfortably — as before your shoulder problems began. This may mean you’re ready to consider shoulder replacement surgery.

In shoulder replacement surgery, the artificial shoulder joint can have either two or three parts, depending on the type of surgery required.

  • The humeral component (metal)
  • The humeral head component (metal)
  • The glenoid component (plastic) replaces the surface of the socket

There are two types of shoulder replacement procedures:

  1. Partial shoulder replacement is performed when the glenoid socket is intact and does not need to be replaced. In this procedure, the humeral component is implanted, and the humeral head is replaced.
  2. Total shoulder replacement is performed when the glenoid socket is damaged and needs to be replaced. All three shoulder joint components are used in this procedure.

What’s involved in shoulder surgery?

Certain parts of your shoulder joint are removed and replaced with a plastic or metal device called a prosthesis, or artificial joint. The artificial shoulder joint can have either two or three parts, depending on the type of surgery required.

  • The humeral component (metal) is implanted in the humerus, or upper arm bone.
  • The humeral head component (metal) replaces the humeral head at the top of the humerus.
  • The glenoid component (plastic) replaces the surface of the glenoid socket, or shoulder socket.

Shoulder Frequently Asked Questions

What is a shoulder replacement?

Also called arthroplasty, shoulder replacement is a surgical procedure in which the damaged or diseased joint is removed and replaced by an artificial shoulder implant (prosthesis) that is designed move like a normal, healthy joint.

How “bad” does my joint pain have to get before I should consider having joint replacement?

This is a very personal decision that only you can make, with the help of an orthopaedic surgeon’s evaluation of your pain and its effect on your daily life.

Why do some people need joint replacement?

When other treatment options no longer provide relief, joint replacement may be recommended — not only to relieve pain but also to prevent the disability it can cause. For example, experiencing joint pain day after day without relief can lead to “staying off” the joint — which often weakens the muscles around it so it becomes even more difficult to move. Your orthopaedic surgeon will tell you whether you might benefit from joint replacement and explain the reasons why it may, or may not, be right for you at this time.

What happens during shoulder replacement surgery?

Certain parts of your shoulder joint are removed and replaced with a plastic or metal device called a prosthesis, or artificial joint. The artificial shoulder joint can have either two or three parts, depending on the type of surgery required.

  • The humeral component (metal) is implanted in the humerus, or upper arm bone.
  • The humeral head component (metal) replaces the humeral head at the top of the humerus.
  • The glenoid component (plastic) replaces the surface of the glenoid socket, or shoulder socket.

If I decide to have joint replacement, what will I need to do before the surgery?

You’ll need routine blood tests, urinalysis, a physical examination, and, if you’re over 50 or your doctor thinks they’re advisable, an electrocardiogram (EKG) and chest X-ray as well. Your own doctor or the hospital where you’ll have the surgery may perform these preoperative tests and evaluations. You may also be asked to donate blood preoperatively or to have a designated donor — usually a family member or relative — do this. Your doctor or orthopaedic surgeon will specify exactly which tests and evaluations you will need and when you should have them. He or she may also recommend that you take an iron supplement before your surgery, and you may be asked to stop taking certain medications — for example, aspirin and other medications that thin the blood. Your doctor or orthopaedic surgeon will also specify how these and any other medication concerns apply to you. Finally, your doctor may advise you not to eat or drink after midnight on the day your surgery takes place.

What will I need to know about postoperative recovery in the hospital?

Following joint replacement surgery, hospital stays vary depending on insurance coverage and individual medical status — a total of four days (including the day of the surgery) is typical. The surgery may take from two to three hours, and you’ll spend about the same amount of time in the recovery room.

On the first day after your surgery, you may be able to get out of bed and begin physical and occupational therapy, typically several brief sessions a day. Usually a case manager is assigned to work with you as you move through your rehabilitation routines. When you’re ready for discharge, the decision will be made concerning whether you can best continue to recover at home or in another facility where you may receive specialized rehabilitative help. If you do go to another facility, the goal will be to return you to your home, able to move about with a safe level of independence, within three to five days.*

What can I expect in the first days after I’m discharged?

You shouldn’t be surprised if you feel a little shaky and uncertain for the first day or two after you’re discharged. But soon you will likely get a routine going and gain confidence in your new joint — the start of a new life with less pain. (As with any surgery, you’ll probably take pain medication for a few days while you are healing.) You’ll also be in touch with your doctor or orthopaedic surgeon, as well as your case manager, so take advantage of opportunities to ask questions or discuss concerns as well as to report on your progress*

* Individuals results vary.

When will I be able to go back to a normal daily routine, such as going to work or driving a car?

This is a decision that only you and your doctor or orthopaedic surgeon can make. However, there are some general guidelines that your doctor may give you:

  • You should have no restrictions on leaving your home as long as your safety and comfort are assured.
  • Don’t tire yourself out — a good balance of exercise, rest, and relaxation is best for helping your body heal and gain strength.

When to resume driving a car, going to work, and/or participating in sports activities are all highly individualized decisions. Be sure to follow your doctor’s or orthopaedic surgeon’s advice and recommendations.

Are there activities I cannot do after shoulder replacement surgery?

When fully recovered, most people with artificial shoulders can return to work and normal daily activities without any problems. Keep in mind, however, that certain activities could affect how long your artificial shoulder will last and how well it will perform. A good rule of thumb is that your physical activities should not cause pain, including pain felt later. You should also not jar your joint or push it to its most extreme range of motion. If, for example, you are considering doing any of the following activities, you should discuss them first with your doctor or orthopaedic surgeon:

  • Any activity involving lifting or pushing heavy objects
  • Any activity that places excessive stress on your shoulder joint
  • Hammering and other forceful arm/shoulder movements
  • Boxing and other arm/shoulder impact sports