Anatomy of the shoulder

The shoulder is a ball-and-socket type joint made up of three bones:

  1. Humerus (upper arm)

  2. Scapula (shoulder blade)

  3. Clavicle (collarbone)

The head of the humerus fits into a socket (called the "Glenoid") in the shoulder blade. A group of muscles and tendons keeps the shoulder centered in the shoulder socket. These muscles are called the rotator cuff. They cover the head of humerus and attach it to your scapula. There is a lubricating sac called a bursa between the rotator cuff and the bone on top of your shoulder (acromion). This bursa allows the rotator cuff tendons to move freely when you move your arm in all directions.

The biceps muscle (in front of your upper arm) helps you bend your elbow and rotate your forearm. It also stabilizes the shoulder. The biceps muscle has two tendons that attach it to bones in the shoulder.

The Glenoid (socket) is lined with soft cartilage structure called the labrum. This tissue helps to stabilize the head of the humerus into the shoulder socket.

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 lift the arm overhead.

  • Directly beneath the deltoid muscle is sub-deltoid bursa, a fluid-filled sac, analogous to a water balloon.

  • A group of muscles and tendons keeps the shoulder centered in the shoulder socket. These muscles are called the rotator cuff.

What is shoulder trauma?

Trauma to the shoulder is common. Injuries range from a separated shoulder resulting from trauma, be it a fall onto the shoulder to a high-speed car accident that fractures the shoulder blade (scapula) or collar bone (clavicle). One thing is certain: everyone injures his or her shoulder at some point in life.

Types of shoulder injuries

There are many types of shoulder injuries:

• Shoulder Fractures

Fractures are broken bones. Fractures of the shoulder commonly involve the clavicle (collar bone), proximal humerus (top of the upper arm bone), and scapula (shoulder blade). Fractures of the clavicle or the proximal humerus can be caused by a direct blow to the area from a fall, collision, or motor vehicle accident.

Because the scapula is protected by the chest and surrounding muscles, it is not easily fractured. Therefore, fractures of the scapula are usually caused by high-energy trauma, such as a high-speed motor vehicle accident. Scapula fractures are often associated with injuries to the chest.


Symptoms of fractures of shoulder are related to the specific type of fracture, but may include:

  • Pain

  • Swelling and bruising

  • Inability to move the shoulder

  • A grinding sensation when the shoulder is moved

  • Deformity – "it does not look right"
  1. Clavicle (collarbone) fracture: Swelling about the middle of the collarbone area with a "bump," and limited range of motion

  2. Proximal Humerus Fracture: Severe pain, a severely swollen shoulder and very limited movement of the shoulder.

  3. Scapular Fracture: Pain, swelling and severe bruising about the shoulder blade.

Shoulder Dislocations

Shoulder dislocations occur when the bones on opposite sides of a joint do not line up. Dislocations can involve any of three different joints.

There are two types of shoulder dislocations:

  1. Anterior shoulder dislocations (to the front) of the shoulder are caused by the arm being forcefully twisted outward (external rotation) when the arm is above the level of the shoulder. These injuries can occur from many different causes, including a fall or a direct blow to the shoulder.

  2. Posterior shoulder dislocations (to the back) of the shoulder are much less common than anterior dislocations of the shoulder. Posterior dislocations often occur from seizures or electric shocks when the muscles of the front of the shoulder contract and forcefully tighten.

A dislocation of the acromioclavicular (AC) joint (collar bone joint) is also called a separated shoulder or acromioclavicular joint separation. Dislocations of the acromioclavicular joint can be caused by a fall onto the shoulder or from lifting heavy objects. The term "shoulder separation" is not correct, because the joint injured is not the true shoulder joint.


Symptoms of a dislocated shoulder may include:

  • Shoulder Instability

  • A prominence or bump on the front or top of the shoulder

  • The sensation of something sticking up on the shoulder

  • The sensation of a "dead arm"

1. Shoulder separation (Acromioclavicular (AC) joint separation): Extreme elevation of the clavicle and pain over the top of the shoulder.

How are shoulder injuries diagnosed?

Most fractures are diagnosed with X-rays of the area and by physical examination. Sometimes, additional imaging techniques, such as computed tomography, are necessary.

Shoulder fractures

Clavicle Fractures: Most clavicle fractures can be treated without surgery. Surgery is necessary when there is a compound fracture that has broken through the skin or the bone is severely out of place. Surgery typically involves fixing of the fracture with plates and screws or rods inside the bone.

Proximal Humerus Fractures: Most fractures of the proximal humerus can be treated without surgery if the bone fragments are not shifted out of position (displaced). If the fragments are shifted out of position, surgery is usually required. Surgery usually involves fixation of the fracture fragments with plates, screws, or pins or it involves shoulder replacement.

Scapula Fractures: Most fractures of the scapula can be treated without surgery. Treatment involves immobilization with a sling or shoulder immobilizer, icing, and pain medications. The patient will be examined for additional injuries. About 10% to 20% of scapula fractures need surgery. Fractures that need surgery usually have fracture fragments involving the shoulder joint or there is an additional fracture of the clavicle. Surgery involves fixation of the fracture fragments with plates and screws.

Shoulder dislocations

Shoulder Dislocations (Glenohumeral Joint): The initial treatment of a shoulder dislocation involves reducing the dislocation ("putting it back in the socket"). This usually involves treatment in the emergency room. The patient is given some mild sedation and pain medicine, usually through an intravenous line. Often, the physician will pull on the shoulder until the joint is realigned. Reduction is confirmed on an X-ray and the shoulder is then placed in a sling or special brace. Additional treatment later is based on the patient's age, evidence of persistent problems with the shoulder going out of place, and the underlying associated soft-tissue injury (either to the rotator cuff or the capsulolabral complex). Patients who are 25 years of age or younger generally require surgery. Persistent instability (repeat dislocations) of the shoulder usually requires surgery. Surgery involves repair of the torn soft tissues.

Shoulder Separations (Acromioclavicular Joint): Treatment of shoulder separations is based on the severity of the injury as well as the direction of the separation and the physical requirements of the patient. Less severe shoulder separations) are usually treated without surgery. Severe separations in an upward direction or dislocations in the backward or downward directions often require surgery. Surgery involves repair of the ligaments. Professional athletes and manual laborers are often treated with surgery, but the results are often unpredictable.

What to expect after a shoulder injury ?

Life after a shoulder fracture, separation, or dislocation can be greatly affected for several weeks or even months. Most shoulder injuries whether treated surgically or non-surgically require a period of immobilization followed by rehabilitation.

If the shoulder trauma was not severe, there is rapid improvement and return of function after the first 4 to 6 weeks. Shoulder exercises, usually as part of a supervised physical therapy program, are usually necessary. Exercises decrease stiffness, improve range of motion, and help the patient regain muscle strength.