Shoulder Anatomy and Rotator Cuff Injury

The shoulder (glenohumeral joint) is a very unique joint in the sense that it permits significant mobility and range of motion. The excessive motion lends the joint to being a bit unstable, though. The ball and socket structure is the reason the shoulder is one of the most flexible joints in the body. As a result of this freedom, though, the shoulder is the site of many common injuries. Repetitive overhead motions place the muscles and tendons of the shoulder in a vulnerable position. Most shoulder injuries can be treated conservatively with rest, ice, mobilization, and physical therapy. However, other shoulder injuries require surgical intervention.

The three bones that form the shoulder joint are secured in place by a number of ligaments, as well as the ever important rotator cuff muscles. The rotator cuff is comprised of four muscles (supraspinatus, infraspinatus, teres minor, and subscapularis) that combine at the shoulder to form a thick “cuff” over the joint. The rotator cuff has the important job of stabilizing the shoulder as well as elevating and rotating the arm. It is important for normal shoulder mobility, strength, and function. Each muscle originates on the shoulder blade (scapula) and inserts on the arm bone (humerus).

A muscle is a type of tissue that can contract to provide mobility and strength.  A tendon is a structure that connects the muscle to the bone. In the shoulder, injury to the rotator cuff is usually within the tendon.  These tendons have a vulnerable blood supply, called a watershed, that can cause susceptibility to injury. When the tendons are inflamed or torn, they cannot function properly.

Rotator cuff muscles can be damaged as well, especially in the setting of chronic rotator cuff tears when the muscles become atrophied (wasted away).  In these cases, the muscle permanently changes as a result of not being used properly.  Atrophy of the rotator cuff muscles usually means a tear in the tendon has been present for a long time and may not be repairable.

Supraspinatus Muscle and Tendon

The supraspinatus muscle is the most commonly injured rotator cuff muscle and tendon.  The supraspinatus is located directly on top of the shoulder, and the most important muscle involved in lifting the arm away from your side.

Injuries to the supraspinatus tendon often seen on an MRI include tendonitis, partial tears, and full-thickness tears (complete tears) of the tendon.

Infraspinatus Muscle and Tendon

The infraspinatus tendon is just behind the supraspinatus and determining the beginning of one tendon and the end of the other can be difficult, they essentially blend into each other.

Larger tears of the rotator cuff often involve more than one tendon (so-called “massive rotator cuff tears”), and the most common large tears involve the supraspinatus and the infraspinatus tendons.

Subscapularis Muscle and Tendon

The subscapularis is a tendon in the front of the shoulder. This tendon is less commonly injured but can cause some unique challenges when it is injured. The motion called internal rotation of the shoulder is dependent on the subscapularis. In addition, the subscapularis helps provide stability to the shoulder and helps maintain the normal position of the biceps tendon.

Tears of the subscapularis can be found in very large tears of the rotator cuff, and also in patients who have had recent surgery. Often shoulder surgery is performed by entering the front of the joint, by detaching the subscapularis tendon. Injuries during recovery can lead to tearing of the healing tendon. This is a complication seen after shoulder replacement or open labral repair surgery.

Teres Minor Muscle and Tendon

The teres minor is the last of the rotator cuff muscles and the least commonly injured. The teres minor is in the back of the shoulder and involved with the movement of external rotation of the joint. External rotation is the movement with your elbow held at your side, and your hand pushes outwards. Usually, your doctor will test this muscle with this manoeuvre.


Rotator Cuff Tendinitis

Rotator cuff tendinitis is most common in young athletes and middle-age people. It occurs when a normal, healthy rotator cuff tendon is injured or inflamed, often as a result of a repetitive overhead activity (for example, painting, tennis, swimming, baseball, volleyball, or weightlifting).

Certain chronic diseases are also associated with rotator cuff tendinitis. For example, diabetes and obesity may be a risk factor.

Rotate Cuff Tear

A rotator cuff tear (when the tendon is torn from the arm bone) is a disease found primarily in middle to older age individuals. A tear may be caused by trauma to the shoulder (for example, a fall directly on the shoulder or direct blow to the shoulder), as well as chronic overuse of the rotator cuff muscles.

Obesity and smoking may also increase a person’s chance of tearing their rotator cuff.

Rotator Cuff Tendinosis

Rotator cuff tendinosis—a condition whereby the rotator cuff tendon degenerates—occurs as a result of increasing age. This is because, as we get older, there is a decreased blood supply to the rotator cuff tendons. As a result, when the tendons become stressed or injured, they do not recover or heal as well. These weakened or frayed tendons are then more vulnerable to inflammation and tearing.

Poor posture, smoking, repetitive overhead activity, and genes may also play a role in the development of rotator cuff tendinosis.


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Rotator cuff pain is most commonly caused by an inflamed tendon (tendinitis) or torn tendon. The quality of the pain may range from a dull, aching sensation to sharp pain that moves down the upper arm when reaching overhead or sleeping on the affected side. Interestingly, the intensity of the pain does necessarily correlate with the degree of the injury. Less commonly, rotator cuff pain may from result from a condition called rotator cuff tendinosis—when the tendons become frayed or worn down as a result of increasing age and overuse.

Patients usually complain of pain over the top of the shoulder and arm. In some patients, the pain can descend down the outside of the arm all the way to the elbow. This has to do with the location of the nerves that pass by the deeper parts of the shoulder.

Some people may experience rotator cuff pain in a less typical location such as the back of the shoulder or within the armpit.  With both a rotator cuff tendinitis and tear, a person often experiences pain over the shoulder that worsens with activities, such as reaching overhead or throwing.

Shoulder weakness is the other common symptom of a rotator cuff tear. Weakness causes difficulty lifting the arm up overhead or difficulty with activities such as reaching, getting dressed, or carrying objects. More specifically, with rotator cuff tears, deficits in strength are very common. For instance, many people noticed they have a hard time putting dishes away in upper cabinets or reaching into the refrigerator to lift a carton of milk.

Keep in mind, some people with rotator cuff tears do not experience any pain—and the severity of the tear (partial versus complete) does not correlate with the pain experience. In other words, a person with a partial tear may report severe pain while a person with a complete tear may report no pain at all.

Like a rotator cuff tear, rotator cuff tendinosis does not always cause pain, especially early on in the disease course. If pain is present, it’s often described as a dull, aching pain that worsens at night and with certain shoulder movements, like reaching out or behind the back.

When to seek advice

Any severe shoulder pain and/or pain that comes on suddenly warrants medical attention, as does any significant swelling or bruising around the shoulder joint or signs of infection like redness and warmth.

Seek medical attention, as well, if your shoulder pain is associated with other unusual symptoms like trouble breathing, dizziness, or abdominal pain.

Other signs that warrant a doctor’s visit include:

  • An inability to lift your arm above your head or carry objects
  • Any trauma or injury to the shoulder, especially if there is deformity to the joint
  • Shoulder pain that is persistent or worsening


After reviewing your medical history, if your primary care doctor suspects a rotator cuff problem, he will perform a series of tests to evaluate the rotator cuff tendons. He will then order an imaging test of your shoulder if a rotator cuff tear is suspected.

At-Home Function Tests

Several tests are used to evaluate the rotator cuff, some of which can be performed at home prior to your appointment. A few of these at-home tests include:

Empty Can Test

The empty can test is used to assess the status of the supraspinatus, located on the upper part of your shoulder. This is a simple test to perform, and the motion involved mimics that of dumping out a soda can.

  • Sit or stand comfortably with a friend present.
  • Lift your painful arm out the side so it is parallel to the floor.
  • Bring your arm forward about 30 to 45 degrees.
  • Turn your hand over so your thumb is pointing toward the floor (as if you were trying to empty a can of soda).
  • Have your friend gently push your arm down.

If pain or weakness prevents you from maintaining your arm in the “empty can” position, you may have a supraspinatus rotator cuff injury. If so, check in with your doctor to confirm the diagnosis.

Lift-Off Test

The lift-off test is a shoulder test to determine if you have a tear in the subscapularis. This muscle is located on the underside of your shoulder blade and is responsible for rotating your shoulder inward. To perform the lift-off test:

  • Stand up and place the back of your hand on the small of your back.
  • Face the palm of your hand away from your back.
  • Attempt to lift your hand away from your body.

If you are unable to lift your hand away from your low back, it is suspected that a subscapularis rotator cuff injury may be present.

Resistance Testing

One way of determining if a rotator cuff tear is possibly causing your shoulder pain is to perform manual strength testing of your rotator cuff muscles. To do this, follow a simple procedure:

  • Sit comfortably in a chair.
  • Bend your elbow 90 degrees and keep your elbow tucked into your side.
  • Have someone push your hand in toward your belly.

If you are unable to hold this position and feel pain, you may have a rotator cuff tear.

Pain-Relief Test

The lidocaine injection test is sometimes used by some doctors (mostly orthopedic surgeons or sports medicine physicians) to help distinguish between a rotator cuff tendinitis and tear. Distinguishing between these two conditions is important because it affects the overall treatment plan.

During this test, lidocaine is injected into the shoulder joint. If a person has a rotator cuff tendonitis, the lidocaine will relieve the pain and muscle strength will remain normal. If a person has a rotator cuff tear, the pain will be relieved, but the muscle will remain weak.


If a rotator cuff tear is suspected, an imaging test will be ordered. The test most commonly used to diagnose a rotator cuff tear is magnetic resonance imaging (MRI), but an arthrogram and an ultrasound may also be used. The MRI is helpful because it can show both complete rotator cuff tears and partial rotator cuff tears. The MRI can also show evidence of rotator cuff tendinosis, shoulder bursitis, and other common shoulder problems.

Besides musculoskeletal issues, several other health conditions can also cause shoulder pain within the rotator cuff region, such as a heart attack, gallbladder disease, or nerve compression in the neck.


The treatment of your rotator cuff problem depends on whether or not you have a tendinitis, tendinosis, or tear, and if there is a tear, how severe it is.

Rotator Cuff Tendinitis and Tendinosis

The treatment of rotator cuff tendinitis and tendinosis is generally straightforward, encompassing six key strategies:

  • Avoiding activities that aggravate the pain, like overhead reaching or reaching behind the back
  • Keep your arm down, in front of and close to your body (avoid an arm sling, as you risk the development of a frozen shoulder)
  • Ice to reduce initial inflammation in tendonitis (apply a cold pack to shoulder for 15 to 20 minutes every four to six hours)
  • Take an anti-inflammatory medication like a nonsteroidal anti-inflammatory (NSAID)
  • Apply heat and perform light shoulder massage prior to home exercise or physical therapy sessions
  • See a physical therapist for stretching and range of motion exercises

After about two to three months of the above strategies, most people report an improvement in their pain. However, if pain persists, be sure to talk to your doctor.

Rotator Cuff Tear

The good news is, not every rotator cuff tear needs surgery. In fact, small rotator cuff tears are treated similarly to a rotator cuff tendonitis. However, when surgery is the best treatment, it’s often better to proceed sooner rather than later, as the rotator cuff muscle can weaken (atrophy) and retract (pull back) over time. This can make repair less successful or even impossible. Therefore, it’s good to discuss your treatment options with your orthopedic surgeon as soon as possible.

For people who choose nonsurgical treatment options, there are a number of ways to find relief of the shoulder pain caused by the rotator cuff tear. Often with physical therapy and a proper exercise program, people can improve the function of their shoulder joint to prevent pain that comes from a torn tendon of the rotator

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