• Structure
  • Impingement
  • Instability
  • AC Joint

The shoulder has two main bones called the humerus (upper arm bone) and the scapula (shoulder blade).  

The end of the scapula, the glenoid, refers to depression of the scapula entering into the formation of the shoulder joint. 

The shoulder joint is a ball-and-socket joint between the glenoid fossa of the scapula and the head of the humerus. 

Articular cartilage cushions this joint by covering the head of the humerus and face of the glenoid.  Stabilizing the joint is the labrum, a ring of fibrous cartilage surrounding the glenoid.

The acromion (highest point of the shoulder) is formed by the outer end of the scapula extending over the shoulder joint.  This is also called the acromial process. The acromioclavicular joint (AC joint) is the joint between the acromion of the scapula and the clavicle.

The shoulder bones are connected by ligaments (bands of tough fibrous tissue) and the bones are connected to the surrounding muscles by tendons. 

Two major tendons of the shoulder are the biceps tendon, which attaches the biceps muscle to the shoulder, and the supraspinatus tendon, which helps form the rotator cuff.





Within the shoulder ball-and-socket joint, the humeral head is held in the socket by the joint capsule and ligaments, and by four muscles and their tendon attachments, collectively referred to as the rotator cuff. This group of flat tendons fuse together and surround the front, back, and top of the shoulder joint.  They connect to muscles originating from the scapula.  When the muscles contract, they cause the rotator cuff tendon to rotate either inward, outward or upward.

The four shoulder muscles are:
1. Supraspinatus
   (elevates the shoulder).
2. Subscapularis
   (internally rotates the shoulder)
3. Infraspinatus
   (external rotator)
4. Teres minor
   (external rotator)



The rotator cuff muscles pass underneath the clavicle (collar bone) and acromion (upper part of the shoulder blade) reaching to the humeral head.  The subacromial bursa, an area of fluid, protects these muscles from the bones above them.  When this bursa becomes inflamed it is called bursitis, which may cause significant pain in the shoulder as well as down the side of the upper arm.


If the tendon itself becomes inflamed it is referred to as rotator cuff tendonitis. 

Impingement Syndrome:

When both the bursa and tendons are inflamed, impingement syndrome can result.  Impinging, or pinching, occurs against the bone overlying the rotator cuff (acromion).  A spur on the acromion or a thickening or curvature of the acromion can rub the tendon to cause impingement.  The rotator cuff tendons are at a risk for actually tearing or pulling away from the attachment on the humerus bone if impingement persists over a long period of time.


The most common complaint of rotator cuff injuries is aching pain on the side of the upper arm or in the top and front of the shoulder.  Often the pain is worse at night and can awaken someone from sleep.  The pain is typically increased when lifting the arm overhead.  Activities which involve forward elevation of the arm are painful, such as throwing a baseball, weightlifting or playing tennis.  At times the shoulder may click due to thickening of the inflamed bursa.  Significant weakness may suggest a torn rotator cuff.  With a complete tear, it is possible that the arm would be unable to be lifted forward or outward at all.


The combination of the patient’s history of injury, the physical examination, tests, x-rays and MRI help diagnose rotator cuff problems. An impingement test by the treating physician can suggest whether impingement is involved in an injury.

A large majority of patients improve from rotator cuff injuries without surgery.  Often this is dependent on the size of the tear.  If the injury is less severe (impingement, tendonitis or bursitis), resting of the muscles, medication, ice and perhaps physical therapy will often decrease inflammation and restore tone to these atrophied muscles.  At times the bursa may be injected with cortisone, a strong anti-inflammatory, to reduce swelling.  When the pain has begun to subside, strengthening exercises for the uninjured portion of the rotator cuff are often encouraged which emphasize internal and external rotation, often with the use of an elastic tubing.

Surgical Treatment for Impingement:

If a patient does not respond to conservative (non-surgical) measures, surgery is discussed and the risks and benefits are carefully reviewed.  Arthroscopic visualization is a procedure which can remove an acromial spur or improve a thickened acromion.  This procedure is performed on an outpatient basis  with repair of minor damage and fraying to the rotator cuff tendon.  If there is scarred bursal tissue, this can also be removed at the same time.  This procedure often cures impingement and prevents further rotator cuff injury.

Surgical Treatment for Rotator Cuff Tears:

If the rotator cuff is already torn and symptoms persist, the tendon will most likely need to be repaired surgically.  Arthroscopic surgery allows a surgeon to visualize the interior of the joint to trim and remove fragments of torn cuff tendon and biceps tendon.  The arthroscope can also be used when grinding or cutting away an acromial spur or thickened acromion. 

If there is a small rotator cuff tear it may be repaired with arthroscopy.  If it is a larger tear a mini-open procedure is often performed.  When a rotator cuff tear has pulled off the bone a suture (stitch) may be needed.  After locating and visualizing the tear with the arthroscope, a two-inch incision can be made directly over the tear so that stitches can connect the tendon back to the bone.  Small suture screw anchors may also be used if a tear is slightly retracted.

After Surgery:

The program after surgery depends greatly on the severity of the injury.  A sling is typically worn immediately following surgery for at least a day to allow healing of the soft tissues.  Range of motion exercises follow this, and then strengthening, particularly of the rotator cuff.  For a completely torn rotator cuff that was treated surgically, it may take at least six months for the muscles to regain their function and for full range of motion to be restored.  The pain itself is usually relieved much sooner that this, however, and normal activities of daily living are often achieved within 2-3 months even for completely torn rotator cuffs.

Who Should Have Surgery:

Each patient has the option of choosing surgery or not.  The factors weighing the choice are the age of the patient, health of the patient, and severity of symptoms.  If a patient is young and working, or leads an aggressive lifestyle in terms of activities, surgery will be suggested.  If an older individual does not require the ability to lift overhead and the pain is not too severe, conservative treatment may be elected.  If disability and ongoing pain are significant factors for any age patient, surgery should be considered to repair the rotator cuff.

What is Instability?

The shoulder joint, one of the most mobile joints in the body, is also one of the most unstable.  Instability is when the bones in one of the shoulder joints move out of their normal position.  This may result in dislocation or subluxation and cause pain and unsteadiness when raising the arm or moving it away from the body.  Subluxation is when the joint partially dislocates.  The ball slides partly out of the socket but does not actually dislocate completely.  Dislocation occurs when the ball is completely displaced out of the socket.  A sensation of this is when lifting the arm overhead the shoulder may feel like it is slipping out of place.  Sometimes the feeling may just be uncomfortable, as if the arm is “dead” or numb.  Patients are often “apprehensive” with certain motions.


Types of Instability:

By far, the most common type of instability is anterior, when the shoulder comes out the front.  Multidirectional instability refers to the joint being unstable in more than one direction.  A typical multidirectional instability involves anterior (front) instability and inferior (down) instability.  However, a posterior (back) direction could also be involved, but is rare and usually only seen with an unusual trauma or seizure disorders.  Multidirectional instability can be seen in swimmers or other athletes who repetitively use their upper arm and shoulder.


Treatment Options:

Depending on the severity of the injury and the patient’s age, treatment options vary.  In younger patients the shoulder is more likely to repeatedly dislocate which can significantly limit a person’s activities and lead to possible joint degeneration.  For recurrent dislocations, surgery may be recommended to repair torn ligaments and capsule. There are arthroscopic and open surgical techniques available for shoulder stabilization.



The AC (acromioclavicular) joint is where the collar bone (clavicle) meets the shoulder.  A fall onto the shoulder can cause the joint to separate, tearing the ligaments that would normally stabilize the clavicle.  The clavicle becomes raised and a bump can be seen on the top of the shoulder.  Most AC joint separations are treated with a sling for several weeks to give the joint time to heal and control movement to minimize pain.



Conservative treatment of AC joint problems usually includes rest, modifying activities and ice as well as possible medication.  A cortisone injection is sometimes given into the joint.  Surgery is performed arthroscopically and the arthritic portion of the clavicle can be removed on an outpatient basis.  Physical therapy and range of motion exercises are usually started right away, with most patients recovering excellent range of motion.  Most patients can return to weight lifting and/or activities involving lifting above the shoulder within several months after surgery.



Talus Medical Plaza • 3875 East Overland Road • Meridian, ID 83642 • 208.884.8300