Shoulder Dislocations (Instability)



What is a shoulder dislocation?


A shoulder dislocation occurs when the upper arm bone (the humerus) rolls forward and out of the socket of the shoulder blade (the scapula).  The term “shoulder dislocation” should not be confused with a “shoulder separation”.  A separation occurs at a different joint in the shoulder.  The shoulder is a complex ball and socket joint, capable of movement in all planes of motion.  The most common way for a shoulder to dislocate is by a mechanism of “abduction and external rotation” of the humerus.  In other words, the upper arm is taken up and away from the body and forced beyond its available range of motion.  This type of injury results in the ligaments of the shoulder being stretched or torn.


Why do shoulders dislocate?


The shoulder is a relatively unstable joint analogous to a basketball sitting on a coffee saucer.  The saucer is galled the glenoid.  It is an oval shaped relatively flat bone.  The ball is called the humeral head and it is part of the upper arm bone.  The stability of the joint is imparted partially by the bones but more importantly the surrounding soft tissues which include the labrum, capsule, and rotator cuff muscles.  The labrum is the soft tissue that is directly connected to the saucer.  The capsule connects the saucer and the ball.  The rotator cuff muscles attach to the humeral head and act to stabilize and steer the shoulder through its complex movements.  In contrast to the hip joint which is a true ball and socket where motions are relative constrained, the shoulder is much “looser” which allows it to move more freely.


Is there a spectrum of instability?


Yes!  Shoulder instability can be classified in several ways.  It can be classified as traumatic or atraumatic.  It can be classified based on the frequency of instability (first time versus recurrent).  It may be classified by the direction of instability.  Most dislocations occur out the front of the shoulder (anteriorly), some occur out the back of the shoulder (posteriorly), and some occur in both directions (multidirectional).  Anterior dislocations occur generally from trauma; examples include falling on an outstretched arm, attempting to tackle a player, having the arm being pulled out and away from the body.  Posterior dislocations have occurred rarely in the past but are seen with increasing frequency based specifically on rules changes in football blocking allowing the player to block with the arms out in front of the body.  Multidirectional instability usually occurs in an atraumatic fashion and often is related to the shoulder capsule being larger, having a greater volume, and therefore less stabilizing effect on the joint.  Instability is also based on a spectrum of instability.  On one hand the patient may actually dislocate the shoulder.  At the  other end of the spectrum is “microinstability” where the athlete may have pain, weakness, lose velocity and accuracy with throwing, and fatigue more quickly as the surrounding shoulder muscles are being asked to “do more work” to help keep the shoulder centered.  In the middle spectrum is a term “subluxation” which means partial dislocation.  In this setting the patient can sense the shoulder starting to dislocate but muscle contraction can control and relocate the shoulder.  Some patients will initially start with the milder forms of instability and may progress to full blown dislocation events.


When a shoulder dislocates are other tissues injured?


Sometimes!  The brachial plexus (nerves) are in close proximity can be stretched or bruised and may take weeks or months to recover.  Occasionally an isolate nerve injury can occur wither to the axillary nerve which allows you to left your arm away from your chest, or the musculocutaneous nerve which allows you to bend or flex your elbow.  In patients over 40 years of age the rotator cuff tendon can be torn or avulsed in addition to the shoulder dislocation.  A fracture can occur either involving the humeral head (great tuberosity fracture) or the glenoid (glenoid rim or Bankart fracture).  The time interval that the shoulder remains dislocated, and / or the severity of the dislocation may also result in an impaction fracture (indentation) in the back of the humeral head (Hill-Sach’s lesion)



How is the shoulder “relocated”?


In most instances, for a first time dislocator, you will need to be seen at an emergency facility where you will be given medications to relieve pain and muscle spasms. This will allow a physician to apply traction to your arm while gently manipulating it back into the shoulder socket.  X-rays should be taken to rule out any bony damage.  A sling should be applied for comfort and support.  In the case of a recurrent dislocator, it may be possible to relocate the shoulder by using your own muscles to “pull” the head of the humerus back into the socket (glenoid) of the scapula.  This “self-reduction” maneuver in a recurrent dislocator can sometimes be performed because the ligaments and other connective tissue holding the ball and socket together have already been stretched out.


How do I prevent my shoulder from dislocating again?


Patients can often compensate for loosened shoulder ligaments by strengthening the surrounding shoulder musculature through physical therapy.  This form of treatment is generally more successful in an older, first time dislocator.  People over the age of 30 have generally “tighter” joints than people in their teens or 20’s. Therefore, they have a much higher likelihood of stabilizing the shoulder through physical therapy and avoiding future dislocations.   Strengthening programs include the rotator cuff and deltoid muscle groups as well as the chest, upper back and shoulder blade musculature.  Exercises to improve shoulder coordination should include core strengthening and exercises with a medicine ball.


When do I need surgery for a dislocating shoulder?


The answer to this question depends on your age, number of dislocations and degree of disability.  Surgical shoulder stabilization is indicated in younger, athletic people who are at a higher risk for recurrent dislocations.  This includes, but is not limited to, wrestlers, baseball, basketball, and volleyball athletes.  Older individuals who dislocate repeatedly and have failed conservative treatment are also surgical candidates.  Usually most surgeons will use 3 dislocations as an indication for recommending surgical treatment.  More recent data from West Point Military Academy aggressively treated cadets following the initial dislocation with surgical treatment because of the extremely high likelihood of recurrences with nonsurgical treatment.  The results of surgical treatment demonstrated a low recurrence rate following surgical treatment.  Hence in some elite level athletes we may recommend surgical treatment after one dislocation if they are participating in activities that will have a high incidence of recurrent dislocation.


What does the surgery involve?


Surgical shoulder stabilization attempts to restore the anatomy of the torn structures that cause the upper arm bone to “pop out of socket”.  Repair focuses on tightening torn or loosened ligaments and/or repairing the labrum (the cartilaginous rim of the shoulder socket).  In most cases this can be performed arthroscopically and on an outpatient basis.  The goal of the procedure is to restore stability of the “ball and socket” without compromising range of motion or function.  Generally speaking, 4 months of physical therapy will be required before you can return to full sports activities.  The surgical outcome is favorable in over 90% of these cases.


How long does the surgical treatment take?


The surgical procedure usually takes between 1.5 and 2 hours to perform.


Will I have to stay in the hospital overnight?


No!  We perform shoulder stabilization procedures on an outpatient basis.


Will I be in a sling or brace after surgery?


Yes!  A shoulder immobilizer is worn generally for 3 weeks after surgery


What kind of anesthesia is used?


Patients usually have a “general anesthesia” which may be supplemented with a scalene (nerve) block.  The scalene block “numbs” up the arm for 8-12 hours postoperatively.


Can all shoulder instability procedures be performed arthroscopically?


Most but not all procedures are performed arthroscopically.  Your surgical consent form will mention “arthroscopic and possible open stabilization”.  Sometimes intraoperative findings will dictate whether we have to proceed at that time with an open incision.


What are some of the complications that can occur with shoulder stabilization surgery?


The chance of infection, blood clots in the legs (thrombophlebitis), and blood clots in the lung (pulmonary emboli) are all less than 1%.  There is a chance that you could lose some motion…most studies show an average loss of external rotation of 5 degrees or less.  Rarely patients can have an exaggerated scar response and lose more motion secondary to shoulder stiffness.  Recurrent instability following shoulder instability procedures seems to vary in most contemporary studies between 5 and 10% with current techniques.