Instability of the Shoulder

By Gregg R. Foos, MD, FACS


Instability of the shoulder is a problem that can occur at any age but most commonly occurs in young athletes.  Instability of the shoulder can present as either a shoulder dislocation from a single traumatic event or as a result of loose shoulder ligaments with recurrent episodes of instability.  Often, laxity of the shoulder ligaments will not result in an actual dislocation of the shoulder but instead presents with pain, particularly during the course of overhead athletic activities such as throwing.  Advances in orthopaedics have been made for both diagnosis and treatment for each of these disorders.

An understanding of the anatomy of the shoulder helps explain the different types of instability that can occur.  A shoulder joint is likened to a golf ball sitting on a tee.  There are ligaments and a joint capsule that surrounded the ball and the tee to help hold the ball in place.  This arrangement is advantageous with regard to shoulder range of motion as there is very little restriction in the movement of the ball in relation to the socket.  On the other hand, the hip joint is a ball sitting within a deep socket.  The socket provides stability but restricts the hip range of motion.  In the shoulder, the very shallow socket (tee) provides no restriction to shoulder range of motion resulting in the tremendous movement that we see in the shoulder in three different planes.  The sacrifice associated with this arrangement is stability of the joint.  Knocking a golf ball off the tee is not a difficult task.

The first type of instability of the shoulder occurs as a result of a traumatic event.  Typically, this involves an athlete who has had a normal shoulder that is acutely injured and dislocated.  This can occur from a blow to the shoulder or simply a fall on an outstretched arm.  The acute dislocation of the shoulder is a very painful event and, usually, the injured athlete requires emergent treatment.  X-rays generally reveal the direction of the dislocation and help guide the reduction of the shoulder.  Reducing the shoulder dislocation is considered an emergent procedure.  The quicker the shoulder can be placed back into the socket the less likely there will be long-term damage to the shoulder.  Additionally, once the shoulder is placed back into its normal position, the patient’s pain is markedly reduced.  Initial treatment following the reduction requires placement of a sling as well as pain medication.  Typically, treatment will include three to four weeks of immobilization in a sling followed by a rehabilitation program to regain shoulder range of motion and strength.  Return to sports activities may take three to four months or possibly longer in cases where repetitive overhead use is required.

Research regarding young patients with acute shoulder dislocation has shown that the majority of these patients are at risk for recurrent instability.  In a young athletic population, the risk of recurrent episodes of shoulder dislocation can be as high as 80%.  For this reason, more and more orthopaedic surgeons are offering patients surgical treatment in the early stages of these injuries to help prevent recurrent episodes of dislocation.

In the case of traumatic instability, the capsule and ligaments that hold the shoulder in place must be torn.  When the shoulder is placed back into the socket, the ligaments remain torn and do not heal in their normal position.  This is what is known as a “Bankhart lesion”.  The result is that the restraining ligaments and capsule heal in an elongated position.  Future events can occur whereby the shoulder is no longer held firmly within the socket.  This can result in subluxation whereby the ball slips out of the socket but returns without having to be physically placed back in the socket.  Alternatively, the shoulder can recurrently dislocate where each recurrent event requires a trip to the emergency department to reduce the patient’s shoulder back into place.

Classic teaching suggested that the patient who dislocated the shoulder three times has earned the right to a surgical procedure.  Because of the known high recurrence rate in young athletes as well as improved surgical techniques, many surgeons are now considering initial operative intervention to help prevent these recurrent episodes of instability.

A second type of instability occurs to the shoulder that is not associated with a single traumatic event.  These patients have capsular laxity.  Every patient has a varying amount of normal shoulder stability.  Whereas some patients have very tight shoulder ligaments and capsules, other patients are born with loose ligaments and capsules.  These patients typically have increased shoulder range of motion in several different directions.  The shoulder laxity is advantageous for many sports including throwing as well as swimming. These sports, which require repetitive overhead use, can also result in gradual stretching of the joint capsule over time.  The problem arises when we cross the threshold between having a loose shoulder and an unstable shoulder.  When the shoulder ligaments and capsule are stretched beyond the point where they can hold the shoulder, this results in subluxation and dislocation.  This can cause pain, particularly when the arm is place in the overhead position as in throwing or serving in tennis.  In more advanced cases, actual dislocation of the shoulder can occur in one or more directions.

Classical surgical treatment for shoulder instability involved “open shoulder surgery” performed through large incisions.  The goal of the surgery was to tighten or repair the stretched or torn ligament and joint capsule.  In order to gain access to the shoulder, the rotator cuff muscles needed to be divided, which led to increases pain and post-operative stiffness.  More recent advances in orthopaedic surgery allow the surgical procedure to be performed through an arthroscopic approach.  This usually involves several small incisions whereby a camera and instruments are passed into the shoulder through cannulas.  The rotator cuff muscle and tendon do not need to be violated with this approach, which leads to decreased post-operative pain and stiffness.

The two types of instability listed above can both be managed with an arthroscopic approach.  First, in the case of traumatic instability where the ligaments are torn from the socket, the arthroscope allows visualization of the torn ligaments and capsule with suturing of the torn tissues directly to the bony socket.  Suture anchors are small implants that are introduced into the bony socket allowing the ligaments to be sutured directly to their normal position.  In the second type of instability whereby patients have capsular laxity, the customary arthroscopic approach is to tighten these ligaments with sutures that create a pleat within the shoulder ligaments and capsule thereby tightening them.  The capsule is sequentially tightened until the shoulder is stable.

As we have developed a better understanding of the different types of shoulder instabilities, as well as advanced arthroscopic surgical techniques, we have seen improved results regarding management of the unstable shoulder.  The results of arthroscopic surgery for shoulder instability are now comparable to those achieved through an open approach.  The advantages of the smaller incisions are decreased post-operative pain and stiffness, which have made the procedure more attractive to many patients.  Additionally, this improves our ability to return patients safely and quickly to the overhead sports and activities that they enjoy.