Why Does It Feel Like
My Shoulder “Pops Out”?
By B. Rodney Comisar, MD
The shoulder joint is extremely mobile, with a tremendous range of motion; it is also the most frequently dislocated large joint in the body. The socket is relatively small and flat relative to the size of the ball; secondary support is provided to the joint by the cartilaginous labrum and the adjacent ligaments and joint capsule. The shoulder joint can dislocate if pulled out to the side, such as when making an arm tackle in football, as well as with a direct blow to the shoulder as occurs with a fall onto the side. A traumatic shoulder dislocation typically results in an anterior labral tear or Bankart lesion. The labrum is like a bumper that deepens the socket and also serves as an attachment site for the ligaments and joint capsule, particularly the critical anteroinferior glenohumeral ligament (AIGHL). The torn anterior labrum displaces from the glenoid socket and leads to laxity in the AIGHL and capsule; since the labrum doesn’t typically heal back in normal position, this disrupted anatomy and lax ligaments make it easier to dislocate the shoulder under similar circumstances.
The majority of the time the shoulder “pops out the front,” or anteriorly and inferiorly. Posterior shoulder dislocations are rare and occur primarily in association with seizures and motor vehicle accidents. In some cases, the shoulder will “pop back in,” or reduce, spontaneously or with gentle movement; in other instances, the dislocated shoulder remains “out” until reduced in an emergency room setting with the aid of sedation.
Shoulder instability can also be subtler, with partial instability, or subluxation, of the joint. This can occur anteriorly, posteriorly, or less commonly in both directions. Subluxations can be traumatic and may also include labral tearing, or can occur with lesser activities of daily living and maybe frequent. Posterior instability in athletes is often a result of repetitive microtrauma, classically in football lineman, with associated labral tearing. Patients with atraumatic instability often have generalized ligamentous and capsular laxity, placing them at increased risk of recurrence with and without surgery. Thus, atraumatic instability is generally treated with a more extended trial of conservative care including physical therapy. Atraumatic, multidirectional instability (MDI) is often bilateral and tends to affect younger patients.
Initial treatment involves:
- sling immobilization
- pain control
- the gradual recovery of range of motion and strength through home exercises and physical therapy if indicated.
Some patients may recover more quickly than others, particularly in the setting of recurrent, or repeat episodes of, instability. An appropriate evaluation includes a comprehensive history and physical exam; x-rays; and frequently an MRI. The MRI can prove helpful in confirming the extent of the injury include the presence of an anterior labral tear and any other injuries. Anterior labral tears have been demonstrated to occur between 67-100% of the time in the setting of a traumatic shoulder dislocation, with the highest rates in young athletes. Similarly, the presence of an anterior labral tear is associated with a high recurrence rate (approaching 100% in some series) of shoulder dislocation in young patients returning to contact or collision sports.
Shoulder dislocations certainly can be managed non-operatively, both in the short-term as well as over the long haul. Rehabilitation and bracing in many cases can allow for a return-to-sport, depending on the sport and the athlete’s position. Harnesses restrict extension, abduction, and external rotation of the arm, effectively the anterior dislocation position; accordingly, it is easier for an offensive lineman to play in a brace compared to a receiver or defensive back. Posterior shoulder instability, be it a subluxation or dislocation phenomena, is more challenging to brace effectively; it is difficult to participate in a sport while restricting forward flexion, adduction, & internal rotation. Scapular strengthening is a critical aspect of shoulder rehabilitation & strengthening in addition to rotator cuff exercises. A return to sport is permitted once the range of motion and strength to protect oneself have returned, understanding the associated risks of continued participation with labral pathology. Recurrent instability, if untreated over time, can lead to glenoid loss anteriorly, resulting in higher failure rates with arthroscopic treatment, resulting in the need for more complex, open surgical treatment. The development of premature shoulder arthritis is a risk with recurrent, neglected shoulder instability as well, occurring up to 25% of the time over 10 years in one series (Hovelius).
Surgery can be performed acutely for a labral tear, or immediately after the season to allow for suitable recovery time prior to the ensuing season. Surgical intervention is primarily arthroscopic, addressing labral and associated capsular & ligamentous pathology when indicated. More traditional open surgery may be indicated for revision surgery, with significant anterior glenoid bone loss, and in certain MDI cases with significant capsular laxity. The rehabilitation period may range from 4 months in certain athletes up to 6 months for collision sports and 8 months or more in the throwing athlete affected on the dominant side.