Shoulder Instability
The shoulder has the greatest motion of any joint in our body. The price it pays for this great mobility is that it is also the joint most at risk of dislocation. There are different degrees of instability. When the shoulder just partially comes out of socket but not completely, this is termed subluxation. When it completely comes out of socket this is termed a dislocation. There are also many causes of shoulder instability. The most common cause is trauma where the ball is forcefully pulled out of socket requiring eventual reduction. This can follow a fall or a direct blow to the arm when it is in a throwing position. Other causes, however, can be simply related to being overly flexible or “double-jointed”. The medical term coined for this is “multi-directional instability” and is frequently seen in teenage girls. In these individuals, the capsular tissue that surrounds the joint is hyper-elastic providing extra “play” to the ball and socket in all planes of motion (front, back, inferior). These patients are routinely treated differently than those sustaining a traumatic onset to their instability.
Traumatic dislocations often times can result in tearing of the bumper of tissue called the labrum that helps provide stability to the shoulder or even an impaction injury to the humeral head called a Hill-Sach’s lesion. The incidence of such associated injuries has ranged from 50-96% in several recent publications.1,2,3 The presence of these associated injuries likely contributes to the risk of recurrent dislocation. Dr. Burkhart and De Beer found that in patients with a bone defect (Hill Sach’s), 67% had a recurrent dislocation as compared to a 4% reoccurrence in those without.4 Finally, the younger you are the higher the probability of sustaining a recurrent dislocation. In fact, patients less than 25 years old have an 85% probability of recurrent instability within five years of the initial injury.5 An MRI may be advised following a dislocation, therefore, to see if any of these defects are evident which may require surgical repair to reduce the risk of recurrent injury.
Classification:
Shoulder dislocations are classified according to the direction that the ball dislocates. The most frequent dislocation is anterior. This will occur when the arm is typically in an abducted and externally rotated position (throwing motion) and is frequently seen in contact sports such as football. Ninety percent of dislocations occur anteriorly. Less frequent directions of dislocations are posteriorly and inferiorly. Posterior dislocations account for less than 10% of dislocations and are also seen in contact sports, particularly football lineman and hockey players where the arm is pushed directly backward.
Symptoms:
Traumatic dislocations are painful and usually fairly obvious. In an anterior dislocation a sulcus will be seen behind the shoulder and the ball will be palpable in the front. The arm is typically “stuck” in position and will not move without pain. The arm may swell and with prolonged dislocation the nerves around the shoulder can get stretched and irritated causing the fingers to tingle or even go to sleep. True dislocations are treated urgently and usually require conscious sedation (anesthesia) to relax the patient and put their shoulder back into socket.
Treatment:
The treatment of shoulder instability is often dictated by the type of instability and the other associated injuries that may factor into recurrent dislocations (i.e. labral tears, Hill Sach’s defects). In patients that are unstable simply as a result of multi-directional instability (again, where the tissue is extra lax), this is generally treated with therapy, therapy and then more therapy. Surgery is only reserved for the patient that fails to respond to conservative management after 6-12 months. This condition is routinely seen in teenage females and, fortunately, as they age, their shoulder has a tendency to “tighten” up and essentially they grow out of the problem. Exercises intended to build the muscles that surround the shoulder can help to better stabilize the joint.
In patients with traumatic dislocations resulting in recurrent instability, further imaging to include an MRI is often necessary. Dye may be injected into the shoulder at your physician’s request to allow better detail of the intra-articular structures. If a labral tear is present, the risk of recurrent instability is dramatically increased. There has been some debatable evidence to suggest that immediate immobilization in a position of external rotation may help to heal this tissue, however, the splint needs to be placed within the first 72 hours which is often outside the window of when the patient may be seen in the office. The splint is also quite cumbersome and patient compliance is routinely poor. Should a labral tear be confirmed, surgery will often be advised as the tissue does not heal itself. This previously was done with open techniques, however, arthroscopic labral repairs have been shown to be equivocal in regards to outcomes with success rates (graded based on recurrent dislocation) between 84-96%.7, 8
References:
- Warren RF. Subluxation of the shoulder in athletes. Clin Sports Med.1983;2:339-54.
- Mizuno K, Hirohata K. Diagnosis of recurrent traumatic anterior subluxation of the shoulder. Clin Orthop Relat Res. 1983;179:160-7.
- Owens BD, et al. Pathoanatomy of First-Time, Traumatic, Anterior Glenohumeral Subluxation Events. JBJS. 2010; 92(A); 1605-12.
- Burkhart SS, De Beer JF. Traumatic glenohumeral bone defects and their relationship to failure of arthroscopic Bankart repairs: significance of the inverted-pear glenoid and the humeral engaging Hill-Sachs lesion. Arthroscopy 2000; 16(7): 677-94.
- Robinson M, et al. Functional Outcome and Risk of Recurrent Instability After Primary Traumatic Anterior Shoulder Dislocation in Young Patients. JBJS 2006;88(11): 2326-36.
- Bottoni CR, et al. Arthroscopic versus open shoulder stabilization for recurrent anterior instability: a prospective randomized clinical trial. Am J Sports Med 2006; 34(11):1730-7.
- Cole BJ, et al. Comparison of arthroscopic and open anterior shoulder stabilization. JBJS 2000; 82: 1108-14.
- Kim SH, Ha KI, Kim YM. Arthroscopic revision Bankart repair: a prospective outcome study. Arthroscopy 2002;18:469-82.
