Anterior Shoulder Instability

Abstract

Shoulder instability is a common problem that involves excessive translation of the humerus over the glenoid surface, which is normally prevented by both static and dynamic stabilizers. Significant trauma or external rotation with abduction, such as in overhead throwing athletes, can cause instability, subluxation, or dislocation. Bony lesions such as Bankart and Hill-Sachs lesions are associated with shoulder dislocations, and larger bony lesions contribute to recurrent dislocations and instability. Rates of instability after primary dislocation vary from 17% to 100%, and are higher in men and patients younger than 20 years old. Important clinical maneuvers include the apprehension test, Jobe’s relocation test, and the load-and-shift test. Radiographs are helpful to identify bony lesions. Differential diagnosis includes rotator cuff tear, labral tear, inflammatory or infectious arthritis, or referred pain. Conservative management with sling immobilization and physical rehabilitation is best for primary dislocations in patients older than 20 and non-elite athletes. Surgical management options include arthroscopic and open approaches. After arthroscopic repair, better functional outcomes were found in patients over 24 years old and with fewer preoperative dislocations. Recurrent instability is more common for patients who are younger, have bony lesions, have significant concomitant ligamentous or labral pathology, or are treated conservatively and return in-season. Return-to-play timing ranges from weeks to months after rehabilitation, and patients should have little or no pain and nearly normal range of motion and functional ability.

Keywords

shoulder, instability, dislocation, subluxation, Hill-Sachs, Bankart

ICD-10-CM Codes

M25.31X	Instability of shoulder joint
M25.3	Other instability of joint
S43.01X	Anterior subluxation and dislocation of humerus/shoulder
S43.00X	Unspecified subluxation and dislocation of shoulder joint
S43.30X	Dislocation of shoulder girdle
M24.41X	Recurrent shoulder dislocation

Key Concepts

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Shoulder instability is defined as excessive translation of the humerus over the glenoid surface to the point that it is symptomatic.
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Both static (glenoid fossa, labrum, joint capsule, ligaments) and dynamic (rotator cuff, long head of the biceps muscle, deltoid muscle) stabilizers are needed to improve the stability of the glenohumeral joint, which is naturally shallow.
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The least stable position of the shoulder is abduction with external rotation, causing anterior subluxation or dislocation.
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Anterior dislocation causes traumatic instability, often with a Bankart lesion (avulsion of the anterior capsule–labral complex below the midline of the glenoid and may include a bony avulsion). Dislocation may also be associated with a Hill-Sachs lesion (injury to the posterolateral aspect of the humeral head).
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Bony lesions >20% of the articular surface may contribute to recurrent dislocations and instability.
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Comorbidities include capsular tearing or stretching, rotator cuff tears (primarily in older patients with primary dislocations), and axillary nerve injuries.
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Chronic, repetitive microinjury, as in the overhead throwing athlete, can result in acquired anterior instability from stretching of the joint capsule or recurrent micro-subluxation of the glenohumeral joint.
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Rates of anterior instability after a primary dislocation vary from 17% to 100%.
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Rates of instability are higher in men and patients younger than 20 years old. Instability decreases with age but may increase again in the elderly as a result of increasing rotator cuff problems.
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Instability can lead to recurrent dislocations.

History

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The diagnosis of anterior instability is primarily clinical and may not be frankly traumatic, but there may be history of joint laxity or prior dislocation or subluxation.
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The patient may complain of shoulder discomfort with contact and overhead activities, often without any restriction of range of motion.
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A history of Marfan syndrome or other hyperlaxity condition in the athlete or immediate family is important to document. However, this does not necessarily increase the risk of recurrent instability after surgical repair.

Physical Examination

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The physical examination should include inspection for any swelling or malformations, palpation for tenderness and regions of anesthesia in the axillary nerve distribution, active and passive range of motion, strength, and neurovascular testing, as well as specific tests to assess for instability.
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A decrease in mobility following an anterior dislocation is primarily from pain versus an anatomic restriction. The strength of the shoulder girdle and arm should be tested and any weaknesses noted.
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The apprehension test (see Video 28.1 in Chapter 28 ) is done with the patient supine or sitting with shoulder abducted and externally rotated to 90 degrees. Apprehension indicates a positive test, as pain can also be elicited with primary impingement.
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Jobe’s apprehension-relocation test (see Video 28.1 in Chapter 28 ) is done after a positive apprehension test. Posterior force is applied to the anterior humeral head, which alleviates the pain and/or apprehension.
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A load-and-shift test and a crank test have also been shown to predict labral tears, which are common in anterior instability.