I. Instability of the Shoulder
A. Overview/terminology
1. Instability is a pathologic state in which excessive translation leads to pain or frank dislocation.
2. Laxity is a physiologic term that refers to the passive translation of the humeral head on the glenoid.
B. Classification
1. Instability should be viewed as a spectrum of pathology from unidirectional traumatic instability to atraumatic multidirectional instability.
2. Classification of the various types of instability can help clarify treatment plans.
a. Traumatic anterior instability—Forced abduction/external rotation
b. Traumatic posterior instability—Results from a posteriorly directed force with the arm forward elevated and adducted (motor vehicle accident or pass blocking in football). A grand mal seizure or electrical shock can also produce a traumatic posterior dislocation.
c. Acquired/atraumatic instability—Subtle instability associated with activities that cause repetitive microtrauma to the capsular structures
d. Multidirectional instability—Symptomatic glenohumeral subluxation or dislocation in more than one direction. For treatment purposes, it is important to differentiate multidirectional instability by the primary direction of the instability.
*Augustus D. Mazzocca, MS, MD, or the department with which he is affiliated has received research or institutional support from Arthrex. Robert A. Arciero, MD, or the department with which he is affiliated has received research or institutional support from Arthrex, Mitek, and Smith & Nephew.
II. Anterior Instability
A. Epidemiology/overview
1. Incidence—The overall incidence of traumatic anterior shoulder instability in the general population is approximately 1.7% annually.
2. Recurrence rates—The patient's age is the most important risk factor for recurrence of anterior instability after an anterior shoulder dislocation occurs.
a. Recent published reports have noted a 90% chance of recurrent instability for patients younger than age 20 years, a 60% recurrence rate for patients aged 20 to 40 years, and a less than 10% recurrence rate for patients older than age 40 years.
b. Long-term studies with 10-year follow up showed a 66% risk of recurrent anterior instability for patients younger than age 22 years, a 56% risk for patients aged 23 to 29 years, and a 20% risk for patients aged 30 to 40 years.
B. Pathoanatomy
1. Glenohumeral stability is dependent on active and passive restraints.
2. The labrum is a cartilaginous ring that deepens the glenoid fossa and serves as an attachment for capsuloligamentous structures.
3. The inferior glenohumeral ligament (IGHL) is the main restraint to anterior translation of the humeral head in the abducted, externally rotated arm position.
4. The rotator cuff muscles are the main active components of joint stability.
5. Anterior shoulder dislocation is typically secondary to a traumatic event that leads to excessive abduction and external rotation.
6. A Bankart lesion (detachment of the anteroinferior labrum and IGHL complex) (
Figure 1) is an important pathoanatomic finding that may be present in 90% of all traumatic glenohumeral dislocations.
[Figure 1. Arthroscopic view of a Bankart lesion (arrow) of the inferior capsulolabral complex. G = glenoid, L = labrum.]
[
Figure 2. Arthroscopic view of an ALPSA lesion. G = glenoid, L = labrum.]
[
Figure 3. MRI showing a HAGL lesion. The arrow indicates extravasated contrast material.]
[
Figure 4. CT scan showing a Hill-Sachs lesion (arrow). HH = humeral head.]
7. A torn labrum may heal to the medial aspect of the glenoid neck (anterior labroligamentous periosteal sleeve avulsion [ALPSA]) (Figure 2).
8. Associated injuries can include a humeral avulsion of the glenohumeral ligaments [HAGL] lesion (Figure 3).
9. Incidence of associated injuries
a. In patients older than age 40 years, the incidence of rotator cuff tears associated with an anterior shoulder dislocation is 30%.
b. In patients older than age 60 years, the incidence of rotator cuff tears associated with shoulder dislocation increases to 80%.
10. Greater tuberosity fractures are common in patients older than age 50 years.
11. Axillary nerve injury can occur in approximately 5% of anterior shoulder dislocations.
12. Bone deficiency associated with instability—Failure to recognize significant bony defects or bone loss can lead to failed surgical stabilization.
a. Humeral bone deficiencies—The Hill-Sachs lesion (Figure 4) is a common impression fracture
[
Figure 5. Normal and abnormal configurations of the glenoid. A, The normal shape of the glenoid is that of a pear, larger below than above. B, A bony Bankart lesion can create an inverted-pear configuration. C, A compression Bankart lesion can also create an inverted-pear configuration.]
that is caused by the humeral head impacting on the anterior glenoid rim. Hill-Sachs lesions occur in 80% of anterior dislocations.
b. Glenoid bone deficiencies
i. Bankart fracture—Anteroinferior bone avulsion with labrum (Figures 5 and
6)
ii. In patients with recurrent anterior shoulder dislocations, the prevalence of anteroinferior glenoid bone defects is 49%.
C. Evaluation
1. Patient history (
Table 1)
2. Physical examination—Testing can assess shoulder instability in general.
a. Thumb or finger hyperextension can be tested to assess for generalized ligamentous laxity.
b. Load-and-shift—Anterior-to-posterior translation of the humerus
i. Grade 1+ (increased translation but no subluxation)
ii. Grade 2+ (humeral head subluxes over the glenoid rim but spontaneously reduces)
iii. Grade 3+ (humeral head locks over the glenoid rim)
c. Apprehension sign—The patient demonstrates apprehension with abduction and external rotation (supine position).
d. The relocation test—The patient demonstrates a decrease in apprehension with the application of posterior force on the shoulder in abduction and external rotation.
e. Sulcus sign—A depression appears when inferior traction is applied to the arm at the side.
[Figure 6. Glenoid bone loss shortens the "safe arc" through which the glenoid can resist axial forces.]
f. Posterior apprehension sign—The patient demonstrates apprehension with internal rotation, flexion, and adduction of the arm.
3. Imaging
a. Radiographs
i. Shoulder AP, scapular AP, and axillary views are standard and should be obtained.
ii. Other helpful views include the West Point view (glenoid bone loss) and the Stryker notch view (Hill-Sachs lesion).
b. CT—Useful for detailed evaluation of bony injuries (
Figure 7)
c. MRI
i. Useful for soft-tissue detail, labral lesions, HAGL lesions, and capsular tears
ii. Intra-articular contrast increases sensitivity for soft-tissue injuries (labral tears and superior labrum anterior-to-posterior [SLAP] tears).
D. Treatment (
Figure 8)
1. Nonsurgical
|
a. |
Nonsurgical management is reasonable for |
[Table 1. Key Questions for Identifying Patients With Traumatic Anterior Shoulder Instability]
[Figure 7. Three-dimensional CT scan showing bone loss in the anteroinferior glenoid fossa (arrow).]
|
most patients with an initial uncomplicated anterior shoulder dislocation. |
|
|
b. |
Immobilization of the shoulder in external rotation may reduce a Bankart lesion to its anatomic origin. |
|
c. |
A brief period of immobilization is followed by range-of-motion exercises and rotator cuff and periscapular strengthening. |
|
d. |
A brace or harness to limit external rotation may help in-season athletes return to activity. |
2. Surgical
a. Indications
i. Failure of nonsurgical management and recurrent episodes of anterior shoulder instability warrant surgical intervention.
ii. Patients younger than age 25 years who engage in athletics or other high-demand activities may benefit from immediate arthroscopic Bankart repair.
iii. Patients with notable bone injuries or rotator cuff tears require immediate surgical intervention.
b. Contraindications
i. Surgery is contraindicated for patients with volitional instability and medical comorbidities.
ii. Contraindications for arthroscopic stabilization
(a) Engaging Hill-Sachs lesions—If the Hill-Sachs lesion is large enough, positioning
[Figure 8. Algorithm for the management of anterior shoulder instability. HAGL = humeral avulsion of the glenohumeral ligaments; ROM = range of motion; RTP = return to play.]
[
Figure 9. Completed arthroscopic Bankart repair with restored labral bumper. L = labrum, G = glenoid.]
the arm in abduction and external rotation allows the shoulder to dislocate with the anterior glenoid falling into or "engaging" the humeral defect.
(b) Bony deficiencies involving >20% of the anteroinferior glenoid (the inverted pear)
3. Surgical procedures
a. Goals are to repair the Bankart lesion and re-tension the anterior capsulolabral complex (Figure 9).
b. Randomized studies show equivalent results with open and arthroscopic techniques.
c. The open Bankart procedure with capsulorrhaphy is an extremely reliable procedure with very high patient satisfaction indices and recurrence rates of approximately 5% to 10%.
d. Bony deficiencies involving >20% of the anteroinferior glenoid require procedures such as open reduction and internal fixation of acute fractures, structural bone grafting, and coracoid transfer procedures (Bristow-Latarjet).
e. Surgical options for engaging Hill-Sachs lesions include allograft reconstruction to restore the humeral surface, arthroplasty, and rotational osteotomy (still under investigation).
f. Thermal capsulorraphy has fallen out of favor as a treatment for any type of shoulder instability.
E. Surgical complications
1. Recurrence
a. After arthroscopic techniques: 4% to 15%
b. After open surgical techniques: 5% to 10%
2. Stiffness, overtightening
3. Subscapularis failure can occur with open surgical techniques
4. Anchor pull-out
5. Injury to the axillary nerve
F. Surgical pearls and pitfalls
1. Rule out concomitant rotator cuff injury.
2. Failure to anatomically reconstruct anteroinferior labrum of the IGHL
3. Failure to recognize bony defects
4. Inadequate capsular shift to re-tension the IGHL
II. Posterior Instability
A. Epidemiology/overview
1. Posterior shoulder instability is much less common than anterior instability, accounting for 2% to 5% of all unstable shoulders.
2. Approximately half of presenting cases are caused by traumatic injury.
3. Posterior shoulder dislocation can occur after a seizure or electrical shock.
4. Up to 50% of traumatic posterior shoulder dislocations go undiagnosed when patients are examined in hospital emergency departments.
B. Pathoanatomy
1. The primary stabilizers of the posterior shoulder are the superior glenohumeral ligament, the coracohumeral ligament, and the posterior portion of the IGHL.
2. The labrum deepens the glenoid and serves as a static restraint to posterior humeral head translation.
3. Repetitive episodes of subluxation may produce a marginal crack or erosion of the posterior labrum, a labral tear, and an incomplete and/or concealed avulsion of the posterior labrum.
4. Posterior shoulder dislocations that do not readily reduce are associated with humeral impression fractures (reverse Hill-Sachs).
5. Less common causes of posterior shoulder instability include retroversion or hypoplasia of the glenoid.
C. Evaluation
1. History
a. A history of trauma with the arm in the flexed, adducted, and internally rotated position may be the inciting event.
b. In patients with undiagnosed dislocations, the posterior shoulder is locked in an internally rotated position.
c. Voluntary dislocation of the shoulder must be ruled out before surgical repair is considered.
2. Physical examination
a. A patient with an acute or undiagnosed posterior dislocation may have a prominent posterior shoulder and anterior coracoid and a limited ability to rotate the shoulder externally.
[
Figure 10. Posterior stress test. A posterior force is applied through the humerus. The test is positive if there is palpable crepitus or subluxation. Pain is often elicited, but this is not as specific a finding.]
b. Posterior instability may lead to compensatory scapular winging.
c. Specialized tests to assess posterior stability
i. Posterior stress test (Figure 10)
ii. Jerk test (
Figure 11)
D. Treatment
1. Nonsurgical
a. Nonsurgical treatment should always be attempted first.
b. The arm should be immobilized in neutral rotation with elbow at the side. A short period of immobilization is followed by rotator cuff strengthening and periscapular stabilization.
2. Surgical
a. Indications—Surgical intervention is indicated for patients who have symptoms that interfere with daily or sports activities, and for patients in whom nonsurgical treatment fails.
b. Contraindications—Surgery is contraindicated for voluntary dislocators.
3. Surgical procedures
a. Soft-tissue procedures
i. Open or arthroscopic labral repair and capsular shift
ii. Some authors recommend plication of the rotator interval as part of an arthroscopic procedure (controversial).
b. Procedures for engaging reverse Hill-Sachs lesions
i. Structural bone graft to humeral head
[Figure 11. Jerk test. A, A posterior force is applied along the axis of the humerus with the arm in forward flexion and internal rotation. This will cause the humeral head to subluxate posteriorly out of the glenoid socket. B, As the arm is brought into extension, a clunk will be felt as the humerus reduces into the glenoid cavity.]
ii. McLaughlin procedure: Transfer of lesser tuberosity into the defect
E. Surgical complications
1. Recurrence is the most common complication. Rates range from 7% to 50%.
2. Generalized stiffness or adhesive capsulitis
3. Overtightening the posterior capsule can lead to anterior subluxation or coracoid impingement.
4. Axillary or suprascapular nerve injury
F. Surgical pearls and pitfalls
1. For arthroscopic posterior labral work, a high lateral portal is better than the standard posterior portal.
2. For arthroscopic stabilization, the lateral decubitus position provides increased visualization.
G. Rehabilitation
1. Postoperatively, the shoulder should be placed in a rigid immobilizer with the arm abducted to 30° and in neutral rotation. The elbow should be posterior to the plane of the body to limit stress on the repair.
2. After a short period of immobilization, range-of-motion and strengthening exercises should begin.
3. The patient may return to full heavy labor or contact sports 6 months after surgery.
III. Multidirectional Instability
A. Epidemiology/overview
1. Multidirectional instability (MDI) has variable presentations and is difficult to quantify.
2. It is characterized by global laxity (anterior, posterior, and inferior) with reproducible symptoms inferiorly and in at least one other direction.
3. Incidence—MDI peaks in the second and third decades of life.
B. Pathoanatomy
1. The two classic lesions of MDI are a patulous inferior capsule (which contains the anterior and posterior bands of the IGHL) (
Figure 12) and a functional deficiency of the rotator interval.
2. Patients often have generalized ligamentous laxity.
3. Although patients with classic MDI do not have labral pathology, repeated subluxations or a traumatic event may lead to a Bankart lesion or a bony erosion of the glenoid.
C. Evaluation
1. History
[Figure 12. Arthroscopic view of a patulous inferior capsule in MDI. CAP = capsule, G = glenoid.]
a. Symptoms include pain, weakness, paresthesia, popping or clicking of the shoulder, instability of the shoulder during sleep, difficulty with throwing, and discomfort in the shoulder when carrying objects.
b. Differential diagnoses include unidirectional instability of the shoulder, cervical disease, brachial plexitis, and thoracic outlet syndrome.
c. Trauma superimposed upon intrinsic laxity may lead to pathologic instability of the shoulder.
2. Physical examination
a. To assess for generalized ligamentous laxity, observe for hyperextension of the elbows, the ability to abduct the thumb to reach the forearm, and genu recurvatum.
b. Tests
i. The sulcus sign assesses the rotator interval.
ii. Additional tests described previously (see section II, Anterior Instability: Evaluation/Physical examination)
c. Rotator cuff tendinitis or impingement in a young individual (age <20 years) should raise suspicion for MDI.
D. Treatment
1. Nonsurgical
a. A physical therapy regimen that includes rotator cuff strengthening and a focus on scapular kinematics should be the first line of treatment for at least 3 to 6 months after injury.
b. A complete nonsurgical treatment program for MDI should include scapular kinematics and proprioceptive training.
2. Surgical
a. Indications
i. Pain and instability that interferes with daily or sports activities
ii. Pain and instability that does not respond to nonsurgical treatment
b. Contraindications
i. Surgery is contraindicated for voluntary dislocators.
ii. Nonsurgical treatment options should be maximized before considering surgery.
3. Surgical procedures
a. Arthroscopic—Pancapsular plication with or without tightening of the rotator interval. If labral pathology is encountered, anterior or posterior Bankart repair is indicated. To avoid asymmetric tightening, capsulorraphy should address the inferior redundancy in a balanced fashion.
b. Open—Anteroinferior capsular shift
E. Complications
1. Recurrence of MDI
2. Axillary nerve injury
3. Stiffness and loss of motion (rare)
4. Subscapularis insufficiency (after open procedure)
F. Rehabilitation
1. Postoperative immobilization through the use of a sling or rigid arthrosis for 4 to 6 weeks (may vary)
2. Minor activities of daily living may be allowed 6 to 10 weeks after surgery, with abduction and external rotation of the shoulder limited to 45°.
3. Gradual range-of-motion exercises should begin 10 to 16 weeks after surgery.
4. Rotator cuff and scapular strengthening may begin approximately 16 weeks after surgery.
5. The patient may resume sports activities when normal strength and motion are achieved, but contact sports should be avoided for approximately 10 months after surgery.
IV. Chronic Dislocations
A. Epidemiology/overview
1. Posterior dislocations of the shoulder go undiagnosed more often than anterior dislocations; some studies suggest that as many as 50% of posterior dislocations may not be recognized.
2. Posterior dislocations of the shoulder that result from a seizure are often missed during the initial physical examination.
[
Figure 13. Radiograph showing the classic "light bulb" sign, which is consistent with the internal rotation contracture of a posterior dislocation.]
3. Undiagnosed dislocations of the shoulder are often associated with fractures of the glenoid or humeral head.
B. Pathoanatomy
1. Chronic anterior dislocations are commonly associated with Bankart fractures of glenoid or Hill-Sachs lesions of the humeral head.
2. Chronic posterior dislocations are commonly associated with reverse Hill-Sachs lesions.
C. Evaluation
1. Physical examination
a. The patient with a chronic anterior dislocation may present with a prominent anterior shoulder.
b. The patient with a chronic posterior dislocation may present with anterior flattening and a prominent posterior shoulder locked in an internally rotated position.
2. Imaging
a. A thorough radiographic evaluation can help prevent missed signs and symptoms of a dislocated shoulder.
b. The classic light bulb sign may indicate a posterior dislocation (Figure 13).
c. A preoperative CT scan of the dislocated shoulder is mandatory to rule out bony defects of the glenoid and the humeral head.
d. MRI may be helpful in evaluating the integrity of the rotator cuff.
D. Treatment
1. Nonsurgical—"Skillful neglect" (ie, nonsurgical management) is reserved for the elderly, debilitated patient who has limited functional deficits or potentially high surgical morbidity/mortality.
2. Surgical
a. Closed treatment—A closed reduction may be attempted up to 3 weeks after initial injury, although this time frame is arbitrary.
b. Open procedures
i. Procedures for a chronic anterior dislocation include transfer of the greater tuberosity into the defect, allograft, resurfacing arthroplasty, hemiarthroplasty, or total shoulder arthroplasty.
ii. Procedures for a large (>30%) defect of the glenoid involve augmentation of the glenoid with a bone graft or bone transfer.
iii. Procedures for a chronic posterior shoulder dislocation include the McLaughlin procedure (transfer of the lesser tuberosity into the defect) and hemiarthroplasty, resurfacing arthroplasty, or total shoulder arthroplasty.
Top Testing Facts
Anterior Instability
1. The patient's age is the most important predictor of recurrent anterior shoulder dislocation after initial injury. Younger patients (age <20 years) have a much higher recurrence rate.
2. Capsulolabral avulsion (Bankart), capsular redundancy, and bony defects of the humeral/glenoid head are the main pathoanatomic components.
3. Failure to recognize significant bony defects or bone loss can lead to failed surgical stabilization.
4. Surgical goals are to repair the Bankart lesion and re-tension the anterior capsulolabral complex.
Posterior Instability
1. Athletic trauma with the arm in a flexed, adducted position can produce a posterior labral tear (reverse Bankart) and injury to the posterior glenoid.
2. Specialized tests to assess posterior shoulder stability include the posterior stress test and the jerk test.
3. Nonsurgical management should always be attempted first.
4. Surgery is contraindicated for voluntary dislocators.
5. An engaging reverse Hill-Sachs lesion can be treated with a structural bone graft to the humeral head or with the McLaughlin procedure.
Multidirectional Instability
1. The main pathoanatomic features of MDI are a patulous inferior capsule and a functional deficiency of the rotator interval.
2. The presentation of MDI is highly variable. Symptoms include pain, weakness, paresthesia, popping or clicking of the shoulder, instability of the shoulder during sleep, difficulty with throwing, and discomfort when carrying objects.
3. A complete nonsurgical treatment program for MDI should include scapular kinematics and proprioceptive training.
4. To avoid asymmetric tightening, capsulorraphy should address the inferior redundancy in a balanced fashion.
Chronic Dislocations
1. Posterior dislocations of the shoulder that result from a seizure are often missed during the initial physical examination.
2. A thorough radiographic evaluation can help prevent missed signs and symptoms of a dislocated shoulder.
3. A preoperative CT scan of the dislocated shoulder is mandatory, to rule out bony defects of the glenoid and the humeral head.
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