Shoulder and Elbow cases posterior GH instability

A 19-year-old, collegiate offensive lineman presents to your clinic with vague shoulder pain that has been ongoing throughout his sophomore season. He managed to play out the season but was having significant discomfort during practice sessions and games. On examination, he has intact strength and range of motion. He

has a negative impingement sign and negative O’Brien’s test. His pain is reproduced with adduction, internal rotation and a posteriorly directed force.

What is the most likely diagnosis?

1. PASTA lesion

2. Rotator cuff tear

3. Multidirectional instability

4. Posterior instability

5. Bankart lesion

 

Discussion

The correct answer is (D). Offensive linemen are continuously subjected to posteriorly directed forces with their arms outstretched and adducted; this places them at an increased risk for developing posterior instability. The test in the question stem describes a jerk test which is helpful in making the diagnosis of posterior instability. While the other answer choices represent possible injuries in a young athlete, the question stem does not specifically support them.

Glenohumeral instability is estimated to occur with an incidence of 2% of these 2–5% represent cases of posterior instability. Similarly, only 4% of all shoulder dislocations are posterior dislocations. These may be classified as traumatic or atraumatic. The traumatic form is more common and is often caused by a single traumatic event, classically a seizure or electrocution; the atraumatic form is usually the result of multiple, smaller traumas, classically seen in an offensive lineman. Atraumatic instability should raise the suspicion for an underlying collagen disease or bony abnormality such as excessive glenoid retroversion.

It is important to understand the normal shoulder stabilizers when discussing posterior instability. These are classified as either static or dynamic stabilizers.

Static stabilizers include:

 

Bony congruency, glenoid version, and humeral version

 

The labrum increases the depth of the glenoid by 50% and increases its surface area and articulation with the humeral head

 

The glenohumeral ligaments act as stabilizers at the end range of motion.

 

 

The superior glenohumeral ligament (SGHL) and coracohumeral ligament resist posterior subluxation with the arm in flexion, adduction and internal rotation.

 

 

Tightening of the axillary pouch and the posterior band of the inferior glenohumeral ligament (IGHL) are the main restraint to posterior subluxation when the arm is abducted.

 

The posterior capsule is also a restraint, although it is the thinnest and weakest portion of the capsule at <1 mm thick.

 

The rotator interval and its constituents (subscapularis, supraspinatus, coracoid, biceps, and humerus) provide resistance to inferior and posterior instability in the adducted and externally rotated position.

Dynamic stabilizers include:

 

Rotator cuff (particularly the subscapularis), biceps, deltoid, serratus anterior, latissimus dorsi, trapezius, and the scapulothoracic complex

In posterior instability, some combination of these stabilizers are damaged or not fully functional.

It is important to obtain a thorough history from patients to appreciate their injury pattern and elicit provocative activities so as to characterize the primary direction of instability. Classically, in posterior instability, patients will have pain or apprehension when placed in adduction, flexion, and internal rotation (“at risk” position). On examination, patients generally show preserved range of motion and strength. Specific tests include the load and shift test, jerk test, and posterior stress test. The load and shift test is performed and graded in a manner similar to that described in cases 11–12 with the exception that the humeral head is being displaced posteriorly. The jerk test is performed with the patient seated. An axial force is applied to the arm in 90 degrees of abduction and internal rotation. The patient’s arm is horizontally adducted while an axial load is maintained, and a jerk is appreciated as the humeral head slides off the glenoid. This is usually painful. The posterior stress test or apprehension test describes a posteriorly directed force applied to the arm in the “at risk” position. This will elicit pain or a sensation of instability.

Imaging should include x-rays, which may demonstrate posterior glenoid bone loss or an impaction fracture on the anterior-superior humeral head (Fig. 2–38). CT images with 3D reconstructions can be very useful when assessing the extent of glenoid bone loss and evaluating glenoid and humeral version. Normal glenoid version is from −2 to −8 degrees of retroversion, and this may be increased in posterior instability. MRI can also be useful when assessing the posterior labrum (Fig. 2–39).

 

 

 

Figure 2–38 Radiographs showing a posterior shoulder dislocation.

 

 

 

 

 

Figure 2–39 MRI showing a posterior labrum tear.

 

Conservative treatment is often successful; it involves physical therapy with a focus on strengthening the dynamic stabilizers (particularly the posterior deltoid, periscapular muscles, and external rotators), activity modification, and biofeedback. This is successful 65% to 80% of the time. Surgical treatment involves arthroscopic or open posterior labral repair and poster-inferior capsular shift for cases with no bony abnormalities or defects. In cases of glenoid retroversion >20 degrees, an opening wedge osteotomy may be used. In cases of normal version with posterior

bone loss, bone grafting along the posterior glenoid rim may be necessary.

Additional Questions

An acute, posterior shoulder dislocation should be suspected in a patient with the shoulder locked in what position?

1. External rotation

2. Internal rotation

3. Abduction

4. Extension

5. Adduction

 

Discussion

The correct answer is (B). Posterior dislocations are significantly less common than anterior dislocations so one must maintain a high index of suspicion for these injuries. Posterior dislocations tend to occur during seizures and electrocution. Patients present with pain and a shoulder locked in internal rotation.

All of these are considered a static stabilizer of the shoulder except?

1. Labrum

2. IGHL

3. Coracohumeral ligament

4. Capsule

5. Supraspinatus

 

Discussion

The correct answer is (E). All of the above are shoulder stabilizers although only the supraspinatus is considered a dynamic stabilizer.

The superior glenohumeral ligament is responsible for resisting which of the following?

1. Posterior glenohumeral subluxation while the arm is in extension, adduction, and IR.

2. Anterior glenohumeral subluxation while the arm is in flexion, abduction, and ER.

3. Inferior glenohumeral subluxation while the arm is in flexion, adduction, and neutral rotation.

4. Anterior glenohumeral subluxation while the arm is in extension, adduction, and ER.

5. Posterior glenohumeral subluxation while the arm is in flexion, adduction, and IR.

Discussion

The correct answer is (E). In flexion, adduction, and internal rotation the posterior glenohumeral ligament is taut and acts like a sling preventing the humeral head from subluxing posteriorly. In posterior instability, this structure is often stretched or torn. The other answers are distractors.

A 30-year-old, basketball player presents to your clinic after an acute shoulder injury. He has significant pain and his shoulder is abducted at 130 degrees. He is unable to lower his arm.

Radiographs will most likely show that his glenohumeral joint has dislocated in what direction?

1. Posterior

2. Anterior

3. Inferior

4. Medial

5. Lateral

 

Discussion

The correct answer is (C). This patient has an inferior shoulder dislocation (luxatio erecta) as seen in Figure 2–40. This is a very rare type of dislocation, which represents 0.5% of all dislocations. It carries the greatest risk of having an associated neurovascular injury, with the axillary nerve being the most frequently injured structure. Patients present with the shoulder locked overhead in full abduction. Closed reduction is generally successful and a subsequent MRI may be needed to assess for soft tissue injuries.

 

 

 

Figure 2–40 Luxatio erecta.

 

Objectives: Did you learn...?

 

To recognize the clinical presentation and physical examination findings associated with posterior GH instability?

 

The different treatment options for this condition?

 

What the dynamic and static stabilizers of the shoulder are?