Clinical case: Dislocated shoulder

Last reviewed: February 22, 2022
Reading time: 13 minutes

In this article we describe a case of bilateral anterior shoulder dislocation following a seizure. Did you know that this type of post-seizure shoulder dislocation is actually very rare? Stick around to find out the reasons, as well as its mechanism, diagnostic procedure, and complicated management. You will also learn the respective anatomical considerations and potentially serious complications of an anterior shoulder dislocation.

Key facts
Anterior shoulder dislocation	It results from a direct blow to, or a fall on, an outstretched arm. The head of the humerus usually tears the inferior part of the joint capsule and the patient maintains the limb in a laterally rotated and slightly abducted position.
Complications of anterior shoulder dislocations	Axillary nerve damage; rupture of the anterior and posterior circumflex arteries
Rotator cuff	Muscles: Supraspinatus, Infraspinatus, Teres minor, Subscapularis Functions: Stabilization and rotation of the humerus Mnemonic: Rotator cuff SITS on the shoulder

After reviewing this case you should be able to describe the following:

The typical mechanism of an anterior shoulder dislocation. What nerve is most at risk in an anterior shoulder dislocation and how to test for its integrity?
The vascular supply of the humeral head. How this supply may be compromised resulting in avascular necrosis in an anterior humeral dislocation.
The components and actions of the rotator cuff group of muscles. The component that is most frequently involved in a rotator cuff tear.

This article is based on a case report published in the Journal "Case Reports in Surgery" in 2015, by Caroline C. Jadlowiec, Beata E. Lobel, Namita Akolkar, Michael D. Bourque, Thomas J. Devers, and David W. McFadden.

Contents

Case description
Anatomical and surgical considerations
Explanations to objectives
Sources

+ Show all

Case description

History

A 35-year-old male presented to the clinic with movement difficulty and pain in both shoulders 30 days after an episode of seizure. The patient had not been evaluated by a physician for the shoulder condition prior to the current visit (i.e., 30 days without treatment). The patient’s history did not reveal any cause for the seizure; that is, there was no history of head trauma, substance abuse/withdrawal or any pre-existing neurological condition. Further, the patient did not report any prior episodes of shoulder dislocation.

Physical exam

On evaluation, the patient complained of having decreased bilateral shoulder function and motion compared to before the event. The examination revealed that normal shoulder contour was lost (Figure 1), shoulder movement was restricted, especially abduction with external rotation, and pain was elicited with movement.

Figure 1. Photograph of a patient (not patient in case) with neglected bilateral anterior shoulder dislocation (three weeks). Note loss of normal shoulder smooth curvature (courtesy of: https://openi.nlm.nih.gov/detailedresult.php?img=PMC2596117_1757-1626-1-342-1&req=4).

Imaging and diagnosis

A clinical diagnosis of bilateral anterior shoulder dislocation was made. Distal motor, sensory and vascular functions were normal. Shoulder radiographs showed bilateral anterior shoulder dislocations with displaced greater tubercle fractures (Figure 2).

Figure 2. A: Right shoulder at the time of initial presentation; B:post-open reduction and surgical fixation of the greater tubercle. C: Left shoulder at the time of initial presentation; D: post-closed reduction with natural incomplete fusion of the greater tubercle.

Management and evolution

A closed reduction was done under general anesthesia on the left followed by three weeks of immobilization and intermittent physical therapy. Closed reduction of the right shoulder had been attempted but was not successful because the shoulder was “locked.” Thus, an open reduction was performed. However, even after complete capsular release, the humerus did not relocate because the greater tubercle was adhered to the underlying bone. The greater tubercle was then surgically freed, repositioned and fixed surgically after repositioning (Figure 2). This shoulder, however, still showed partial displacement of the greater tubercle.

At the three-week post-operative follow-up, the left side had full abduction, but the right, which had undergone the open procedure, had only pendular movements (Figure 3A).

Figure 3. A. Three weeks post-reduction. Left side shows full abduction. B. Three months post-reduction with both left and right sides showing nearly normal range of abduction.

At the end of 3 months, the side that had the closed reduction still had full abduction and no complaints of pain, and the side that had undergone the open reduction had 150-160 degrees range of motion (Figure 3B). At the three-month follow-up, radiographs showed union of greater tubercle (Figure 2).

Anatomical and surgical considerations

The glenohumeral joint is a relatively unstable joint because of the very shallow glenoid fossa and the large humeral head compared to the much more stable hip joint. However, the shoulder’s relative instability is associated with great mobility, whereas the stability of the hip joint results in a much smaller range of movements compared to the shoulder (Figure 4).

Figure 4. The articulation of the glenohumeral joint is between a very shallow socket (glenoid fossa of the scapula) and a large globular humeral head, resulting in a relatively unstable joint.

Ninety-five percent of all shoulder dislocations are anterior. However, bilateral dislocation is most commonly posterior and typically results from seizure or convulsion due to epilepsy, electric shock or other causes. Simultaneous bilateral anterior shoulder dislocation is very rare and usually results from trauma.

Figure 5. Cadaver image showing mainly the subscapularis muscle, which is part of the rotator cuff group and functions primarily as a medial rotator of the humerus.

Posterior dislocations associated with seizure occur because of contraction of the subscapularis muscle (medial rotator; Figure 5) overcomes that of the relatively weak teres minor, infraspinatus and the posterior fibers of the deltoid (lateral rotators; Figure 6&7), leading to powerful medial rotation and posterior subluxation.

Figure 6. Cadaver image showing many of the muscles that support the glenohumeral joint.

Isolated displaced greater tubercle fractures are often associated with anterior shoulder dislocations. The greater tubercle fragment detaches with its attached rotator cuff and is pulled superiorly by the supraspinatus, and posteriorly by the infraspinatus and teres minor muscles. Based on this analysis, it is difficult to explain why an episode of seizure would result in bilateral anterior shoulder dislocation. One possible explanation is that anterior dislocation with seizure may occur not during the muscle contractions, but from the trauma of the shoulders striking the floor when the patient falls (this could have been so in the case presented here but the patient could not recall falling).

In cases with an uncorrected fracture, the patient may have long-term instability and functional impairment. The locked shoulder in this patient, which prevented closed reduction on the left, can be caused by either soft tissue interposition, especially by the long head of the biceps brachii or subscapularis tendons), or, by a connective tissue block such as caused by a displaced glenoid labrum, a bony fragment from the glenoid rim or greater tubercle, or an impacted humeral head. In the case presented here, both soft tissue interposition caused by tissue and capsular contractures as well as a bony block due to greater tubercle fracture were observed during open reduction. Closed reduction of an untreated anterior shoulder dislocation can be performed only up to six weeks post-injury. After this period the risk of an iatrogenic fracture or neurovascular damage (e.g., avascular necrosis) is very high and operative procedures should be done.

Figure 7. Cadaver image depicting the axillary nerve and the surrounding muscles. This image clearly demonstrates how a humeral dislocation can stretch or tear the nerve as it traverses across the surgical neck of the humerus.

Explanations to objectives

Objectives

The typical mechanism of an anterior shoulder dislocation. What nerve is most at risk in an anterior shoulder dislocation and how to test for its integrity?
The vascular supply of the humeral head. How this supply may be compromised resulting in avascular necrosis in an anterior humeral dislocation.
The components and actions of the rotator cuff group of muscles. The component that is most frequently involved in a rotator cuff tear.

Mechanism of anterior shoulder dislocations

The vast majority of shoulder dislocations are anterior dislocations. In an anterior dislocation, the head of the humerus comes to rest inferior to the coracoid process of the scapula. Anterior dislocations typically result from a direct blow to, or a fall on, an outstretched arm. The head of the humerus usually tears the inferior part of the joint capsule because this region is the least protected part of the capsule; that is, there is no protection from the rotator cuff muscles. Only the long head of the triceps brachii is located inferiorly. The patient typically maintains the limb in a laterally rotated and slightly abducted position.

Damage to the axillary nerve (C5, C6) occurs in about 1/3 of anterior shoulder dislocations (Figure 7). Axillary nerve damage results in a weakened or paralyzed deltoid muscle. A patient with a complete rupture of the axillary nerve will have difficulty in abducting the arm from approximately 15° away from the body. The supraspinatus muscle initiates abduction from a completely adducted position. The axillary nerve has a cutaneous branch, the superior lateral cutaneous nerve of the arm. This branch, as its name implies, provides cutaneous innervation to the upper lateral arm. Thus testing for intact sensation in this region provides a very effective method of assessing the integrity of the axillary nerve.

Vascular supply of the humeral head

The head of the humerus received its blood supply from the anterior and posterior humeral circumflex arteries (Figure 8). The anterior circumflex artery travels deep to the long head of the biceps brachii and gives off an ascending branch, terminating as the arcuate artery, which penetrates the proximal humerus at the superior end of the bicipital groove, supplying both the lesser and greater tubercles. The posterior circumflex artery traverses around the posterior humeral surgical neck and terminates in small perforating branches that enter the humerus.

Figure 8. Cadaver photograph showing the origin of the right anterior and posterior humeral circumflex arteries from axillary artery. The two arteries loop around the surgical neck of the humerus and give off branches to supply the humeral head.

Rupture of these small arteries is rarely associated with simple anterior dislocation. Fracture of the greater tubercle increases the likelihood of avascular necrosis. Further, as indicated by this case, forced closed reduction, especially after the injury has been neglected increases the likelihood of avascular necrosis, presumably because of the development of adhesions (scar tissue) that contain the small blood vessels supplying the humeral head.

Components and actions of the rotator cuff

The rotator cuff is a group of four muscles that act primarily to rotate and stabilize the humerus. The four muscles are the supraspinatus, subscapularis, infraspinatus, and teres minor (Figures 5&6). The last two are lateral rotators; the subscapularis is a powerful medial rotator, and the supraspinatus is primarily an abductor of the arm (especially for the initial 15 degrees). The tendon of the supraspinatus is the most frequently torn of the four muscles and the term “rotator cuff tear” is usually meant to refer to a supraspinatus tear (Figure 9).

Figure 9. Coronal (approximate) T2 MRI images of the shoulder in a patient with a normal supraspinatus tendon (A) and a patient with a torn tendon (B). A supraspinatus tear is clinically synonymous with a “rotator cuff” tear. In a supraspinatus tear, the space formerly occupied by the tendon fills with fluid and thus become hyperintense in a T2 MRI. Images courtesy of Dr. Edward Weber.

Do you want to learn the rotator cuff muscles as easy as 'A, B, C'? Then use the following mnemonic!

Rotator cuff SITS on the shoulder

Supraspinatus
Infraspinatus
Teres minor
Subscapularis

Sources

All content published on Kenhub is reviewed by medical and anatomy experts. The information we provide is grounded on academic literature and peer-reviewed research. Kenhub does not provide medical advice. You can learn more about our content creation and review standards by reading our content quality guidelines.

Reference:

Upasani T, Bhatnagar A, Mehta S. Bilateral Neglected Anterior Shoulder Dislocation with Greater Tuberosity Fractures. Journal of Orthopaedic Case Reports 2016 April-June: 6(2) :Page 53-56.
Modified by Joel A. Vilensky PhD , Carlos A. Suárez-Quian PhD , Aykut Üren, MD.

Authors:

Joel A. Vilensky
Carlos A. Suárez-Quian
Aykut Üren

Layout:

Abdulmalek Albakkar
Adrian Rad

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