Tips on using this imaging technique for the emergency physician
A 28-year-old male presents to the ED with moderate to severe right shoulder pain. The patient states that he fell while playing football with his friends and has 10/10 pain in his right shoulder. He has no other injuries, and the neurovascular exam of the affected extremity is normal.
You perform a point-of-care ultrasound examination of the affected shoulder and clearly see an anterior glenohumeral dislocation. Intravenous analgesia is administered, and the patient is moved to an appropriate bed for closed reduction.
Shoulder (glenohumeral) dislocation is a common clinical presentation in the emergency department, comprising about 50 percent of all major joint dislocations.1 The large range of motion of the shoulder with minimal inferior tendinous support makes it prone to dislocation. Plain film radiography has been the imaging modality of choice for most clinicians when evaluating the ED patient with a suspected shoulder dislocation. Recent literature has demonstrated the superiority of point-of-care ultrasound (POCUS) in detecting both anterior and posterior shoulder dislocations, making it another rapidly evolving tool to improve accuracy, decrease error, and improve efficiency.2-4
Also, real-time ultrasonographic assessment of the articulation between the glenoid fossa and the humeral head is the ideal test when patients undergo procedural sedation for reduction. After shoulder manipulation, confirmation of the reduction attempt by plain film radiography incurs a delay that can prolong the length of stay. POCUS allows for a dynamic evaluation of the glenohumeral joint, immediately informing the clinician of a successful reduction or the need for additional shoulder manipulation without having to rely on plain film radiography.
The shoulder is composed of the bony articulation between the humeral head and the flat glenoid fossa that arises from the scapula. Anterior shoulder dislocations commonly occur when a large external force pushes the humeral head inferiorly below the glenoid fossa. Secondary contractions of the more powerful pectoralis and biceps muscles then pull the humeral head anteriorly, placing the humeral head just below the glenoid fossa or coracoid. Posterior shoulder dislocations are less common, representing only 2–5 percent of all dislocations, and are often missed during the initial patient presentation.5 Posterior shoulder dislocations are caused by forceful internal rotation and adduction of the shoulder, and classic mechanisms include seizures, trauma, and electrical shock. The posterior aspect of the shoulder is more stable than the anterior, making it less prone to dislocation. POCUS is an appealing and superior imaging alternative for the detection of both anterior and posterior dislocations.
POCUS allows for a dynamic evaluation of the glenohumeral joint, immediately informing the clinician of a successful reduction or the need for additional shoulder manipulation without having to rely on plain film radiography.
Ultrasound Evaluation of the Shoulder for Dislocation
We recommend the low-frequency (5-2 MHz) curvilinear transducer for this examination. While standing behind the affected shoulder, place the ultrasound system in front of the patient so that a clear view of the screen can be obtained (see Figure 1). If possible, ask the patient to adduct the humerus while supporting the elbow inferiorly for comfort. Palpate the scapular spine and follow it laterally toward the humerus (see also Figure 1). Place the probe parallel and just below the scapular spine with the probe indicator to the patient’s left, at the level of the glenoid. Adjust the depth until both the glenoid and humeral head are clearly seen (see Figure 2). The humeral head appears as a circular object located just lateral to the glenoid fossa. With the more common anterior dislocation, the humeral head will be deep on the screen (see Figure 3), while with a posterior dislocation, the humeral head will be closer to the probe and, therefore, more superficial on the screen (see Figure 4). If the shoulder is not dislocated, the patient should be able to internally and externally rotate the shoulder while adducted, and the rotational articulation between the humeral head and glenoid fossa will be seen clearly on the ultrasound screen.