Abstract
Sternoclavicular joint instability, like glenohumeral joint instability, is classified by severity (subluxation vs dislocation), direction (anterior or posterior), and mechanism of injury (traumatic or atraumatic). Posterior sternoclavicular joint dislocations represent an orthopedic emergency because of the potential for damage to the mediastinal contents. Athletes with suspected sternoclavicular joint dislocation should undergo emergency transportation to the hospital for assessment and imaging, and computed tomography (CT) is required, with assessment of vasculature for posterior dislocations. Team physicians should be especially vigilant for this injury because it may be difficult to determine on the field whether the dislocation is anterior or posterior.
Keywords
anatomy, clinical concerns, epidemiology, imaging, mechanism of injury, sternoclavicular joint
Anatomy, Epidemiology, and Etiology
Although injuries to the sternoclavicular joint are relatively rare in athletes, team physicians must be vigilant for such injuries because they represent one of the few potentially life-threatening injuries in sports. The sternoclavicular joint is a saddle-shaped, diarthrodial joint, with minimal osseous constraint and inherent stability in the joint. Motion at this joint is important for shoulder function. With forward elevation of the arm, the clavicle elevates 35 degrees and rotates posteriorly 45 degrees. With extension of the arm, the clavicle elevates 35 degrees and moves posteriorly 35 degrees. Because it is a relatively unconstrained joint, the ligamentous structures about the sternoclavicular joint are critical in allowing motion while preserving stability. The ligamentous structures include the anterior capsule, the posterior capsule, the interclavicular ligament, and the costoclavicular ligament ( Fig. 16.1 ). Biomechanical studies have determined that the interclavicular ligament is important in keeping the clavicle elevated and the shoulder poised ( ). The anterior capsule and posterior capsules have been found to be the most important restraints to anterior displacement of the joint, and the posterior capsule to be the most important restraint to posterior displacement ( ).
The retrosternal contents, which lie immediately behind the sternoclavicular joint, include the subclavian and carotid arteries, the subclavian and jugular veins, and the trachea and esophagus. Because of these contents, when instability occurs in the posterior direction, the potential for life-threatening complications exists ( ).
Instability of the sternoclavicular joint is rare, with dislocations representing 3% of all shoulder dislocations ( ) and anterior dislocations occurring more frequently than posterior ( ).
As a result of the stout ligamentous structures that envelop this joint, dislocations require high-energy traumatic events to develop. Subluxations of the sternoclavicular joint may occur as a result of either a single traumatic event or the accumulation of repetitive microtraumatic events.
Classification, Assessment, and Imaging
Injuries to the sternoclavicular joint are classified by their severity and direction. As with the acromioclavicular joint, the capsule of the sternoclavicular joint may be sprained without displacement or instability. Subluxations of the joint may occur, and recurrent subluxation episodes may be symptomatic. Dislocations of the sternoclavicular joint may occur as well, and it is critically important to differentiate anterior dislocations of the clavicle head from posterior dislocations, because the latter may injure the retrosternal contents.
Subluxation of the Sternoclavicular Joint
In sports, subluxation of the sternoclavicular joint may manifest as a history of one traumatic event or of repetitive microtrauma (e.g., swimming backstroke). Patients with a history of repetitive microtrauma are predisposed to recurrent symptoms with their sport. The severity of symptoms is patient specific. Some patients find the subluxation events mildly symptomatic, whereas others will present with significant discomfort.
Patients without a history of trauma may present with the insidious onset of symptoms. These patients are usually younger than 25 years, are often female, and may have generalized ligamentous laxity or a collagen disorder. Instability is often bilateral and typically anterior. Alternatively, perimenopausal females are subject to the insidious onset of pain and swelling of the sternoclavicular joint, known as pseudosubluxation ( ), which is arthritic and not true instability.
Patients with subluxation of the joint sometimes have tenderness and can often demonstrate the subluxation of the joint by forward elevation of the arm ( 
). Imaging studies in these patients, including radiographs, CT, and magnetic resonance imaging (MRI), usually have normal findings. The dynamic nature of ultrasonography can detect subluxation of the sternoclavicular joint if it is not apparent on clinical examination.
- Video 16.1
Female patient with anterior atraumatic anterior subluxation.
Anterior Dislocations of the Sternoclavicular Joint
Anterior dislocations of the sternoclavicular joint are typically described as occurring from a blow to the front of the shoulder. The acromial end of the clavicle is pushed back, the clavicle pivots over the first rib, and the sternal portion of the clavicle is forced anteriorly ( Fig. 16.2 ). These injuries always occur with relatively high-energy trauma, which in sports could occur in a contact sport or fall from a height.
Patients with anterior dislocations of the clavicle head have immediate and significant pain. They often walk off the field with the arm dangling, like someone with an anterior dislocation of the shoulder. They have swelling and tenderness to palpation of the sternal end of the clavicle. Patients are not comfortable trying to elevate, abduct, or extend the arm. Glenohumeral rotation of the adducted arm is tolerated well and can distinguish this injury from a glenohumeral joint dislocation.
As a result of the patient’s discomfort and swelling in the joint, it can be extremely difficult to determine whether the dislocation is anterior or posterior, and imaging is usually required. Patients should be transported to the hospital immediately for imaging. Although a number of imaging options are available, computed tomography has been most helpful to assess sternoclavicular joint injuries. CT is the imaging technique of choice ( Fig. 16.3 ). It is important to know that the physis of the medial clavicle does not close in some people until age 25, so in younger individuals, injury to this region may represent a physeal injury and not a dislocation. In addition, fracture of the medial clavicle, although rare, may manifest like a dislocation of the sternoclavicular joint ( ).
Posterior Dislocations of the Sternoclavicular Joint
Posterior dislocations of the sternoclavicular joint always follow significant trauma and may occur as a result of direct trauma to the anterior chest wall or may occur from a blow to the back of the shoulder that allows the clavicle to pivot over the first rib, driving the head of the clavicle posteriorly ( Fig. 16.2 ). Clinically these injuries are difficult to distinguish from anterior dislocations. Patients have significant pain and do not want to move the arm. They may exhibit symptoms related to injury to the mediastinal structures, such as dysphagia, hoarseness, decreased pulses in the arm on the involved side, swelling of the arm due to a reduction in venous return, and symptoms of thoracic outlet syndrome.
Examination of such patients demonstrates swelling and tenderness at the sternoclavicular joint. Occasionally examination of the affected arm may demonstrate signs of vascular compression (decreased pulses, swelling, bluish discoloration from lack of venous return). Again, it may be difficult to distinguish this injury from anterior dislocation, so patients should be transported to the hospital urgently so appropriate imaging can be obtained. CT demonstrates the posteriorly displaced head of the clavicle ( Fig. 16.4 ). If vascular injury is suspected, an intravascular contrast agent should be added to the CT scan, because damage to the great vessels has been reported as a consequence of this injury. Posteriorly displaced physeal injuries and fractures are also at risk for mediastinal structure damage.
