Running Title:
Acute posterior sternoclavicular fracture-dislocation in a 10-year-old boy
Authors:
Joseph Y. Choi, MD, PhD, Devin P. McFadden, MD, Vipul N. Nanavati, MD
Corresponding Author:
Francis G. O’Connor, MD

Introduction
A 10-year-old male was referred to the office after falling onto his left shoulder while playing football. At presentation, he denied any numbness, tingling or loss of sensation of his left upper extremity. Examination of his shoulder girdles revealed an internally rotated left shoulder and shortened clavicular distance. He did have a visible deformation of his left clavicle when compared to the contralateral, uninjured side and had excruciating pain to palpation of the clavicular and sternoclavicular area. The patient had full flexion and extension at the elbow. Shoulder deltoid was intact as were internal and external rotation of his shoulder. Furthermore, the patient denied being short of breath, feeling dizzy, or with difficulty swallowing. Radiographs of the left clavicle and sternoclavicular joint (SCJ) at the initial visit were remarkable for a posterior dislocation of the clavicle. A magnetic resonance imaging (MRI) study of the left clavicle and SCJ revealed that it was posteriorly displaced and edema was present at the fracture site. The physeal attachment to the manubrium was intact. Furthermore, the anterior portion of the clavicle was abutting the brachiocephalic and left subclavian vein (Figure 1). The patient was admitted and a closed reduction was attempted. Postoperatively, the patient developed paresthesia of the fingers of his left hand. An urgent CT scan with contrast was performed to evaluate any potential bleeding from the subclavian vessels. No active bleeding was discovered, however, a retrosternal hematoma with mass-effect on the adjacent vasculature was identified and the SCJ was found to be redislocated back to its original position (Figure 2). The patient was taken back to the operating room the next day and an open reduction internal fixation was undertaken. Disrupted capsular tissue was repaired and the clavicle was reduced and stabilized with Mersilene tape in an anatomic position. The SCJ was found to be stable with intraoperative ballotment testing. Postoperatively, the patients symptoms resolved and was discharged home two days later with a shoulder immobilizer. In his subsequent visits the shoulder immobilizer was discontinued six weeks post-surgery and the patient was advanced to full activities at his three month visit. There was radiographic evidence of healing in a reduced position. Furthermore, he had no neurovascular complaints and had full range of motion of his left upper extremity with a stable SCJ.

Discussion
Posterior dislocations of the SCJ are rare, but potentially catastrophic injury that are unnervingly difficult to diagnose. While composing less than 1% all joint dislocations and 3% of all shoulder girdle injuries [1,2], the potential morbidity and mortality of a missed diagnosis make this an important topic for review. The available literature on the subject proposes a variety of ways to make the diagnosis, but spiral CT is without question the gold standard of diagnostic imaging. Treatment is preferably accomplished by closed reduction in an operating room, but this is difficult to attain after 48 hours have elapsed from time of injury making early diagnosis and intervention even more vital [3].

Anatomy
The unique clinical anatomy of the SCJ accounts for many of the difficulties in diagnosis as well as the potentially catastrophic consequences if missed. The SCJ is a diarthroidial synovial joint composed of the articulations of the medial surface of the clavicle, the clavicular notch of the sternum, and the superior surface of the first costal cartilage. As such, it provides the sole true articulation between the upper extremity and trunk. While the relative rarity of SCJ dislocations would suggest this to be an extremely stable joint, the anatomic design of the bony articulation is surprisingly mismatched. The medial end of the clavicle is bulbous and oversized for a precise articulation with the clavicular notch of the sternum. In fact, less than half of the medial clavicle articulates with the upper angle of the sternum, giving the SCJ the distinction of having the least osseous stability of any of the major joints in the body [3]. It is therefore the joint capsule, anterior and posterior sternoclavicular ligaments, interclavicular ligaments, and costoclavicular ligaments that provide the majority of the stability to the joint, thus allowing it to function as a modified ball and socket joint, rotating and moving in all planes [4]. Of note, the posterior sternoclavicular ligament has been shown to be much stronger and more difficulty to rupture than the anterior sternoclavicular ligament, possibly accounting for the approximately 9:1 ratio of anterior to posterior dislocations [5,6]. Further complicating matters is the fact that the secondary ossification center at the medial end of the clavicle is the last epiphysis in the body to fuse, not even appearing until the age of 18 and frequently remaining open until the age of 25 [7]. A Salter-Haris type 1 fracture must therefore be considered in any pediatric patient in whom posterior SCJ dislocation is suspected, and definitive diagnosis can frequently only be made by direct visualization as radiographic imaging, including CT, is usually incapable of discerning the two injury types. Fortunately definitive diagnosis is often unnecessary if successful closed reduction can be attained. Finally, the anatomic location of the SCJ directly overlying the great vessels of the heart, pleural dome and apex of the lung, anterior roots of the nerves of the brachial plexus, esophagus, and trachea explains the potentially catastrophic consequences a missed diagnosis can carry. The SCJ is joined in the thoracic inlet by many vitally important structures including the brachiocephalic arteries, subclavian arteries and veins, great vessels, vagus nerve, recurrent laryngeal nerve, esophagus, and trachea, which account for the most common symptoms of dyspnea, dysphagia, dysphonia, weakness, and numbness. Each of these structures is susceptible to either compression or catastrophic disruption making early identification and definitive treatment, typically reduction as presented in the case above, of a posterior SCJ dislocation of the utmost importance.

Pathopysiology
There are two primary mechanisms of injury which account for the vast majority of posterior SCJ dislocations. The most common involves a blow to the posterolateral aspect of the shoulder while the arm is adducted and flexed as if to brace for a fall. In this case, the costoclavicular ligament acts as a fulcrum transmitting the anterior force applied laterally in a posterior plane at the SCJ. Somewhat less frequently, a direct blow to the anteromedial aspect of the SCJ with a high impact force may cause a posterior displacement of the joint. Regardless of the mechanism, athletic competition and motor vehicle accidents are the two most frequently cited cause of such trauma [3,4,6,9,13].

Physical Exam
The key to successfully identifying a posterior SCJ dislocation is maintaining a high index of suspicion, as a palpable posteriorly directed step-off is frequently masked by marked edema by the time the patient reaches care [3]. Fortunately for the diagnostician, there are several clues that indicate a posterior SCJ dislocation should be part of the differential diagnosis. The patient will typically complain of severe pain that is increased with any movement of the arm, particularly when the shoulders are pressed together by a lateral force. The patient usually supports the injured arm across the trunk with the uninjured arm, and if the joint is dislocated, the affected shoulder appears to be shortened and thrust forward compared with the normal shoulder. The head may also be tilted toward the side of the dislocated joint. The anterosuperior fullness of the chest produced by the clavicle is less prominent compared with the normal side if the patient is seen immediately following the injury, and the corner of the sternum may be more easily palpated than the normal SCJ. Assuming a supine position frequently exacerbates the patient’s discomfort, and concomitant shortness of breath, or breathing difficulties may be noted. The patient may complain of difficulty in swallowing or a tight feeling in the throat. Moreover, venous congestion may be present in the neck or in the upper extremity. Circulation to the ipsilateral arm may be decreased as well, and in severe cases the patient may present hypotensive and in a state of shock [14].

Radiologic Diagnosis
As stated previously, a posterior SCJ dislocation can prove very difficult to diagnose radiographically, and is commonly missed with plain sternoclavicular views [8]. As such, several methods have been developed to better visualize the SCJ in those patients in whom there is a clinical suspicion that such an injury exists. The Rockwood or "serendipity" projection employs a 50 degree tube tilt while centering on the manubrium and requires a large exposure as the contralateral SCJ is the primary landmark used for comparison [9]. In the Hobbs view a seated patient hunches over the cassette and a PA film is taken again centering on the manubrium [10]. Other methods, proposed by Heinig and Kattan may be useful as well if one were forced to make a diagnosis with plain films [11,12]. Ultrasound is yet another method of evaluating the SCJ, previously used intraoperatively to confirm successful closed reduction of displaced physeal injuries, and recommended by at least one author to be an effective means of diagnosis if neccesary [13]. Without question, however, spiral CT is a more sensitive and specific test and the unrivaled gold standard in diagnosis of posterior SCJ dislocations. CT takes less expertise on the part of the radiographer than the specialized views mentioned above, and can clearly delineate between a medial clavicular fracture not involving the physis and a posterior SCJ dislocation. In addition, when contrast is used a CT can assist in evaluating the patency of the major structures a posterior SCJ dislocation could conceivably occlude, namely the trachea, esophagus, and vasculature. For these reasons, when available, obtaining a CT should never be delayed in favor of another radiologic study. Prompt diagnosis can be vital and CT is the most effective way to make that diagnosis.

Outcomes
If early identification and treatment are attained healing of the joint is frequently swift and stable. While no established standards have been published, a perusal of the literature suggests using a sling for a minimum of one month with 4-8 weeks as a target for return to competition if all goes well and the patient has full, pain-free range of motion [3,6,15].

References
1) Nettles JL, Linscheid RL: Sternoclavicular Dislocations. J Trauma 1968, 8:158-64.
2) Cave ER, Burke JF, Boyd RJ: Trauma management. Chicago: Year Book Medical; 1974. 409-11.
3) Asplund C, Pollard ME: Posterior Sternoclavicular Joint Dislocation in a Wrestler. Mil Med 2004, 2:134-6.
4) Cope R, Riddervold HO: Posterior Dislocation of the Sternoclavicular Joint: report of two cases, with emphasis on radiologic management. Skel Rad 1988, 17: 247-50
5) Marker LB, Klareskov B: Posterior sternoclavicular dislocation: an American football injury. Br J Sports Med 1996, 30:71-72
6) Kuzak N, Ishkanian A, Abu-Laban RB: Posterior sternoclavicular joint dislocation: case report and discussion. Can J Emerg Med 2006, 8:355-7
7) Denham RH, Dingley AF: Epiphyseal separation of the medial end of the clavicle. J Bone Joint Surg 1967, 49A:1179-1183.
8) Gale DW, Dunn ID, McPherson S, Oni OOA: Retrosternal dislocation of the clavicle: the 'stealth' dislocation. Injury 1992, 23:563
9) Cope R, Riddervold HO, Shore JL, Sistrom CL: Dislocations of the sternoclavicular joint: anatomic basis, etiologies, and radiologic diagnosis. J Ortho Trauma 1991, 3:379-84
10) Hobbs DW: Sternoclavicular joint: a new axial radiographic view. Radiology 1968, 90:801
11) Heinig CF: Retrosternal dislocation of the clavicle: early recognition, x-ray diagnosis and management. J Bone Joint Surg 1968, 50:830
12) Kattan KR: Modified view for use in roentogram examination of the sternoclavicular joints. Radiology 1973, 108: 8
13) Pollock RC, Bankes MJK, Emery RJH: Diagnosis of retrosternal dislocation of the clavicle with ultrasound. Injury 1991, 9:670-1
14) Wirth MA, Rockwood CA: Acute and chronic traumatic injuries of the sternoclavicular joint. J Am Acad Ortho Surg 1996, 4:268-278.
15) Doss A, Lang IM, Roberts I, Bell MJ, Smith TWD: Posterior sternoclavicular joint dislocation in children- role of spiral computed tomography. Ped Emerg Care 2005, 5:325-6.

[pic]
Figure 1. Representative axial (A)T1, and (B)T2-weighted MRI of the right and left clavicle. Posterior dislocation (arrow) of the left clavicle. There is edema around the fracture-dislocation site extending into the superior anterior mediastinum. Furthermore, the anterior portion of the left clavicle is abutting the brachiocephalic vein and the left sublcavian vein is compressed between the clavicle and the rib cage.
[pic][pic]
Figure 2. Representative (A)axial CT scan, and (B)reconstruction of the right and left clavicle. Persistent posterior dislocation (arrow) of the left clavicle.