Imaging of Clavicular Fractures and Dislocations

The clavicle derives its name from the Latin word clavicula, or small key, because of its unique curvature. Despite the high frequency of injuries to the clavicle, our understanding of its injuries and function is based on only a modest amount of data. It has long been thought that the inherent reparative capacity of the bone leads to its rapid healing with little more than symptomatic treatment. Deformity has been described as merely a cosmetic concern, because function is satisfactory despite malunion. ^{[1, 2, 3, 4, 5, 6, 7]} Tenting and blanching of the skin at the fracture site may indicate an impending open fracture, which most often requires surgical stabilization. ^[8]

Clavicular fractures are classified by their location. The most common injury is a type 1 fracture (seen in the images below), which affects the middle third of the clavicle and accounts for approximately 80% of cases. Type 2 fractures represent 12-15% of cases; type 3 is the least common fracture and is seen in less than 5% of cases. ^[9]

Imaging modalities

The preferred method for radiologic evaluation of clavicular fractures varies according to the location of the injury and the need to identify potential associated injuries. In general, radiography is the only modality required, and fractures of the middle third of the clavicle are seen with an isolated anteroposterior (AP) projection centered on the midshaft of the clavicle. If clinical suspicion is high and if the AP view does not reveal a fracture, a 30° cephalic view can be helpful. On the converse, radiographs are extremely difficult to interpret when injuries to the medial clavicle and the sternoclavicular (SC) joint are being evaluated, even when both sides are included or oblique views are used. Computed tomography (CT) scanning is currently the best technique to evaluate these injuries. It provides true orthogonal views, which are unobtainable with plain radiography. ^{[10, 11, 12, 13, 14]}

Finally, a single AP radiograph often suffices for diagnosing distal clavicular fractures and injuries to the acromioclavicular (AC) joint. However, certain clinicians prefer to obtain comparison views of the opposite shoulder or stress images. Some believe that the value of stress, or weighted, images is controversial. Use of these images has essentially been abandoned in current practice. A specialized Zanca view may help visualize the joint by eliminating overlying structures.

(See the images below.)

Type 2 fractures (demonstrated in the image below) involve the lateral third of the clavicle, distal to the coracoclavicular ligament. These can be further subdivided into fractures with or without disruption of the ligament itself.

The least common injury, type 3 (seen in the image below), is a fracture of the proximal third of the clavicle.

Midclavicle

Evaluation of the clavicle requires a standard AP view centered on the midshaft of the clavicle. The image should be large enough to permit evaluation of the AC joint and the SC joint, as well as the rest of the shoulder girdle and the upper lung fields.

Oblique views can be used to further gauge the degree and direction of displacement. In practice, an AP view with a 20-60° cephalic tilt provides an adequate second view, because interference with thoracic structures is minimized.

(See the image below.)

Because of the shape of the clavicle, fractures of the midclavicle represent multiplanar deformities, and accurate estimates of shortening are difficult to obtain with plain radiographs. CT scans, especially with 3-dimensional reconstructions, improve the accuracy. However, this level of accuracy is rarely required.

Medial clavicle and SC joint

Standard projections for the evaluation of the SC joint include posteroanterior (PA), lateral, and oblique views. Medial clavicular fractures and SC joint injuries may be difficult to appreciate on standard views because of the overlap of the clavicle with the sternum and the first rib. Special projections include Rockwood, Hobbs, Heinig, and Kattan views. The most popular additional view is the Rockwood, or Serendipity, view (seen in the image below). This projection requires a 40° cephalic tilt of both SC joints centering on the manubrium.

The full extent of these injuries is often unclear despite the use of additional radiographic views. The diagnosis is best confirmed with CT scanning, which has the added benefit of the depiction of rib fractures, pulmonary contusion, and pneumothorax.

Of note, the secondary ossification center at the medial end of the clavicle does not appear before the age of 12 years, and it may not unite until the age of 25 years. Therefore, a physeal fracture can be confused with a dislocation of the SC joint on plain radiographs. This possibility should be carefully considered when studies in children or adolescents are being evaluated.

Lateral clavicle and AC joint

A single AP radiograph of the injured side often suffices, but some prefer to obtain comparison views of the opposite shoulder. AP views of the AC joint are performed at 15° of cephalic inclination, along the scapular spine. Normal alignment of the joint is present on an AP view when the joint space measures less than 5 mm wide and when the undersurfaces of the acromion and the distal clavicle form an uninterrupted arc.

Type 1 AC injuries (not to be confused with type 1 clavicular fractures) consist of a minor tear in the AC ligament, with an intact coracoclavicular ligament. This injury is clinically diagnosed when radiographs appear normal but tenderness is present over the joint.

Type 2 AC injuries represent a complete tear of the AC ligaments, with partial tearing of the coracoclavicular ligament. The clavicle is superiorly displaced by less than half of its own width.

(See the image below.)

Type 3 AC injuries signify complete disruption of the AC and coracoclavicular ligaments. Displacement greater than half of the width of the clavicle is present.

(See the image below.)

Radiographic findings are evident in 75% of type 1 and type 2 AC injuries but in virtually 100% of type 3 injuries.

Three additional categories have been introduced to help distinguish severe injuries for which surgical treatment may be warranted:

• Type 4 injuries are similar to type 3 injuries, except that posterior displacement of the distal clavicle is also present. This can be verified on an axillary view.
• Type 5 injuries are characterized by inferior displacement of the scapula, with an increase of the coracoclavicular interspace of 2-3 times its normal size. Such extreme displacement is usually associated with extensive stripping of the trapezius, pectoralis major, and deltoid muscles.
• Type 6 injuries involve inferior displacement of the clavicle. This is a rare type of injury resulting from a direct downward blow.

In the past, stress radiographs were used to differentiate type 2 and 3 injuries (partial vs complete ligamentous tears). Because most surgeons now treat type 2 and type 3 injuries nonsurgically, this distinction is no longer critical, and the use of stress views has fallen out of favor.

Postoperative radiography

Buenter et al performed a retrospective study of 241 patients who underwent operative repair for clavicular fracture to determine how often there is a change in the postoperative treatment plan because of findings on postoperative radiography, which according to the authors is standard procedure in most hospitals. They found that only one patient had an abnormality on postoperative radiography that necessitated additional CT scanning, and no additional re-interventions or deviations from standard postoperative protocol were required. ^[15]

The most important role of CT scanning in clavicular fracture evaluation is the assessment of medial clavicular fractures and injuries affecting the SC joint when plain images are not sufficient to do so. CT scans should include the SC joints and at least half of both clavicles to allow for side-to-side comparison. If vascular compromise or impingement is a concern, the study can be performed with intravenous contrast enhancement. ^[14]

(See the image below.)

CT scans for the assessment of the medial clavicle and the SC joint can be acquired in a neutral position or with stress maneuvers, which increase scan sensitivity. A stress maneuver requires that the ipsilateral humerus be internally rotated and brought medially across the chest by forcefully pulling against the opposite elbow.

CT scanning is occasionally required to elucidate intra-articular fractures or stress fractures involving the AC joint. However, CT is limited in the evaluation of the surrounding soft tissues, including the capsule, ligaments, and synovium.

In most cases, the medial clavicle and SC joint can be adequately evaluated with standard radiography or CT scanning. However, magnetic resonance imaging (MRI) is superior to CT scanning in depicting bone marrow abnormalities, disc or cartilaginous injury, and joint effusions. MRI is also better than other methods for evaluating extra-articular soft tissues. Furthermore, MRI does not expose patients to radiation, and it directly provides multiplanar data rather than reformations. Coronal, sagittal, axial, and oblique axial planes have been used in the MRI evaluation of the SC joint, depending on the specific area of concern.

When vascular injury is a concern, magnetic resonance angiography (MRA) may be performed.

MRI is occasionally required to elucidate intra-articular fractures or stress fractures involving the AC joint. MRI is now well established as an important modality in the assessment of rotator cuff disease.

Katz et al suggested that ultrasonography is a sensitive diagnostic tool for the evaluation of clavicular fractures in newborn infants and should be the procedure of choice in the diagnosis of neonatal clavicular fracture. The authors examined 41 clavicular fractures in newborns, using radiography and ultrasonography, and found no substantial difference between the modalities. ^[16] Further, a prospective study of 58 pediatric patients found that ultrasonography accurately diagnosed clavicle fracture with 89.5% specificity and may reduce length of stay in the emergency department. ^[11]

The role of ultrasonography in examination of the SC joint is limited. Although ultrasonography has been suggested as a screening tool for the identification of SC joint dislocation, it is, in practice, used only if other modalities are not readily available.

Ultrasonography has been reported to be a useful intraoperative study to guide relocation of a dislocated joint, and Doppler ultrasonography can be used for a quick assessment of vasculature.

Research indicates that ultrasonography contributes to information on soft tissues in the examination of the AC joint in suspected high-grade injuries and that it may be useful in the delineation of type 3 injuries. ^[17]

(An ultrasonogram of a clavicular fracture is shown below.)