CT scanning is of little diagnostic value in an acute clavicle injury and is often reserved for cases of suspected neurovascular and/or visceral injury ; CT angiogram is indicated in the setting of a distal vascular deficit following a clavicle fracture. The other utility of CT lies in the evaluation of delayed union or non-union of a clavicle fracture.

The patient is placed in the scanner in the supine and neutral position, with the arms at their sides. If the study aims to primarily evaluate the fracture, intravenous contrast material would not typically be used. Depending on the area to be scanned, the spiral length will generally vary from 30 to 40 s. Depending on the scanner used, a pitch up to 2 will be satisfactory [6]. Additionally, slice thickness is usually between 2 and 3 mm. Data reconstruction should be in 1 mm increments and using high (or ultra-high) reconstruction mode, which makes the images sharper [7]. Generation of both coronal and sagittal reformatted images is standard practice in the diagnostic CT imaging. Because of the obliquity of the clavicle, three-dimensional (3D) reconstructions are an excellent illustration of the fracture (Fig. 4.3). Recently, the development of 3D printing for fracture modeling has been used to help the surgeon manipulate accurate anatomical replicas of the fractured bone to assist in fracture reduction prior to surgery [8].

An important pitfall during the interpretation of clavicular fractures with CT relates to correctly identifying the rhomboid fossa, which is a variable and frequently irregular concavity on the undersurface of the medial clavicle above the costal cartilage of the first rib, being more common in males. The normal variant should not be mistaken for a lytic or erosive process (Fig. 4.4). It is also important to comment on several muscles that have their origins or insertions on the clavicle. Of the many surrounding muscles, the trapezius plays the most important role in clavicular support [9]. The sternohyoid and sternothyroid muscles should also be assessed medially as well as the subclavius and deltoid attachments.

Medial clavicular fractures are uncommon and comprise 2–3% of all clavicle fractures [10]. Most medial clavicle fractures are non-displaced, do not involve the SC joint, and are usually managed non-operatively. Conversely, a posterior-directed fracture has the potential to injure superior mediastinal structures. These types of fractures should be evaluated preferably with CT angiography to exclude vascular injury and closed or open reduction should be performed in an emergent fashion to reduce the displaced fragment (Fig. 4.5) [11].

While the incidence of clavicular non-unions is low (0.1–15%), they can cause significant discomfort and deformity in these patients [4]. Clavicular non-unions are best evaluated with CT that typically demonstrates sclerotic margins as well as 3D anatomy (Fig. 4.6). Additionally, the presence of infection can be readily evaluated with CT demonstrating periostitis, bone resorption, as well as surrounding soft tissue edema and fluid. If indicated, aspiration for culture and sensitivity can subsequently be performed under ultrasound or CT guidance by the clinician (Fig. 4.7).

CT is also useful in evaluating hardware failure and related complications. Steel alloys are commonly used in fixation hardware and constitute most of the hardware used by orthopaedic trauma surgeons. One of the benefits of multi-detector row CT (MDCT) is its capability to reduce the severity of metal or streak artifacts. These streak artifacts are essentially photopenic holes or black holes, in the X-ray beam projection [12]. With MDCT, adjacent channels pick up excess tissue irradiation in the penumbra of the beam, which partially fills these “black holes” [13]. Other techniques that contribute to the lessening of metal artifacts include augmentation of peak kilovoltage (kV) and tube current settings, as well as the use of decreased collimation as well as pitch values [14]. Additionally, the use of post-processing techniques such as multi-planar and 3D reformation with volume rendering also contributes to producing CT images with less severe metal artifacts (Fig. 4.8) [15].

Most recently, dual-energy CT has been used as a means to reduce beam-hardening metal artifacts by generating monoenergetic images. This is encouraging as recent studies have demonstrated that dual-energy CT with iterative reconstruction algorithms allows a reduction of radiation dose with similar signal-to-noise ratio relative to conventional MDCT [16, 17]. However, there is still little information available regarding the effect of acquisition parameters and hardware composition on the severity of artifacts and more research needs to be done.

MRI of the clavicle, while not routinely performed, can be helpful in the evaluation of the osseous structures in the case of clavicular non-union. However, the prominent advantages of MRI relate to visualization of the associated soft tissues while assessing for infection, injury to the adjacent brachial plexus, vascular compression in post-traumatic-induced thoracic outlet syndrome (TOS) and during evaluation of the AC and SC joints. Most recently, there has been investigation in determining patient’s bone age by using MRI to determine the presence of a fully ossified clavicular epiphyseal plate as evidence of completion of the 20th year of life [18].

At our institution, MRI is performed on the patient in the supine position, as this allows the most comfort for the patient and subsequently less motion with higher quality images acquired. Routine images are obtained of the patient’s chest in coronal, axial, and sagittal planes. Traditionally, we perform high-resolution proton density images in three planes with the addition of a fluid-sensitive sequence called a short-inversion-time inversion-recovery (STIR) image . This provides uniform fat suppression; however, this technique is sensitive to B₁ field inhomogeneities, requires additional time for inversion pulses, and suffers from a low signal-to-noise ratio (SNR) [19]. Iterative decomposition of water and fat with echo asymmetry and least-squares estimation (IDEA L ) is a newer method that provides uniform and reliable fat suppression creating high-quality fat-suppressed MR images [20].

The coronal and axial planes of imaging are useful for the evaluation of articular surfaces and optimal for the evaluation of a clavicular non-union (Fig. 4.9). Thoracic outlet syndrome (TOS ) is a rare complication of a clavicular non-union and the sagittal plane of imaging can be used to measure and determine narrowing of the costoclavicular space and the IDEAL sequence is useful to determine hyperintensity, in the nerves, indicative of a plexitis (Fig. 4.10). Both the axial and coronal plane of imaging can be used to detect subtle cord entrapment of the plexus by callus formation (Fig. 4.11).

Despite its small size, the acromioclavicular (AC) joint plays a crucial role in upper-extremity function . It is essential in all motion of the arm/scapula, except in pronation and supination [21]. The AC joint unites the distal end of the clavicle with the acromion, at the lateral extension of the scapular spine. The AC joint itself is a simple diarthrodial joint made up of a fibrocartilaginous articular disc, intra-articular synovium, with articular cartilage, and a weak capsule. Of note, the size of the articular disc is highly variable and it can be completely absent [22]. The hyaline articular cartilage becomes fibrocartilage on the acromial side of the joint by the age of 17 and on the clavicular side by the age of 24 [23, 24].

Because the AC joint capsule is relatively thin, it has substantial ligamentous support. There are four AC ligaments : superior, inferior, anterior, and posterior, and the superior AC ligament has been found to be larger and thicker than the inferior ligament [25, 26]. Fukuda et al. found that the AC ligaments acted as the major restraint to posterior displacement of the clavicle [26]. Follow-up biomechanical studies have confirmed this observation by noting a 100% posterior displacement after complete transection of the AC joint ligaments [27].

The coracoclavicular (CC) ligament complex consists of the conoid and trapezoid ligaments, which insert on the posteromedial and anterolateral regions of the undersurface of the distal clavicle, respectively. Whereas the AC ligament works as the primary restraint to horizontal stability, the CC ligaments act as the primary restraint to vertical stability. Costic et al. have evaluated the geometric and structural properties of the conoid and trapezoid portions of the ligament and have found no significant differences between them [28]. Load-to-failure test results by Mazzocca et al. have established that the conoid ligament fails initially when a load is applied to the CC complex in a superior direction [29]. Furthermore, they found the most common site of rupture was the mid-substance portion of the ligament, followed by rupture at the origin.

The deltoid, pectoralis major, and trapezius muscles have attachments on the clavicle; the deltoid inserts onto the anterior surface of the lateral third of the clavicle, and the trapezius inserts at its posterior aspect. The pectoralis major inserts onto the medial two-thirds of the clavicle, anteriorly [30]. Anteriorly, the acromion has a coarsened surface where the coracoacromial ligament inserts and it has fibers that merge medially with the inferior AC ligament [31].

Both the AP standing and AP weighted stress views (using 5–15 lb weight suspended from each wrist) of the AC joint are performed at 15° of cephalad inclination, along the scapular spine. This technique aids in opening the joint and avoids superimposition of the acromion at the distal clavicle (Fig. 4.12). Lateral and Alexander views can also be performed; the latter is obtained while the patient is standing, shoulders projected forward, with the ipsilateral hand in the contralateral axilla [32]. Additionally, the lateral view of the acromion is particularly helpful in posterior dislocations, which are often missed on stress views [33]. Often, contralateral views of the AC joint are helpful for comparison, as are outlet views of the supraspinatus, particularly for subtle injuries.

The radiographic classification of AC joint injuries, as described by Rockwood et al., embodies a gamut of progressive soft tissue injury. In a type I injury, the AC ligaments are sprained, but the joint is intact and radiographically there is no abnormality (Fig. 4.13). The AC ligaments are torn, in type II injuries, but the CC ligaments are intact. Radiographically, the joint can be widened or the clavicle is displaced superiorly. However, it is important to remember that radiographic abnormalities are evident in 70–75% of type I or II AC injuries but in virtually 100% of type III injuries [32]. In type III injuries, both the AC and the CC ligaments are torn and the clavicle is always superiorly displaced relative to the acromion. Type IV injuries are characterized by complete dislocation with posterior displacement of the distal clavicle. The posterior displacement of the clavicle will extend into or through the fascia of the trapezius, the latter of which can only be seen with MRI. Type V injuries are characterized by a larger degree of soft tissue damage to the trapezius, whereas Type VI injuries are inferior AC joint dislocations into a subacromial or subcoracoid location.

Petersson et al. found the AC joint space to be 3.1 mm +/− 0.8 mm on average when studying healthy volunteers. According to their data, the normal AC joint space is significantly wider in men as compared with women. Moreover, their data demonstrates that a joint space wider than 7 mm in men and 6 mm in women is abnormal [34]. Increased joint space widening can be seen most commonly status-post trauma or after stress-induced osteolysis (Fig. 4.14) [35]. The differential diagnosis also includes rheumatoid arthritis, septic arthritis, gout, scleroderma, hyperparathyroidism, and lytic neoplasms.

Joint space narrowing, osteophytes, and cystic changes of osteoarthritis can be easily seen on radiographs of the AC joint, shoulder, or chest. Although specific in the evaluation of these osseous alterations, routine radiography is not sensitive [36]. Other important AC joint radiographic findings are fracture lines and joint capsule or ligamentous calcifications .

CT with its superior contrast resolution is the best modality for fine osseous detail. It is also ideal for the careful characterization of clavicular fractures involving the AC joint including its capacity for multi-planar 3D reformations (Fig. 4.15). CT demonstrates the extent of the fracture lines and the number, relationship, and alignment of fracture fragments. CT is also useful in the evaluation of intra-articular bodies in the AC joint. Improvements in the speed of image acquisition make CT imaging generally well tolerated, even in the setting of more severe trauma. However, CT is limited in the evaluation of the surrounding soft tissues including capsular, ligamentous, and synovial abnormalities.

On MRI, the oblique coronal plane, parallel to the distal clavicle, best demonstrates the AC joint, and this orientation purposefully displays the CC ligaments in the same plane in which they tear (Fig. 4.16a, b). The oblique sagittal plane roughly corresponds to the radiographic supraspinatus outlet view and also demonstrates the CC ligaments well (Fig. 4.16c) [37]. In addition to soft tissue injury, MRI offers the added advantage of the assessment of cartilage, which, in the author’s opinion, is best evaluated in the axial plane of imaging. The distal clavicle can also be evaluated for osteolysis or an os acromiale (Fig. 4.17).

At our institution, patients undergo oblique coronal MR imaging performed parallel to the anterior fibers of the supraspinatus, with the humerus in the neutral position. This optimizes evaluation of the AC joint and the CC ligaments. Proton density-weighted fast spin echo as well as inversion-recovery fluid-sensitive sequences are performed in the described plane. These sequences are then accompanied with sagittal and axial proton density–weighted imaging, and injuries are graded according to the Rockwood classification.

Type I AC joint disruption results from injury to the acromioclavicular ligament and there is no complete disruption. In this setting, radiographs may demonstrate swelling but are usually normal. Although Schaefer et al. described no specific MR imaging findings for this injury [38], it is the author’s experience that patients, in the acute setting, have capsular edema and/or a partial tear of the superior or inferior ligaments or both. In the chronic setting, the diagnosis of type I AC joint injury becomes much more difficult. In contrast, type II injuries result in disruption of the AC joint capsule and ligaments, and radiographs typically display a widened joint space (secondary to medial scapular rotation) [39]. MRI is key in demonstrating type I versus II injury as it can show that the acromioclavicular ligaments are torn and the CC ligaments are injured or partially torn (Fig. 4.18). The conoid component is most frequently involved in this injury [26].

Type III injuries lead to complete disruptions of both the AC and CC ligaments. The tear may extend to involve the deltoid and trapezius muscles and blood as well as fluid within the interspace of the CC ligaments may be seen (Fig. 4.19). Type IV injury occurs when the patient receives a blow to the acromion, with sufficient force to push the scapula posteriorly. Consequently, there is disruption of the acromioclavicular and CC ligaments with posterior and superior displacement of the clavicle, and the trapezius and deltoid are separated from their distal clavicular insertions (Fig. 4.20). The term “buttonholing” refers to the clavicle extending superiorly through the trapezius muscle. A type V injury is virtually an extremely severe type III injury, where the lateral trapezius and deltoid insertions as well as the acromioclavicular and CC ligaments are torn. Additionally, unrestricted contraction of the sternocleidomastoid muscle can result in a large separation of the CC distance (Fig. 4.21). Finally, type VI injuries occur from superior trauma to the clavicle causing a reduction of the CC distance and a tear of the acromioclavicular ligament solely [40]. This type of injury pattern is extremely rare.