Midshaft Clavicle Fractures

Introduction

Clavicle fractures are among the most common bony injuries in the body, representing 2.5%–10% of all adult fractures and over 40% of shoulder girdle fractures. ^, Common injury mechanisms include skiing, mountain biking, American football, soccer/European football, as well as higher energy mechanisms like motor vehicle accidents. Due to the small bone diameter and limited soft tissue attachments, approximately 70%–80% of clavicle fractures occur in the middle one-third shaft. In the past nearly all clavicle fractures were treated nonoperatively. This was likely due to the low nonunion rates reported in several studies. In 1960 Neer et al. published an analysis of 2000 patients with midshaft clavicle fractures reporting a nonunion rate of 0.13%. Following this in 1968 Rowe subsequently published a nonunion rate of 0.8% in 566 midshaft clavicular fractures. In addition to the extremely low nonunion rates reported, malunion was essentially not considered to be a real clinical entity as function and satisfaction were believed to be excellent no matter the orientation, alignment, or morphology of the healed fracture. ^, Today, nonoperative management remains the predominant treatment for most clavicle fractures but there has been a significant increase in surgical fixation. This shift in management is largely driven by investigations with an emphasis on patient outcomes that showed malunion to be a clear clinical entity, careful reporting of outcomes that has shown a significantly higher nonunion rate with certain fracture patterns, as well as multiple modern randomized trials that have shown benefit to fixation in certain types of clavicle fractures. ^,

Relevant Anatomy

The clavicle acts as a bony strut maintaining the distance between the lateral glenohumeral joint and medial axial skeleton at the sternoclavicular joint. It also serves a shoulder suspensory function maintaining the position of the shoulder girdle via coracoclavicular (CC) ligamentous attachment. The clavicle is a thin tubular S-shaped bone on average 12–15 cm in length with medial sternoclavicular and lateral acromioclavicular articulations. ^, The medial and lateral segments form widened flairs leaving the middle third with the smallest diameter. Because of this, the middle-third clavicle is the most susceptible and thus the most commonly fractured portion of the bone. The clavicle has a characteristic coronal plane S-shape with convex curvature medially and concave curvature involving middle and lateral portions of the bone.

The clavicle forms ligamentous attachments at the acromioclavicular joint, sternoclavicular joint, and coracoid. The acromioclavicular joint is a synovial joint that is stabilized by both superior and inferior acromioclavicular ligaments in addition to the CC ligaments. The conoid ligament medially and trapezoid ligament laterally make up the CC ligaments. The two ligaments come together to attach to the posterosuperior aspect of the coracoid base. Superiorly they separate and are often divided by a bursa at their superior attachment on the inferior aspect of the clavicle. ^, These ligaments provide stabilization of the clavicle mainly in the coronal plane. Injury to these ligaments can be associated with concomitant injuries to the acromioclavicular and/or sternoclavicular joints leading to dislocations at these sites.

The muscular attachments also play an important role in stabilization as well as creating the typical midshaft deformity often seen in clavicle fractures ( Fig. 6.1 ). Medially, the pectoralis major attaches to the inferior aspect of the clavicle with the sternocleidomastoid (SCM) attaching to the superomedial aspect of the bone. The unopposed pull of the SCM results in the commonly observed superior displacement of the medial fragment. Laterally, the anterior attachments include both the deltoid and the pectoralis origins. The superolateral attachments are comprised of a combination of deltoid and trapezius fibers. The classic deformity of the lateral fragment is that of inferior and medial (shortening) caused by a combination of deltoid and pectoralis pull inferiorly and medially, respectively.

The relative proximity of major neurovascular structures including subclavian artery/vein, thoracoacromial vessels, supraclavicular nerves, and brachial plexus requires significant anatomic knowledge and surgical awareness in order to avoid injury when performing clavicle fixation. Multiple studies have described the anatomic relationship of these structures to the clavicle. ^{, ,} The mean distance from the subclavian and axillary vessels to the nearest surface of the clavicle has been reported to be 17–26 mm for the arteries and 3–12 mm for the veins. However, the artery can be as close as 5 mm, and in rare situations the vein may be directly opposed to the undersurface of the clavicle. This is most commonly observed in revision situations where the vessels are distorted by scar tissue.

Robinson et al. performed a separate cadaveric study to evaluate these anatomic relationships and found the subclavian vein and artery were most closely associated with the clavicle medially (4.8 and 18.6 mm, respectively). The brachial plexus, however, was most closely associated with the clavicle (15.2 mm) in the middle third of the clavicle. In the lateral third of the clavicle, the subclavian vein was consistently identified as the closest structure and was never found to be within 2 cm of the clavicular cortex. In an attempt to determine “safe zones” for fracture fixation, Steinmetz et al. performed a computed tomography (CT) angiogram-based study in which they evaluated the location of the major vascular structures around the clavicle and again determined that the subclavian vein is most closely located to the clavicle averaging <10 mm to the clavicular cortex in the medial half of the bone. These studies highlight the importance of anatomic awareness and the surgeon’s ability to refrain from “plunging” during drill or screw placement, leading to possible neurovascular injury. Although often debated, the surgical approach and plate placement do not appear to significantly affect the proximity of neurovascular structures. Hussey et al. compared the distance of hardware to neurovascular structures between anterior and superior plating. They found no significant difference in the distance to the subclavian vein/artery and brachial plexus in the superior plate position (9.2 ± 4.6, 12.2 ± 5.8, and 9.8 ± 5.2 mm, respectively) compared with the anterior plate position (8.3 ± 3.5, 12.2 ± 6.5, and 9.7 ± 5.3 mm, respectively).

Another structure in relative proximity and thus at-risk during clavicle fixation is the pleural space. A recent CT-based study by Mulder et al. reported the average distance of 15.4 mm between the inferior aspect of the clavicle and the pleural space at the closest location which was medial. The average distances of 22 and 44 mm were also reported from the middle and lateral clavicle, respectively. Due to the close proximity of the pleural space to the clavicle, iatrogenic pneumothorax is a potential complication of aberrant drilling during fixation.

The supraclavicular nerve is a superficial sensory nerve that originates from the C3 and C4 nerve roots of the superficial cervical plexus. This nerve ramifies proximally to provide sensation over the clavicle, anteromedial shoulder, and proximal chest and has three major branches (anterior, middle, posterior). These branches often cross the surgical field in the subcutaneous tissue during clavicle fracture fixation. Although high-level studies are lacking on this subject, some surgeons recommend identifying and preserving these cutaneous branches during approach while others do not. In either scenario, it is recommended to discuss with the patient the possibility of some numbness inferior to the clavicle postoperatively.

Pathoanatomy

Clavicle fractures are common injuries frequently resulting from a direct blow to the shoulder. Although previously thought to be caused by falls on the outstretched hand, current data suggest a direct blow to the shoulder is the more commonly observed mechanism. A force directed inferomedially is applied to the shoulder or lateral aspect of the clavicle ( Fig. 6.2 ). This places a compressive stress on the clavicle often leading to resultant injuries which can affect either the laterally positioned acromioclavicular joint, the clavicle itself, or more infrequently resulting in a medial injury at the sternoclavicular joint injury. A common deformity seen after midshaft clavicle fracture is one in which the distal fragment is translated or rotated anteriorly, medialized (shortened), and inferiorly translated compared with the medial fragment ( Fig. 6.3 ). As previously mentioned, this common deformity is due to a combination of force vector, bone morphology, gravity, and the deforming forces from muscle attachments.

Classification

An ideal classification system provides some direction towards treatment while describing the type of injury with high intra- and interobserver reliability. There are several proposed clavicle fracture classification systems. The original system developed by Allman placed fractures into one of three groups based on location with group I occurring proximally, group II mid-clavicle, and group III in the distal third. However, because this system lacked important descriptive qualities such as displacement, comminution, or shortening, other systems emerged in order to address these important characteristics. The Edinburgh classification subclassifies type II (midshaft) fractures based on the degree of comminution. Simple or wedge-type fracture patterns make up subgroup 1, and comminuted or segmental fracture patterns represent subgroup 2.