The clavicle serves as a strut connecting the shoulder girdle to the axial skeleton [9]. Optimal scapulohumeral rhythm and arm function require optimal clavicle anatomy. Its “S”-shaped design allows a wide range of rotation (40–50°) about its long axis, a motion that is key to placing the shoulder and arm in positions for function [13]. In this respect, it is similar to radius function at the wrist. Any loss of the normal curvature of the bone could result in decreased functional ability at the distal joint.

Clavicle length is also an important mechanical factor. Loss of normal proximal (medial) to distal (lateral) length, either by comminution, overriding, or angulation, shortens the strut and, in the presence of an intact acromioclavicular joint, results in scapular internal rotation and anterior tilt, most commonly characterized as scapular protraction [7, 9, 11, 12]. Protraction has been associated with multiple types of pathology such as impingement, rotator cuff tendinopathy, rotator cuff injury, labral injury, and functional muscle weakness [14–21].

Multiple deforming forces can be factors effecting the relative position of the clavicle fracture fragments. Of most concern is the lateral fragment, as this is attached to the scapula. The amount of the initial impacting force can create multiple fracture fragments with capability of displacement, shortening, and angulation. The gravitational force of the weight of the arm will pull the lateral fragment inferiorly and medially around the ellipsoid curvature of the thorax. This position is accentuated by placing the arm in a sling across the front of the body.

Muscle forces will become deforming forces. Medially, the sternocleidomastoid muscle can exert a superior and external rotation force on the proximal fragment. However, the main deforming forces are exerted on the lateral fragment, indirectly through attachments to the coracoid and humerus. The pectoralis major and minor, the latissimus dorsi, and the anterior deltoid can produce inferior, medial, and internal rotation forces on the lateral fragment. These forces can also produce a position of scapular protraction.

Collectively, these deforming forces frequently produce a position of the lateral fragment that may be overriding the medial fragment but also may be angulated in the anterior/posterior or inferior/superior direction and/or may be anteriorly rotated in relation to the medial fragment (Fig. 8.2). These positions represent a tri-planar or three-dimensional deformity which may not be obvious on two-dimensional radiographs but will be more clearly delineated by a dynamic shoulder examination. Evaluation of the scapula can frequently demonstrate the deformity, since the scapular position will have to conform to the position of the lateral fragment. The presence of scapular protraction, in addition to demonstrating the clavicle deformity, also predicts the functional deficits that may occur if the scapula is maintained in this position by not correcting the clavicle deformity.

The tri-planar deformation subsequent to clavicle fracture shortening, rotation, and/or angulation yields loss of strut efficiency and may produce dyskinetic patterns for simple activities of daily living as well as more physically demanding pursuits. There is limited, focused anatomic lab work detailing and correlating the deficiencies of clavicle malunion [22]. Malunion is associated with strength loss, rapid fatigue, pain, and limb and shoulder girdle paresthesia (Fig. 8.3). As high as 70% of nonoperatively treated mid-shaft clavicle fractures developed clinically evident scapular dyskinesis [12].

Shields et al. provided the first study to report rates of scapulothoracic dyskinesis following mid-shaft clavicle fractures and showed that SICK scapula scores were worse in these patients with ST dyskinesis [12]. In this retrospective cohort design including 24 patients, the operative group had only 1 of 12 (8%) patients demonstrate ST dyskinesis compared to 8 out of 12 (67%) in the nonoperative group. The nonoperative group reported more pain, decreased strength, and compromised range of motion along with scapula position change.

Ledger et al. reported that shortening of the clavicle changes the shoulder girdle by altering movement constraints with increased upward sternoclavicular angulation by 10° and increased protraction by 6°, which then yields diminished strength of at least 10% in extension, adduction, and internal rotation [22].

Shortening of the clavicle results not just in a reduced moment arm of the pectoralis major inserting on the clavicle mostly decreasing flexion and abduction strength in higher abduction but with secondary challenges to all musculature as scapula orientation to all soft tissue orientations is altered. Veeger and van der Helm described this positional and moment arm alteration changing muscle balance relationships [23]. This concept of maladapted tendons losing mechanical advantage is supported by Jupiter [24].

A simulated clavicle fracture model cadaveric study by Hillen et al. that placed cluster markers on the clavicle, sternum, humerus, and scapula provided rare anatomic insight into scapula positioning in this population [8]. The study performed manual motion trials on intact, resected, and plate-fixed clavicles and demonstrated that in the specimen with the 3.6 cm shortened clavicle, the scapula with the arm at 30° abduction was 20° more protracted, 12° more laterally rotated with 7° decreased posterior tilt, and more retracted in the sternoclavicular joint an average of 1.2° per 1.2 cm of shortening.

In the controlled shortening study, the AC joint was unaffected due to the stabilizing effect of the coracoclavicular ligaments; however, increased movement and rotation occurred at the sternoclavicular joint with implication of arthrosis risk.

Kibler and Sciascia described how diminished tilt and increased lateral rotation alter the acromion position supporting the concept of subsequent impingement and limited rotator cuff function as the anterolateral part of the acromion assumes a more anterior and more lateral position [9].

Andermahr et al. offer that the altered scapula position means that the glenoid orientation is changed as well such that the glenohumeral contact force direction is also impacted with the inference being to subject the labrum and capsule to shear forces not normally anticipated [7]. Veeger and van der Helm supported this concept as rotator cuff stabilizing forces may be altered and potentially yield a higher glenohumeral joint contact force with increased capsulolabral shear [23].

The longer the delay to surgery, the greater the scapular malposition with less than 6 weeks better and more than 40 weeks worse [25, 26].

Acute ORIF with a mean of 0.6 months was preferred to delayed with mean of 63 months [27]. Shoulder flexion endurance decreased in the delayed group, and constant scores were better in the acute group.

Plain radiographs are utilized to make the diagnosis of a clavicle fracture and provide information regarding comminution and overriding. However, as two-dimensional tools, they are frequently not able to accurately demonstrate the tri-planar deformity of the fracture or accurately assess scapular position. Scrutiny of radiographs may demonstrate subtle architectural alterations which may suggest scapula malpositioning and resulting dyskinesis and shoulder functional compromise. Be certain to compare like images, at similar trajectory, when making the decision for conservative or surgical care.

Figure 8.4 and 8.5 demonstrate the potential of increased fracture displacement over one week along with altered acromial projection and also suggests the need to compare like radiographs. Also notice the acromion orientation inconsistency which may also be valuable in understanding the degree of rotation and angulation of the lateral fragment (Fig. 8.5). Advanced imaging such as CT scans may be helpful in identifying the severity of the fracture (Fig. 8.6a, b).