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Jan Bartoníček Christopher Colton Michal Tuček Ondřej Naňka

SCAPULAR FRACTURES

MAXDORF

INJURY MECHANISMS Scapular fractures have traditionally been considered to be caused, in a majority of cases, by high-energy trauma. The current experience, however, shows that they are caused by different mechanisms of varying violence [4]. Important determinants, in this respect, are age, associated illnesses, quality of bone stock, chronic stress, etc. Depending on the mechanism and the intensity of the violence, a number of scapular fractures are often associated with other injuries, involving not only the ipsilateral extremity, but also other parts of the body [1, 3, 8, 11, 13, 22, 27, 31, 38, 40–45, 49].

MECHANISM OF INJURY Scapular fractures result from several basic injury mecha nisms, either exogenous, or endogenous [4]. The scapula may directly impact, or be hit by, an object. Another mechanism is a direct impact of the humeral head onto the glenoid, or onto surrounding processes. The third cause is dislocation of the glenohumeral joint, and the fourth possibility, relatively rare, is a violent muscular contraction. In addition to injuries to a “healthy” scapula, fractures affect also scapulae stigmatized by pre-existing pathology, or abnormal load patterns.

DIRECT BLOW TO THE SCAPULA A direct blow to the scapula, during a traffic accident, a fall from a height, or the fall of a heavy object (e.g., a tree) onto the shoulder, are frequent causes of a scapular fracture [4, 28]. The fracture pattern depends on the energy and direction of the impact, size and shape of the object hitting the scapula, or being hit by the scapula. The range of injuries is relatively wide, including involvement of the acromion (Fig. 4-1) up to open complex fractures of the scapula (Fig. 4-2).

racoid and/or the acromion, or the lateral scapular spine (Fig. 4-3). With the arm in marked abduction, the humeral head is driven against the inferior area of the glenoid. As a result of such an impact, the distal glenoid may separate off, together with the adjacent lateral border of the scapular body (Fig. 4-4). With the arm abducted approximately horizontally, the humeral head hits the central part of the glenoid which may result in the split of the entire glenoid, or only separation of its anterior part. Sometimes the injury may also involve the coracoid (Fig. 4-5). With the arm in adduction, the subluxated humeral head hits the surrounding processes that form an osseoligamentous vault over it, causing fractures of the superior pole of the glenoid fossa, the coracoid, the acromion, the lateral scapular spine, the lateral clavicle, or AC dislocation (Fig. 4-6).

GLENOHUMERAL DISLOCATION Glenohumeral dislocation may be associated with fracture-separation of a rim of the glenoid fossa. Anterior dislocation of the humeral head may result in separation of the anteroinferior rim of the glenoid (Fig. 4-7), posterior dislocation in separation of its posterior rim. The frequency of the two types of dislocation varies. Separation of the anterior rim is much more common and is occasionally combined with an injury to the coracoid, or fracture of the greater tubercle [9, 24]. Injuries to the posterior rim are rare.

IMPACT OF THE HUMERAL HEAD ONTO THE SCAPULA In this mechanism, external violence acts primarily onto the arm, more specifically onto the humerus. It may be, for instance, impact on the elbow transmitted to the humeral head. According to its position in the glenohumeral joint and the force vector at the time of injury, the humeral head impacts the adjacent parts of the scapula, i.e., the glenoid, the co-

Fig. 4-1 Fracture of the acromion resulting from a direct impact on the shoulder after a fall. 65

SC APULAR FRAC TURES

Fig. 4-2 Open complex intraarticular fracture caused by motor vehicle accident.

a Fig. 4-3 Proximal displacement of the humeral head causing scapular process fractures. The arrows indicate fractures of the scapular spine and the coracoid.

Fig. 4-4 Glenoid fracture with the arm in marked abduction: a) the humeral head is driven against the inferior area of the glenoid; b) as a result of such an impact, the inferior glenoid separates off, together with the adjacent infraspinous part of the scapular body.

MUSCLE CONTRACTIONS Avulsion injuries caused by muscle contractions are often over emphasized in the literature [2, 5, 20, 21, 23, 32, 34, 46, 51]. A detailed analysis has shown that most such so-called avulsion injuries, particularly coracoid or acromion fractures, could not be caused by this mechanism, but rather by direct violence. A violent muscle contraction, causing a scapular fracture, occurs mostly as a result of electrical injury, or epileptic seizure; rarely as a result of hypocalcemia, or an uncoordinated

s udden movement [10, 16, 19, 26, 39, 50, 53]. Typical of this mechanism are compression fractures of the scapular body, often bilateral, and, less frequently, fractures of the glenoid, or avulsion of the inferior angle of the scapula (Fig. 4-8). A case of bilateral coracoid fracture also has been reported, associated with a bilateral anterior dislocation of the glenohumeral joint and bilateral fracture of the greater tubercle, caused by a hypoglycemic seizure [9].

I n j u r y m e ch a n i s m s

Fig. 4-5 Glenoid fracture with the arm abducted horizontally. The humeral head is driven against the central part of the glenoid, its impact results in avulsion of the anterior rim of the glenoid and coracoid process: a) anterior view; b) CT transverse scan; c) superior-anterior view; d) lateral view.

Fig. 4-6 Process fracture with the arm in adduction, the humeral head is driven proximally and hits the surrounding processes: a) comminuted fracture of the coracoid, fracture of the lateral scapular spine and AC dislocation; b) subtraction of the humeral head; c) subtraction of the humeral head and the clavicle. 67

SC APULAR FRAC TURES

INTENSITY OF TRAUMA ENERGY Thanks to its robust muscular envelope, its mobility and its location on the elastic chest wall, the scapula is well-cushioned against injury. This explains the relatively low frequency of injuries to the scapula among the total number of all fractures. The intensity of trauma energy resulting in scapular fractures varies considerably in individual cases. Three basic groups of injuries may be identified in these terms; high-, medium- and low-energy trauma.

HIGH-ENERGY TRAUMA c Fig. 4-7 Fracture of the anterior rim of the glenoid in anterior dislocation of the humeral head: a) post-injury radiograph; b) post-reduction radiograph; c) 3D CT reconstruction after reduction.

This group comprises injuries sustained during traffic accidents, fall from a great height, or by the fall of a heavy object onto the patient. A great majority of them are scapular fractures in polytrauma patients [1, 3, 8, 11, 13, 22, 27, 31, 38, 40–45, 49], with a correspondingly wide range of associated injuries to individual organ systems, i.e., chest, head, spine,

OTHER INJURY MECHANISMS Penetrating injuries to the scapula resulting from gunshot, or stab, wounds, quite frequent in the past, are rare nowadays. However, the number of fractures of a scapula pathologically altered by, e.g., a bone cyst (Fig. 4-9), an intraosseous ganglion, osteodystrophy, metastases, is increasing (Fig. 4-10) [29, 33, 36]. Stress fractures, resulting from various causes and involving individual parts of the scapula have more often been reported [6, 7, 17, 25, 35, 36, 47, 48]. Elderly patients with rotator cuff insufficiency and a consequent proximal migration of the humeral head may sustain stress fractures of the acromion, or of the lateral scapular spine [14, 37]. Stress fractures are reported also after bisphosphonate therapy [18]. An acromial fracture has been encountered after arthroscopic, subacromial decompression [30]. A unique case of a scapular fracture was described after chronic cough attacks [12]. Fig. 4-8 Fracture of the inferior angle of the scapula resulting from muscle contraction. The white arrow shows the fracture. 68