Scapular and Glenoid Fractures

Charles Getz

Allen Deutsch

Gerald R. Williams Jr.

C. Getz: Fellow, Shoulder and Elbow Service, Department of Orthopaedic Surgery, University of Pennsylvania, Philadelphia, Pennsylvania.

A. Deutsch: Department of Orthopaedic Surgery, Kelsey-Seybold Clinic, Houston, Texas.

G. R. Williams, Jr.: Chief, Shoulder and Elbow Service, Department of Orthopaedic Surgery, University of Pennsylvania, Philadelphia, Pennsylvania.

INTRODUCTION

The scapula is intimately linked to shoulder function and mobility. Through the clavicle, acromioclavicular, sternoclavicular, and glenohumeral joints, the shoulder connects the axial and appendicular skeletons and presents a stable platform for the upper extremity. Injury to the scapula may disrupt normal shoulder function. The incidence of scapular fracture has been reported to be 3% to 5% of shoulder girdle injuries⁴⁰,⁹⁰ and 0.4% to 1% of all fractures.⁷⁵ The low incidence of scapula fracture is because of its protected position along the rib cage, the enveloping musculature, and its relative mobility, which permits dissipation of forces. Scapular fractures most commonly involve the scapular body (49%-89%), the glenoid neck (10%-60%), and the glenoid cavity (10%) (Fig. 18-1).¹,².¹⁸,⁴⁹,⁶⁹,¹⁰⁶

Scapular fractures usually are sustained as the result of severe trauma. Most series report motor vehicle or motorcycle accidents as the cause of injury in more than 50% of the cases.¹,²,⁴⁹,⁶⁹,¹⁰⁶ Associated injuries are common, including rib fracture, pneumothorax, and head injury. Rowe⁹⁰,⁹¹ reported that 71% of the patients in his series of scapular fractures had other associated injuries; 45% had fracture of other bones, including the ribs, sternum, and spine; 3% sustained a pneumothorax; 4% sustained brachial plexus injuries; and 19% sustained other shoulder girdle dislocations. Since the earliest modern series of scapula fractures, emphasis has been placed on the high association of other serious injuries.²⁴,⁵⁶,⁷⁷,¹¹⁰ Table 18-1 summarizes the associated injuries with scapula fractures from several series.

ANATOMY AND BIOMECHANICS

Anatomy

The scapula is enveloped by multiple layers of muscles. The anterior surface provides attachment for the subscapularis, serratus anterior, omohyoid, pectoralis minor, conjoined tendon of the coracobrachialis and short head of the biceps, long head of the biceps, and long head of the triceps (Fig. 18-2).³⁷ The posterior surface of the scapula provides muscular attachment sites for the levator scapulae, the rhomboid major, the rhomboid minor, the latissimus dorsi, the teres major, the teres minor, a portion of the long head of the triceps, the deltoid, the trapezius, the supraspinatus, the infraspinatus, and a portion of the omohyoid (Fig. 18-2).³⁷ The intramuscular position of the scapula provides it with great mobility and a protective cushion that are no doubt responsible for the low incidence of scapular injury.

The close proximity of neurovascular structures to the scapula places them at risk for injury. The pectoralis minor tendon inserts at the base of the coracoid process and the lateral border of the suprascapular notch. The brachial plexus and axillary artery travel posterior to the pectoralis minor tendon. The suprascapular nerve traverses through the suprascapular notch to innervate the supraspinatus muscle, whereas the suprascapular artery passes over it. The suprascapular nerve continues through the spinoglenoid
notch to innervate the infraspinatus muscle. At the medial border of the scapula, the dorsal scapular and spinal accessory nerves descend along the thorax, along with branches of the transverse cervical artery.

Figure 18-1 Relative incidence of scapular fractures. (Reprinted with permission from McGahan JP, Rab GT, Dublin A. Fractures of the scapula. J Trauma 1980;20(10):880.)

The osseous components of the scapula, which consist of the body and spine, coracoid process, acromion process, glenoid, and inferior angle, arise from several ossification centers.⁶⁷ At birth, the body and spine form one ossified mass. However, the coracoid process, acromion process, glenoid, and inferior angle are all cartilaginous. The coracoid process is a coalescence of four or five centers of ossification. The center of ossification for the midportion of the coracoid appears at age 3 to 18 months and may be bipolar. The ossification center for the base of the coracoid, which includes the upper third of the glenoid, appears at 7 to 10 years. Two ossification centers appear at age 14 to 16 years: a center for the tip and a shell-like center at the medial apex of the coracoid process. The ossification centers for the base and the midportion of the coracoid coalesce during adolescence at age 14 to 16 years. The other ossification centers fuse at the age of 18 to 25 years.

TABLE 18-1 ASSOCIATED INJURIES WITH SCAPULA FRACTURE

Study	Leung and Lam	Wilbur and Evans	Findlay	Ada and Miller	Nordqvist and Petersson	Zdravkovic and Damholt
Patients	15	40	37	113	129	40
Rib fracture	4 (27%)	17 (42.5%)	20 (54%)	NR^*	28 (22%)	NR
Hemothorax/pneumothorax	2 (13%)	NR	NR	42 (37%)	7 (5%)	NR
Head injury	6 (40%)	2 (5%)	NR	38 (34%)	22 (17%)	NR
Pulmonary contusion	2 (13%)	NR	NR	8%	NR	NR
Long bone fracture	2 (13%)	7 (17.5%)	NR	NR	13 (10%)	NR
Spine fracture	1 (7%)	NR	NR	4 (3.5%)	8 (6%)	NR
Death	NR	NR	4 (11%)	NR	NR	4 (10%)
Ipsilateral clavicle fracture	15 (100%)	7 (17.5%)	NR	28 (25%)	18 (14%)	NR
Brachial plexus injury	NR	NR	NR	4 (3.5%)	NR	4 (10%)
Subclavian artery injury	NR	NR	NR	1 (<1%))	NR	1 (2.5%)
Ipsilateral acromioclavicular separation	NR	NR	NR	6 (5%)	NR	NR
Aorta injury	NR	NR	NR	NR	1 (<1%)	NR
Suprascapular nerve injury	NR	NR	NR	NR	1 (<1%)	NR
^*No percentage reported but referred to as the most common associated injury.

The acromion is a coalescence of two or three centers of ossification that appear between the ages of 14 and 16 years, coalesce at the age of 19 years, and fuse to the spine at the age of 20 to 25 years. Failure of the anterior acromion ossification center to fuse to the spine gives rise to the os acromiale. This unfused apophysis is present in 2.7% of random patients and is bilateral in 60% of cases.⁵⁷ The size of the os acromiale depends on which of the four ossification centers of the acromion have failed to fuse (Fig. 18-3). The most common site of nonunion is between the meso-acromion and the meta-acromion, which corresponds to the midacromioclavicular joint level. An axillary lateral radiograph clearly demonstrates the lesion. Norris has reported that the os acromiale has been mistaken for fracture and that there is an association between the os acromiale and a rotator cuff tear.⁷⁸

The inferior angle of the scapula arises from an ossification center that appears at age 15 years and fuses with the remainder of the scapula at age 20 years. The vertebral border
arises from an ossification center that appears at age 16 to 18 years and fuses by the age of 25 years.

Figure 18-2 Muscular attachments of the posterior (A) and anterior (B) aspects of the scapula. (Reprinted with permission from Goss TP. Fractures of the scapula: diagnosis and treatment. In: Williams GR Jr., ed. Disorders of the shoulder: diagnosis and management. Philadelphia, PA, Lippincott Williams & Wilkins, 1999:597.)

The glenoid fossa ossifies from four sources: (a) the coracoid base (including the upper third of the glenoid), (b) the deep portion of the coracoid process, (c) the body, and (d) the lower pole, which joins with the remainder of the body of the scapula at age 20 to 25 years.

Caution must be exercised when interpreting radiographs of the scapula in adolescents and young adults. The os acromiale is the most frequently quoted unfused apophysis and can be confused with fracture.⁵⁷,⁷⁸ In addition, the physes at the base of the coracoid and the tip of the coracoid process can be difficult to distinguish from fracture. In the appropriate setting, a radiograph of the contralateral scapula is useful in determining whether a radiographic “line” is truly a fracture or an unfused apophysis. Furthermore, the junction between the upper and lower glenoid in adults represents the coalescence of the previous ossification centers and is the site of origin of many glenoid fossa fractures with a transverse component.

Biomechanics

The scapula is suspended from the clavicle through the acromial clavicular joint and coracoclavicular ligament. The clavicle, in turn, joins the trunk at the sternoclavicular joint. The sternoclavicular joint is the only true joint attaching the upper extremity to the body. However, the scapula articulates with the posterior chest wall and spine through numerous muscular attachments. Although not a
synovial joint, the scapulothoracic articulation is a stable construct that is rarely disrupted.¹⁶,¹⁷,⁴⁵,⁸³

Figure 18-3 The types of os acromiale, depending on which ossification fails to fuse. (Reprinted with permission from Liberson F. Os acromiale—a contested anomaly. J Bone Joint Surg Am 1937;19:683.)

Figure 18-4 The superior shoulder suspensory complex (SSSC) described by Goss consists of a bone-soft-tissue ring supported by two bone struts.

The reliance of overhead activity on the relationships among the clavicle, coracoclavicular ligaments, acromioclavicular joint, acromion, and glenoid neck has led to the development of the concept of the superior shoulder suspensory complex (SSSC) by Goss.³², ³³ and ³⁴ He likened the SSSC to a ring with two links. The ring is composed of the clavicle lateral to the coracoclavicular ligament, the coracoclavicular ligament itself, the glenoid, the coracoid process, and the acromion. The links are composed of the clavicle and the lateral scapular body and scapular spine (Fig. 18-4). The SSSC is thought to provide stability for the shoulder complex. Moreover, disruption of two or more components of the SSSC may result in enough loss of stability of the shoulder complex to require operative fixation.²⁶,³², ³³ and ³⁴, ⁴⁰, ⁴¹ and ⁴²,⁶⁰,⁹⁹

Williams and colleagues¹⁰⁷ investigated the biomechanics of the SSSC in a cadaveric model, with particular reference to one specific type of double disruption of the SSSC—the “floating shoulder” (fracture of the glenoid neck and clavicular shaft). In their model, the coracoacromial ligament, which was not included in Goss’s original description of the SSSC, provided significant stability to the shoulder girdle. Complete lack of suspensory support of the shoulder did not occur as a result of ipsilateral clavicle and glenoid neck fractures without additional injuries to the coracoacromial and acromioclavicular ligaments. Williams et al. suggested that the coracoacromial ligament should be added to the SSSC (Fig. 18-5).

Figure 18-5 The coracoacromial ligament was not included in Goss’s original description, but should be included.

MECHANISM OF INJURY

The body of the scapula is flat and encompassed within thick layers of muscle that allow movement in numerous directions. It has three projections, two synovial joints, and one articulation. In addition to its varied bony anatomy, the scapula serves as an attachment for 17 muscles. The body, a projection, an articulation, or a muscular attachment can be the site of a scapular fracture.¹,²³,²⁴,⁵⁶,⁷⁷,¹⁰⁶,¹¹⁰ Fracture may occur through direct or indirect trauma.

Direct Trauma

Fractures of the scapula are the result of energy transmitted in one of several means. A direct blow to the body or any of the projections can result in a fracture. The scapula is well protected; therefore, the body, spine, glenoid neck, and coracoid fractures that occur by this mechanism are commonly secondary to high-energy injuries. Numerous reports cite motor vehicle accidents, falls, pedestrian-vehicle accidents, and motorcycle accidents as the most common precipitating events.

Indirect Trauma

Indirect Injury from the Humeral Head

Trauma that loads the arm and subsequently impacts the humerus into the glenoid may result in glenoid fracture. The direction of loading and position of the humeral head on the glenoid face at the time of loading determine the fracture pattern. If the humeral head is positioned anterior on the face when the energy is delivered, the resulting fracture will be an anterior rim fracture. Similarly, if the head is posterior on the face when impact occurs, a posterior glenoid rim fracture will occur. Medial impaction of the humeral head when it is centered on the glenoid fossa often produces a transverse glenoid fracture that may exit the superior, medial, or lateral borders of the scapula. The humerus has also been implicated in coracoid and acromial process fractures.⁶,¹⁴,²⁷,¹⁰⁸,¹⁰⁹

Avulsion Fractures

Indirect trauma through forceful contraction of any of the scapular muscle attachments may cause an avulsion-type scapular fracture. Goss has proposed three mechanisms of
injury: (a) severe contraction from seizure, electric shock, or electroconvulsive therapy; (b) overloading the strength of the bone by a forceful contraction; and (c) repetitive loading (stress or fatigue fractures).³⁵,⁴³,⁵⁰,⁵³,⁹³,⁹⁷

CLASSIFICATION

Several classification systems for scapular fractures have been reported in the literature. Classification systems that involve a specific anatomic location, such as the coracoid, acromion, or glenoid processes, will be discussed in the individual sections pertaining to those injuries. However, Zdravkovic and Damholt¹¹⁰ divided scapular fractures into three general types: type I fractures, or fractures of the body; type II fractures, or fractures of the apophyses (including the coracoid and acromion); and type III fractures, or fractures of the superior lateral angle (i.e., scapular neck and glenoid). Zdravkovic and Damholt considered the type III fracture to be the most difficult to treat; these represented only 6% of their series.

Thompson and coworkers⁹⁸ presented a classification system that divided scapular fractures according to the likelihood that associated injuries would be present. Their cases all resulted from blunt trauma. Class I fractures included fractures of the coracoid and acromion process and small fractures of the body. Class II fractures comprised glenoid and scapular neck fractures. Class III fractures included major scapular body fractures. Thompson and colleagues reported that class II and III fractures were much more likely to have associated injuries.⁹⁸

Wilbur and Evans¹⁰⁶ described 40 patients with 52 scapular fractures. The patients were divided into two groups based on fracture location: group I, which included patients with fractures of the scapular body, neck, and spine; and group II, which included patients with fractures of the acromion process, coracoid process, or glenoid. They reported unsatisfactory results of treatment in patients in group II because of residual pain and loss of glenohumeral motion.

CLINICAL EVALUATION

History and Physical Examination

It is important to reemphasize that scapular fracture is often associated with other injuries that require more urgent treatment. In these patients, the standard trauma protocol of stabilizing airway, breathing, and circulation must be performed before definitive evaluation. Once the patient has been stabilized, physical examination should be directed toward identifying any of the concomitant injuries previously described. McLennan and Ungersma⁷⁰ highlighted the importance of follow-up examination in patients with scapular fracture, because the development of pneumothorax may be delayed 1 to 3 days.

Scapular fracture typically presents with the arm adducted and protected from all movements. Abduction is especially painful. Although ecchymosis is less than expected from the degree of bony injury present, severe local tenderness is a reliable finding.¹⁰ Patients with scapular body fractures or coracoid process fractures frequently experience increasing pain with deep inspiration secondary to the pull of the pectoralis minor or serratus anterior muscles. Frequently, rotator cuff function is extremely painful and weak secondary to inhibition from intramuscular hemorrhage. This has been described as a “pseudo-rupture” of the rotator cuff and frequently resolves within a few weeks.⁷⁴ If this weakness does not resolve, concomitant rotator cuff or nerve injury should be suspected.

Radiographic Evaluation

Most scapular fractures can be adequately visualized with routine radiographic views. A true anteroposterior view of the scapula combined with an axillary or true scapular lateral view will demonstrate most scapular body or spine fractures, glenoid neck fractures, and acromion fractures. “Special” views may be required in selected circumstances. The Stryker notch view is useful for coracoid fractures (Fig. 18-6).¹⁰ The apical oblique view, described by Garth et al.,²⁸ and the West Point lateral view are useful views for evaluating anterior glenoid rim fractures.⁸⁸

The majority of scapula fractures can be diagnosed and classified properly by plain radiographs. Computed tomography (CT) is not necessary in most scapular fractures.⁶⁶ However, the evaluation of intra-articular glenoid fractures is facilitated by CT scanning. The contralateral normal shoulder may be scanned as well as the involved shoulder to provide a means for comparison of the pathologic findings noted in the involved shoulder, especially in adolescents.¹⁰ CT scanning also allows for confirmation of the size, location, and degree of displacement of fracture fragments, and may detect the presence of instability. With the appropriate software, three-dimensional images can be generated and the humeral head can be subtracted from the image so that an unobstructed view of the scapula and glenoid can be obtained (Fig. 18-7). These three-dimensional CT reconstructions can be extremely useful in surgical planning.

TREATMENT

The recommended treatment for specific types of scapular fractures varies depending on the fracture’s location (intraor extra-articular), displacement, and effect on shoulder stability. The great majority of extra-articular fractures
(i.e., glenoid neck, scapular body, or spine, acromion, and coracoid fractures) are managed nonoperatively.¹⁰,¹⁵,⁵⁹ Intra-articular fractures, particularly those associated with glenohumeral instability or substantial displacement, are most often managed operatively.¹⁵,³⁴,⁴⁶,⁷³

Figure 18-6 Fracture of the coracoid base is often not visualized well on routine anteroposterior radiographs (A), but are seen well on a Stryker Notch view (B and C).

Figure 18-7 Computed tomography (CT) scans are not necessary in all scapular fractures but can aid in quantifying the amount of intra-articular displacement. Three-dimensional reconstruction allows visualization of the glenoid fossa with (A) and without (B) the humeral image.

Extra-articular Fractures

Scapular Body Fracture

Fracture of the scapula’s body is the most common type of scapular fracture and is correlated with the highest incidence of associated injury.¹⁰ The musculature surrounding the scapula makes nonunion a rare occurrence. Scapular malunion is uncommonly associated with clinical symptoms.¹⁵,⁹⁰,⁹¹ Consequently, most authors favor a sling, ice, and supportive measures until the initial pain subsides, followed by early motion.¹⁵,⁹⁰,⁹¹ Several large series of scapular body fractures treated nonoperatively have been reported, with union generally being the rule.²³,²⁴,⁷⁷,¹¹⁰ Shoulder function scores are rarely reported, but function is generally referred to as good. Nordqvist and Petersson,⁷⁷ however, found poor long-term results in some patients with greater than 10 mm of displacement.

When scapular body malunion is associated with painful crepitus that interferes with range of motion, excision of the bony prominence is usually curative.⁶² Nonunions of the scapular body often involve the inferior angle and its serratus anterior insertion. Therefore, weakness, pain, and limited motion are the common complaints. Fortunately, symptomatic nonunion routinely responds well to open reduction, internal fixation, and bone grafting (Fig. 18-8).²²,³⁸ Although excision of small fragments may be successful,⁵¹ caution should be exercised when considering excision of large inferior angle fragments because of the potential for serratus anterior insufficiency.

Author’s Preferred Treatment

With the assumption that serious associated injuries have been ruled out, symptomatic treatment is indicated for almost all patients with scapular body fracture. Displacement is often well tolerated, except when the fracture traverses the inferior angle and the inferior fragment is displaced anteriorly, deep to the superior fragment. Under these rare circumstances, particularly when the inferior fragment is large and involves a large portion of the serratus insertion, primary open reduction and plate fixation are indicated. Stable fixation usually requires two plates—one along the lateral border and one along the medial border of the scapula. These can be placed through a single skin incision, paralleling the lateral border, midway between the medial and lateral margins of the scapula. The lateral border is exposed by anterior retraction of the posterior border of the latissimus dorsi and elevation of the dorsal origin of the teres minor and major. The medial border is exposed by superomedial retraction of the lateral border of the lower and middle trapezius. Rarely will detaching a small portion of the trapezius insertion on the base of the scapular spine be required (Fig. 18-9).

Nonoperative treatment for the majority of scapular body fractures consists of ice and sling immobilization, initially. Within 1 to 2 weeks, passive range of motion can be instituted. An overhead pulley is added at 3 to 4 weeks postinjury; active range of motion and progressive-resistance exercises can usually be instituted at 6 weeks postinjury. Recovery from fracture usually requires 6 to 12 months. This rehabilitation protocol is also followed postoperatively for stably fixed fractures.

Glenoid Neck

Fracture of the neck of the scapula is the second most common scapular fracture.¹⁰ By definition, glenoid neck fractures are extra-articular. Three common fracture patterns have been described, depending on the point of exit of the superior extent of the fracture. These fracture patterns include one that exits the superior border of the scapula medial to the coracoid base, one that exits lateral to the coracoid base (anatomic neck), and one that exits the medial border of the scapula, inferior to the scapular spine, without traversing the glenoid neck (Fig. 18-10).¹,³³,⁷⁷,¹¹⁰ The most common fracture, by far, is the first pattern, whereby the fracture line exits the superior scapular border, medial to the base of the coracoid. Glenoid neck fractures have been classified as type I (nondisplaced) and type II (displaced), in which displacement is defined as 1 cm of translation or 40 degrees of angulation (Fig. 18-11).¹,³³,⁷⁷,¹¹⁰

Recommended methods of closed treatment for glenoid neck fractures include closed reduction and olecranon pin traction for 3 weeks followed by a sling, closed reduction, and a shoulder spica cast for 6 to 8 weeks, and brief sling immobilization followed by progressive mobilization.²,¹¹,¹⁵,⁴⁴,⁵⁹,¹¹⁰ Regardless of the method of closed treatment, permanent reduction of glenoid neck displacement is unlikely.¹⁵,⁵⁹ Therefore, when nonoperative treatment is indicated, a brief period of sling immobilization followed by progressive mobilization seems most reasonable. Most series report good functional results in patients with glenoid neck fractures regardless of the treatment method.²,⁴⁴,¹¹⁰

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