Acromioclavicular and Sternoclavicular Joint Injuries

Authors: Koval, Kenneth J.; Zuckerman, Joseph D.

Title: Handbook of Fractures, 3rd Edition

Copyright ©2006 Lippincott Williams & Wilkins

Epidemiology

• Most common in the second decade of life, associated with contact athletic activities
• More common in males (5 to 10:1)

Anatomy (Fig. 12.1)

• The AC joint is a diarthrodial joint, with fibrocartilage-covered articular surfaces, located between the lateral end of the clavicle and the medial acromion.
• Inclination of the plane of the joint may be vertical or inclined medially 50 degrees.
• The AC ligaments (anterior, posterior, superior, inferior) strengthen the thin capsule. Fibers of the deltoid and trapezius muscles blend with the superior AC ligament to strengthen the joint.
• The AC joint has minimal mobility through a meniscoid, intraarticular disc that demonstrates an age-dependent degeneration until it is essentially nonfunctional beyond the fourth decade.
• The horizontal stability of the AC joint is conferred by the AC ligaments, whereas the vertical stability is maintained by the coracoclavicular ligaments.
• The average coracoclavicular distance is 1.1 to 1.3 cm.

Mechanism of Injury

• Direct: This is the most common mechanism, resulting from a fall onto the shoulder with the arm adducted, driving the acromion medial and inferior.
• Indirect: This is caused by a fall onto an outstretched hand with force transmission through the humeral head and into the AC articulation (Fig. 12.2).

Clavicle Fractures

Authors: Koval, Kenneth J.; Zuckerman, Joseph D.

Title: Handbook of Fractures, 3rd Edition

Copyright ©2006 Lippincott Williams & Wilkins

EPIDEMIOLOGY

• Clavicle fractures account for 2.6% to 12% of all fractures and for 44% to 66% of fractures about the shoulder.
• Middle third fractures account for 80% of all clavicle fractures, whereas fractures of the lateral and medial third of the clavicle account for 15% and 5%, respectively.

ANATOMY

• The clavicle is the first bone to ossify (fifth week of gestation) and the last ossification center (sternal end) to fuse, at 22 to 25 years of age.
• The clavicle is S-shaped, with the medial end convex forward and the lateral end concave forward.
• It is widest at its medial end and thins laterally.
• The medial and lateral ends have flat expanses that are linked by a tubular middle, which has sparse medullary bone.
• The clavicle functions as a strut, bracing the shoulder from the trunk and allowing the shoulder to function at optimal strength.
• The medial one-third protects the brachial plexus, the subclavian and axillary vessels, and the superior lung. It is strongest in axial load.
• The junction between the two cross-sectional configurations occurs in the middle third and constitutes a vulnerable area to fracture, especially with axial loading. Moreover, the middle third lacks reinforcement by muscles or ligaments distal to the subclavius insertion, resulting in additional vulnerability.
• The distal clavicle contains the coracoclavicular ligaments.
  • The two components are the trapezoid and conoid ligaments.
  • They provide vertical stability to the acromioclavicular (AC) joint.
  • They are stronger than the AC ligaments.

MECHANISM OF INJURY

• Falls onto the affected shoulder account for most (87%) of clavicular fractures, with direct impact accounting for only 7% and falls onto an outstretched hand accounting for 6%.
• Although rare, clavicle fractures can occur secondary to muscle contractions during seizures or atraumatically from pathologic mechanisms or as stress fractures.

CLINICAL EVALUATION

• Patients usually present with splinting of the affected extremity, with the arm adducted across the chest and supported by the contralateral hand to unload the injured shoulder.
• A careful neurovascular examination is necessary to assess the integrity of neural and vascular elements lying posterior to the clavicle.
  P.122
  
  
• The proximal fracture end is usually prominent and may tent the skin. Assessment of skin integrity is essential to rule out open fracture.
• The chest should be auscultated for symmetric breath sounds. Tachypnea may be present as a result of pain with inspiratory effort; this should not be confused with diminished breath sounds, which may be present from an ipsilateral pneumothorax caused by an apical lung injury.

ASSOCIATED INJURIES

• Up to 9% of patients with clavicle fractures have additional fractures, most commonly rib fractures.
• Most brachial plexus injuries are associated with proximal third clavicle fractures.

RADIOGRAPHIC EVALUATION

• Standard anteroposterior radiographs are generally sufficient to confirm the presence of a clavicle fracture and the degree of fracture displacement.
• A 30-degree cephalad tilt view provides an image without the overlap of the thoracic anatomy.
• An apical oblique view can be helpful in diagnosing minimally displaced fractures, especially in children. This view is taken with the involved shoulder angled 45 degrees toward the x-ray source, which is angled 20 degrees cephalad.
• Computed tomography may be useful, especially in proximal third fractures, to differentiate sternoclavicular dislocation from epiphyseal injury, or distal third fractures, to identify articular involvement.

CLASSIFICATION

Descriptive

Clavicle fractures may be classified according to anatomic description, including location, displacement, angulation, pattern (e.g., greenstick, oblique, transverse), and comminution.

Allman

• Group I: fracture of the middle third (80%). This is the most common fracture in both children and adults; proximal and distal segments are secured by ligamentous and muscular attachments.
• Group II: fracture of the distal third (15%). This is subclassified according to the location of the coracoclavicular ligaments relative to the fracture:

Type I:	Minimal displacement: interligamentous fracture between the conoid and trapezoid or between the coracoclavicular and AC ligaments; ligaments still intact (Fig. 11.1)
Type II:	Displaced secondary to a fracture medial to the coracoclavicular ligaments: higher incidence of nonunion
IIA:	Conoid and trapezoid attached to the distal segment (Fig. 11.2)
IIB:	Conoid torn, trapezoid attached to the distal segment (Fig. 11.3)
Type III:	Fracture of the articular surface of the AC joint with no ligamentous injury: may be confused with first-degree AC joint separation (Fig. 11.4)

Figure 11.1. A type I fracture of the distal clavicle (group II). The intact ligaments hold the fragments in place. (From Rockwood CA Jr, Green DP, Bucholz RW, Heckman JD, eds. Rockwood and Green’s Fractures in Adults, 4th ed, vol. 1. Philadelphia: Lippincott-Raven, 1996:1117.)

P.123

• Group III: fracture of the proximal third (5%). Minimal displacement results if the costoclavicular ligaments remain intact. It may represent epiphyseal injury in children and teenagers. Subgroups include:

  Type I:	Minimal displacement
  Type II:	Displaced
  Type III:	Intraarticular
  Type IV:	Epiphyseal separation
  Type V:	Comminuted

  
  
  

  Figure 11.2. A type IIA distal clavicle fracture. In type IIA, both conoid and trapezoid ligaments are on the distal segment, whereas the proximal segment without ligamentous attachments is displaced. (From Rockwood CA Jr, Green DP, Bucholz RW, Heckman JD, eds. Rockwood and Green’s Fractures in Adults, 4th ed, vol. 1. Philadelphia: Lippincott-Raven, 1996:1118.)

Figure 11.3. A type IIB fracture of the distal clavicle. The conoid ligament is ruptured, whereas the trapezoid ligament remains attached to the distal segment. The proximal fragment is displaced. (From Rockwood CA Jr, Green DP, Bucholz RW, Heckman JD, eds. Rockwood and Green’s Fractures in Adults, 4th ed, vol. 1. Philadelphia: Lippincott-Raven, 1996:1118.)

P.124