Acromioclavicular Joint Injury
Rehabilitation Rationale
Anatomy
The acromioclavicular (AC) joint is a diarthrodial joint with a fibrocartilaginous intra-articular disc. Two significant ligamentous structures are associated with the joint: the AC ligaments, which provide horizontal stability (Fig. 3 – 74), and the coracoclavicular ligaments, which are the main supensory ligament of the upper extremity, providing vertical stability to the joint.
Recent studies show that only 5 to 8 degrees of motion of the AC joint is possible in any plane.
The most common mechanism of injury of the AC joint is a direct force from a fall on the point of the shoulder (Fig. 3–75).
Rockwood (1990) classifies AC joint injuries into six types (Fig. 3–76).
Type I
- Mild sprain of the AC ligament.
- No disruption of AC or coracoclavicular ligaments.
Type II
- Disruption of AC joint.
- AC joint wider because of disruption (<4 mm or 40% difference).
- Sprained but intact coracoclavicular ligaments with coracoclavicular space essentially the same as the normal shoulder on radiographs.
- Downward force (weight) may disrupt AC ligament, but not the coracoacromial ligament.
Type III
- Coracoclavicular and AC ligaments disrupted.
- Shoulder complex displaced inferiorly.
- Coracoclavicular interspace 25 to 100% greater than in normal shoulder, or 4 mm distance (especially with weights applied).
Type IV
- Clavicle is displaced posteriorly through fibers of trapezius.
- AC ligament and coracoclavicular ligaments disrupted.
- Deltoid and trapezius muscles detached from distal clavicle.
Type V
- Vertical separation of clavicle is greatly separated from scapula over a type III injury (100 to 300% more than normal shoulder).
Type VI
- Clavicle is dislocated inferiorly under the coracoid process.
Types I and II injuries are treated conservatively, as are type III injuries in nonactive, nonlaboring patients. Most types IV, V and VI injuries require open reduction and internal fixation, as do type III injuries in more active individuals. |
