Acromioclavicular Separations (Types 1-6)
Anne S. Boyd, MD, FAAFP, FACSM
BASICS
Separation of the clavicle and acromion due to injury of the acromioclavicular (AC) and coracoclavicular (CC) ligaments
Classified based on radiographic findings, indicating severity of injury to the capsular and extracapsular ligaments and supporting structures (types I to VI) (1)
AC and CC ligaments are responsible for maintaining the joint in physiologic position (2).
AC ligament is the main static stabilizing force for the AC joint in the anterior-posterior direction (3):
This ligament blends with the trapezius and deltoid fascia to form the AC capsule.
CC ligament is an indirect stabilizing force for the AC joint in the inferior direction:
The two CC ligaments can be divided into two parts: the trapezoid and conoid ligaments.
Synonym(s): shoulder separation; shoulder sprain; AC sprain; AC dislocation
Note: The term shoulder dislocation primarily refers to glenohumeral dislocation, not disruption of the AC joint.
DESCRIPTION
Type I:
Sprain of the AC ligament, some fiber disruption
Intact CC ligament and AC joint capsule
Type II:
Complete tear of the AC ligament
Sprained but intact CC ligament
Disrupted, widened AC joint
Type III:
Complete tear of AC and CC ligaments
Dislocated AC joint
Superior displacement of distal clavicle (<100%)
Probable disruption of deltoid and trapezius attachments
Type IV:
Complete tear of AC ligament
Partial or complete disruption of CC ligament
Dislocation of AC joint
Posterior displacement of distal clavicle into trapezius muscle
High probability of detachment of deltoid and trapezius muscle from distal clavicle
Type V:
Complete tear of AC and CC ligaments
Dislocated AC joint
100% superior displacement of distal clavicle
Position of clavicle: also thought of as a large type III; there is 100-300% widening of CC interval.
High probability of detachment of deltoid and trapezius muscle from distal clavicle
Type VI: rare
Complete tear of AC
CC ligaments intact or torn
Dislocated AC joint
Inferior displacement of the distal clavicle relative to the acromion or coracoid
Position of clavicle: 100% inferior AC joint displacement, usually with distal clavicle wedged underneath coracoid process. There is potential damage to the underlying brachial plexus and subclavian vessels.
EPIDEMIOLOGY
Severity of injury is directly related to the force of impact (2).
Mechanism of injury is primarily by direct impact over the superolateral shoulder forcing the AC joint inferiorly (2,4).
Primary injury is depression of the scapular complex (not elevation of the clavicle) causing disruption of the AC and CC ligaments (3).
Direct trauma commonly due to tackling with the shoulder or falling directly on the “point” of shoulder
Indirect trauma: fall on outstretched hand, causing the humeral head to be driven upward into the inferior aspect of the AC joint (2,5)
Downward indirect force, sudden change in load through upper extremity, usually heavier weight
Incidence
