Blunt Shoulder Trauma: Fracture, Glenohumeral Dislocation, or Acromioclavicular Separation?
Radiology Cases in Pediatric Emergency Medicine
Volume 4, Case 13
Alson S. Inaba, MD
Kapiolani Medical Center For Women And Children
University of Hawaii John A. Burns School of Medicine
     An 18-year old surfer presents to the Emergency 
Department complaining of right upper shoulder pain.  
He states that the tip of another surfer's board struck 
him on the top of his shoulder while he was paddling 
out to catch a wave.  He immediately felt a pop when 
the surfboard struck his shoulder and states that he had 
difficulty paddling back to shore secondary to the pain.  
He denies any other trauma to his head, neck or chest.  
He also denies any paresthesias of his left hand.
     Upon presentation to the ED, he prefers to hold his 
right arm adducted against his body.  Inspection of the 
right shoulder region is only significant for superficial 
abrasions and mild erythema over the superior aspect 
of the shoulder joint without any obvious swelling or 
deformity.

View his shoulder.

     The angle (contour) of the right shoulder appears 
symmetric when compared to the left shoulder (i.e., 
there is no obvious drooping of the affected shoulder).  
There is no fullness or tenderness in the deltopectoral 
groove.  There is no tenderness over the humeral head 
or neck.  With the right arm in the adducted position, he 
is able to fully internally and externally rotate the right 
arm without any exacerbation of the shoulder pain.  
Palpation of the clavicle does not reveal any crepitus or 
obvious fractures.  His distal neurovascular examination 
is intact.

Questions:
     a)  What is the most likely diagnosis based on the 
above history and clinical examination?
     b)  What radiographic view(s) would you obtain to 
confirm your clinical diagnosis?

     Based on the mechanism of injury and the clinical 
examination, the most likely diagnosis would be an 
acromioclavicular separation.  To radiographically 
confirm this diagnosis, an AP view of the affected 
shoulder (specifically looking at the acromioclavicular 
and coracoclavicular joints) is obtained.

View shoulder radiograph.

Questions:
     a)  What is your radiologic diagnosis?
     b)  Would you classify this type of acromioclavicular 
injury as a type I, type II or type III acromioclavicular 
separation?
     c)  How should this type of injury be treated?

Discussion:
     In order to thoroughly understand the clinical 
assessment, radiographic evaluation and treatment of 
acromioclavicular separations, one must first have a 
very clear understanding of the anatomy of this region 
of the shoulder.

View shoulder anatomy.

     The function of the acromioclavicular (AC) joint is to 
elevate and abduct the arm.  Although the term "AC 
separation" refers solely to the AC ligament, stability of 
the shoulder joint is actually dependent upon two 
ligaments; the AC ligament and the coracoclavicular 
(CC) ligament.  The AC ligament anchors the distal tip 
of the clavicle to the acromion process of the scapula.  
The CC ligament consists of two separate ligaments 
which anchor the distal clavicle to the coracoid process 
of the scapula.  The degree of injury to this CC ligament 
largely determines the classification of AC separation 
injuries.
     The two most common mechanisms which cause 
AC separations are either direct trauma to the point of 
the shoulder (i.e., a direct blow to the AC joint region, 
as in the case of our patient) or secondary to falling and 
landing on the deltoid region with the arm in the 
adducted position.  An indirect mechanism which can 
also produce an AC separation is when force is 
indirectly transmitted to the AC joint secondary to a fall 
on the outstretched hand.
     The physical examination of a patient with an AC 
separation will depend upon the degree of AC 
separation.  If there is no accompanying dislocation of 
the glenohumeral joint, one would not expect to see the 
typical signs of an anterior shoulder dislocation (i.e., 
asymmetric contour of the shoulder, fullness with 
tenderness in the deltopectoral groove, exacerbation of 
pain with external rotation, etc.).  The majority of 
patients with AC separations will have some degree of 
tenderness directly over the AC joint.  However, with 
severe AC separations (type III), the normal AC joint 
prominence may be exaggerated.  This exaggeration of 
the AC joint prominence is secondary to the upward 
displacement of the distal tip of the clavicle and the 
downward pull of the shoulder (caused by the weight of 
the arm) and the loss of the integrity of the suspending 
CC ligament.
     Although the term "AC injuries" refers to the AC 
ligament, the classification and treatment of "AC 
injuries" are dependent upon the degree of injury of 
both the AC and CC ligaments.

Type I (or first-degree) AC separation:
     This degree of AC injury (typically referred to as an 
AC "sprain") involves an incomplete tear of the AC 
ligament.  Because this tear is incomplete and the CC 
ligament remains intact, the radiographs are normal 
EVEN WITH stress views (i.e., no radiologic evidence 
of subluxation).

Type II (or second-degree) AC separation:
     View the diagram of a type II injury.     

     This degree of AC injury involves a subluxation of 
the AC joint (secondary to a partial or complete tear of 
the AC ligament).  As with type I injuries, the CC 
ligament also remains intact with type II AC 
separations.  The subluxation of the AC joint (i.e., 
widening of the AC joint space as compared to the 
unaffected side) may or may not be evident on the 
routine shoulder radiographs (AP erect view).  
Therefore, when a type II AC separation is clinically 
suspected and the routine radiographs are within 
normal limits, stress views can be obtained.  These AP 
stress views are obtained (in the erect position) with 
weights (5-15 pounds or 2-7 kg) suspended by the 
patient's wrist (Do not have the patient hold the 
weights).  This stress view will bring out any degree of 
AC joint subluxation that was not evident on the initial 
routine radiographs.  Subluxation of the AC joint is 
radiologically confirmed if the AC joint appears wider on 
the stress view (as compared to the routine nonstress 
views) and/or if the inferior border of the distal tip of the 
clavicle is not in alignment with the inferior border of the 
acromion process.

View this alignment of the inferior border of the clavicle
     and the inferior border of the acromion process.

     With type II separations, this malalignment of the 
inferior borders of the distal clavicle and acromion 
process should not be more than half the diameter of 
the clavicle.  Separation of the distal clavicle by more 
than one-half of its diameter from the acromion process 
indicates a type III AC injury.

Type III (or third-degree) AC separation:
     View the diagram of a type III injury.     

     This type of injury involves a complete tear of both 
the AC and CC ligaments which then results in a 
complete dislocation of the AC joint.  Clinically, type III 
injuries will present with an exaggeration of the normal 
AC prominence secondary to the upward displacement 
of the distal tip of the clavicle and the downward pull of 
the shoulder (caused by the weight of the arm) and the 
loss of the integrity of the suspending CC ligament.  If a 
type III injury is clinically suspected, the AP view of the 
shoulder should be obtained in the erect position to 
allow the weight of the suspended arm to bring out the 
classic radiographic findings of a type III separation.  
The radiographic findings of a type III AC separation 
may not be evident if the AP radiograph of the shoulder 
is obtained with the patient in the supine position.  
Radiographically type III injuries reveal:  a) a widening 
of both the AC and CC joint spaces on the routine erect 
AP views (as compared to the AC and CC joint spaces 
of the unaffected shoulder) and b) the inferior border of 
the distal clavicle is clearly malaligned (i.e., separated 
by more than one-half the diameter of the clavicle) with 
the inferior border of the acromion process [Click on 
Align].  When a type III AC separation is confirmed on 
the routine AP erect views, stress views with weights 
are not necessary.

Treatment & Prognosis of AC separations:
     The initial ED treatment of all three types of AC 
injuries involves placing the patient in a shoulder 
immobilizer with the arm adducted against the chest.  
This can be accomplished with any of the commercially 
available shoulder immobilizers or by placing the patient 
in a sling and swathe immobilizer.  Early range of 
motion exercises are encouraged for type I injuries.  
Type II and type III injuries should be referred to an 
orthopedic surgeon for further evaluation and 
rehabilitation.  Although internal fixation used to be 
advocated for the majority of type III injuries, some 
authorities are now attempting to treat these types of 
injuries with three weeks of immobilization in a 
Kenney-Howard sling or other similar shoulder 
immobilizers.

Post-Case Quiz Questions:
     1.  Name the two ligaments that make up the AC 
joint?
     2.  Describe the two most common mechanisms of 
injury that can cause an AC injury
     3.  The classification of AC separations is dependent 
upon the integrity of the coracoclavicular ligament.  
True or False?
     4.  If the line connecting the inferior border of the 
distal clavicle to the inferior border of the acromion 
process is malaligned, this is by definition a type III AC 
separation.  True or False?
     5.  Stress views are always required to 
radiographically confirm the diagnosis of a type III AC 
separation.  True or False?

References
     Shoulder, including clavicle and scapula.  In:  Harris 
JH, et al.  The Radiology of Emergency Medicine, third 
edition.  Baltimore, Williams & Wilkins, 1993, pp. 
283-290.
     The shoulder and upper arm.  In:  Simon RR, 
Koenigsknecht SJ.  Emergency Orthopedics:  The 
Extremities, third edition.  Norwalk, CT, Appleton & 
Lange, 1995, pp. 387-389.

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Web Page Author:
Loren Yamamoto, MD, MPH
Associate Professor of Pediatrics
University of Hawaii John A. Burns School of Medicine
loreny@hawaii.edu