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related talks: shoulder dislocation; broken collar bone (clavicle fracture); shoulder instability (torn labrum); broken shoulder (proximal humerus fracture)

What is a Shoulder Separation?

The term shoulder separation refers to a dislocation of the AC joint (an abbreviation for Acromio-clavicular joint).  A shoulder separation is different than a shoulder dislocation (see talk).  

The AC joint is the connection between the clavicle (aka the collar bone) and the acromion (the bony prominence of your shoulder). Injury to the joint will cause these bones to move out of alignment.

Lets quickly look at some anatomy of the AC joint.  Like all joints, the AC has important ligaments that hold the bones together and prevent dislocation.  The AC joint is kept stable by two sets of ligaments: 1) the AC ligaments that give front-to-back stability (especially the superior and inferior ligaments), and 2) the CC ligament (coracoclavicular ligaments: conoid, and trapezoid parts) that provides up and down stability. The pectoral and trapezius muscles also give the AC joint stability.

A tear to these ligaments (the AC and the CC) will lead to a shoulder separation because the joint is unstable without them ligaments. The collar bone will appear to move upward when dislocated, but what is actually happening is the whole shoulder complex droops down.

Shoulder separations occur mostly in active males in their 20s, it’s a common sports injury.   Injury occurs with a direct blow to the shoulder when the arm is positioned close to the chest.  

How is a Shoulder Separation diagnosed?

A person that sustains a shoulder separation will report being whacked in the shoulder and feeling immediate pain. The shoulder will often look abnormal to a well trained eye.  Its easy to see an injury to the AC joint because theres only a thin layer of skin sitting over the joint.  If the collar bone moves out of position, you will see an abnormal bump.  

Diagnosis of a separation is confirmed with x-ray (AP and zanca view).  These x-rays will show that the two bones making the AC (the acromion and clavicle) joint fail to line up. 

The severity of the separation is ranked 1 to 6 (six is the most severe) based on the x-ray findings.  

A mild injury (type 1 and 2) are isolated strain or tears to the ligaments around this joint.  This causes no displacement (type 1) or minimal displacement (type 2) of the collar bone. 

A type 3 injury is a complete tear of the AC ligaments and the CC ligaments. The collar bone has moved upward 100% from its normal position (and no longer makes contact with the acromion).

Sometimes the collar bone will get displaced more than 100% due to a high energy force causing it to separate.  If the collar bone displaces backwards (posterior) and buttonholes through the trapezius ("trap") muscle its a type  4 injury.  An x-ray of the armpit (called an Axillary View) gives the best picture of this.   

A type 5 injury is even more severe because not only are the ligaments torn, but also the muscles (deltoid and traps).  Now the end of the collar bone is just flapping in the the wind and displaces 100-300%.  It may look similar to a type 3 injury (where the collar bone is also sticking up), however its much worse.  It can also be distinguished from a type 3 injury by taking an extra x-ray with the person shrugging their injured shoulder (ouch!).  Shrugging the shoulder pushes the AC joint back together: if the AC joint temporarily return to normal alignment, then its a Stage 3 injury, if it remain separated then its probably a Stage 5). 

If the collar bone displaces downwards, underneath the bicep muscle (very rare) then its a Stage 6 injury.  

How is a Shoulder Separation treated?

Treatment depends on the severity of the injury (look at the Stages in the diagnosis section).

A Stage 1 or 2 injury can be treated with a sling for comfort.  Athletes can return to play once the pain has resolved, and they have rehab'd the arm to full strength and motion.  Contact sports should be avoided for about 2-3 months to prevent a type 1 or 2 injury from becoming a type 3 injury. 

A Stage 4, 5, or 6 injury is typically treated with surgery because there is significant damage to the soft tissue that holds the collar bone and shoulder together.  The procedure is called a "Weaver-Dunn", and it takes a non-injured ligament (the coroco-acromial ligament) and moves it over to the collar bone to provide stability.  

A Stage 3 injury is an area of debate because it has been successfully treated with and without surgery.  People playing contact sports like football, lacrosse, hockey have high risk of re-injury so they probably should not have surgery.  However some elite athletes will have this injury repaired to avoid any risk to their future performance, most athletes elect for bracing.

What is the Outcome of a Shoulder Separation

Stage 1 and 2 injuries typically heal very well without complication.  People can return to sport within a few weeks (some top athletes will push the envelop and return much earlier).  Less than 5% of people will report persistent pain or weakness in the shoulder, which is probably from post-traumatic arthritis.  Grade 3 injuries treated nonsurgically have an 80% success rate (although success is really depends on expectations).  

Early surgery for a Grade 3 injury has about a 90% success rate when the ligaments alone are repaired.  The Weever Dunn procedure is typically very successful, however, post-traumatic arthritis many develop regardless of the collar bone stability after surgery.  Sometimes irreparable damage to the cartilage occurs during the initial injury. In such cases, AC arthritis will be treated as a separate condition down the road (see talk).


1) Simovitch R, Lavery K et al. Acromioclavicular joint injuries: diagnosis and management. JAAOS 2009; 17: 207-19. full article. review.

1) Debski RE et al. Effect of capsular injury on acromioclavicular joint mechanics. JBJS 2001; 83: 1344-51. full article.  superior aspect AC capsule (superior AC ligament) provides 50% restraint against AP translation. must preserve in distal clavicle resection. conoid/trapezoid lig resist superior translation. cc space is 1 cm.

1) Kaplan LD et al. Prevalence and variance of shoulder injuries in elite collegiate football players. Am J Sports Med 2005; 33: 1142-46. full article. AC injuries are 50% all shoulder injuries in athletes.

1) Williams GR Jr et al. Classification and radiographic analysis of acromioclavicular dislocations. Appl Radio 1989; 18: 29-34. full article. basis of current classification system. 

1) O'Brien SJ et al. The active compression test: a new and effective test for diagnosing labrral tears and acromioclavicular joint abnromality.  Am J Sports Med 1998; 26: 610-13. full article. cross body compression test to stress the ac joint and labrum. 


4) Mouhsine E et al. Grade I and II acromioclavicular dislocations: results of conservative treatment. J Shoulder Elbow Surg 2003. full article. 30% persistant mild symptoms, pain, esp. with push ups and dips.  Also with naval midshipman (Bergfeld et al). biggest concern is for late arthritis (in up to 50%)

4) Lemos MJ. The evaluation and treatment of the injured acromioclavicular joint in athletes. Am J Sports Med 1998; 26: 137-44. full article. review. delay return to sports for type 1-2 injury for 2 months to prevent reinjury.

2) Schlegel TF et al. A prospective evaluation of untreated acute grade III acromioclavicular separations. Am J Sports Med 2001; 29: 699-703. full article. looking at 25 patients no significant limitations in strength or ROM; but 20% thought result suboptimal (yet 3/4 didnt feel it warrented surgery)

2) Wojtys EM, Nelson G. Conservative treatment of grade III acromioclavicular dislocations. CORR 1991; 268: 112-119. full article. look at 22 pt, slight dec endurance/strength isnt significant limitation for athletes/laborers, however, also continued soreness/pain, may want to consider repair in certain people. 

3) Spencer EE. Treatment of grade III acromioclavicular joint injuries: a systematic review. CORR 2007; 455: 38-44. full article. review treatment. no obvious benefit to rx, but higher complication rate, longer recovery time. 

3) Glick JM et al. Dislocated acromioclavicular joint: follow-up study of 35 unreduced acromioclavicular dislocations. Am J Sports Med 1977; 5: 264-270. full article. key to good nonop outcome is professional rehab. 

4) Weaver JK, Dunn HK. Treatment of acromioclavicular injuries, especially complete acromioclavicular separation. JBJS 1972; 54: 1187-1194. full article. original description of technique to use coracoacromial lig to recreate . 

6) Bannister GC et al. The management of acute acromioclavicular dislocation: a randomised prospective controlled trial. JBJS Br 1989; 71: 848-50. full article. <2 cm displaced better nonop. >2 cm surgery 70% good-excellent results (only 20% good-excellent with nonop).

7) Faraj AA, Ketzer B. The use of a hook-plate in the management of acromioclavicular injuries: report of ten cases. Acta Ortho Belg 2001; 67: 448-451. full article.  good fixation but req. ROH at 8 weeks. 

8) Morrison DS, Lemos MJ. Acromioclavicular separation: reconstruction using synthetic loop augmentation. Am J Sports Med 1995; 23: 105-110. full articlebetter than clavicle to CC screw b/c doesnt req. removal.  risk cutout if improper placement. 


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