AC Joint Separation

An Acromioclavicular Joint Separation or AC Joint Separation or AC Joint Sprain or simply Shoulder Separation is a common shoulder injury among active people like athletes. In this injury, the clavicle (collar bone) separates from the scapula (shoulder blade). The clavicle and scapula together form the socket that holds the ball of the upper arm bone. AC Joint Separation is generally caused due to a direct injury like a fall or a blow to that spot. It is a common sports injury, frequently seen in football and hockey players and cyclists.

Classification of AC Joint Injuries

AC Joint injuries range from very mild (Grade 1) to a severe injury (Grade 6). AC Joint Dislocations are classified by Tossy (3-grade classification), Allman (3-grade classification) and Rockwood (6-grade classification). Rockwood’s classification is the one most commonly used.

Classification Description
Grade 1 AC Joint Strain
Grade 2 AC disrupted, CC Strain
Grade 3 AC and CC disrupted
Grade 4 Distal Clavicle positioned posterior to acromion
Grade 5 Subcutaneous distal clavicle
Grade 6 Distal clavicle positioned inferior to coracoid
Acromioclavicular (AC) Joint Separation
Rockwood classification of AC Joint Separation

PC –

Symptoms of AC Joint Separation

Symptoms include pain and swelling on the shoulder. The pain generally increases when trying to make overhead movements or trying to sleep on the affected side. In some cases, there will be limited movement in the shoulder area and in some severe cases, a lump will be formed on top of the shoulder joint.


Diagnosis of Shoulder Separation

Your doctor might diagnose AC joint separation by any or all of the following methods: Medical history, Physical examination, X-ray or some tests to evaluate the pain and the range of motion.


Treatment of Acromioclavicular Joint Separation

Most AC Joint injuries don’t need surgery however in some severe cases surgery is required. People with low grade AC joint injuries will be put on standard medical treatment which includes:

    • Rest
    • Icing
    • Using Sling
    • Anti-inflammatory Drugs
    • Physical Therapy

Such injuries (generally Grade 1 to 3) will be healed in two to three weeks.

People with high grade AC Joint injuries (generally Grade 4 to 6 and in some cases Grade 3) will be required to undergo surgery in cases where standard non-surgical methods does not help relieve the pain and swelling. A surgeon will try to put the clavicle back to scapula. For this, a variety of implants are available as per the need of the patient. These surgeries are generally performed using Arthroscopy, which is less painful and with better recovery time. However, in some cases open surgical methods are used. Suitable rehabilitation will be required post-surgery including wearing of sling, medications and physio/occupational therapy.

Causes of AC joint separation:

More often than not, AC joint separation occurs out of a fall directly onto the shoulder.  As a result, the ligaments that surround and stabilize the AC joint get injured.  If the fall is a severe, the ligaments that support the underside of the clavicle are also torn, resulting in the separation of the scapula and the collar bone.  The fall results in the shoulder blade moving down due to the weight of the arm, thus creating a bump or bulge at the top of the shoulder.

The AC joint separation injury can range from a mild injury without any further complications or a complete tear with a large bulge.  With proper treatment and rehabilitation, good pain-free range of motion of the shoulder is possible even with a very large bulge.  A severe deformity may require a longer time for the pain-free motion to return.  If the AC joint separation is mild, there may be a sprain of the AC joint ligament that does not affect the collar bone and it looks normal on imaging such as x-ray.  However, a serious injury tears the AC joint, either sprains or slightly tears the coracoclavicular ligament.  It may also cause dislocation of the collar bone with a small bulge.  In the case of a complete AC joint separation, acromioclavicular joint and coracoclavicular ligaments are torn extensively.  This puts the acromioclavicular ligament completely out of alignment and there will be a larger bulge.


Identifying an AC joint separation:

If there is AC joint deformity, the injury can be identified easily.  However, if the intensity of the injury is less, the location of the tenderness and x-rays can help the doctor to arrive at a diagnosis.  At times, carrying a weight in hand makes the injury more prominent, thereby making the injury more significant on x-rays.


Symptoms of AC joint separation at various grades:

As already mentioned, an AC joint separation is classified into different grades, so it triggers different symptoms at different grades.  Let’s have a look at the kind of symptoms that one may experience in grade I to III.

If the separation is in grade I category, one or more of the following symptoms can be present:

    • Joint feeling very tender on touching
    • Presence of bruises around the shoulder
    • Arm movement triggers pain
    • Coracoclavicular ligament area is devoid of pain

If the separation is in grade II category, one or more of the following symptoms can be present:

    • On touching, moderate to severe pain can be elicited
    • There may be swelling in the joint
    • Arm movement triggers pain
    • Presence of a small bump on top of the shoulder where the clavicle ends
    • On pushing, clavicle moves
    • Touching elicits pain in the area of coracoclavicular ligaments

If the separation is in grade III category, one or more of the following symptoms can be present:

    • The injured person cannot hold the arm close to the side without immediately supporting the elbow
    • Presence of pain with any arm movement
    • Areas around the joint and coracoclavicular ligaments are painful
    • Presence of evident swelling
    • Hearing a popping sound as the joint moves
    • Bump on top of the shoulder coupled with a joint deformity
    • Unstable AC joint


People with AC joint separation generally return to activities of daily life with conservative treatment modalities even if there is a persistent deformity or bulge at the AC joint.  Rarely, a doctor resorts to advanced methods of treatment to help bring back the AC joint in its original place.  However, some people may experience continued pain in the area of AC joint even with a mild separation.  This may be the result of:

It is advisable to wait and see if the injury settles itself and reasonable range of motion returns without resorting to advanced methods of correction such as an operative intervention.  Even relatively severe injuries are managed without surgical intervention.

When should surgical route be pursued?

Operative intervention can be considered if the pain is recalcitrant to conservative treatment methodologies and the deformity is severe.  Trimming back the end of the collar bone to prevent it from rubbing against the shoulder blade is what surgeons generally do in the operative setting.  However, if the degree of the deformity is significant, the ligaments that support the underside of the collarbone are reconstructed.  This route of surgical intervention is generally pursued if there is a significant time lag between the occurrence of the injury and the medical intervention.  It can be performed either open or arthroscopically.  Sometimes, a plate is used to aid the surgical process and it is removed post complete healing of the shoulder.

Whichever treatment modality is followed, be it conservative or operative, the shoulder requires enough time for healing before it is used extensively for day-to-day activities.  Proper rehabilitation is essential to restore and rebuild the shoulder tissues and to regain strength and flexibility.


Anatomy and biomechanics

  • Diarthoidal joint – plane type of synovial joint
  • Superior capsule blended with deltoid and trepizius
  • supero inferior and antero posterior movents
  • Fibrous capsule

Typical features

  • Cartilage – fibrocartilage
  • Joint partially devided by articular disc.


  • AC ligament :
    • horizontal stabilizer
    • Resist 90% of A-P translation and joint distraction
    • Posterior and superior AC capsular ligaments provide greatest stability
    • Clinical importance of distal clavicale resection
  • CC ligament :
    • vertical stabilizer
    • Conoid– primary restraint to superior translation
    • Trepizoid resists 75% of AC joint compressionz
  •  Fukuda et al.,jbjs 1986; klimkiewicz et al.,jses 1999
    • Conoid– attaches posterior and medial on clavicle
    • 2ndligament to fail after ac ligament
    • Trepizoid– attaches anterior and lateral on clavicle
    • Movements : ac joint have passive movements with coordination of scapular movements
    • 5 to8 deg of movement present during elevation of arm above 90deg

Mechanism of injury


  • Most common
  • Direct force to acromion with shoulder adducted only
  • Acromion is moves inferiorly and medially (clavicle stabilized by sc joint)


  • Less common
  • Out stretched hand
  • Typically affects AC ligaments

Order of failure –

  • ac ligaments/capsule
  • CC ligaments
  • Deltotrapezial fascia


Clinical :

  • tenderness over lateral end of clavicle or shouler
  • swelling or deformity
  • Stability of joint and reducible or not
  • Special tests – O Brein‘s active compression test. Paxinos sign cross body addiction test and resisted extension test
  • Sc joint and neurological examination

Imaging :

  • X ray : AP view Stress view zanca view – specific and sensitive for ac joint Axillary view – ap translation
  • Ct/mri– rare suspected other injuries


  • Mainly based on vertical and horizontal instability
  • Allman (Allman F L, JBJS (am) 49:774-784, 1967)
  • Tossyet al – (Tossy et al, CORR, 28: 111-119, 1963)
  • Later modified by Rockwood(In: Fractures in adults, edited by Rockwood, CA, 1341-1414, Lippincott-Raven, 1996)


Reid et al 2012 – conservative management is the main recommendation for grades 1-3

Conservative management

Gladstone protocol (1997)

 pain relief and protection

Phase 2 – ROM and early isotonic strengthening

Phase 3- advanced strengthening and dynamic AC joint stability strengthening

Phase 4– sports specific training


  • Early focus is on passive and active ROM
  • Once symmetric and painless ROM achieved then progress to isometric shoulder strengthening
  • Isotonic strengthening
  • Sport specific training
  • Return to sports by 2-3months

Surgical management

  • For type IV and above
  • Methods :
    • Fixation across AC joint
    • Fixation between coracoid and clavicle
    • Ligament repair +/- augmentation or fixation
    • Anatomical Ligament reconstruction
    • Distal clavicle excision

Phemister technique

    • Recently not used alone because of complications
    • Used with other procedures to augment them
    • Complications-
    • Pin breakage and migration
    • Recurrence of lesion

Hook plate

    • Only used for acute cases
    • Requires subsequent removal
    • Osteolysis – 17%
    • Protrusion and irritation of skin

Bosworth technique


Mazzocca et al, AJSM 2007

    • Cadaveric study
    • Distance between lateral end of clavicle to conoid tuberosity : 45mm
    • To trapezoid tuberosity : 25mm

Tight rope

    • Instead of screw using tight rope with endobuttons
    • Used along with the repair of ligaments to augment

Ligament reconstruction

    • Resection of distal clavicle incresar the horizontal translation so it should be graded and determental
    • Intact of distal clavicle decreases the force on postero superior aspect of AC ligaments

    • Results: There were significant increases in AP translation with the cut AC joint capsule, and significant increases in SI translation with the cut CC ligaments (P < 0.0001). Compression significantly decreased translation (P < 0.0001).
    • To conclude
    • Distal clavicle resection is determental but
    • Ac ligament and capule repair or re construction gives good results

Waver Dunn procedure

    • Distal clavicle excision
    • The ca ligament is transferred to the distal clavicle
    • CC ligaments are repaired +/augmentation
    • Repair of deltotrapezial fascia
    • Ac joint not addressed

Mazzocca technique

    • Campell describes
    • Anatomic reconstruction of cc ligaments

Anatomical reconstruction

  • Grafts :autigrafs (hamstrings)
  • Allografts :
    • LARS
    • RotaLok system
    • Keio Leeds system


  • Braided polyethylenetraphthalate
  • 100N tensile strength
  • Vascularisation and fibrous ingrowth – type I collagen
  • Failure may be due to malposition of tunnels in the clavicle
  • Anatomic reconstruction has higher loads of failure 

 Newer techniques

  • Gritter and Petersen technique

Complications of ac joint dislocation

  • Arthritis
  • Cosmetic
  • Scapular dyskinesia
  • Sick scapula syndrome
  • Shoulder weakness and stiffness
  • Rotator cuff problems

Sick scapula syndrome

  • Scapular malposition
  • Inferomedial prominence of scapula
  • Coracoid pain and Kinesial abnormalities of scapula

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Q&As on AC Joint Separation

1) What is AC separation?

Your shoulder is made up of three bones that form a ball-and-socket joint:  the collarbone (clavicle), the shoulder blade (scapula), and the arm bone (humerus). The scapula and clavicle form the socket of the joint, and the humerus has a round head that fits within this socket. The end of the scapula is called the acromion, and the joint between this part of the scapula and clavicle is called the acromioclavicular joint. An acromioclavicular joint separation, or AC joint separation or shoulder separation, occurs when the clavicle separates from the scapula. It is commonly caused by a fall directly on the ‘point’ of the shoulder or by a direct blow received in a contact sport. It is one of the most common sports injuries too. 

2) How are AC Joint Injuries classified?

All separated joints do not fall under the same category. They are graded according to the severity of the injury and the position of the displaced bones. Classification of  AC Joint injuries ranges from very mild (Grade 1) to severe injury (Grade 6). AC Joint Dislocations are classified by Tossy (3-grade classification), Allman (3-grade classification) and Rockwood (6-grade classification). Rockwood’s classification is the one most commonly used.

3) What causes an AC joint separation?

A shoulder separation is almost always the result of a sudden, traumatic event that can be attributed to a specific incident or action. The two most common descriptions of a shoulder separation are either a direct blow to the shoulder (often seen in sports) or a fall onto an outstretched hand (commonly seen after falling off a bicycle or horse). The AC joint separation injury can range from a mild injury without any further complications or a complete tear with a large bulge. 

4) What are the typical symptoms of AC joint separation?

The typical symptoms of AC Joint separation are the following: 

Pain and swelling around the joint and Pain on movement of the arm

Depending on the grade, a bump may be present on the top of the shoulder where the clavicle ends. The joint may be very unstable and you have to ensure that you make minimal movements till you see a doctor. 

5) How to Identify an AC joint separation

Your doctor will listen to your medical history and prescribe the necessary tests.  An x-ray should be performed to ensure there is no fracture of these bones. If the diagnosis is unclear, an x-ray while holding a weight in your hand may be helpful. When this type of x-ray is performed, the force of the weight will accentuate any shoulder joint instability and better show the effects of the separated shoulder.

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