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AC Joint Injury: Anatomy, Diagnostics and Treatment

ac joint separation image

This type of shoulder dislocation is not really an injury to the shoulder joint. Instead, damage occurs in the acromioclavicular joint: the junction of the clavicle with the shoulder process of the scapula – the acromion.

Anatomy of the Acromioclavicular Joint

The shoulder joint with the scapula is connected to the rest of the skeleton using one bone – the clavicle.

The clavicle, in turn, is connected to the sternum through the sternoclavicular joint. And the scapula is connected to the clavicle by means of an acromioclavicular joint (ACS).

The acromioclavicular joint is held in place by the clavicular-acromial and clavicular-coracoid ligaments.

The following image from rehabmypatient.com illustrates the whole anatomy of ac separation in great detail:

Anatomy of AC separation – Rehabmypatient.com

The acromioclavicular joint consists of two bones that are firmly connected to each other by means of an articular capsule and ligaments. At the same time, some mobility remains between the bones, which is necessary to increase the amplitude of movements in the shoulder.

Damage to the acromioclavicular joint usually occurs when falling on the shoulder joint, rarely from a standing or walking height. It happens more often when falling from a bicycle, motorcycle, or while practicing high-impact contact sports. According to different authors, dislocations of the acromial end of the clavicle account for approximately 20% among all other dislocations and occupy third place, second only to dislocations of the shoulder and forearm.

Shoulder dislocations are the most common joint dislocation seen by emergency room doctors, accounting for more than 50% of all dislocations treated in hospitals. Young adult men and older women tend to be the groups with the highest rate of shoulder dislocations.

Shoulder Dislocation – Harvard Health – published April 2019, access on January 25, 2020

Accidents are a common cause for this kind of injury: it can occur when falling on an outstretched arm during sports, rollerblading, ice skating, snowboarding or when falling on a straight arm in winter during ice.

In cases where the damage is limited to rupture of the clavicle-acromial ligaments, an incomplete dislocation or subluxation of the acromial end of the clavicle is observed. If powerful clavicular-coracoid ligaments (trapezoidal and conical) are torn, a complete supra-acromial dislocation of the clavicle occurs.

Diagnostic of AC Separation

On examination, the shortening of the shoulder girdle, the apparent lengthening of the arm are noteworthy. In fresh cases, before the development of significant edema, a step-like deformation in the area of ​​the clavicular-acromial joint is visible. The characteristic symptom of the “key” is clearly revealed: when the patient is standing, they press on the acromial end of the clavicle, while slightly shifting the patient’s shoulder above the elbow. The end of the collarbone is easily adjusted, “sunk” and returned to a vicious position when pressure ceases. After 1-2 days, a bruising usually appears on the skin in the joint area.

The appearance of bruising in the subclavian region, in the region of the pectoralis major muscle, pain in this area is usually accompanied by rupture of the clavicular-coracoid ligaments, that is, a complete dislocation. The final diagnosis is made by analyzing the x-ray, which should be performed in a standing position with hands freely lowered along the torso. The expansion of the clavicular-coracoid space during dissociation of articulated surfaces indicates a complete dislocation. In doubtful cases, take a picture of a healthy joint for comparison.


Incomplete dislocations of the acromioclavicular joint are usually treated conservatively. The upper limb is placed on the scarf, the clavicular-acromial joint is anesthetized by local injection of 10-15 ml of a 1-2% solution of novocaine, prolonged immobilization is not required. After 2-3 days, exercise therapy, physiotherapy treatment are prescribed.

Complete dislocations of the acromial end of the clavicle are treated surgically. Surgical treatment using modern methods of strong fixation allows you to abandon external immobilization, early to begin rehabilitation treatment and significantly reduce the period of disability.

The tactics for treating ACS rupture is chosen by the doctor based on the degree of damage to the joint and the duration of the injury. As a rule, the 1st and 2nd degree of damage is treated conservatively. On the border between the 2nd and 3rd degree of damage and at the 3rd degree, surgery is necessary.

How can I get a gap acromioclavicular joint AKS.

What do you feel if you damaged the AKC.

With the 1st degree of damage, swelling is determined in the area of ​​attachment of the acromial end of the clavicle to the scapula,

at the 2nd degree, we can see the “key syndrome”, the collarbone is recessed when pressed and, when released, comes back like a piano key.

At the 3rd degree of AKC rupture, there is visible deformation, the end of the clavicle protrudes above the scapula to its entire diameter.

How to help yourself with a shoulder region injury.

First aid for injuries of the shoulder joint consists in applying cold to the site of greatest pain and in immobilizing the upper limb with a scarf bandage.

Diagnosis is based on an x-ray.


What is needed for diagnosis in case of ACS damage.

For making a diagnosis and for determining the degree of damage to the acromioclavicular joint, the most informative method of research is x-ray.

On the X-ray at the first degree of rupture of the acromioclavicular joint, a discrepancy between the clavicle and the acromion will be visible.

In the second degree, we see the protrusion of the clavicle above the acromion at a distance of no more than half its diameter.

In the third degree, the clavicle protrudes above the scapula to its full diameter and even more so.

On the basis of x-rays, with the third degree of damage, the patient is additionally assigned an MRI – this study will allow us to accurately determine which ligaments were broken, the degree of rupture, and will help with the choice of surgical treatment tactics.

Treatment of rupture of the acromioclavicular joint.


There are several methods for the surgical treatment of ACS rupture:

– open surgery, performed through an incision in the tissues of the shoulder joint.

– arthroscopic, the most modern, less traumatic operation on the ACS.

Open surgery on the acromioclavicular joint.

With an open operation, an incision is made in the area of ​​the clavicle, while the deltoid muscle is separated (anatomically separated not by cutting, but by cleaning) from the clavicle, torn ligaments are exposed, at the base of the coracoid process, or around it, a thin synthetic tape is held that presses the clavicle to the coracoid process providing, thereby, the healing of ligaments (conical and trapezoidal).

Arthroscopy of the acromioclavicular joint in acute

up to 2 weeks from the moment of injury, the degree of damage.

Having performed arthroscopic approaches under the deltoid muscle and under the acromion, we visualize torn ligaments. At the base of the coracoid process, a hole is made into which we conduct a special synthetic 2 mm Fiber Tape tape and a titanium button Endo Button, which is wedged under the coracoid process. Then, between the conical and trapezoid ligaments, through the clavicle, without damaging the fibers of the deltoid muscle and ligament, a second hole is made into which the same tape passes and then it is fixed to the clavicle using the second reconstructive endo button retainer.

Arthroscopy of the acromioclavicular joint with subacute,

up to 3 months from the moment of injury, the degree of damage.

With a subacute degree of ACS damage, we perform a modified WEAVER-DUNN operation.

In addition to the established buttons that press the clavicle to the coracoid process, the previously stitched part of the coraco-acromial ligament unfolds and fixes to the clavicle. Thus, the non-free plastic of the clavicular-coracoid ligaments is produced using the acromioclavicular ligament.

The modified WEAVER-DUNN operation is not easy to execute. To conduct it with sufficient visualization, high-level anesthetic support is required, which our clinic is equipped with.

Arthroscopy of acromioclavicular articulation in old

more than 3 months from the moment of injury, the degree of damage.

At this time, it is possible to help a patient with a rupture of the acromioclavicular joint by performing an ACS tendon plastic. During this operation, in addition to the buttons-fixators and the synthetic tape, a loop is formed from the patient’s semi-tendon muscle, selected from the popliteal region, which is held around the coracoid process, fixed in the canals in the clavicle and fixed to the acromia process.

Why can we move the coraco-acromial ligament?

The cortex-acromial ligament is a rudimentary formation that has lost its main significance in the process of evolutionary development, often causing impingement syndrome and its movement can be considered rather a boon for the patient.  

We use a misaligned technique for drilling tunnels in the places of anatomical attachment of ligaments, allowing us to make a complex operation most elegantly. This method of execution is more difficult for the surgeon, but the most optimal for the recovery of the patient.

Why you should choose a method of arthroscopy for surgery on the AKC.

In 30 percent of cases, with trauma of the acromioclavicular joint, the anterior-upper segment of the joint lip of the shoulder joint ruptures- SLAP. That is, every third patient performing an operation on the ACS using an arthroscopic method, we, using the same approaches, can additionally perform an arthroscopic suture of the articular lip. If in the acute state the damage to the articular lip can be fixed in an anatomical position, then in advanced cases, tendon tenodesis of the long biceps head is performed, which is somewhat physiological.

Timely arthroscopic treatment aimed at eliminating instability in the acromioclavicular joint provides fusion of not only the ligaments, but also the intraarticular disk. The shoulder joint begins to function physiologically, thereby preventing the development of arthrosis of the ACS, the development of impingement of the shoulder syndrome and, as a result, such a terrible condition as a rupture of the  rotational (rotator) cuff of the shoulder.

The postoperative period during surgery on the acromioclavicular joint.

Ligaments of the AKC fuse 3-4 weeks after the operation.

All this time, the patient is recommended immobilization in a soft take-off tire with neutral rotation.

For 3-4 weeks, a rehabilitation program is prescribed, with the successful completion of which and after 4 months after the operation, any sports loads are possible without any restrictions.


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