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Bone & Joint Expert Care

Acromio-Clavicular joint (ACJ) Instability and Dislocation Introduction

A shoulder separation is a fairly common injury, especially in certain sports. Most shoulder separations are actually injuries to the acromioclavicular (AC) joint. The AC joint is the connection between the scapula (shoulder blade) and the clavicle (collarbone). Shoulder dislocations and AC joint separations are often mistaken for each other. But they are very different injuries.


The Acromio-Clavicular Joint (ACJ) is formed by the articulation (joint) between the outer (distal) end of the collarbone (Clavicle) and the Acromion of the shoulder blade (Scapula). The joint is stabilised by 2 main ligament groups. The Acromio-Clavicular ligaments are essentially thickenings of the joint capsule above (superior) and below (inferior) the joint. The main stabilisers of the Joint are the two Coraco-Clavicular ligaments, which bind the Clavicle to the Scapula. The Trapezoid lies towards the outer end of the collarbone (laterally) and the Conoid more medially.

Structures damaged.

The ACJ is commonly injured following a fall onto the hand, elbow or the point of the shoulder.

The Joint may be injured resulting in pain but the ligaments and joint capsule may remain structurally sound. If the force of the injury is sufficient the Acromio-Clavicular ligaments may be disrupted and a partial dislocation or subluxation may occur. If the force is sufficient to damage both the Acromio-Clavicular and the Coraco-Clavicular ligaments an ACJ separation or dislocation develops.

Signs and symptoms:


Pain may be generalised to the shoulder region and arm. Typically the site of the pain or maximal pain is localised to the region of the ACJ at the top of the shoulder.


If the ACJ is subluxed there may be a bump, or more pronounced bump over the top of the shoulder. If the joint is dislocated the shoulder may appear drooped with a prominence of the end of the collarbone (clavicle). The deformity may not be pronounced but may become more so as the arm is moved particularly across the chest when a lump formed by the end of the collarbone may appear at the back of the shoulder.

Diagnosis and investigations:

The diagnosis is typically apparent from the history and the examination.

X-Rays (plain radiographs) are usually taken to confirm the diagnosis and grade the severity of the injury. It is important to identify associated fractures or injuries. Stress X-Rays may used to identify the maximal extent of the deformity.

Occasionally further investigations in the form of Ultrasound scans (USS), Magnetic Resonance Imaging (MRI) and Computerised Tomography (CT) may be undertaken.


Pain relief.

Simple painkillers (analgesics) and anti-inflammatories may be helpful.


It is reasonable to provide support for the shoulder with a broad arm sling or Polysling. There are a wide variety of straps and braces designed to reduce ACJ dislocations. There is little evidence that any offer any advantage over symptomatic relief with a simple sling.

The shoulder and arm can be used a pain allows and the sling can be discarded as discomfort settles.

The majority of these injuries will settle without further treatment and are likely to give a satisfactory long-term result.

If the ACJ is significantly displaced either vertically or horizontally then surgical stabilisation may offer some benefit with regard to function as well as offering correction of the deformity.

Surgical Treatment.

There are numerous methods of stabilising or reconstructing the ACJ.

Surgical treatment may be divided into early (acute) stabilisation procedures and later (chronic) reconstruction procedures. Severely displaced fractures may have better long term function and outcome with surgery. The management of less severe dislocations remains somewhat controversial but there is increasing evidence supporting earlier surgical stabilisation.


What is the AC joint, and how does it work?

The shoulder is made up of three bones: the scapula (shoulder blade), the humerus (upper arm bone), and the clavicle (collarbone).

The part of the scapula that makes up the top of the shoulder is called the acromion. The AC joint is where the acromion and the clavicle meet. Ligaments hold these two bones together.

Ligaments are soft tissue structures that connect bone to bone. The AC ligaments surround and support the AC joint. Together, they form the joint capsule. The joint capsule is a watertight sac that encloses the joint and the fluids that bathe the joint. Two other ligaments, the coracoclavicular ligaments, hold the clavicle down by attaching it to a bony knob on the scapula called the coracoid process.

AC joint separations are graded from mild to severe, depending on which ligaments are sprained or torn. The mildest type of injury is a simple sprain of the AC ligaments. Doctors call this a grade one injury. A grade two AC separation involves a tear of the AC ligaments and a sprain of the coracoclavicular ligaments. A complete tear of the AC ligaments and the coracoclavicular ligaments is a grade three AC separation. This injury results in the obvious bump on the shoulder.


How does AC joint separation happen?

The most common cause of an AC joint separation is falling on the shoulder. As the shoulder strikes the ground, the force from the fall pushes the scapula down. The collarbone, because it is attached to the rib cage, cannot move enough to follow the motion of the scapula. Something has to give. The result is that the ligaments around the AC joint begin to tear, separating (dislocating) the joint.


What symptoms does this condition cause?

Symptoms range from mild tenderness felt over the joint after a ligament sprain to the intense pain of a complete separation. Grade two and three separations can cause a considerable amount of swelling. Bruising may make the skin bluish several days after the injury.

In grade three separations, you may feel a popping sensation due to shifting of the loose joint. Grade three separations usually cause a noticeable bump on the shoulder.


What tests will my doctor run?

Your doctor will need to get information about your injury and a detailed medical history. You will need to answer questions about past injuries to your shoulder. You may be asked to rate your pain on a scale of one to 10.

Diagnosis is usually made by the physical examination. Your doctor may move and feel your sore joint. This may hurt, but it is very important that your doctor understand exactly where your joint hurts and what movements cause you pain.

Your doctor may order X-rays. X-rays can show an AC joint disruption, and they may be necessary to rule out a fracture of the clavicle. In some cases, X-rays are taken while holding a weight in each hand to stress the joint and show how unstable it is.


What treatment options are available?

Nonsurgical Treatment

Treatment for a grade one or grade two separation usually consists of pain medications and a short period of rest using a shoulder sling. Your rehabilitation program may be directed by a physical or occupational therapist.

The treatment of grade three AC separations is somewhat controversial. Many studies show no difference whether a person is treated with surgery or conservative treatment. Even with surgery, a bump may still be present where the separation occurred. And a significant portion of people who undergo surgery will need another operation later.

Several studies have looked at what happens to the AC joint after this injury. It appears that many people, whether they had the joint repaired surgically or not, will need an operation at some time in the future. The injured joint degenerates faster than normal. Over time it becomes arthritic and painful. This process may take years to develop, but sometimes it happens within one or two years.

Surgery Acute Acromio-Clavicular Joint (ACJ) Stabilisation

Indication for surgery:

The indication for AC joint stabilisation is current or anticipated future symptomatic impairment of shoulder function or pain as a consequence of an AC Joint dislocation. If the AC Joint is markedly displaced upwards or backwards then surgery may well improve the long-term outcome. When the deformity is less marked the benefit of surgical stabilisation is less clear. If there is concern regarding the appropriateness of surgery it is best to seek early advice.

Acute stabilisation is generally considered to be within 2-3 weeks of the injury and may involve reduction and stabilisation of the AC Joint allowing the Coraco-Clavicular ligaments to heal or scar at the appropriate length.

Stabilisation of a chronic injury (beyond a few weeks) typically involves a reconstructive procedure, where ligaments or tendons are transferred from elsewhere to reconstruct the Coraco-Clavicular ligaments. This is sometimes termed a Weaver-Dunn procedure after one of the early techniques described.


Surgery is typically undertaken as a day-case procedure, that is you come into hospital and are discharged the same day. If the surgery is undertaken in the afternoon or evening then you may wish to stay in over night and go home first thing the next morning.

The operation is undertaken with a general anaesthetic often with an interscalene nerve block, that is you are fully asleep with further pain relief from a local anaesthetic injection above the Clavicle (collarbone) block. The block typically results in arm numbness and pain relief for 12 to 48 hours following the operation.

Acute Stabilisation:

Acute stabilisation may be obtained using a TightropeTM technique. This can be undertaken as a keyhole (arthroscopic) or mini-open technique.


The arthroscopic technique typically involves three or four, half to one-centimetre incisions. One at the back of the shoulder, one or two at the front of the shoulder and one over the top of the shoulder near the AC joint itself.

The mini-open technique uses a single three to four centimetre scar at the top of the shoulder near the AC Joint. The scar typically lies under clothing straps and is usually cosmetically acceptable.

There is little cosmetic difference between the arthroscopic and mini-open techniques


Arthroscopic Technique:

The arthroscopic (keyhole) technique allows assessment of the Gleno-Humeral Joint with a camera. The Coracoid is cleared and the undersurface exposed through a small incision or portal at the front of the shoulder. A special jig is used to guide a wire and then a drill through the Clavicle and then through the Coracoid. The TightropeTM system allows a strong pulley mechanism to be pulled though both bones before being ‘flipped’, securing a hold on both the top of the Clavicle and bottom of the Coracoid. The TightropeTM pulley can then be tightened to the appropriate length and by so doing the AC Joint can be reduced and held in the correct position. A second TightropeTM may be passed to offer improved strength and stiffness of the reduction and stabilisation.

Mini-Open Technique:

A small incision is made over the end of the Clavicle (Collarbone). The top of the clavicle is exposed. To allow one or two drill holes to be placed in the optimal positions. The top of the coracoid can be readily identified and exposed without extensive tissue clearance. One or two drill holes can then be drilled through the coracoid with appropriate care. One or two TightropesTM can then be pulled through the Clavicle. The Coracoid button may then be pushed through Coracoid drill holes at which point the button will ‘flip’ spontaneously securing the TightropeTM to both the Clavicle and Coracoid. The pulley mechanism then allows reduction and stabilisation of the AC Joint in the correct position. This technique allows the placement of two Tightropes under direct vision with minimal soft tissue disturbance. The soft tissue attachments to the distal clavicle, which may stripped at the time of the dislocation may also be repaired using this technique.

Wound Closure:

Arthroscopic wounds are typically closed using SteriStripsTM, small butterfly paper stitches, but a single absorbable stitch may be used which does not require removal. These wounds are then typically covered by a number of OpsiteTM dressings.

A mini-open incision is typically closed with an absorbable stitch that does not require removal. Occasionally the ends of this suture need to be trimmed when the dressing is removed at 10 to 14 days. The wound is then usually covered with a number of SteriStripsTM to protect the wound and minimise scarring. The wound is then covered by an OpsiteTM dressing

Following surgery:

The arm is typically placed in a sling, which is worn for three to four weeks. It is important to follow the rehabilitation protocols for AC Joint stabilistion supervised by a physiotherapist.

Risks associated with the operation:

All operations are associated with a degree of risk but complications associated with an Acute stabilisation are uncommon

Infection (<1%)

Anaesthetic Risks (Anaestheic complications are rare but include Heart Attack (Myocardial Infarction, MI), Stroke (Cerbero-Vascular Accident, CVA) and a clot in the leg (Deep Vein Thrombosis, DVT) or lungs (Pulmonary Embolus, PE).

Damage to nerve or blood vessels (Neuro-Vascular Damage). There may be a small patch of numbness beyond the shoulder scar. These patches when they do occur do not normally cause an issue. More significant injury is very rare.

Stiffness. There is a small risk of developing a stiff or frozen shoulder after the surgery. This should get better on its own but does occasionally require treatment.

Deformity. There is a small risk that the reduction of the joint will be lost resulting in recurrence of the deformity.

Fracture. Further injury to the shoulder may result in a fracture (break) of either the Coracoid or Clavicle. The likelihood of this may be increased by the presence of the small drill holes.

While the probability of symptom improvement is high it remains possible that symptoms may remain unchanged or deteriorate.

Further surgery (Re-operation) Rehabilitation

What should I expect after treatment?

Nonsurgical Rehabilitation

If you don't need surgery, range-of-motion exercises should be started as pain eases, followed by a program of strengthening. At first, exercises are done with the arm kept below shoulder level. The program advances to include strength exercises for the rotator cuff and shoulder blade muscles. In most cases, the pain goes away almost completely within three weeks. Full recovery can take up to six weeks for grade two separations and up to 12 weeks for grade three separations. Since there is little danger of making the condition worse, you can usually do whatever activities you can tolerate.

After Surgery

Your surgeon may have you wear a sling to support and protect the shoulder for a few days. A physical or occupational therapist will probably direct your recovery program. The first few therapy treatments will focus on controlling the pain and swelling from surgery. Ice and electrical stimulation treatments may help. Your therapist may also use massage and other types of hands-on treatments to ease muscle spasm and pain.

Therapists usually wait four weeks before starting range-of-motion exercises. You will probably begin with passive exercises. In passive exercises, the shoulder joint is moved, but your muscles stay relaxed. Your therapist gently moves your joint and gradually stretches your arm. You may be taught how to do passive exercises at home.

Active therapy starts six to eight weeks after surgery, giving the ligaments time to heal. Active range-of-motion exercises help you regain shoulder movement using your own muscle power. You might begin with light isometric strengthening exercises. These exercises work the muscles without straining the healing joint.

After about three months, you will start more active strengthening. Exercises will focus on improving strength and control of the rotator cuff muscles and the muscles around the shoulder blade. Your therapist will help you retrain these muscles to keep the ball of the humerus centered in the socket. This helps your shoulder move smoothly during all your activities.

Recovery from shoulder surgery can take some time. You will need to be patient and stick to your therapy program. Some of the exercises you'll do are designed get your shoulder working in ways that are similar to your work tasks and sport activities. Your therapist will help you find ways to do your tasks that don't put too much stress on your shoulder. Before your therapy sessions end, your therapist will teach you a number of ways to avoid future problems.