AC Joint Injury





The acromioclavicular (AC) joint is formed by the cap of the shoulder (acromion) and the collar bone (clavicle). It is held together by three taut ligaments. The outer end of clavicle furthest from the body is held in alignment with the acromion by the acromioclavicular ligaments and the coracoclavicular (CC) ligaments.


The AC joint is strong, but its location makes it vulnerable to injury from trauma. Injury to the ligaments (also called shoulder separation) can occur as a result of a fall, direct blow, or hyperextension.


Acromioclavicular injury — Acromioclavicular injury is labeled as a type I, II, III, IV, V, or VI, depending upon the extent of injury and number of ligaments involved. The type of injury can usually be determined with a physical examination and x-rays.

Type I injuries involve a sprain or partial tear of AC ligaments with no injury to the CC ligaments. This causes a tender AC joint that often has mild swellings

 Type I sprains usually heal within a few weeks.

Type II injuries involve a complete tear of the AC ligaments and a sprain or partial tear of the coracoclavicular (CC) ligaments. This causes a tender AC joint, often with significant swelling

Type III injuries involve a complete tear of both the AC and CC ligaments. The AC joint will appear abnormal, although swelling may obscure the degree of injury. People with type III injuries have significant tenderness of the CC ligaments, which helps distinguish type III from type II injuries. Type III injuries often take longer to heal (several weeks to months).

Type IV, V, VI injuries are the most severe Treatment often requires surgery.


Pain at the end of the collar bone where it sticks up into the shoulder . Pain when you move your shoulder, especially when raising your arms above the shoulders. Pulling the affected arm across the opposite shoulder provokes discomfort. If you have had neglected the injury for a while, you may notice a weakness in the upper arm and an aching pain on performing overhead activities.


  • Imaging Studies


As with all skeletal injuries, a minimum of 2 radiographic views is necessary to evaluate the individual injury in cases of suspected acromioclavicular joint injury.

AP and lateral views are the minimum needed to evaluate an acromioclavicular joint injury. The AP view should be taken with the arms at the side, and both acromioclavicular joints should be imaged for comparison. If a true AP view is obtained, the acromioclavicular joint can be seen superimposed on the spine of the scapula; hence, some authorities have recommended the Zanca view, in which 10-15° of cephalic tilt of the radiographic beam provides a clearer image of the acromioclavicular joint.

An axillary lateral view is also needed in suspected acromioclavicular joint injuries to account for any anterior or posterior displacement of the distal clavicle.

If an unstable acromioclavicular joint injury is suspected, yet not confirmed on routine AP and lateral views, stress views may be indicated.

Ten to 15 lb of weight should be attached to the wrist of the affected side, and an AP view can be taken. This stress tests the integrity of the coracoclavicular ligament, and, if the ligament has been disrupted completely, the test will demonstrate the complete dislocation.

Routine use of stress radiographs is not recommended in the emergency department setting because of the painful nature of the test. Weighted stress tests may be valuable in follow-up care if the clinician has any doubt about the instability of the acromioclavicular joint. Even with conservative care of types III-VI acromioclavicular disruptions, this test may be helpful for determining a timetable for return to conditioning and sporting activities.

Athletes with a previous history of acromioclavicular injury or a history of heavy weight lifting may present with relatively acute shoulder pain over the distal clavicle, and they may have classic radiographic findings of distal clavicle osteolysis or acromioclavicular osteoarthritis (ie, joint narrowing, distal clavicle or acromial spurring). When these radiographic findings are present, the clinician may expect that seemingly little trauma may result in significant pain.

Magnetic resonance imaging (MRI)

MRI is not routinely ordered in the management of straightforward acromioclavicular disruptions. Detailed knowledge of acromioclavicular and coracoclavicular ligamentous injury is not needed for conservative or, in rare cases, surgical care.

In middle-aged and older patients who continue to have disabling shoulder pain after the acute pain of an acromioclavicular disruption abates, one may consider an MRI to evaluate for a possible rotator cuff tear.

Very rarely, athletes with persistent pain over the acromioclavicular joint merit an MRI to determine whether or not the cartilaginous disk has been damaged irreversibly and to determine whether or not the process of distal clavicle osteolysis or early osteoarthritis has begun.


Pain relief — If needed, a pain medication such as acetaminophen can be taken; the usual dose of acetaminophen is two 375 mg tablets every four to six hours as needed. No more than 4000 mg of acetaminophen is recommended per day, and anyone with liver disease or who drinks alcohol regularly should speak with their healthcare provider before using acetaminophen.

A nonsteroidal antiinflammatory drug (NSAID), such as ibuprofen (eg, Advil®, Motrin®) or naproxen (eg, Aleve®) can also be used for pain. The dose of these NSAIDs is available.

Type 1 — Type I injuries are best treated initially with rest, ice, and protection, often with an arm sling. Ice can be applied for 15 minutes every four to six hours as needed. Rest includes avoiding overhead reaching, reaching across the chest, lifting, leaning on the elbows, and sleeping directly on the shoulder.

Range of motion exercises — Range of motion exercises are recommended early in the recovery period. These exercises are intended to help maintain joint mobility and flexibility of the muscles and tendons in the shoulder. Pain should not exceed mild levels with any range of motion/flexibility exercise. Anyone who feels sharp or tearing pain while stretching should stop exercising immediately and consult with a healthcare provider.

Weighted pendulum stretch — The weighted pendulum stretching exercise performs two functions:

Gently stretches the space in which the tendons pass to relieve pressure on the tendons

Prevents the development of a frozen (stiff) shoulder

This exercise can be started almost immediately after a shoulder injury. This exercise should be performed after heating for five minutes once or twice per day. The exercise is performed as follows:

  • Relax your shoulder muscles
  • While standing or sitting, keep your arm vertical and close to your body (bending over too far may pinch the rotator cuff tendons)
  • Allow your arm to swing forward to back, then side to side, then in small circles in each direction (no greater than 1 foot in any direction). Only minimal pain should be felt.
  • Stretch the arm only (without added weight) for three to seven days. Progress this exercise by adding 1 to 2 pounds (0.5 to 1 kg) each week and gradually increasing the diameter of the movements (not to exceed 18 to 24 inches or 45 to 60 cm )
  • After a few weeks this exercise should be supplemented or replaced by other exercises to target specific areas of tightness/restriction. The pendulum stretch may be recommended as a warm up for more localized flexibility exercises and/or strengthening exercises.
  • When performed correctly the pendulum exercise should not result in more than mild discomfort.

Return to activity — Most people are able to return to full activities between 3 days and 2 weeks after an acromioclavicular joint injury. Athletes who use overhand motions (eg, those who play tennis and serve volleyball, baseball pitchers, American football quarterbacks) may require 2 to 3 weeks to return to full activity. Complete healing may take 4 to 6 weeks. Type I injuries generally heal well without an increased risk of reinjury.

Type II — Type II injuries usually cause greater pain and swelling than type I injuries. Initial treatment may include rest, ice, pain medication, and three to seven days of shoulder immobilization in a sling. Range of motion exercises can be started when tolerable

Strengthening exercises — Muscle strengthening exercises are necessary to improve shoulder muscle strength and help to prevent further injury. These exercises can often be started approximately one to two weeks after beginning the pendulum stretch exercises (described above), depending upon the level of pain.

As pain improves, the level of difficulty of these exercises should be increased. Increased difficulty is necessary to improve muscle strength to a degree that reduces the risk of re-injury. Mild soreness is expected with these exercises, although pain should not continue for more than 24 hours. Sharp or severe pain during or after exercising may indicate a flare of the underlying problem; stop these exercises for a few days if this occurs.

Preparing for strengthening exercises — Once the swelling has decreased, the shoulder may be warmed with cardiovascular exercise or a warm pack and stretched with range of motion exercises before beginning strengthening exercises 

Rest after stretching for two or three minutes, then perform 15 to 20 repetitions of each exercise slowly, holding for one to two seconds during each exercise. Flexible rubber tubing, a bungee cord, or a large rubber band can be used for each exercise.

Scapular squeezes — Lie on your back with your knees bent and feet flat. Your arms should be straight out, six to 12 inches (15 to 30 cm) away from the side of your body, with palms facing upward. Keeping your low back flat against the ground, squeeze your shoulder blades downward and towards each other, towards the spine. Make a conscious effort not to shrug your shoulders and keep the neck relaxed. You should feel the lower muscles between your shoulder blades contracting. Hold for five seconds and repeat 20 times. Do this exercise two to three times per day.

The difficulty can be increased by performing it while sitting and then by holding a piece of tubing in each hand and pulling the hands apart while squeezing the shoulder blades, as described above.

Outward rotation exercise — Hold your elbows at 90 degrees, close to your sides; holding a towel between your torso and the inside of your elbow will cue you to keep your elbow by your side. Hold one end of a rubber band in each hand and rotate the affected lower arm outward two or three inches, holding for five seconds 

Perform the exercise through all available pain-free ranges of motion. Keep the shoulder blades squeezed down and back while performing this exercise.

Return to activities — After a type II AC injury, most people are able to return to full activities when full range of motion and strength are regained, usually after 2 to 4 weeks. Complete healing generally requires several more weeks.

Type III — The majority of people with type III injuries can be managed with non-surgical treatment, including rest, ice, immobilization with a sling, and pain medication. A sling may be recommended for 3 to 4 weeks to aid in healing and to relieve pain.

Range of motion and strengthening exercises can begin as soon as they are tolerable. The intensity of these exercises should be increased gradually, based upon pain.

Return to activities — Patients with a type III injury may return to normal activities between six and twelve weeks following injury, when full range of motion and strength are regained. Some people return to activity sooner or later, depending upon the demands of the specific activities

Type IV, V, VI — Type IV, V, and VI AC injuries are the most severe. People who have this type of injury should see a physician who specializes in bones and joints (an orthopedist). If nerves or muscles are compressed as a result of the injury, treatment is needed urgently to reduce the risk of long-term complications. Surgery is often recommended.