The AC joint or acromioclavicular joint is where the acromion (a part of the shoulder blade) connects to the clavicle (collar bone) at the top of the shoulder.
The AC joint helps to maintain the proper position of the shoulder as well as control motion and strength. It is stabilized by a capsule and ligaments, and injury occurs when these structures are damaged.
When the capsule and ligaments are injured, the joint can become unstable and painful, and shoulder function can be affected.
This type of injury is referred to as an “AC joint sprain” or a “separation.”
These injuries typically occur after a sudden fall onto the shoulder or overuse (repeated lifting of heavy weights or objects overhead with poor mechanics).
The AC joint is also a common place that arthritis develops, which can become painful when irritated.
In this article I'll share a few tests, exercises and treatments that could help with AC joint injuries.
Causes of AC Joint Shoulder Pain
Sudden AC joint injuries (“sprains” or “separations”) typically occur by one of the following ways:
A fall onto the shoulder or blunt force trauma
Lifting weights or heavy objects using poor biomechanics
Alternatively, AC joint arthritis typically occurs slowly over time as a result of overuse and can become flared resulting in short bouts of pain.
Acromioclavicular (AC) joint injuries are the most common reason for medical consults following an acute shoulder injury, yet remain a frequently overlooked problem due to diagnostic bias toward other shoulder problems. 
Pain from an acromioclavicular injury can be from the joint capsule itself, or any number of four ligaments (superior, inferior, anterior and posterior ligaments).
In general, ligament sprain injuries are graded based on the degree of tissue damage:
Grade 1 (mild strain with no fiber disruption)
Grade 2 (partial fiber disruption)
Grade 3 (complete ligamentous rupture).
AC joint injuries are categorized based upon the following Rockwood classification:
Type I – mild, unseparated sprain of the AC ligaments with no disruption of the coracoclavicular ligaments.
Type II – complete disruption of the AC ligaments with joint separation (less than 4 mm or 40% difference) and sprained but intact coracoclavicular ligaments.
Type III – complete disruption of AC and coracoclavicular ligaments with joint separation and inferior displacement of the shoulder complex.
Type IV – complete disruption of AC and coracoclavicular ligaments with posterior displacement of the clavicle through the fibers of the trapezius, and detachment of deltoid and trapezius muscles from the distal clavicle.
Type V – complete disruption of the AC and coracoclavicular ligaments with significant inferior displacement of the shoulder complex from the clavicle as compared to a typical Type III injury.
Type VI – complete disruption of the AC and coracoclavicular ligaments, and the clavicle has dislocated inferiorly, below the coracoid process.
It's estimated that AC joint injuries are responsible for 40-50% of all athletic shoulder injuries and males are affected five times more often than females.
Symptoms of AC Joint Shoulder Pain
The classic presentation of AC joint pain involves pain and swelling on the superior (top) aspect of the shoulder following acute trauma.
Initially, symptoms are often generalized to the trapezius and entire shoulder region but become progressively more localized to the AC joint as acute swelling improves.
Symptoms may intensify with specific movements, including bench pressing, dips, or when the individual rolls onto the affected side at night.
Range of motion testing will be painful and limited, particularly in abduction (moves the limb laterally away from the midline of the body).
For a review of self-assessment tests, watch this video:
Treatment for AC Joint Shoulder Pain
AC joint injuries result in sport-specific and activities of daily living disabilities, ranging from 1 to 10 weeks.
Passive mobility exercises should be initiated early and gradually progress into full active ROM.
The goal of strengthening is to maximize stability of the AC joint and return to your prior level of activity.
Strength training should begin with closed chain scapular stabilization exercises, progressing to isotonic strengthening, and eventually sport-specific training. Pain tolerance should dictate progression during the flexibility and strengthening phases of care.
There are 3 levels of physical therapeutic or corrective exercises to consider. In this article, I'm going to share the first.
Codman's Pendulum Exercise
Begin by bending forward until the spine is at a 45 degree angle to the floor. Support upper body with opposite arm on sturdy chair without wheels. Maintain a straight spine and do not round low back. Arm should hang directly below shoulder. Grasp a light dumbbell or weight (1-5lbs.).
Initiate slight forward and back movement with shoulder, trying to minimize any tension in arm. Arm should swing like a pendulum. Keep movement range of motion small. Repeat for prescribed duration and sets. Then repeat, this time initiate slight inward and outward movement with shoulder, trying to minimize any tension in arm. Repeat for prescribed duration and sets. Lastly, initiate small clockwise movement with shoulder, trying to minimize any tension in arm. Keep movement range of motion small. Follow this by counter clockwise movement. Repeat for prescribed duration and sets. Alternate sides as directed.
Begin by sitting alongside a table with a towel between the hand and table.
Slowly slide hand directly forward, simultaneously flex trunk forward while sliding hand as far forward until end of shoulder flexion range of motion. Slowly return to starting position by slowly sliding the hand back and sitting up slowly. Repeat for prescribed number of repetitions before switching sides.
Begin lying down on your back. A pillow may be placed under head for support. Grasp a dowel with the uninvolved hand while placing the other end against the hand of the involved side.
Slowly lift arm upward as tolerated. Allow dowel to gently assist arm flexion to 180°. Maintain a neutral spine position paying close attention not to arch your low back. Slowly return to start position. Repeat for recommended sets and repetitions.
Isometric Internal and External Rotation
Begin by standing next to a firm object or a doorway. Maintain good posture, so that spine is straight with shoulders back and head up. Bend arm with elbow at side and place back of hand against door frame.
While maintaining good posture, exert pressure with back of hand against the firm object or door frame until muscle contraction is felt in shoulder. Keep elbow next to side during entire movement. Hold for 5-10 seconds or for recommended duration. Repeat for prescribed repetitions and sets.
Begin by standing next to a firm object or doorway. Maintain good posture, so that spine is straight with shoulders back and head up. Bend arm with elbow at side and lightly grasp the firm object or door frame.
While maintaining good posture, exert pressure with hand against the firm object or door frame until muscle contraction is felt in shoulder. Keep elbow next to side during entire movement. Hold for 5-10 seconds or for recommended duration. Repeat for prescribed repetitions and sets.
AC Joint Shoulder Pain and Chiropractic Care
Chiropractic has been proven to be very effective for AC joint pain. A chiropractor can perform shoulder or AC adjustments which involves manipulation of the shoulder girdle.
While it can be a little uncomfortable for the patient, it is one of the best ways to quickly decrease the pain. After the procedure, a chiropractor may recommend icing as well as corrective exercises similar to the ones presented in this article.
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