Separated Shoulder and AC Joint Injury Explained

Discover the causes behind a Separated Shoulder, plus the correct treatment and prevention strategies.

by Brad Walker | First Published April 10, 2009 | Updated September 1, 2021
A separated shoulder, also known as acromioclavicular joint injury, is a common injury to the shoulder (acromioclavicular) joint.

Injuries can occur in either of the joints in the shoulder complex. Arthritis and fractures can occur at both joints. Dislocations occur in the glenohumeral joint, and separations occur in the AC joint.

High impact contact sports, or falling on an outstretched hand or onto the shoulder, can cause AC joint separations, resulting in pain and limited movement and function.

Separated Shoulder and AC Joint Injury Explained

What is a Separated Shoulder Injury?

There are two main shoulder injuries common to the AC joint.

  • The first common injury to the AC joint is a shoulder separation. This is when the scapula and clavicle separate and the two ligaments that connect the bones to form the joint are stretched or torn.
  • The second, a chronic condition, is arthritis. This leads to a loss of cartilage in the joint, causing friction between the bone ends. This leads to pain and inflammation, especially during use. Swelling often occurs with this condition, as well. Overtime the joint may wear out and spurs may form.

AC Joint Injury Classifications

AC separations are commonly classified I through III, but there are classes IV, V and VI as well, although they are much less common.

  • A class I separation involves just some stretching of the ligaments and pain in the joint.
  • Class II separations include a tear of one of the ligaments and no, or partial, tearing of the other ligament.
  • Class III separations are complete tears of both ligaments with a complete separation of the clavicle.
  • Class IV is very rare and occurs when the clavicle is pushed behind the AC joint.
  • Class V separations are an extension of class III separations, where the muscle above the joint is punctured by the clavicle end.
  • And class VI separations are also rare and occur when the clavicle is pushed downward and becomes lodged below the coracoid (a structure of the scapula.)
Separated shoulder joint anatomy

Anatomy of a Separated Shoulder

The shoulder joint is a complex joint. It is the meeting point of three bones: the clavicle, the scapula and the humerus.

The shoulder complex consists of two joints, the glenohumeral joint and the acromioclavicular (AC) joint. The glenohumeral joint is the ball and socket joint of the shoulder, where the head of the humerus connects. The AC joint is where the acromion of the scapula and the clavicle come together.

The scapula and clavicle form the socket for the head of the humerus, so these two joints work together to form the shoulder complex.

The AC joint is formed by the joining of the lateral end of the clavicle with the acromion of the scapula. The joint is cushioned by cartilage encapsulated in the joint. The joint is held together by two ligaments: the acromioclavicular and the coracoclavicular ligaments. The joining of the scapula and the clavicle forms the socket for the head of the humerus, forming the glenohumeral joint.

What Causes Separated Shoulder Injury?

An AC separation is commonly attributed to a sudden, traumatic event. It may be caused by a violent blow or collision to the shoulder complex (as seen in football, rugby, hockey, and other high impact sports) or a fall on an outstretched arm or onto the shoulder.

Signs and Symptoms

A shoulder separation is usually accompanied by moderate to severe pain at the site of the injury. It is often a sharp pain at the time of injury gradually changing to a dull, aching pain over time.

Deformity at the joint may be noted, as well, especially with grade III separations. A loss of function, due to the pain and instability, often accompany the higher-grade separations. Instability in the joint may also accompany this injury. In more severe cases the fingers and hand on the affected side may begin to tingle or go numb, a sign that swelling in the shoulder is affecting circulation and nerve impulse transmission.

Preventing a Separated Shoulder

Mark my words, “Prevention is much better than Cure.” Anything you can do to prevent an injury from occurring is worth it. The prevention of shoulder injuries comes down to the conditioning of the shoulder muscles and tendons, which ultimately involves both stretching and strengthening of the shoulder joint.

Also, don’t forget the common injury prevention techniques like, warming up properly and using a bit of old-fashioned common-sense. However, for the most part, stretching and strengthening are going to be your best defense against shoulder problems. Even if you don’t have a shoulder problem now, the following suggestions will be helpful.

  • A general warm up, followed by an activity specific warm up, will help to prepare the muscles and tendons for any activity to come.
  • Reducing the frequency of, or stopping completely, any activities that aggravate the shoulder.
  • A good strengthening program to develop musculature around the shoulder joint will help to protect it from violent trauma during sports and reduce the chance of an AC separation occurring.
  • Stretching the shoulder girdle to keep the muscles loose and the ligaments supple will reduce the damage sustained when trauma to the shoulder is inevitable.
  • The use of proper protective equipment when involved in contact, or collision, sports will also reduce injuries to the shoulder.
  • Rest in between training sessions or competition allows the body to heal the minor injuries and repair the muscles to be ready for the next round of activity. Rest is the time that the body uses to repair and rebuild.

Separated Shoulder Treatment

A shoulder separation requires immediate rest, support for the arm (especially in class II and III separations) with a sling and ice on the joint to reduce inflammation. NSAID’s may be helpful, also. Beginning to move the fingers, then the wrist and on up to the shoulder, as pain allows, will help to reduce the chance of developing frozen shoulder. This may be best directed by a physical therapist or sports medicine professional.

In severe grade III cases (and often in grades IV through VI) surgery may be required. Recovery time varies depending on the class of separation, with grade I separations returning to full activity in 10 to 14 days while grade III separations may take six to eight weeks (or more if surgical interventions are required.)

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Research and References

Brad Walker - AKA The Stretch CoachAbout the Author: Brad Walker is often referred to as the "Stretch Coach" and has even been called the Stretching Guru. Magazines such as Runners World, Bicycling, Triathlete, Swimming & Fitness, and Triathlon Sports have all featured his work. Amazon (author page) has listed his books on five Best-Seller lists. Google cites over 100,000 references to him and his work on the internet. And satisfied customers from 122 countries have sent 1,000's of verified customer reviews. If you want to know about stretching, flexibility or sports injury management, Brad Walker is the go-to-guy.

Disclaimer: The health and fitness information presented on this website is intended as an educational resource and is not intended as a substitute for proper medical advice. Please consult your physician or physical therapist before performing any of the exercises described on this website, particularly if you are pregnant, elderly or have any chronic or recurring muscle or joint pain.