An acromioclavicular (AC) joint sprain is a common shoulder injury that usually results from falling onto the shoulder. Another cause of this injury is falling onto an outstretched arm with which you are trying to break the fall.
Another common name for this injury is shoulder separation since it causes an increase in the space between the shoulder blade and collarbone.
This type of injury frequently occurs in contact sports when athletes collide with each other and fall to the ground. Typical sports in which it occurs are hockey, rugby, skiing, football, cycling and snowboarding. It is also sometimes seen in victims of motor vehicle accidents.
Because the AC joint has many ligaments that connect its constituent bones together, an injury to the joint usually damages one or several ligaments.
The typical symptoms of an AC joint sprain are pain and tenderness at the location of the joint (see below).
The acromioclavicular joint is the point at which the shoulder blade meets the collarbone, or clavicle. The two bones are connected by several strong (ac) ligaments that hold the highest point of the shoulder blade (the acromion) to the collarbone. These are the ligaments that are damaged when an AC joint injury occurs. Although the ligaments are strong, the superficial location of the AC joint makes it particularly vulnerable to injury through trauma.
There are actually two types of ligaments in the ac joint. The ligaments responsible for horizontal stabilization of the joint are acromioclavicular (ac) ligaments. Those responsible for vertical stability are the coracoclavicular (cc) ligaments. Both the ac and cc ligaments are susceptible to injury when an ac joint injury occurs.
The ac joint is one of the two shoulder joints. The other joint is the glenohumeral joint where the upper arm bone meets the shoulder blade in a ball and socket connection. The AC joint is more likely than the glenohumeral joint to be affected when a shoulder injury occurs.
Typical Causes Of An AC Joint Sprain
As mentioned above, the most typical circumstances that lead to this injury are:
Falling onto the shoulder;
Falling onto the outstretched hand (while trying to break the fall);
Receiving a blow to the shoulder, possible due to colliding with something or someone.
What Are The Symptoms Of An AC Joint Sprain?
As with many types of soft tissue injury, the symptoms can vary widely depending on the severity of the injury. Specifically, they can vary significantly depending on whether ligaments have been stretched without tearing, or have been torn.
In general, people with an ac joint sprain experience:
The shoulder may feel sore and “tender to the touch”;
For more severe injuries, there may also be bruising on the skin of the shoulder;
The shoulder may appear to “droop” compared to its normal shape;
The collarbone may appear to have moved upwards, producing a bulge above the shoulder;
The patient may also experience reduced shoulder function and range of movement.
Both the drooping of the shoulder and the upward movement of the collarbone are direct results of the ligament damage. When healthy, the ligaments are supposed to hold the two bones together. However, when damaged, the ligaments are unable to hold the collarbone as close to the shoulder blade as they should.
People experiencing some or all of these symptoms, especially after a fall, should seek medical advice. Injuries causing symptoms suggestive of nerve or muscle compression should be referred immediately to a doctor who specializes in bones and joints (orthopaedic surgeon).
Treatment of an acromioclavicular joint sprain will, of course, depend on the severity of the injury. However, in most cases, the treatment plan below is sufficient to produce a full recovery, given enough time to work:
Resting the shoulder by avoiding activities that could stress the joint. In particular, avoid reaching overhead or sleeping on the injured shoulder;
Apply a cold compress (for example ice blocks wrapped in a towel) to the shoulder every 2-3 hours for periods of around 20 minutes. This will reduce blood flow through the area and ease pain and swelling;
For further pain mitigation, consider a simple OTC painkiller like Tylenol (paracetamol) or an oral NSAID like ibuprofen (advil) or naproxen (aleve);
Have a therapist design a physical therapy program that will improve shoulder strength and keep your shoulder muscles supple. This should take place when the patient is more comfortable and will help to reduce the risk of recurrence of the injury;
Patients whose symptoms do not improve after conservative treatment should be referred to orthopaedics.
The healing process for an acromioclavicular joint injury usually takes about 6 weeks. However, in more severe injuries, it can take as long as 3 months.