An AC joint separation, or AC joint sprain, is an injury to the ligaments which hold the acromioclavicular joint together at the top of the shoulder. Here we explain the symptoms, causes, and treatment for AC joint sprains.
AC joint sprains are often caused by a fall onto an outstretched arm. Symptoms include:
- Pain on top of the shoulder, at the end of the collarbone.
- Pain may be widespread throughout the shoulder initially, but later, more localized to a bony point on the top of the shoulder.
- Pain will be worse when trying to move the arm out sideways (abduction) and overhead.
- If you have a more severe injury then you may have a visible deformity (an obvious lump) as the clavicle is displaced upwards from the shoulder.
- The top of your shoulder will be tender, with swelling and inflammation over the acromioclavicular joint itself.
How bad is my AC joint sprain?
AC joint injuries are graded from 1-6 using the Rockwood scale which classifies injuries in relation to the extent of ligament damage and the space between the acromion and clavicle.
- Grade 1 is a simple sprain to the AC joint with minor damage to the ligament and no separation of bones.
- Grade 2 involves rupture of the AC ligament or acromioclavicular ligament.
- Grade 3 rupture of both AC and CC or coracoclavicular ligaments which often results in an upward displacement of the clavicle bone.
- Grade 4 involves posterior displacement or displacement backward.
- Grade 5 superior displacement, to a greater degree than grade 3, with an increase in coracoclavicular space by 3-5 times the norm. A step deformity may be apparent with grade 3, 4 & 5 injuries.
- Grade 6 involves full rupture of both AC and CC ligaments with the clavicle being displaced inferiorly or downwards.
Special assessment tests
A professional therapist may do a number of special tests to confirm the diagnosis:
- Distraction test (piano key sign) involves the athlete sitting with both arms relaxed down by their sides. The professional therapist or athletic trainer pulls down on the wrists and looks for a ‘hollowing out’ just behind the joint.
- Crossover test – the therapist or trainer abducts (moves) the athlete’s arm across the front of the body whilst compressing the joint.
What is an AC joint sprain/separation?
An Acromioclavicular joint sprain is a tear (or stretching) of the ligaments which hold the clavicle bone to the top of the shoulder blade. It is usually caused by a fall onto an outstretched arm.
The acromioclavicular joint is formed by the outer end of the clavicle (collar bone), and the acromion process of the scapular (shoulder blade). The main ligament that joins the two bones is called the acromioclavicular ligament.
A minor AC joint sprain may involve stretching only of this ligament. A more severe injury will result in the acromioclavicular ligament rupturing completely as well as the coracoacromial and coracoclavicular ligaments. If this happens then the clavicle bone will protrude upwards. As a result, the injured shoulder will look deformed.
What causes an AC joint sprain
The most common way of injuring the AC joint is by landing on the shoulder, elbow, or onto an outstretched hand. The athlete falls and automatically places their hand out to break the fall. The forces are then transmitted up the wrist and arm to the shoulder joint.
Treatment for ac joint sprains
- Immediate first aid for any AC joint injury is to apply the PRICE principles of rest, ice, compression and elevation.
- Apply ice or cold therapy and compression wrap as soon as possible to reduce pain and swelling.
- Wear a sling to immobilize the shoulder and ease pain by taking the weight of the arm.
If a bad AC joint injury is not properly treated it can lead to long-term deformity in the form of a lump on top of the shoulder.
What can a professional/doctor do?
- A doctor may prescribe anti-inflammatory such as ibuprofen medication to reduce pain and inflammation.
- They will do a full assessment to diagnose the injury and assess how bad it is.
- They may tape the joint to keep it stable whilst healing.
- Ultrasound for minor injuries or TENS for pain relief can be used in more severe cases.
Cross friction massage may be applied to the injured ligaments after the acute phase. This will help soften scar tissue.
Rehabilitation & exercises
As pain allows shoulder exercises specifically recommended for AC joint sprain rehabilitation should be progressed. Initially, the aim is to restore normal mobility and ‘scapular rhythm’. The scapula and humerus (upper arm bone) should move together with the correct timing. In the injured athlete this rhythm is often lost.
As your shoulder heals, more advanced stretching and strengthening exercises are done. Strengthening begins with static or isometric exercises and progress to dynamic, functional and sports specific exercises.
Read more on AC joint sprain rehab exercises.
Do I need surgery?
- A grade 1, 2 or 3 injury is usually treated conservatively without surgery.
- Grade 4, 5 and 6 injuries and grade 3 sprains which do not respond to treatment usually require surgery
If this injury is neglected and allowed to heal out of place this could increase the wear and tear on your joint causing you problems in the future.