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.
It is usually caused by a fall onto an outstretched arm with severe pain and swelling on top of the shoulder, especially when trying to move the arm overhead. Treatment includes cold therapy, taping, and rehabilitation exercises.
On this page:
- Symptoms & diagnosis
- Causes & anatomy
- AC joint taping
AC joint sprains range from very mild (grade 1) to a severe (grade 6) injury. Early treatment and support through taping are important to avoid long-term problems or shoulder deformity.
Symptoms include pain right at the end of the collarbone on the top of the shoulder, often following a fall onto the shoulder or onto an outstretched arm. The pain may be widespread throughout the shoulder initially but later on more localized to a bony point on the top of the shoulder.
Pain will be worse when trying to move the arm overhead and there is often swelling and depending on the extent of the injury a deformity may be seen in the form of an obvious lump on top of the shoulder joint. There will be tenderness and swelling and inflammation over the acromioclavicular joint itself. When pressing in there will be point tenderness over the site of injury. In particular, the athlete is likely to have pain on moving their arm out to the sides and upwards (abduction). With more severe injuries a visible deformity in the form of a lump or bump on top of the shoulder is likely.
Grading of AC joint sprains
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.
From this point onwards the scale and grade of injury depend on the degree of displacement of the clavicle.
- 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:
Distracion 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.
AC joint separation causes & anatomy
The AC joint is short for the acromioclavicular joint. Separation of the two bones forming this joint is caused by damage to the ligaments connecting them. It is sometimes also referred to as a shoulder separation injury. The acromioclavicular joint is formed by the outer end of the clavicle or collar bone and the acromion process of the scapular or shoulder blade. The acromion is a bony process which protrudes forwards from the top of the scapular.
The two bones involved in an AC joint separation are attached by the acromioclavicular or AC ligament. There are several other ligaments which can be of importance in AC joint injuries, including the coracoclavicular or CC ligament which joins the clavicle to the coracoid process which is another forward protruding part of the scapula.
A third ligament involved in an AC joint injury is the coracoacromial ligament which attaches the acromion process to the coracoid process, although it is rarely involved in this type of injury. 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.
A doctor may prescribe Anti-inflammatory such as ibuprofen medication to reduce pain and inflammation as well as diagnose the injury and assess how bad it is. 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. Ultrasound for minor injuries or TENS for pain relief can be used in more severe cases.
AC joint sprain taping
An AC joint taping should be applied which fixes and supports the joint into the correct position to assist with healing. The joint may need taping for 2-3 weeks.
First, apply two or three strips of 2.5cm zinc oxide tape over the top of the shoulder covering the AC joint. This will provide an anchor for the support strip to attach to. Next pass a support strip of tape from the front of the shoulder, down the side of the arm applying tension to the tape. Pass it under the elbow and back up to the top. This support strip will help pull the AC joint down. Secure the support strip with a piece elastic adhesive bandage getting the patient to tense the bicep muscle when it is applied to allow for muscle expansion. Finally, trim the lower part of the support taping away to finish.
First, apply two or three strips of 2.5cm zinc oxide tape over the top of the shoulder covering the AC joint. This will provide an anchor for the support strip to attach to. Next pass a support strip of tape from the front of the shoulder, down the side of the arm applying tension to the tape. Pass it under the elbow and back up to the top. This support strip will help pull the AC joint down.
Secure the support strip with a piece elastic adhesive bandage getting the patient to tense the bicep muscle when it is applied to allow for muscle expansion. Finally, trim the lower part of the support taping away to finish.
As pain allows shoulder exercises specifically recommended for AC joint sprain rehabilitation should be progressed.
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.