John went in for the ball but was tackled off it and ended up falling onto his shoulder to the ground. He was able to finish the game but had a lot of pain when he stretched his arm across the front of his chest.
AC joint anatomy
The acromioclavicular (AC) joint combines the distal clavicle and the acromion (the superolateral part of the scapula). The joint is supported by a ligament complex as well as the surrounding fascia and muscles. The main ligaments involved are the acromioclavicular ligaments and the coracoclavicular (CC) ligament. The CC ligament is made up of the lateral trapezoid ligament and the medial conoid ligament.
Mechanism of injury
Injury to the AC joint means disruption of the AC ligaments with or without disruption of the CC ligament. It occurs in up to 10% shoulder girdle injuries and is more common in athletes. Injury typically occurs from a direct blow or following a fall onto the superior or lateral part of the shoulder with the arm adducted. This results in the acromion being forced inferiorly and medially to the clavicle. Injury with a low force causes an AC sprain, with progressively increased force causing AC ligament rupture and then additional sprain and rupture of the CC ligaments.
AC joint injury presents with pain and tenderness over a possibly swollen AC joint. The pain may also be referred to the trapezius muscle. When compared to the contralateral side there may be an abnormal contour.
If the diagnosis is in doubt you can perform the crossbody ADDuction (Scarf test) to compress the AC Joint. If this is painful, this is suggests AC joint injury. A careful distal neurovascular exam of the involved extremity shoulder be performed, documenting radial, ulnar and median nerve function (take a look at the examining paediatric elbow post for top tips on conducting a proper neurovascular assessment in upper limb injuries).
It is important to rule out atraumatic distal clavicle osteolysis, a repetitive stress injury in young athletes who do high level upper weight training.
There are two approaches to plain film imaging in suspected AC joint injury:
- a single AP view including both AC joints
- one AP view of each shoulder comparing affected with the unaffected side
This image from Orthobullets.com shows AC joint widening on the left compared to a normal AC joint on the right.
If there is still some doubt the AC joints can be better seen on Zanca views using a 10-15 degrees of cephalic tilt. Stress views are often used with weights in each hand to determine AC joint instability. This is important also to out-rule coracoid fractures often seen in stress overuse as in young athletes who do repetitive weight training.
Look carefully at the clavicle for any associated occult clavicle fractures.
Paediatric AC joint injuries are classified as grades I – VI by the Rockwood classification.
In the ED, the most common injuries, occurring after minor trauma, are types I to III, ranging from stretching of the AC ligament to complete tear with clavicle lifting:
- I – AC ligament sprain with intact periosteal sleeve
- II – Partial periosteal sleeve disruption with AC Joint widening (CC distance <25% contralateral side)
- III – Disrupted periosteal sleeve with superior (upwards) displacement of the clavicle, with between 25 – 100% displacement
Types IV to VI typically occur after high energy trauma and need surgical intervention:
- IV – Distal clavicle displaced posteriorly through the trapezius
- V – Deltoid and trapezius detachment and clavicle displacement >100%
- VI – Clavicle displaced inferiorly under the coracoid
Rockwood Grades I – III AC joint injuries: Non-operative management is the mainstay as these are low energy injuries. Analgesia, ice and rest in a sling or figure-of-eight braces followed by gentle range of motion exercise once the pain has settled. Early rehabilitation with cautious exercise results in earlier return of normal shoulder range of motion, with functional motion by 6 weeks and normal activity by 12 weeks. The lower the grade the earlier the return to normal function. Caution needs to be taken to avoid manoeuvres that that strain the ligaments and cause pain. Avoid cross-body ADDuction, extreme internal rotation (i.e. behind the back) and overhead movements.
Rockwood Grades IV to VI injuries: Operative management is indicated in grades IV to VI but also in Grade III that have failed non operative treatment or in elite athletes and for cosmesis.
Up to 30 – 50% of patients with AC joint injuries complain of residual pain.
John thankfully only had a Grade II AC joint injury and wore a shoulder immobilizer for 3 weeks. He’s already back training but is a little more cautious when he goes in for the tackle.
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S. Evrim. N. Aydin, OM. Topkar. Acromioclavicular joint injuries: diagnosis, classification and ligamentoplasty procedures. EFORT Open Rev 2018;3:426-433