The AC (Acromioclavicular) joint is a common cause of traumatic shoulder pain. This injury almost always has a traumatic cause, commonly due to direct forceful contact to the region. Contact or collision sports such as rugby, rugby league and Australian rules football have an increased prevalence of these injuries. The AC joint comprises the end of the clavicle (collar bone) and the acromion process of the scapula (shoulder blade). Therefore, it is a joint which connects the front to the back of the shoulder. The AC joint is stabilised by the acromioclavicular ligament and joint capsule, as well as the strong coracoclavicular ligaments (trapezoid & conoid). The deltoid and trapezius muscle complex also aid in dynamic support to the AC joint. The role of these ligaments is to resits and prevent the collarbone from translating posteriorly.

It is reported that 40-50% of athletic shoulder injuries which present for medical attention, are due to AC joint injuries. The male population are five times more likely to sustain this injury, which would be largely influenced by the historical data of collision sports. More women are playing collision sports, so the prevalence of females suffering these injuries may very well increase.

How is it injured?

Direct blows (high force bumps) to the point of the shoulder where the AC joint is located is one mechanism that is possible. The primary mechanism of injury however, involves a direct fall on the point of the AC joint at the tip of the outer shoulder. The arm is typically positioned in adduction (towards midline) at the point of contact, which translates the acromion medially & inferiorly.

The acromioclavicular ligament fails first, leading to more load being transferred to the coracoclavicular ligament. If this stronger ligament also fails, the deltoid and trapezius muscles have an increased demand to stabilise the joint. It is possible for these muscles to also be injured at their attachment sites, if extreme high force was provided through the mechanism of injury.

Classification of AC joint Injuries

AC joint injuries have been historically classified using the ‘Rockwood system’. This system grades the injury into 6 different grades based purely off imaging findings. This system has received a lot of criticism for not considering the actual patients pain experience and their function. Furthermore, there is confusion around the grading system and its agreement amongst surgeons. This is quite alarming as often the grading of injuries is related to whether surgery is the treatment of choice.

Thankfully at The Reform Lab Osteopathy we pride ourselves on being evidenced based. Our assessment is thorough and will take into account your pain, function, goals and if required refer off for imaging.

Treatment

Like most injuries, the primary treatment options are conservative management (osteopathy & exercise rehabilitation) or surgery. With surgical procedures being invasive, the risk of complications and no certainty surgical fixation will work, a conservative approach is recommended in most cases. Conservative management should include 8-12 weeks of graded and progressive rehabilitation working on function and pain.

In more severe AC joint sprains (grades 4-6), a surgical opinion will likely be warranted. If surgery is required, exercise rehabilitation will be completed afterwards to return to normal activities and sport if the individual has that goal.

At The Reform Lab Osteopathy, we provide exercise rehabilitation out of the elite gym Project Reform.