Acromion-Clavicular (AC) Joint Dislocation (Collar Bone Dislocation)

The acromio-clavicular joint (ACJ) is a small joint in the shoulder between the acromion process of the scapula (shoulder blade) and the clavicle (collar bone). It is typically injured when a sizeable force is directed onto the tip of the shoulder, usually as a result of a fall onto the shoulder. ACJ injuries and dislocations are hence common in athletes who engage in sports like cycling, roller blading, skiing, snowboarding, and skate boarding, as well as in athletes who engage in contact sports like rugby and American football. It is also common in motorcyclists falling off their bike during road traffic accidents.

Patients with ACJ injury or dislocation will typically report a fall onto their shoulder. They will notice pain stiffness, and swelling around the tip of the shoulder. When the dislocation is severe, patients may also notice a ‘step deformity’ of the shoulder, which is not present in the opposite shoulder.

X-ray showing right ACJ dislocation
(X-ray of a patient with a right ACJ dislocation illustrating the step deformity as a result of the superior dislocation of the end of the collarbone, as compared to the normal left ACJ)

Assessment of the shoulder by your doctor will include a routine examination. A series of x-rays will usually clinch the diagnosis of an ACJ dislocation.

Not all ACJ injuries and dislocation require surgical reduction. The majority of low grade injuries and dislocation can be treated non-operatively with a sling and a course for physiotherapy, and gradual return to normal activities from 6 weeks to 3 months.

Surgery is reserved for high grade separations, usually in the case of young and active individuals. There is clinical evidence that high grade ACJ dislocation in active individuals do better in terms of shoulder function after surgery than when treated non-operatively.

Surgery, ACJ fixation, is typically done as a day surgery, under general anaesthesia. The joint is exposed through an open incision and a fixation device in the form of a metal plate or a suspensory rope is utilised to reduce the ACJ dislocation. The most commonly used metal device for this condition, called the hook plate, typically require removal 3 to 6 months after the initial surgery, as it can result in a fracture of the surrounding bone if left un-removed after healing of the ACJ.

ACJ dislocation before and after open surgical reduction
(X-rays of a patient with right ACJ dislocation before and after open surgical reduction using a hook plate. Despite succsessful fixation and healing of the ACJ, this patient required surgical removal of the plate at 4 months after initial surgery)

There has been a recent push towards more minimally invasive ways of doing this surgery with the same efficacy and safety, and Dr Wee is well versed in performing this minimally invasive technique. This minimally invasive technique, better known as arthroscopic assisted ACJ fixation, utilises a key-hole arthroscopy technique to achieve reduction and fixation. The join is typically held reduced with a suspensory fixation device. The benefits of this technique, other than cosmetic reasons, are two-fold: firstly, it affords us the ability to use the arthroscope to look for associated injuries within the shoulder joint which are oftentimes missed with the open technique; secondly, it potentially allows an earlier return to activity as a result of less damage and muscle takedown as we perform the surgery. The minimally invasive and low-profile suspensory device used to maintain the joint reduction in this key-hole technique also does not require subsequent removal via a repeat surgery.

minimally invasive arthroscopic surgery
(Clinical photo of a minimally invasive arthroscopic surgery being performed for ACJ fixation)

minimally invasive arthrosscopic suspensory fixation technique
(X-rays of a patient with right ACJ dislocation before and after surgical reduction using a minimally invasive arthrosscopic suspensory fixation technique)

Most patients will require the use a sling for about 4 to 6 weeks after surgery. Using the minimally invasive arthroscopic technique, Dr Wee will start physiotherapy immediately after surgery, and allow pendular exercises for the 1st 2 weeks. We will then allow passive range of motion for the next 4 weeks. Once the sling is taken off after 6 weeks, we will allow full range of motion exercises. Normal routine daily activities should be achievable by this time. Return to sport or active upper limb activity will usually be allowed at about 3 to 6 months after surgery.

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