AC Joint Dislocations

The acromioclavicular (AC) joint is the joint between the part of the shoulder blade known as the acromion and the collarbone (clavicle). The joint is stabilised by the AC and coraco-clavicular (C-C) ligaments (yellow in AC joint diagram). The joint is injured by falls onto the shoulder tip commonly seen in cyclists and contact athletes.

To assist with treatment the injuries have been classified based on the number of ligaments torn and the displacement between the shoulder blade and collarbone.

• Type 1: partial tear of the AC ligament
• Type 2: complete tear of the AC ligament
• Type 3: complete tear of the AC and CC ligaments

Types 1, 2 &3 AC joint injuries are generally treated without surgery. The arm is placed in a sling with elbow support. Painkillers and anti-inflammatory medication may be required for several weeks. Eventually the traumatised tissue around the joint will form scar and stabilise the joint. Patients will have difficulty swimming until 6 weeks after the injury and it may take up to a year before they can comfortably sleep on that shoulder. There may always be a lump on the injured shoulder. Even in Type 3 injuries there is no obvious change in function (strength, fatigue, range of motion) at assessment 5 years after injury. A small percentage of patients (<5%) remain unhappy with their AC joint and request surgery. The results of delayed AC joint stabilisation are similar to those of acute repair.

Surgical treatment of AC joint dislocations is reserved for a small percentage of cases that include:

1. Type 5 dislocations. In addition to complete tearing of the AC and CC ligaments in type 5 dislocations the muscular attachments are also torn off around the AC joint. This leads to a greater separation of the shoulder blade and collarbone. The local scarring is not sufficient to provide long-term stabilisation of the shoulder blade. Positioning of the shoulder blade requires chronic neck and back muscle activation that can lead to a low grade ache and fatigue pain at the end of the day
2. Type 4 & 6 dislocations are rare but result in a locked position of the end of the clavicle
3. Type 3 dislocations in overhead manual workers and athletes
4. Failed non-operative management

The surgical techniques for AC joint reconstruction are many and varied. In acute reconstructions (< 2 weeks post injury) if the original anatomy can be restored the native ligaments can scar to provide long-term stability. In delayed reconstructions, in addition to restoring anatomy, a biological ligament must be passed between the shoulder blade and collarbone to provide long-term stability.

My Preferred Procedure for:

1. Acute reconstructions: is restoring anatomy using a plate and screw device (AO hookplate). The hook of the plate runs behind the AC joint and holds the shoulder blade up to the collarbone. The procedure requires an anaesthetic, takes about 1 hour and requires an overnight hospital stay. The pain after surgery needs to be controlled on oral medications before discharge. A sling is required until 4 weeks post surgery and range of motion is gradually restored. There may be residual shoulder pain with above shoulder activity that is generally cured by plate removal. The hookplate must be removed at 3 months post surgery. This requires another operation with the recovery limited to the 2 weeks of wound healing.

2. Delayed reconstructions: uses a biological ligament (local or distant) and coraco-clavicular approximation with devices such as the hookplate or tightrope. These require sling immobilisation for six weeks. Restoration of movement and strength is slower than in acute reconstructions.

The operation specific risks include but are not limited to infection, local skin nerve damage, shoulder stiffness and failed ligament healing and loss of stabilisation. There is a risk of acromial fracture in hookplate reconstructions, if repeat injury occurred while the device remained in the body. If the hookplate is not removed around 3 months post insertion there can be bony erosion with time. There can be a slight loss of reduction of AC joint alignment with hookplate removal that does not seem to affect the long-term result.