ACG DISLOCATION

The acromioclavicular joint is surrounded by a tight capsule and intertwined ligaments, which allows it to withstand enormous loads. 

Typically, the AC joint receives little attention until it is ruptured after a fall or causes pain due to osteoarthritis. 

You can find out what to do here:

What causes the AC joint to crack?

"In types III, IV, V and VI, both the capsule and the CC ligaments mentioned are torn and there is a tear in the AC joint."

The acromioclavicular joint connects the clavicle with the acromion. It is the only joint connection between the arm and the chest and is therefore subject to extremely high loads. 

Over the course of life, many people experience wear and tear naturally, but not all osteoarthritis of the acromioclavicular joint becomes symptomatic. The acromioclavicular joint often draws attention to itself after a fall (e.g. from a bicycle or soccer ball). 

This occurs when the joint capsule or the ligament connections between the collarbone and shoulder blade are injured. This happens with direct impact trauma to the shoulder roof, the acromion, the upper outer bony prominence of the shoulder blade.

This can lead to overstretching or tearing of the ligaments that otherwise stabilize the two bones in the joint. 

If there is only one injury to the joint capsule, it is called a type I injury according to Rockwood. If the ligaments between the clavicle and shoulder blade are also overstretched or partially torn, this is type II. 

In types III, IV, V and VI, both the capsule and the CC ligaments mentioned are torn and there is a tear in the AC joint. 

Typically, the acromion occurs below and slightly in front of the collarbone, which reveals instability in the joint. 

This instability can be very painful and lead to impairment of shoulder function. 

Piano key phenomenon - This is what it means.

"If the acromioclavicular joint is completely split, the collarbone protrudes upwards from the shoulder girdle."

The position of the AC joint is influenced by muscle pull from the sternocleidomastoid and trapezius muscles at the clavicle.

Over many years, the image of the piano key has become established and has earned its place in many textbooks. 

The piano key phenomenon suggests that the key (clavicle) must be pressed down in order to achieve a tone or the desired result, in this case the reduction of the clavicle. 

If you look more closely, you will notice that it is the acromion that, following the force of gravity, moves under and in front of the collarbone during a complete AC explosion. 

In order to achieve the desired result (reposition), you would not, figuratively speaking, have to press the piano key down, but rather lift the piano and turn it slightly backwards. 

This is of course a bit more complicated and would certainly never have found its way into the books so easily. Be that as it may, in the end it is crucial that you hit the right note at the right time and that the patients do well!

The Rockwood classification has this meaning:

Rockwood I: Strain of the capsular/ligamentous apparatus. No acromioclavicular joint instability.

Rockwood II: Partial tear of the capsular/ligamentous apparatus (rupture of the acromioclavicular ligaments) with partial dislocation of the acromioclavicular joint.

Rockwood III: Tear of the entire capsular/ligamentous apparatus (rupture of the acromioclavicular ligaments and the coracoclavicular ligaments) with complete dislocation of the acromioclavicular joint in the vertical plane towards the head, so-called acromioclavicular joint separation.

Rockwood IV: The lateral end of the clavicle dislocates in the horizontal plane. It can get caught in the trapezius muscle.

Rockwood V: Extreme clavicle elevation with extensive detachment of the muscle attachments at the lateral end of the clavicle.

Rockwood VI: Dislocation of the lateral end of the clavicle towards the foot under the coracoid.