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Disorders and injuries of the rotator cuff
Loosening of the rotator cuff, thinning and formation of a bottleneck beneath the acromion (impingement syndrome)
Loosening of the ligaments and the rotator cuff can occur as a result of exercise, hard work, intensive sporting activity or, quite simply, the advancing years. The RC muscles are no longer able to centre the humerus properly during movements, and the humeral head rises up against the acromion at the start of arm elevation, leading to a bottleneck situation. This, in turn, causes further wear and tear on the RC and starts a vicious circle. But individual clinical conditions or injuries can also lead to constriction of the space beneath the acromion, producing the same impingement problem. For example:
- Displaced fractures of the humeral head
- Constitutional changes in the acromion
- Acquired changes in the acromion and AC joint: e.g. flare-ups of arthrosis.
- Tears in the rotator cuff
- Calcium deposits in the rotator cuff
- Bursitis

1. As described in the section on humeral head fractures, such "bony" RC tear injuries can lead to an impingement syndrome beneath the acromion. Only minimal shifting of the fragments can be tolerated, as further shifting will interfere with the free movement and free sliding of the cuff beneath the acromion.

2. Changes and ossification in the acromion and AC joint. These usually involve flare-ups of arthrosis in the AC joint, which progress downwards and hinder the sliding of the underlying RC. The bursa is also affected by this process.

3. Cartilaginous, unstable acromion. This is a predisposition in which the growth plate of the acromion fails to ossify during adolescence and remains cartilaginous. An accident (fall) or overexertion can subsequently cause "incorrect mobility" in this cartilaginous plate, which can lead to secondary signs of impingement beneath the acromion. When the arm is raised, the strong tension exerted by the deltoid muscle pulls the acromion downwards. Because the cartilaginous plate is not stably ossified and movement is possible, the anterior, mobile part of the acromion is pulled downwards by the muscle tension and presses directly against the bursa and RC.
4. The acromion can be tilted at varying angles. An acromion that is severely bent downwards tends to be more conducive to the onset of bottleneck symptoms beneath the acromion than a steep shoulder roof that is open at the front.

5. Inflammation of or injury to the bursa itself can lead to thickening of the wall of the bursa, resulting in a lack of space beneath the acromion. Bursitis is most often caused by tendon calcification and its consequences or by a crush injury to the bursa, e.g. falling onto the arm.

Type I: flat
Type II: curved
Type III: hooked

Rotator cuff impingement syndrome occurs in three stages.
In stage I there is no definite damage as a result of tissue constriction, just swelling accompanied by fluid accumulation in the tissue. The treatment at this stage consists of rest, anti-inflammatory medication and treatments, application of cold, physiotherapy to strengthen the centring muscles, etc.

Stage II is characterised by sustained constriction and impingement of the tissues with initial chafing of the rotator cuff, partial lesions, tissue hardening.

In stage III we then see the established damage, with destruction of the bursa and tear lesions on the RC. Stages two and three have to be surgically treated. The tissue beneath the acromion has to be relieved and the roof widened, either to produce a wedge shape or in the form of a lift-up osteotomy of the acromion. The bursa is removed.

But in addition to these roof-widening and space-creating measures, the causes of the constriction in particular must be eliminated, e.g. RC reconstruction for tears, correction of constricting fracture fragments from humeral head injuries, restoration of the centring function in the shoulder.