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Anatomy and biomechanics of the shoulder
Deep muscle layer: "centring cuff = rotator cuff"

The centring cuff is located beneath the superficial layer and consists of the rotator cuff muscles and the biceps tendon. It encloses the humeral head with its tendinous components. It is responsible for ensuring that the shoulder - the humeral head - is held within its centre of rotation very precisely during any movement of the arm. The surrounding muscles of the shoulder girdle are only able to function precisely and apply force if the centre of rotation remains stable.

Rotator cuff = centring cuff

18 muscle pairs, known as agonists and antagonists, allow the shoulder to carry out its "normal movements".

A sliding surface known as a subacromial bursa is located between the rotator cuff and the acromion. When the centring force is weakened, this bursa is placed under pressure and can become injured or inflamed. At the same time, the rotator cuff rubs against the acromion.

1. Supraspinatus
2. Subacromial bursa
3. Subscapularis

View of the burse and rotator cuff beneath the acromion