The muscles of the shoulder and shoulder girdle

Trapezius, rhomboids, serratus anterior, deltoid, pectoralis major and the rotator cuff: what moves the scapula, what moves the arm.

The outline, topic by topic

Each topic is weighted the way the exam weighs it.

Rotator cuff: what is it?
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Supraspinatus, infraspinatus, teres minor and subscapularis, which wrap the head of the humerus.
They hold the humeral head in a very shallow glenoid cavity.
A swimmer has pain lifting the arm sideways between 60° and 120°. Which tendon is most often at fault?
- The supraspinatus tendon
- The teres major tendon
- The pectoralis major tendon
- The long head of triceps tendon
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The supraspinatus tendon
It runs under the acromion, where it can be pinched.
Deltoid: what is it?
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The triangular muscle covering the shoulder, the main abductor of the arm.
Its three parts also allow flexion and extension.
Why is the shoulder the most mobile and least stable joint?
- A deep glenoid cavity that encloses the whole humeral head
- A large humeral head in a small cavity, held mainly by muscles
- No capsule at all, only a few ligaments instead
- Flat surfaces that slide with no stabilising muscle
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A large humeral head in a small cavity, held mainly by muscles
Stability comes from the cuff, hence the value of strengthening it.