How is the shoulder joint structured?

The shoulder joint comprises parts of the following bone structures:

  • the head of the humerus: spherical end of the humerus
  • the glenoid cavity: shallow concave surface on the shoulder blade
  • the acromioclavicular joint: connection to the clavicle
Anatomy Shoulder Joint

When in a healthy condition, all parts of the joint are surrounded by joint cartilage which acts as a lubricant in order to reduce friction between the parts of the joint. Additionally it helps absorb shock; it distributes and reduces the forces which act upon the shoulder joint.

Role of the joint capsule

The fixed joint capsule forms an envelope around the shoulder joint to seal it off from the surrounding tissue. This capsule produces synovial fluid which serves to ensure friction-free movement of the shoulder joint and also supplies the joint cartilage with essential nutrients.

Stability and movement thanks to muscles

The spherical head of the humerus is only held very loosely in the small, shallow glenoid cavity of the shoulder blade. That is why muscles, tendons and ligaments assume the important role of stabilising the shoulder joint and at the same time making it as mobile as possible. This is mainly achieved by a complex set of muscles, the rotator cuff. It consists of four muscles which surround the shoulder joint like a cuff, protect it and make it possible to raise and rotate the arm.