How does an artificial shoulder joint work?

The artificial prosthesis components are made of different materials:

  • metal alloys (due to good tolerance and durability)
  • special plastic polymers (imitation of the lubricative cartilage layer)

The surgeon will decide which materials to use depending on the patient's anatomy.

Types of prosthesis

Depending on the disease and patient, the following different types of prostheses can be used: partial endoprosthesis, total endoprosthesis or shoulder resurfacing.

Artificial should joint: partial endoprosthesis

If the cartilage layer in the glenoid cavity is in good condition (for example after a humeral fracture), this does not need to be replaced. Then only the humeral head is replaced by an artificial humeral head fitted to a prosthesis stem. Following the operation, the artificial humeral head sits in the natural glenoid cavity. This is referred to as a partial endoprosthesis (or hemi-endoprosthesis).

Artificial shoulder joint: total endoprosthesis

If the joint cartilage is damaged on both parts of the joint, both on the humeral head and in the glenoid cavity, all the components of the diseased shoulder joint are replaced. The damaged glenoid cavity is replaced by a prosthetic cup and the deformed humeral head is replaced by an artificial humeral head, which is fitted to a prosthesis stem. This is referred to as a total endoprosthesis. A total endoprosthesis requires a functioning rotator cuff, which provides the artificial joint with stability and mobility.

If the rotator cuff is severely damaged, a special type of prosthesis is implanted for functional compensation, an inverted total endoprosthesis: This consists of a spherical component, which is attached to the shoulder blade at the position of the natural glenoid cavity, and a cup-shaped part, which is mounted on a prosthesis stem and is inserted into the humerus. This design achieves a certain amount of stability. Mobility, however, depends on a properly functioning large shoulder muscle, the deltoid muscle. Since this type of prosthesis has not been in use for long, there are no long-term results available yet.

With this method, only the damaged joint surface of the humeral head is replaced and lined with a metal spherical cup.

The prosthesis thus comprises a cap for the natural humeral head.

The advantage of this method is that the bone tissue of the humerus is preserved, the surgical intervention is smaller and the loss of blood remains minimal. However, the method is still very new so there are no long-term results available yet.