Inverse prosthetic shoulder

General

The inverse shoulder prosthesis is a form of shoulder joint replacement that does not correspond to the anatomical shape. This type of prosthesis is used when the muscles of the shoulder are no longer functional and the shoulder joint has degenerated. The operation offers the possibility of pain relief and brings back some of the function. A major disadvantage is a possibly necessary revision operation after a few years, which can result in a loss of function of the shoulder joint.

The term "inverse shoulder prosthesis" refers to a prosthesis that is constructed in reverse to the normal shoulder joint. The joint head sits anatomically correct on the humerus, the joint socket is located on the shoulder joint. With the inverse shoulder prosthesis, the joint head is now placed in the place of the bony joint socket, and the artificial joint socket sits on the upper arm.

Who will benefit from an inverse shoulder prosthesis?

A shoulder prosthesis is always necessary if the affected patient suffers from one of the following diseases:

• advanced shoulder joint arthrosis
• rheumatic disease
• a joint infection (Omarthritis)
• chronic shoulder instability (shoulder dislocation)
• fractures in the articular surface or necrosis of the humeral head

An inverse shoulder prosthesis in particular always benefits when, in addition to these ailments, there is also pronounced damage to the muscles that stabilize the shoulder joint (Rotator cuff) consists.

Reasons for an operation

The inverse shoulder prosthesis is used when the joint is worn out, so that an artificial joint is necessary. At the same time, the rotator cuff muscles must be inoperable so that a normal shoulder prosthesis would fail. The inverse shoulder prosthesis is also used in the context of accidents and humerus head fractures or when the shoulder has been dislocated for years. This reverse construction of the shoulder joint changes the biomechanics of the shoulder. Usually, to move the shoulder, several muscles called the rotator cuff have to contract. However, due to the reverse construction, the center of rotation of the shoulder shifts downwards and inwards.

As a result, the patient only has to rely on one functioning muscle to use the prosthesis. This is the deltoid muscle (Deltoid muscle), which is not part of the rotator cuff.

Duration of the operation

The duration of the operation when using an inverse shoulder prosthesis is not always the same; it also depends, among other things, on the extent of the damage to the shoulder joint and the patient's anatomy. On average, one to two hours of operation time should be expected. General anesthesia are suitable as an anesthetic form for this period, but partial anesthesia (regional anesthesia in which only the shoulder and arm are anesthetized) is possible and safe.

Complications / risks

When using an inverse shoulder prosthesis, the same risks apply as with shoulder prostheses in general:
During the operation:

• Vascular and nerve injuries
• low risk of injuring surrounding structures in the operating area (e.g. broken bones)

After the operation:

• Bleeding and wound healing disorders
• Slipping of the prosthesis (dislocation)
• Loosening of the prosthesis

Other general but rare risks:

• Infection
• thrombosis
• embolism
• Nerve damage

In addition, the inverse shoulder prosthesis, like any other artificial joint, can loosen after a few years. In addition, the shoulder prosthesis, like the previous natural joint, can also dislocate. Falls on the shoulder, especially in older patients, can cause the prosthesis to break out.

How long does a shoulder prosthesis last?

The lifespan of a shoulder prosthesis cannot be given across the board, as it depends on the one hand on the prosthesis model and prosthesis material and on the other hand on the degree of damage to the shoulder joint itself.

On average, however, it can be assumed that the prosthesis material will last 10 years or more. This also means that the use of a prosthesis - if it is medically justifiable - should be waited for as long as possible in order to avoid repeated or even multiple changes of material in repeated surgical interventions.

advantages

The advantages of an inverse shoulder prosthesis are:

• the very good therapy option for seriously ill shoulder joints.
• a worn shoulder joint (arthrosis) and an inoperative rotator cuff can be treated
• Existing pain can often be well contained by the operation
• Moving the arm forward is usually well restored
• In addition, no initial screwing, plating or nailing is necessary in the event of a massive fracture of the humerus head

disadvantage

In most cases, the weakness of the rotational movement remains as it was before the operation. An additional muscle transfer may improve this in the future. In addition, this implant is a large prosthesis, which has to be removed after 10 to 20 years if it becomes loose. In this case, the revision interventions are often very complex and the implantation of a new prosthesis is often no longer possible, so that the function of the shoulder joint may be lost.

Aftercare

The follow-up treatment time strongly depends on the time of the operation. If this is done early, the muscles and tendons can be spared when the prosthesis is installed. Then in some cases the shoulder can be slowly exercised again after 1 to 2 weeks under physiotherapeutic guidance. If the operation is waited too long, most of the tendons and muscles often have to be removed as well. Then post-operative immobilization in the Gilchrist bandage for 6 weeks is not uncommon.

Summary

The inverse shoulder prosthesis offers the possibility of restoring the function of shoulder joint wear in combination with an inability to function of the rotator cuff.
By reversing the natural joint construction, the center of rotation of the shoulder is shifted downwards and inwards. This means that only the deltoid muscle is required for movement, the rotator cuff muscles become unnecessary. This operation can particularly reduce pain in the shoulder joint. Likewise, the forward mobility of the arm is often not restricted. In many cases, however, the rotational movements are no longer possible. In addition to the usual complications during an operation, the prosthesis can loosen or break out.

If the prosthesis has to be removed after one to two decades, this is often a massive revision surgery and in many cases a complete loss of function of the shoulder joint. With early therapy, follow-up treatment can be started after one to two weeks; if the operation is complicated, consistent immobilization is necessary for up to 6 weeks.