This is a procedure performed to provide pain relief and improve movement in painful and stiff shoulders.
It differs from normal shoulder replacement, as the implant reverses the anatomy of the ball and socket of the shoulder joint. This is done so that lever arm for shoulder abduction, which is done by the deltoid, is increased. This allows abduction even when the rotator cuff muscles are completely torn or non functional.
The rotator cuff is a layer of muscles around the shoulder which initiates shoulder movements and also provides stability to the shoulder.

Indications:

Painful, stiff shoulders which have little movement i.e Pseudoparalysis of the shoulder are the conditions in which reverse shoulder replacement is indicated.

1. Rotator cuff arthropathy (Milwaukee shoulder). 
2. Rheumatoid arthritis or Osteoarthritis with torn rotator cuffs.
3. Comminuted multi fragmentary fractures of proximal humerus in elderly with very osteoporotic bone.
4. Failed fracture fixation of proximal humerus.
5. Revision of shoulder arthroplasties which have failed because of failure of the rotator cuff.
6. Tumours of proximal humerus which require excision of rotator cuff and its bony attachment.

In these cases a normal shoulder replacement would not work and would fail at an early stage.

Procedure:

In place of the socket of the shoulder called the glenoid, a Base plate is inserted on top of which, a ball like Glenosphere is implanted.
In the humerus, a socket is implanted on top of a stem inserted in the medullary cavity of the humerus.
Thus, this procedure increases the lever arm for abduction by the Deltoid muscle and also Pre- tensions the deltoid muscle. This will allow better movement even when the muscles which normally initiate movement i.e. the rotator cuff are absent. Also, pain is relieved as the worn-out bony surfaces are replaced by metal and plastic surfaces.
Post operatively the shoulder is placed in a shoulder immobilizer with it being removed for exercises daily.
After soft tissue healing, the immobilizer is removed and exercise continue to strengthen muscles and improve range of movement.

Complications and Disadvantages:

1. Infection, dislocation and scapular fractures. Rates are higher than for a normal shoulder replacement.
2. Implant is 2 to 3 times more expensive then the routine implants used for shoulder replacement. Hence Reverse shoulder replacement is not done in all cases but is a boon for a small group of patients in which a normal shoulder replacement would not be possible.