Reverse Total Shoulder Replacement
/ Further Readings and References
History and the come about of the reverse design
The first prosthetic shoulder arthroplasty performed has widely been ascribed to the French surgeon Jules Emile Pe´an in 1893.  Arthroplasty played a limited role in the treatment of shoulder problems until in 1955 when Neer reported the use of a proximal humeral arthroplasty (replacing the humeral head) to treat shoulder fractures.  Later he extended the use of hemi-arthroplasty to treat osteoarthritis of the shoulder. The procedure had been largely successfully except when there was a tear or loss of function of the rotator cuff, the results became poor. The rotator cuff muscles act together to center the humeral head during shoulder movements. Failure of rotator cuff led to a loss of fulcrum of the shoulder movement.
Some thought that the creation of a fixed fulcrum design might solve this problem. There were two approaches to this. One was to put a deep socket component on the glenoid side and have a humeral component with a small head so that the humeral component became constrained in the deep socket during shoulder movement. The glenoid is naturally a small bony structure and can only provide limited support and fixation area for these glenoid designs. Due to the large forces going through the glenoid components during movement, they quickly became loose. The other school explored the concept of reversing the ball and socket arrangement of the shoulder. By putting a ball on the glenoid, the upper humerus can then pivot around this ball based on a shallow socket put at the end of the humerus. Proponents for this design argued this change would allow improved motion and strength without the increased risk of dislocation and loosening.
A number of reverse implant systems were designed beginning in the 1970s with variable designs for scapular fixation. As reverse shoulder arthroplasty design progressed, maximizing deltoid function became a greater focus. A larger ball and socket construct was shown to increase the glenohumeral motion and increase the deltoid lever arm. The system created by Paul Grammont in 1985 emphasized the importance of moving the centre of the sphere to be at or within the glenoid neck; and that the deltoid function could be increased by moving the centre of rotation
distally and medially.  This soon became the milestone and provided basis for modern reverse total shoulder replacement designs. Modern designs aim to improve on the range of movement, stability, and decrease some specific complications such as notching of the scapula (the metal edge of the humeral tray impinges on the lateral edge of the scapular body as they were brought closer to each other by the reverse shoulder replacement. Over time, bone on the scapula becomes eroded.)
More about the Results
Both anatomic total shoulder arthroplasty and reverse total shoulder arthroplasty reliably result in improved patient outcomes. Both have similar complication rates, need for revision, patient-reported outcomes, and range of motion at 2 years of follow-up.1 However, anatomic total shoulder arthroplasty more reliably improves range of motion, particularly external rotation. Most improvement occurs by 6 months, with some additional improvement up to 2 years for both anatomic total shoulder arthroplasty and reverse total shoulder arthroplasty. 
5 Lugli T. Artificial shoulder joint by Pean (1893): the facts of an exceptional intervention and the prosthetic method. Clin Orthop Relat Res. 1978;133:215–218.
6 Neer CS 2nd. Articular replacement for the humeral head. J Bone Joint Surg Am. 1955;37:215–228.
7 Grammont P, Trouilloud P, Laffay J, Deries X. Concept study and realization of a new total shoulder prosthesis. Rhumatologie. 1987;39:407–418.
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