Tuesday, September 30, 2014
Conversion of an anatomic to a reverse total shoulder, when is a ‘platform’ prosthesis of benefit?
In certain cases, such as that shown here, a well fixed stem can be retained and the proximal end converted to a reverse total shoulder with insertion of a glenosphere. Here’s another post regarding conversion with retention of the anatomic stem.
Recently, there has been the advent of ‘platform’ prostheses, in which a humeral stem is fixed in the humeral canal that can be attached to either an anatomic or a reverse proximal humeral prosthesis. Several examples are shown below.
It is important to recognize that in a reverse, (1) the glenosphere is placed inferiorly on the glenoid face, (2) the proximal humeral part of the reverse is bigger than that of an anatomic humeral arthroplasty and (3) the soft tissue tensioning considerations of a reverse are different from those of an anatomic arthroplasty. Therefore, the proximal-distal positioning of the humeral component needs to be fine tuned to achieve the ideal reverse arthroplasty. While some systems provide various adaptors to adjust the height, inclination and version of the proximal humeral prosthesis, the flexibility in positioning is limited by the use of the ‘platform’ fixed in the humeral canal.
Fortunately, we now have a clearer understanding of the indications for a reverse total shoulder, so that the needs for convertible prostheses is diminishing. For example, it is becoming evident that proximal humeral fractures in elderly individuals are often best managed by a primary reverse total shoulder – the idea of ‘trying’ an anatomic arthroplasty that is convertible to a reverse later is not so appealing. Similarly, individuals with arthritis, cuff deficiency, and instability are also best managed by a primary reverse.