James
In contrast to Total Elbow Replacement, the indications for Uni-arthroplasty are much less frequently encountered in practice. In addition, this implant is relatively new, in terms of commercial availability, so fewer surgeons have experience with the implant.
I would estimate that there are fewer than 100 procedures performed each year. You may try to get a more accurate figure by contacting the company that sells the implant--Small Bone Innovations.
http://www.totalsmallbone.com/
For more information on this procedure visit:
http://www.drtomaino.com/article.php?id=121