In May of 2015, three well known medical centers took a pledge to eliminate the performance of certain procedures by surgeons who performed relatively few of those procedures.  The campaign, called The Volume Pledge, received attention and sparked discussion.  More recently, research has questioned whether there is some other useful, broadly applicable metric to predict surgical outcome.  To that end, whether a surgeon specializes in a particular procedure, or group of procedures, is being explored as a marker for excellent outcome...independent of surgeon volume.  Here's one study now: