Defense lawyers in love blaming empty chairs. A jury trial is about assigning blame and the easy out for the defense is to get the jury to blame another doctor who is not named at trial. (This is also why plaintiffs’ lawyers get maligned over naming too many defendants — sometimes there is no choice.)
Usually, the doctor’s lawyer will not provide expert testimony to blame the doctor. Normally, the allegation is made indirectly with the hope that the jury blames a non-defendant doctor on their own.
This is a good strategy. Jurors like reaching their own conclusions without getting beat over the head and most malpractice defense lawyers do not try to directly blame the empty chair for fear of running afoul of Maryland law.