Dr. Marc Garnick is the Gorman Brothers Professor of Medicine at Harvard Medical School and Beth Israel Deaconess Medical Center, and founder of the Hershey Family Foundation for Prostate Cancer Research at BIDMC. His recommendation is based on having performed thousands of DREs:
I prefer having patients assume a left lateral decubitus position. This allows excellent visualization of the perianal area and anal area and allows elevation of the right gluteal muscle to allow easier insertion of the gloved examining finger. For patients who have difficulty getting into this position (due to arthritis or other mobility issues), I have the patient assume a standing position over the edge of the examining table, have his hands placed on the table for stability, and perform the exam in that fashion. This is more uncomfortable for the clinician, however, and does not allow the same visualization of the anal and perianal area.