The positioning of a patient’s head prior to clinical evaluation is critical, and incorrect positioning will inevitably lead to errors in diagnosis and treatment planning. Despite its importance, the concept of head positioning in facial aesthetic evaluation is often misunderstood. The reasons for this are partly historical.1
Anthropologists in the mid to late 19th century in Germany had endeavored for some time to reach a general agreement among themselves as to a method of measuring skulls, obtained from archaeological excavation sites, that could be generally adopted. The purpose was to standardize the techniques used by physical anthropologists, particularly in order to undertake comparative studies of the crania from various ethnic populations. The outcome of deliberations at 2 craniometric conferences, held in Munich in 1877 and subsequently in Berlin in 1880, was drawn up by the anthropologists Julius Kollman, Johannes Ranke, and Rudolf Virchow and submitted for consideration to the 13th General Congress of the German Anthropological Society held in Frankfort (or Frankfurt) in 1882. Their scheme was adopted and designated the Frankfort Agreement (1882) and was published in Germany in 1884.2 To compare various crania in a standardized way, it was necessary to place the dry skulls in a defined position. Therefore, the choice of a horizontal reference plane for the orientation of the skulls was agreed on, based on but slightly modified from a plane described by von Ihering in 1872.1 This so-called German horizontal plane passed through the “lowest point of the under edge of the orbits and the upper edge of the ear-aperture,”2 though such a plane is clearly visible on a number of Leonardo da Vinci’s proportional drawings.3 Nevertheless, the Frankfort Agreement of 1882 was the birth of the use of the Frankfort horizontal plane.