[Walcher's hat brim line rule--a literature review]

The first description in the forensic medical literature of a demarcation line for the localization of head injuries resulting from falling to the ground appears in Kratter (1919). Regarding a similar line, Walcher (1931) later introduced the relation to the hat brim (Hutkrempe), which gave the rule its name: the hat brim line rule (Hutkrempenregel). Thenceforth it was supposed to be called Kratter's and Walcher's hat brim line rule (Kratter-Walcher'sche Hutkrempenregel). Over the following decades, not only its content but also the area of application and the definition of the hat brim line rule were repeatedly, and in part significantly, altered. This could be one of the reasons for the confusing diversity of academic opinions about the rule's applicability. Generally, the hat brim line rule should be retained in its original sense: Fall-related injuries do not lie above the hat brim line if the fall occurred from a standing position to the ground, without intermediary blows to the head. If applied in this way, the rule can be a helpful point of orientation for experts. The demarcation line in the original anatomical definition according to Kratter (1919) should also be used henceforth: the line which connects "the frontal eminence, the parietal eminence and the tip of the occipital plate" and lies "somewhat.above the usual saw-line of the calvarium". This line corresponds roughly to the hat brim line as it is understood by hat makers. The hat brim line rule should not be applied with regard to small children, as they show a different falling behaviour due to their disproportionately large and heavy heads. The rule is also in no way applicable to the assessment of injuries from blows, falls from a height (including from stairs) or traffic accidents. There is an urgent need for research as to the applicability of the hat brim line rule in relation to falling backwards, particularly in cases of high alcohol consumption.