Defects of the femoral head-neck junction: A new method of classification and observed frequency in Hamann-Todd skeletal collection

Femoral head-neck defects (FHNDs) are commonly reported in the anatomical and anthropological literature. The best known types are Allen's fossa and Poirier's facet; however, their definition and etiology are still debated. The aims of this study were to revise the categorization and identification of FHNDs and to reveal their prevalence in a skeletal sample. The femora of 238 individuals (161 males and 77 females) aged between 21 and 93 years old from the Hamann-Todd osteological collections (Cleveland Museum of Natural History) were examined. FHNDs were classified according to their location, size, and appearance. Six different types of defects in the femoral head and neck were defined: ditch (it appears like Allen's fossa), tongue (it appears like Poirier's facet), indentate, sunken, groove, and pit. This classification method was found to be reliable (κ ≥ 0.907). FHNDs are very common among adult human populations (69.3%), especially the ditch (25.2%) and the tongue types (38.2%). All types were sex and age independent; however, the age of onset varied. The tongue type was more prevalent among the elderly, whereas the ditch type was more prevalent among younger individuals. To conclude, there are six distinct types of FHNDs, which varied in their location, appearance, and prevalence. The most common defects, tongue and ditch, were sex and age independent. These defects are easily identified by naked eye or via CT images and therefore can be studied both in skeletal and modern populations, respectively.