Stepping Up: Accessory Bones of the Foot in the 21st Century Identified Skeletal Collection (Portugal)

Background/Objectives: The anatomical variability of the human foot represents a subject of substantial interest, offering valuable insights in anthropological research as well as in clinical practice. The aim of this study is to document anatomical variants of the tarsal bones in a CISC//XXI skeletal sample (21st Century Identified Skeletal Collection), with a particular focus on the prevalence of accessory ossicles. Methods: The studied sample consisted of 163 individuals (83 females and 80 males). The prevalence of six accessory tarsal bones was recorded (os trigonum, calcaneum secundarium, the accessory navicular bone, os sustentaculum, os vesalianum and os intermetatarseum). Results: A total of 35 individuals (21.4%; 35/163) exhibited at least one accessory ossicle, with 13 females (15.7%; 13/83) and 22 males (27.5%; 22/80). The os trigonum and calcaneum secundarium were the most frequently observed accessory bones, respectively, in 9.3% (15/162) and 6.9% (11/159) of the individuals. No sex differences were observed. All accessory bones occurred more frequently unilaterally, and no co-occurrences of accessory bones were observed. Conclusions: These findings are crucial in both the biomedical and anthropological fields, where a detailed knowledge of foot anatomy and its variations is relevant.