Data from dry bone samples, collected from anatomical or archaeological collections, can improve the knowledge regarding accessory foot bones, including prevalence, size, shape and laterality, that can be useful in disparate fields of research, from medicine to bioarcheology. In the present study, the prevalence of six accessory foot bones (os trigonum, calcaneus secundarium, accessory navicular bone, os vesalianum, os sustentaculum and os intermetatarseum) was assessed in a sample of 486 individuals (226 females, 260 males) from the Coimbra Identified Skeletal Collection (CISC). The most frequent accessory bones are os trigonum (9.9%; 48/485) and calcaneus secundarium (6.0%; 29/486), while the most uncommon is os sustentaculum (0.4%; 2/486). No sex differences were observed. All accessory bones occur more often unilaterally, with the exception of the accessory navicular bone that, in the majority of cases, occurs bilaterally. The unilateral expression of os trigonum, calcaneus secundarium and os vesalianum was mostly in the right foot. The co-occurrence of accessory foot bones was recorded in 1.7% of the individuals (8/486), and the combinations of os trigonum and calcaneus secundarium were the most frequently observed. This research emphasizes the relevance of conducting studies on reference skeletal collections in order to gain a comprehensive understanding of anatomical variations in the foot. This understanding is crucial for accurate diagnoses and successful treatment in clinical settings, as well as for establishing population comparison standards in the fields of bioarchaeology and forensic anthropology.

Accessory navicular (AN) is a developmental variation of the secondary ossification center of the navicular tuberosity. Ten percent of patients with AN will have pain symptoms that affect walking and life. As the AN changes the position of the posterior tibial tendon insertion, children with AN often have posterior tibial tendon function insufficiency and flexible flat foot. Surgical treatment is often required after failure of conservative treatment. This article reviewed the etiology, clinical manifestations, complications, and treatment methods of AN.