Developmental Anomalies of the Foot Bones: Coalitions and Bipartitions in the Coimbra Identified Skeletal Collection

Foot coalitions and bipartitions are developmental anatomical variants of the bones of the foot that can be of clinical relevance. The aim of the present study is to document the frequency of tarsal and metatarsal coalitions and bipartitions according to biological sex, age at death, co-occurrence, and laterality in the Identified Skeletal Collection of Coimbra (CEIC). The study sample consisted of 486 individuals (226 females and 260 males), with ages at death ranging from 12 to 96 years. Twelve tarsal coalitions and three bipartitions were investigated. Tarsal coalitions were observed in 4.7% (23/486) of the individuals in the sample. Ten were bilateral (43.5%) and 13 unilateral (56.5%), with eight in the left foot (8/13, 61.5%) and five in the right foot (5/13, 38.5%). Females were significantly more affected than males (females: 7.1%, 16/226; males: 2.7%, 7/260; chi-square: 5.162, p = 0.006). The age at death of individuals with (mean = 43.6 years; SD = 23.0) and without (mean = 46.2 years; SD = 19.2) coalitions was similar (Student's t-test: 0.640, p = 0.522). No coexistence of coalitions was observed. The calcaneonavicular coalition was the most commonly observed in this study, found in nine individuals (1.9%, 9/486). Only one case of calcaneocuboid coalition was recorded: a fusion in the left foot of a 78-year-old woman. Knowledge of the prevalence and anatomical distribution of foot coalitions and bipartitions can be clinically significant, especially to avoid confusion with fractures, and its diachronic bioanthropological study may reveal secular trends and population differences.