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Objective. To study the correlative between the sesamoid bones under the head of the first metatarsal and the development of hallux valgus determined with radiographs.Methods.The measurements were performed on the X-ray of 300 normal feet and 300 cases of hallux valgus. The following parameters were measured: hallux valgus angle(HVA); the first-second intermetatarsal angle(IMA) between the axes of the first and second metatarsal;the length of the second metatarsal（CD）;the position of tibial sesamoid(TSP ) measured the percent formed between the tibial sesamoid and the centreline of the first metatarsal;the position of fibular sesamoid(FSP) measured tangent value between fibular sesamoid bone and lateral cortex of first metatarsal bone ; the absolute distances (AB) from the centre of the tibial sesamoid to the long axis of the second metatarsal, the absolute distances (EF) from the centre of the fibular sesamoid to the long axis of the second metatarsal and the absolute distance (GH) from the centre of the tibial sesamoid to the centre of the fibular sesamoid. Then calculate the ratio of AB to CD (K1), EF to CD (K2) and GH to CD (K3). Results.HVA moderately positively correlates with TSP and moderately negatively correlates with FSP in subjects with HVA ≥ 20°. HVA and FSP are strongly negatively correlated in the hallux valgus group. Conclusion.The dislocation of sesamoid bone under the first metatarsal head is an important pathological factor leading to valgus. HVA is positively correlated with TSP and negatively correlated with FSP.