ObjectiveTo examine the presence of certain shapes of the first metatarsal-cuneiform joint (MTC) joint in feet with hallux valgus (HV) deformity. To determine whether the anatomical orientation of this joint affects the size of the hallux valgus angle (HVA) and the first intermetatarsal angle (IMA) and whether it contributes to the dynamics of the developmental course of HV deformity.MethodsThe shape of the first MTC joint was determined on a sample of 315 feet with HV deformity. The influence of the shape of this joint on the values of HVA and IMA was explored. The relation between the position of the tibial sesamoid and the size of HVA and IMA as well as the dynamics of the development of this deformity depending on the shape of the first MTC joint, was examined.ResultsThe oblique shape of the first MTC joint was found in 165 (52.4%) feet, the transverse in 145 (46%), and the convex shape was registered in five feet (1.6%). In the oblique shape of this joint, a moderate and severe degree of HV deformity is predominant, while in the transverse shape a mild degree dominates. A statistically significant dependence of HVA on the shape of the first MTC joint was found (Sig. = 0.010), while the dependence of IMA did not show statistical significance (Sig. = 0.105). HVA values follow the position of the tibial sesamoid in both shapes of the MTC joint while the size of the IMA in the transverse shape does not follow the change of the position of this sesamoid.ConclusionThe oblique shape of the first MTC joint is associated with the more severe form of HV deformity and its faster developmental course. In the analyzed sample, it was shown that HVA is higher in the oblique shape of the MTC joint and significantly depends on the anatomical orientation of this joint. Furthermore, IMA has a higher value in the oblique shape compared to transverse but this dependence is not statistically significant. The analysis showed that the oblique shape of the first MTC joint contributes to the development of HV deformity.