The orthogonal spin-momentum locking in the electronic surface state of topological materials is commonly observed experimentally which is well understood in the independent particle picture by the strong spin-orbit coupling and the spin-1/2 vortex. In recent experiments, a number of spin texture anomalies have been observed on the topological state of some Dirac materials. It is a tradition in the community to attribute these anomalies to the higher order spectral effects in the independent particle picture. On the other hand, the existence of the many-body interactions are being verified in a large number of experiments of which effects on the spin is largely unexplored. In this talk we introduce an interacting theory for the spin in the presence of strong spin-orbit interaction. We observe that the weak interactions, while merely affecting the energy bands, can change the spin texture in the presence of a Fermi surface anisotropy. We apply our results to the specific optical phonon experimentally found to be coupled to the topological surface state in the $Bi_{2−y} Sb_y Se_{3−x} Te_x$ family of strong topological insulators. We obtain large deviations from the perfect spin-momentum orthogonality. We interpret our results in the light of existing experiments and compare with other rival theories based on the non-interacting picture.