A unidirectional nanotexture alters the wettability of a substrate and can be used to create patterned polymer films, tailored polymer coverage/reflow, or aligned polymer molecules. However, the physical mechanisms underlying polymer spreading on nanoscale textures are not well-understood, and competing theories exist to explain how texture peaks and grooves alter the wettability of a substrate. We use molecular dynamics to simulate polymer spreading on substrates with unidirectional nanoscale textures as a function of texture shape and size and compare to polymer spreading on a flat substrate. We show that the texture groove shape is the primary factor that modifies polymer spreading on unidirectionally nanotextured substrates because the texture groove shape determines the minimum potential energy of a substrate. At the texture groove, the energy potentials of several surfaces combine, which increases polymer attraction and drives spreading along the texture groove. A texture groove also acts as a sink that inhibits polymer spreading perpendicular to the texture. Texture peaks create energy barriers that inhibit polymer spreading perpendicular to the texture, but this is a secondary mechanism that does not significantly affect anisotropic spreading. This research unifies competing theories of anisotropic liquid spreading documented in the literature and aims to aid in the design of nanoscale textures and ultrathin liquid film systems.