Abstract: Embodiments include a prosthetic thumb device that includes a track configured to attach to a prosthetic socket, a carriage, and a locking mechanism. The carriage can include a first component that couples to the track such that the carriage is operable to move along the track, and a second component that is configured to couple with a prosthetic digit and operable to rotate with respect to the first component. The locking mechanism can be coupled to the carriage and configured such that, in a first state, it prevents the carriage from moving along the track in a first direction and, in a second state, it allows the carriage to move along the track in the first direction. Embodiments can also include the track having a curved profile, and the carriage is operable to move along the curved profile of the track.