A vehicle seat includes a seat back having a support frame coupled to a seat foundation. The seat back also further includes a deformable seat shell adapted to assume various shapes between initial position and final positions in response to variable rearward loads applied by a seated passenger. The seat shell is coupled to the support frame by a compliant shell-motion controller via upper and lower motion-control links. The motion-control links allow pivotal motion, and at least one of the links includes a spheroidal joint. A link foundation extends between and interconnects the upper and lower motion-control links and is coupled to the support frame so that the link foundation does not move during seat shell deformation. The shell-motion controller may be pre-assembled as part of a backrest or the motion-control links may be formed after the link foundation is attached to the support frame.