Until the 1980s, three-point belts were commonly available only in the front outboard seats of cars; the back seats were only often fitted with lap belts. Evidence of the potential of lap belts to cause separation of the lumbar vertebrae and the sometimes associated paralysis, or "seat belt syndrome" led to the progressive revision of passenger safety regulations in nearly all developed countries to require three-point belts first in all outboard seating positions and eventually in all seating positions in passenger vehicles. Since September 1, 2007, all new cars sold in the US require a lap and shoulder belt in the center rear seat.